JP2008192731A - Semiconductor light emitting element and optical tomographic imaging apparatus including the element - Google Patents

Abstract

In a semiconductor light emitting device, the structure irregularity of a waveguide is reduced and a current confinement structure is improved.
A semiconductor light emitting device includes a first conductive type lower cladding layer, a semiconductor active layer, and a first conductive type semiconductor substrate on a first surface of the first conductive type semiconductor substrate. , A current confinement portion 24 for injecting a current into the specific region 15 a of the semiconductor active layer 15, a second conductivity type contact layer 23, and a second conductivity type electrode 25, sequentially, and below the semiconductor active layer 15, It has one conductivity type electrode 26. The current confinement part 24 has a layer width smaller than the layer width of the second conductive type upper first clad layer 17 and the upper first clad layer from the semiconductor active layer 15 side, and has a first conductive type current block. A second conductivity type upper second cladding layer 19 buried in the layer 21 is sequentially provided.
[Selection] Figure 1

Description

  The present invention relates to a semiconductor light-emitting element that can be used as a superluminescent diode (SLD), a semiconductor optical amplifier (SOA), and the like, and an optical tomographic imaging apparatus including the same.

  An OCT (Optical Coherence Tomography) apparatus that uses optical interference by low-coherence light when acquiring a tomographic image of a living tissue has been put into practical use in the ophthalmic field. The performance of the OCT apparatus largely depends on the performance of the light source. Since the resolution in the optical axis direction is determined by the coherence length of the light source, the light source is preferably a low-coherence light source. The coherence length Δz of the low-coherence light can be expressed by the following equation when the center wavelength λc and the spectral half width Δλ are set.

Δz = 2ln2 / π · (λc ² / Δλ)
As shown in the above equation, the light source having a wider spectral width has a shorter coherence length, so that the OCT light source is desirably of a wider band.

  In recent years, OCT devices have been put into practical use in the ophthalmic field, and research aimed at application to endoscopes has been underway. In the OCT for endoscopes, the part to be measured is often covered with a substance containing a large amount of water, so that the total of the scattering loss and absorption loss in the living body tissue and the absorption loss due to water is minimized. Investigations of light sources with designed emission wavelengths are in progress, and further, consideration is given to the influence of dispersion that occurs with the increase in bandwidth. Since absorption by water has an absorption peak at a specific wavelength, the low-coherence light used in OCT for endoscopes and the like used in an environment covered with a substance rich in moisture has a high wavelength. A beam characteristic with controlled characteristics is required.

  Japanese Patent Application Laid-Open No. 2006-267071 discloses low coherence light for an OCT apparatus that acquires a tomographic image of a measurement target covered with a substance containing a lot of moisture, considering light absorption characteristics, scattering characteristics, and dispersion characteristics of a living tissue. Then, it is described that the optimum center wavelength band is 0.90 μm or more and 1.15 μm or less, and in the OCT apparatus, by using a light source having a center wavelength within this range, the living tissue absorbs moisture. It is described that an optical tomographic image up to a desired depth of a living tissue can be obtained with high accuracy even when it is covered with a substance containing a large amount. However, conventionally, a titanium sapphire laser or the like has been used as a light source in this wavelength range, and many are expensive and not easy to handle.

  On the other hand, a superluminescent diode (SLD) is promising as a low-coherence light source for an OCT apparatus that is inexpensive and easy to handle. As an SLD having a central wavelength within the above wavelength range, an SLD having an oblique optical waveguide structure is already known. However, as described above, the resolution of the OCT apparatus increases as the light source has a wider band. Therefore, in order to obtain a clearer and higher-definition tomographic image, an SLD having a wider band is required.

  As one of the methods for manufacturing a broadband SLD, there is a method for forming a wide band by forming a structure that generates light having different emission wavelengths in the waveguide direction of emitted light in a semiconductor light emitting device. Specifically, by using selective growth to form an active layer in which the quantum well thickness and quantum well composition are changed in the optical axis direction, light having a different emission wavelength is generated in the waveguide direction of the emitted light. Get the structure.

In this method, when a dielectric mask formed of _two striped SiO ₂ or the like is formed in parallel with a certain distance from each other and crystal growth is performed thereon, the growth rate of the growth region sandwiched between the masks is increased. Utilizing the phenomenon that the composition changes, the thickness and composition of the active layer grown can be changed in the waveguide direction of the emitted light by changing the mask width. With this method, it is possible to produce a broadband SLD compared to a normal SLD, but with this method, if the rate of change in film thickness or composition is increased, crystal degradation will occur rapidly. There's a problem.

Patent Document 1 discloses a method for suppressing crystal degradation by gradually changing the composition of Group III source species by increasing the inter-mask stripe width to 10 μm or more in a semiconductor optical integrated device, and the method manufactured by the method. A semiconductor optical integrated device is disclosed.
Japanese Patent Laid-Open No. 7-50443

However, in Patent Document 1, since the ridge is formed by etching a selective growth layer having a large film thickness difference, it is difficult to make the ridge width constant, and the waveguide characteristics of the device are reduced. Also, in the region on the short wavelength side where the film thickness is thin, damage to the stripe structure due to over-etching and deterioration of current confinement characteristics due to an extremely thin current blocking layer are likely to occur, and good beam characteristics may not be obtained.
The semiconductor optical amplifier (SOA) is also a semiconductor light emitting element having the same element configuration as the SLD and has the same problems.

  The present invention has been made in view of the above circumstances, and it is intended to provide a semiconductor light emitting device such as SLD or SOA having a good current confinement structure with less irregular structure of the waveguide and good beam characteristics. It is the purpose.

  It is another object of the present invention to provide an optical tomographic imaging apparatus (OCT apparatus) using the semiconductor light emitting element.

  An object of the present invention is to provide a broadband semiconductor light-emitting element having a light emission wavelength in the range of 0.90 μm or more and 1.15 μm or less, which is particularly suitable as a light source for an endoscope OCT apparatus or the like. However, the present invention can also be applied to a broadband semiconductor light emitting device in which the center wavelength of the emitted light is outside the above wavelength range.

The semiconductor light emitting device of the present invention is formed on one surface of a first conductivity type semiconductor substrate, on a first conductivity type lower cladding layer, a semiconductor active layer, and a specific region of the semiconductor active layer from the semiconductor substrate side. In a semiconductor light emitting device having a current confinement part for injecting current, a second conductivity type contact layer and a second conductivity type electrode in sequence, and having a first conductivity type electrode below the semiconductor active layer,
The semiconductor active layer has a structure in which a composition and a film thickness are changed stepwise or continuously in a waveguide direction of light emitted from the semiconductor light emitting element,
The current confinement part has a layer width smaller than a layer width of the second conductivity type upper first cladding layer and the upper first cladding layer, and the first conductivity type current blocking layer upward from the semiconductor active layer side And a second conductive type upper second cladding layer buried in the step.

  In this specification, “first conductivity type” and “second conductivity type” correspond to p-type or n-type, and indicate that the conductivity types are different.

  A preferred embodiment of the semiconductor light emitting device of the present invention is one in which at least the semiconductor active layer and the upper first cladding layer constitute a ridge structure portion, and the width of the ridge structure portion is 8 μm. It is preferably 30 μm or less.

  In this specification, the width of the ridge structure portion is defined as the lowermost layer width of the semiconductor crystal layers forming the ridge structure.

  The layer width of the upper second cladding layer is preferably 2 μm or more and 3 μm or less.

  The semiconductor light emitting device of the present invention is characterized in that the emission wavelength is 0.95 μm or more and 1.15 μm or less.

  The semiconductor light-emitting device of the present invention is a superluminescent diode or a semiconductor optical amplifier.

An optical tomographic imaging apparatus of the present invention includes a light source unit that emits low coherence light,
A splitting unit that splits the low-coherence light into measurement light and reference light; an irradiation optical system that irradiates the measurement target with the measurement light;
A combining means for combining the reference light and the reflected light from an external measurement object when the reference light or the measurement light is irradiated;
A plurality of measurement objects in which the optical path length of the reference light and the total optical path length of the measurement light and the reflected light substantially match based on the light intensity of the combined reflected light and the interference light of the reference light In an optical tomographic imaging apparatus comprising: an image acquisition means for detecting the intensity of reflected light at a position of a depth and acquiring a tomographic image of a measurement object based on the intensity at these depth positions;
The light source section includes the semiconductor light emitting device of the present invention as a light source of the low coherence light.

  The semiconductor light emitting device of the present invention has a current confinement structure having a second conductivity type upper first cladding layer and a second conductivity type having a layer width smaller than the layer width and embedded with the first conductivity type current blocking layer. Since the upper second cladding layer is formed, when the current confinement structure is formed, the etching process may be performed only on the second conductivity type upper second cladding layer, and the optical waveguide region including the active layer is etched. There is no need. For this reason, the waveguide structure is not easily damaged due to an etching failure such as over-etching, and therefore the current confinement characteristic is hardly deteriorated.

  In particular, in broadband semiconductor light emitting devices such as SLD and SOA, where etching defects are likely to occur and the film thickness is different in the waveguide direction of the emitted light, the effect on the device characteristics due to the etching defects is greatly reduced. can do.

  Therefore, according to the present invention, it is possible to provide a semiconductor light emitting device such as an SLD or an SOA having a good current confinement structure with less structural irregularities of the waveguide and good beam characteristics.

  Further, when the width of the ridge structure portion is 8 μm or more and 30 μm or less, the crystallinity can be improved.

"Semiconductor light emitting device"
A semiconductor light emitting device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall perspective view of the semiconductor light emitting device 1 of the present embodiment. This embodiment has a buried ridge stripe structure.

In the semiconductor light emitting device 1 of this embodiment shown in FIG. 1, the device end surface on the far side in the drawing is the rear end surface 1R, and the device end surface on the near side in the drawing is the front end surface (end surface on the light output side) 1F. In the present embodiment, the rear end surface 1R and the front end surface 1F are both perpendicular to the substrate surface of the semiconductor substrate 11, and the rear end surface 1R and the front end surface 1F are parallel to each other.
Hereinafter, the layer configuration of the semiconductor light emitting device 1 of the present embodiment will be described.

  In the semiconductor light emitting device 1, an n-type buffer layer 12 and an n-type lower cladding layer 13 are sequentially stacked on the upper surface of an n-type (first conductivity type) semiconductor substrate 11 from the substrate side. On the n-type lower cladding layer 13, a striped structure comprising a laminated structure of an undoped lower light guide layer 14, a semiconductor active layer 15, an undoped upper light guide layer 16 and a p-type (second conductivity type) upper first cladding layer 17. A ridge structure 20 is formed.

  The semiconductor active layer 15 is preferably a multiple quantum well active layer. In this embodiment, the composition and film thickness of each layer forming the ridge structure portion 20 are changed stepwise or continuously in the waveguide direction of the emitted light, and the wavelength of the emitted light is changed in the optical axis direction. The emission wavelength of the emitted light is modulated (see FIG. 1).

  On the ridge structure portion 20, the layer width is smaller than the layer width of the p-type upper first cladding layer 17 that is the uppermost layer of the ridge structure portion 20, and the p-type upper second layer laminated on the etching stop layer 18. A clad layer 19 is formed. The p-type upper second cladding layer 19 and the ridge structure portion 20 are sandwiched by an n-type current blocking layer 21 provided on the n-type lower cladding layer 13. Further, a p-type upper third cladding layer 22, a p-type contact layer 23, and a p-type electrode 25 are sequentially stacked on the p-type upper second cladding layer 19 and the n-type current blocking layer 21. The n-type electrode 26 is formed on the lower surface of the n-type semiconductor substrate 11.

  In the present embodiment, the current confinement portion 24 is formed of the second conductivity type upper first cladding layer 17 and a p-type upper second cladding having a layer width smaller than the layer width and embedded with the n-type current blocking layer 21. The layer 19 is formed. In the current confinement portion 24, the current block layer 21 and the other layers are designed to have different conductivity types. In such a configuration, the reverse-biased structure between the p-type upper second cladding layer 19 and the current blocking layer 21 narrows the current flowing region to the layer width of the p-type upper second cladding layer 19. Even in the ridge structure portion 20 located below the upper second cladding layer 19, current is selectively injected into the specific region 15 a corresponding to the layer width of the p-type upper second cladding layer 19. A current flows in a region having a width corresponding to the layer width of the cladding layer 19 so that the output light is converted into a single mode. Accordingly, light is guided through the current injection region 15a of the semiconductor active layer 15 and its vicinity (such as the vicinity of the current injection region 15a of the light guide layers 14 and 16). Hereinafter, the specific region 15a is referred to as a current injection region. In the drawing, for convenience, the boundary between the current injection region 15a and the non-current injection region of the semiconductor active layer 15 is clearly shown, but the boundary between the current injection region 15a and the non-current injection region is clear. is not.

The layer composition of the semiconductor light emitting device 1 and the film thickness of each layer can be appropriately designed according to the wavelength characteristics of the emitted light. For example, when emitting a broadband low-coherence light having an emission wavelength of 0.90 μm or more and 1.15 μm or less, which is suitable as a low-coherence light source for an OCT apparatus for an endoscope or the like, an InGaAs multiple quantum is used as an active layer. A well active layer or the like may be employed. Hereinafter, design examples of the composition and film thickness of the semiconductor substrate 11 and each layer will be given. In a layer that changes stepwise or continuously in the light guiding direction, the thicker value is shown.
Semiconductor substrate 11: n-GaAs substrate,
n-type buffer layer 12: n-GaAs layer (0.2 μm thick, carrier concentration 5.0 × 10 ¹⁷ cm ⁻³ ),
n-type lower cladding layer 13: n-In _0.49 Ga _0.51 P layer (2.0 μm thick, carrier concentration 5.0 × 10 ¹⁷ cm ⁻³ ),
Lower light guide layer 14: undoped GaAs layer (34 nm thick),
Semiconductor active layer 15: InGaAs multiple quantum well active layer (laminated structure in which 6 nm thick quantum well layers and 10 nm thick barrier layers are alternately stacked),
Upper light guide layer 16: undoped GaAs layer (34 nm thick),
p-type upper first cladding layer 17: p-In _0.49 Ga _0.51 P layer (0.2 μm thickness, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ),
p-type etching stop layer 18: p-GaAs layer (10 nm thick, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ),
p-type upper second cladding layer 19: p-In _0.49 Ga _0.51 P layer (0.5 μm thick, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ),
n-type current blocking layer 21: n-In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P layer (0.5 μm thickness, carrier concentration 1.0 × 10 ¹⁸ cm ⁻³ ),
p-type upper third cladding layer 22: p-In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P layer (1.3 μm thickness, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ),
p-type contact layer 23: p-GaAs layer (2.0 μm thick, carrier concentration 1.0 × 10 ¹⁹ cm ⁻³ ).

  It has been described that the thickness and composition of each layer forming the ridge structure portion 20 and the p-type etching stop layer 18 change stepwise or continuously in the light guiding direction. In the present embodiment, as shown in the drawing, the semiconductor light emitting device 1 has different film thicknesses and compositions in the respective layers forming the ridge structure portion 20 in two regions in the light guiding direction (e region, The thickness of the e region on the light output side is thicker. At the boundary between the e region and the f region, both the film thickness and the composition are inclined so that the film thickness and the composition continuously change between the two regions. The width in the waveguide direction of the emitted light in the e region and the f region is not particularly limited and can be appropriately designed according to the wavelength characteristics of the emitted light.

  2A and 2B are a cross-sectional view along A-A ′ and a cross-sectional view along B-B ′ in FIG. 1. 2A and 2B, each of the layers constituting the ridge structure portion 20 is thicker in the direction of FIG. 2A, and the thickness of the layers other than the ridge structure portion 20 varies between FIG. 2A and FIG. 2B. And is substantially uniform in a plane. The energy band gap Eg of a semiconductor crystal varies depending on the film thickness and composition. In the present embodiment, the e region on the light output side is designed so that Eg is smaller than that in the f region, that is, the emission wavelength in the e region is longer.

  As described above, light having different emission (center) wavelengths is emitted in the e region and the f region inside the semiconductor light emitting device 1, and thus the light emitted from each region is mixed. Broadband light La having a wide spectrum half width is emitted. Therefore, according to the semiconductor light emitting device 1, by changing the film thickness and composition of the e region and the f region and adjusting the energy band gap of the e region and the f region, broadband light La having desired wavelength characteristics can be obtained. Can be injected.

  The width d of the ridge structure 20 is preferably 8 μm or more and more preferably 10 μm or more in order to make each semiconductor layer forming the ridge structure 20 have good crystallinity. Further, if the width d is excessively wide, it is difficult to obtain a desired energy band gap Eg, and therefore desired wavelength modulation cannot be performed.

  In the case of having such a ridge structure portion 20, in the semiconductor light emitting device 1, the broadband light La is made to be a single mode light by setting the layer width of the p-type upper second cladding layer 19 to 2 μm to 3 μm. Can do. Since such a ridge structure portion 20 positioned at the layer width of the p-type upper second cladding layer 19 has good crystallinity, it can be a broadband single-mode light La with good beam characteristics. The crystallinity of the ridge structure 20 will be described later.

Below, the manufacturing method of the semiconductor light-emitting device 1 of this embodiment is shown.
A manufacturing example of the semiconductor light emitting device 1 of the present embodiment will be described with reference to FIGS. 3A to 3F.
In the present embodiment, the semiconductor light emitting device 1 is manufactured by a selective growth technique using a dielectric patterning mask.

  First, a semiconductor substrate 11 is prepared, and an n-type buffer layer 12 and an n-type lower cladding layer 13 are sequentially formed on substantially the entire surface of the substrate. In this embodiment, the method for forming each semiconductor layer and various films is not particularly limited, and examples thereof include a metal organic chemical vapor deposition method (MOCVD method) and a molecular beam epitaxy method.

Next, a dielectric mask M for selective growth having a pattern corresponding to the ridge structure portion 20 is formed on the n-type lower cladding layer 13 (FIG. 3A). First, a SiO ₂ film is formed on substantially the entire surface of the n-type lower cladding layer 13, and the selective growth dielectric mask M is patterned by photolithography.

  The selective growth technique is a method in which a semiconductor crystal is vapor-phase grown only in a region not masked by the dielectric mask M. In the case of a mixed crystal semiconductor crystal, the mixed crystal semiconductor crystal is formed by changing the width of the mask. The concentration gradient in the gas phase of each source species including atoms and the effective movement distance due to surface migration change, and the growth layer thickness and composition can be varied. Therefore, according to the selective growth technique, the semiconductor light emitting devices 1 having two regions having different film thicknesses and compositions in the waveguide direction of the emitted light can be collectively manufactured without dividing each region.

  In the semiconductor light emitting device 1 according to the present embodiment, since the film thickness and composition of the ridge structure 20 can be changed in the waveguide direction of the emitted light, the emission wavelength can be modulated. The pattern of the dielectric mask M (mask width, inter-mask width, etc.) may be formed so as to have a desired film thickness and composition.

  The semiconductor light emitting device 1 of the present embodiment has a different film thickness and composition (e region, f region) in each layer forming the ridge structure portion 20 in two regions in the light guiding direction, and the light output side The film thickness in the e region is larger. At the boundary between the e region and the f region, both the film thickness and the composition are inclined so that the film thickness and the composition continuously change between the two regions. The mask pattern of the dielectric mask M shown in FIG. 3A is an example of a mask pattern used when configuring such a semiconductor light emitting element 1.

  In FIG. 3A, since the ridge structure portion 20 is formed in a region sandwiched between the dielectric masks M, the opening width D of the dielectric mask M is the same as the width d of the ridge structure portion 20.

  In the selective growth technology, it has been stated that the source species move due to surface migration, but in the region of 2 to 3 μm near the mask, it is difficult to achieve good crystal growth due to the effect of surface migration from the side, and the resulting crystals deteriorate. As a result, a semiconductor light emitting device with good light emission characteristics cannot be obtained. Accordingly, the opening width D is preferably 8 μm or more, more preferably 10 μm or more, considering the influence of migration from both sides and the width of the light emitting region. On the other hand, if the opening width D is too wide, a composition distribution and a film thickness distribution are likely to be formed in the direction of the opening width D, the device characteristics are deteriorated, and it is difficult to obtain a desired energy band gap Eg. Accordingly, the desired wavelength modulation cannot be performed, so that the thickness is preferably 30 μm or less. As described above, when single mode light is used, the light emitting region is 2 to 3 μm. Therefore, if the aperture width D is in the above range, a portion having good crystallinity that is not affected by surface migration is considered to be a light emitting region. It can be.

  The width of the dielectric mask M may be determined in accordance with the film thickness and composition of the ridge structure portion 20, and the width of the film whose thickness is desired to be relatively increased may be increased. As shown in the drawing, in the present embodiment, the width of the dielectric mask M is increased so that the film thickness is increased in the e region on the light output side.

  Next, the ridge structure 20 is formed by selective growth. With the dielectric mask M placed thereon, the undoped lower light guide layer 14, the multiple quantum well active layer 15, the undoped upper light guide layer 16, and the p-type upper first cladding layer 17 are sequentially formed to form the ridge structure portion 20. Then, an etching stop layer 18 is formed thereon. Since these layers are selectively grown by the dielectric mask M having a pattern as shown in FIG. 3A, as shown in FIG. 3B, the ridge whose thickness is changed by changing in the waveguide direction of the emitted light. The structure part 20 is formed. Similar to the change in the film thickness, the composition of each layer also changes in the waveguide direction, so that the emission wavelength can be made different at different film thickness portions in the ridge structure portion 20.

  Next, the dielectric mask M is removed (FIG. 3C), and a p-type upper second cladding layer 19 is formed thereon (FIG. 3D). Since the dielectric mask M is removed, the film thickness of the p-type upper second cladding layer 19 and the layer formed after the layer is substantially uniform in the entire region.

  Next, a current confinement portion 24 comprising a p-type upper first cladding layer 17 and a p-type upper second cladding layer 19 having a layer width smaller than the layer width and embedded with an n-type current blocking layer 21 is formed. Form.

  An etching mask is arranged on the p-type upper second cladding layer 19 so that the cladding layer 19 has a desired layer width, and the p-type upper second cladding layer 19 is etched. (FIG. 3E), and an n-type current blocking layer 21 is formed so that the p-type upper second cladding layer 19 is embedded. The layer width of the p-type upper second cladding layer 19 only needs to be smaller than that of the p-type upper first cladding layer 17, and is preferably in the range of 2 μm or more and 3 μm or less in order to obtain single mode light.

  As described above, in the present embodiment, the current confinement part 24 etches only the p-type second cladding layer having a substantially uniform thickness in the entire region without etching the optical waveguide region including the active layer 15. It is formed by embedding it with an n-type current blocking layer 21. Therefore, the current confinement structure can be formed with almost no influence on the waveguide structure due to etching defects such as overetching, and the thickness of the current blocking layer 21 can be made substantially uniform in the entire region. it can. For this reason, the waveguide structure is not easily damaged due to an etching failure such as overetching, and element characteristics are not easily deteriorated due to a current constriction failure.

  In particular, as in the semiconductor light emitting device 1 of this embodiment, a broadband semiconductor light emitting device having a ridge structure portion 20 having a different thickness in the waveguide direction of emitted light is obtained by directly etching the ridge structure portion 20. Due to the difference in film thickness, over-etching is likely to occur in a thin region, and there is a high possibility that the device characteristics will be greatly deteriorated. As described above, according to the present embodiment, since it is not necessary to etch the ridge structure portion 20 having a different thickness in the light guiding direction, a broadband semiconductor light emitting device 1 having good device characteristics is provided. be able to.

  The current confinement portion having such a structure and the method of manufacturing the current confinement portion have not only a ridge structure portion having a different film thickness in the waveguide direction of emitted light as in the present embodiment, but also the film thickness in the light waveguide direction. The present invention can also be applied to a substantially uniform semiconductor light emitting device. Similarly, the waveguide structure is not easily damaged due to etching failure, and device characteristic deterioration due to current confinement failure is less likely to occur. For example, the present invention can be applied to a narrow band semiconductor light emitting device such as a semiconductor laser.

Finally, the etching mask on the p-type upper second cladding layer is removed, and then a p-type upper third cladding layer 22 and a p-type contact layer 23 are sequentially formed, and a p-type electrode 25 is further formed thereon. The n-type electrode 26 is formed on the lower surface of the type semiconductor substrate 11 to complete the semiconductor light emitting device 1 (FIG. 3F).
As described above, the semiconductor light emitting device 1 of this embodiment is manufactured.

  In the semiconductor light emitting device 1 of the present embodiment, the current confinement structure is embedded with the second conductivity type upper first cladding layer 17 and the first conductivity type current blocking layer 21 having a layer width smaller than the layer width. Since the second conductive type upper second cladding layer 19 is formed, when the current confinement structure is formed, the etching process may be performed only on the second conductive type upper second cladding layer 19. There is no need to etch the included optical waveguide region. For this reason, the waveguide structure is not easily damaged due to an etching failure such as over-etching, and therefore the current confinement characteristic is hardly deteriorated.

  In particular, even in a wide-band semiconductor light emitting device in which the film thickness is varied in the waveguide direction of the emitted light, which is likely to cause etching defects, the influence on the element characteristics due to the etching defects can be greatly reduced. .

  Therefore, according to the present invention, it is possible to provide a semiconductor light emitting device 1 such as an SLD or SOA having a good current confinement structure with few waveguide irregularities and good beam characteristics.

  Further, when the width of the ridge structure portion is 8 μm or more and 30 μm or less, the crystallinity can be improved.

  The semiconductor light emitting device 1 of the present embodiment manufactured with the thickness and composition of the above design example has a center wavelength of 1.102 μm, a light emission half width of 186.3 nm, and an output of 19.6 mW, as shown in the examples described later. It is an SLD that can emit a wide-band and high-output low-coherence light. This emission wavelength band is in the range of 0.90 μm or more and 1.15 μm or less suitable as a low coherence light source for the endoscope OCT apparatus described in the background art section, and by appropriately designing the layer structure, Wavelength modulation is also possible within a certain range. Therefore, the semiconductor light emitting element 1 of the present embodiment can be preferably used as a low-coherence light source for an endoscope OCT apparatus having a wide band and a high output.

  In the SLD, the emission wavelength band can be adjusted by the composition, layer structure, and the like of the active layer. Therefore, according to the present embodiment, it is possible to provide a wide band and high output SLD as well as the emission wavelength band. .

  Further, the semiconductor light emitting device 1 of the present embodiment can be used as a semiconductor optical amplifier (SOA).

(Design change example)
The semiconductor light emitting device 1 of the present embodiment is not limited to the above configuration, and can be appropriately changed in design.
In the above embodiment, the semiconductor light emitting device 1 has the buried ridge stripe structure, but may have other structures such as an internal stripe structure.

  In the above embodiment, the optical waveguide has a waveguide structure extending in the same direction as the normal direction of the element end face. However, at least a part of the optical waveguide extends obliquely with respect to the normal direction of the element end face. A waveguide structure may be used.

  In the above embodiment, the ridge structure 20 is manufactured by the selective growth technique, but the manufacturing method is not limited.

  Moreover, in the said embodiment, although it was set as the structure from which the light emission wavelength differs in two area | regions of the waveguide direction of the light to inject | emitted, the number of area | regions is not restrict | limited and it can design suitably according to the wavelength characteristic of the light to inject | emits.

  Furthermore, since the semiconductor light emitting device 1 of the present embodiment has a configuration in which a plurality of continuous regions emitting different wavelengths are provided in the waveguide direction of emitted light on the same substrate, a single semiconductor substrate is used. In addition, it can be applied to a semiconductor optical integrated device in which a plurality of optical devices having different functions are integrated.

"Optical tomography system"
With reference to the drawings, an optical tomographic imaging apparatus including the semiconductor light emitting device 1 of the above embodiment will be described. FIG. 4 is a schematic configuration diagram of the optical tomographic imaging apparatus of the present embodiment.

  An optical tomographic imaging apparatus 200 shown in FIG. 4 acquires a tomographic image to be measured by the above-described TD-OCT (Time Domain Optical Coherence Tomography) measurement. The optical tomographic imaging apparatus 200 emits a laser beam La and collects light. A light source unit (light source unit) 210 composed of a lens 51, a light splitting means 2 for splitting a laser beam La emitted from the light source unit 210 and propagating through an optical fiber FB1, and a laser beam La passing through the light beam measuring unit L1 The light splitting means 3 that splits the light into the reference light L2, the optical path length adjusting means 220 that adjusts the optical path length of the reference light L2 split by the light splitting means 3 and propagated through the optical fiber FB3, and the light splitting means 3 The optical probe 230 for irradiating the measuring object S with the measuring light L1 propagated through the optical fiber FB2, and the measuring light L1 is irradiated from the optical probe 230 to the measuring object S. When the reflected light L3 from the measurement object and the reference light L2 are combined, the combining means 4 (also serving as the light splitting means 3) combines the reflected light L3 and the reference light. Interference light detection means 240 for detecting interference light L4 with L2.

  The light source 50 is an SLD that emits low-coherent light La having a center wavelength (λc) of 1.1 μm and a spectral full width at half maximum of 75 nm. The light source unit 210 transmits the light emitted from the light source 50 and the light source 50 to the optical fiber FB1. And an optical system 51 for making the light incident inside. This light source 50 is the semiconductor light emitting device 1 of the above embodiment.

  The optical path length adjusting means 220 is a mirror that is movable in the direction of arrow A in the figure so as to change the distance between the collimator lens 61 that collimates the reference light L2 emitted from the optical fiber FB3 and the collimator lens 61. 63 and mirror moving means 64 for moving the mirror 63, and has a function of changing the optical path length of the reference light L2 in order to change the measurement position in the measurement object S in the depth direction. . The reference light L 2 whose optical path length has been changed by the optical path length adjusting means 220 is guided to the multiplexing means 4.

  The optical probe 230 includes a cylindrical probe outer cylinder 55 whose tip is closed, and one optical fiber 53 disposed in the inner space of the probe outer cylinder 55 so as to extend in the axial direction of the outer cylinder 55. A prism mirror 57 that deflects the light L emitted from the tip of the optical fiber 53 in the circumferential direction of the probe outer cylinder 55, and the light L emitted from the tip of the optical fiber 53 is arranged on the outer circumference of the probe outer cylinder 55. A rod lens 58 that condenses light so as to converge on the measurement target S as a body to be scanned, and a motor 54 that rotates the prism mirror 57 about the axis of the optical fiber 53 are provided.

  The light splitting means 3 is composed of, for example, a 2 × 2 optical fiber coupler, and splits the light La guided from the light source unit 210 through the optical fiber FB1 into the measurement light L1 and the reference light L2. The light splitting means 3 is optically connected to the two optical fibers FB2 and FB3, respectively. The measurement light L1 is guided through the optical fiber FB2, and the reference light L2 is guided through the optical fiber FB3. The light splitting means 3 in this example also functions as the multiplexing means 4.

  An optical probe 230 is optically connected to the optical fiber FB2, and the measurement light L1 is guided from the optical fiber FB2 to the optical probe 230. The optical probe 230 is inserted into a body cavity from a forceps port through a forceps channel, for example, and is detachably attached to the optical fiber FB2 by an optical connector 31.

  Further, the multiplexing means 4 is composed of a 2 × 2 optical fiber coupler as described above, and the reference light L2 that has been subjected to frequency shift and change of the optical path length by the optical path length adjusting means 230, and the reflected light L3 from the measurement object S. Are combined and emitted to the interference light detection means 240 side via the optical fiber FB4.

  The interference light detection means 240 detects the light intensity of the interference light L4. The light detectors 40a and 40b that measure the light intensity of the interference light L4, the detection value of the light detector 40a, and the light detector 40b. And an arithmetic unit 41 that performs balance detection by adjusting the input balance of the detected values. Specifically, when the difference between the total optical path length of the measuring light L1 and the reflected light L3 reflected or backscattered at a point on the measuring object S and the optical path length of the reference light L2 is shorter than the coherence length of the light source Only an interference signal with an amplitude proportional to the amount of reflected light is detected. By scanning the optical path length by the optical path length adjusting unit 220, the reflection point position (depth) of the measurement target S from which the interference signal is obtained changes, and the interference light detection unit 240 reflects the reflection at each measurement position of the measurement target S. A rate signal is detected. The information on the measurement position is output from the optical path length adjustment unit 220 to the image acquisition unit 250. Based on the information on the measurement position in the mirror moving unit 64 and the signal detected by the interference light detection unit 240, the image acquisition unit 250 obtains the reflected light intensity distribution information in the depth direction of the measurement target S.

  The operation of the optical tomographic imaging apparatus 1 having the above configuration will be described below. When acquiring a tomographic image, the optical path length is adjusted so that the measuring object S is positioned within the measurable region by first moving the mirror 63 in the direction of arrow A. Thereafter, the light La is emitted from the light source unit 210, and the light La is split into the measurement light L1 and the reference light L2 by the light splitting means 3. The measurement light L1 is emitted from the optical probe 230 into the body cavity and irradiated to the measurement object S.

  Then, the reflected light L3 from the measuring object S is combined with the reference light L2 reflected by the reflecting mirror 62 to generate interference light L4.

  The interference light L4 is split by the light splitting means 3 (multiplexing means 4), one of which is input to the photodetector 40a and the other is input to the photodetector 40a.

  The interference light detection means 240 adjusts the input balance between the detection value of the light detector 40 a and the detection value of the light detector 40 b to perform balance detection, detects the light intensity of the interference light L 4, and sends it to the image acquisition means 250. Output.

  Based on the detected light intensity of the interference light L4, the image acquisition means 250 obtains reflected light intensity information at a predetermined depth of the measuring object S. Next, the optical path length adjustment unit 330 changes the optical path length of the reference light L2, similarly detects the light intensity of the interference light L4, and acquires reflected light intensity information at different predetermined depths. By repeating such an operation, the reflected light intensity information in the depth direction (one-dimensional) of the measuring object S can be acquired.

  Then, if the measurement light L1 is scanned on the measurement target S by rotating the prism mirror 57 by the motor 54 of the optical probe 230, the depth direction of the measurement target S in each portion along the scanning direction. Since information is obtained, a tomographic image of a tomographic plane including this scanning direction can be acquired. The tomographic image acquired in this way is displayed on the display device 260. For example, by moving the optical probe 230 in the left-right direction in FIG. 9 and causing the measuring object S to scan in the second direction orthogonal to the scanning direction, the second object is obtained. It is also possible to obtain a tomographic image of a tomographic plane including the direction.

The tomographic image acquired in this way is displayed on the display device 260. For example, by moving the optical probe 230 in the left-right direction in FIG. 9 and causing the measuring object S to scan in the second direction orthogonal to the scanning direction, the second object is obtained. It is also possible to obtain a tomographic image of a tomographic plane including the direction.
The optical tomographic imaging apparatus 200 of the present embodiment is configured as described above.

  As described in the background section, the performance of the optical tomographic imaging apparatus largely depends on the broadband property of the light source. Since the optical tomographic imaging apparatus 200 according to the present embodiment is configured using the semiconductor light emitting element (SLD) 1 according to the present embodiment having a wide band and high output, a clear and high-definition tomographic image is acquired. can do.

(Design changes)
The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate. In the above-described embodiment, an optical tomographic imaging apparatus that acquires an image by TD-OCT measurement is described as an example, but the present invention can also be applied to other optical tomographic imaging apparatuses.

  Embodiments according to the present invention will be described.

  The semiconductor light emitting device (SLD) 1 of the above embodiment was manufactured by the following procedure. The composition and thickness of the semiconductor substrate 11 and each layer were as in the design example given in the embodiment.

Crystal growth was performed by metal organic chemical vapor deposition (MOCVD). Crystal growth was performed by metal organic chemical vapor deposition (MOCVD). As the source gas, TEG (triethylgallium) / TMA (trimethylaluminum) / TMI (trimethylindium) / AsH ₃ (arsine) / PH ₃ (phosphine) was used. SiH ₄ (monosilane) was used as the n-type dopant source, and DEZ (diethyl zinc) was used as the p-type dopant source.

First, an n-type buffer layer 12 and an n-type lower first cladding layer 13 are successively grown on an n-type semiconductor substrate 11 under the conditions of a growth temperature of 600 to 700 ° C. and a pressure of 10.1 kPa (first time Crystal growth), a SiO ₂ film for selective growth was formed and patterned using photolithography to form a dielectric mask M (FIG. 3A).

  Next, using the dielectric mask M as a selective growth mask, the undoped lower light guide layer 14, the InGaAs strained quantum well active layer 15, the undoped upper light guide layer 16, and the p-type upper first cladding layer 17 are selectively grown to form a ridge structure portion. 20 is formed, and a p-type etching stop layer 18 is selectively grown thereon (second crystal growth) (FIG. 3B), and the dielectric mask M for selective growth is removed (FIG. 3C). The upper second cladding layer 19 was formed by the third growth (FIG. 3D).

Next, an etching SiO ₂ film was formed, and the etching SiO ₂ film was patterned such that the p-type upper second cladding layer 19 had a layer width of 2 μm by etching. Then, a striped p-type upper second cladding layer 19 having a layer width of 2 μm was formed by etching (FIG. 3E).

Next, the etching stop layer 18 exposed on the surface was removed, and an n-type current blocking layer 21 was formed so that the p-type upper second cladding layer 19 was embedded (fourth crystal growth). Thereafter, the SiO ₂ mask on the stripe is removed, a p-type upper third cladding layer 22 and a p-type contact layer 23 are formed, and a p-type electrode 25 and an n-type electrode 29 are formed by vapor deposition and heat treatment (FIG. 3F).

  A comparison was made between the spectrum shape and output of the semiconductor light emitting device (SLD) 1 of the present embodiment manufactured as described above and the conventional SLD in which a ridge was formed by etching a selective growth layer. The waveguide length of the device was 1.5 mm, the ridge width was 3 μm, and the measurement current was 200 mA. In the conventional SLD, the peak on the short wave side is low, the spectrum shape is asymmetric, the wavelength is 1.102 μm, and the half width is 55 nm. The output was as low as 1.2 mW, which was a performance that could not be used as a light source for an OCT apparatus. In comparison, the peak of the SLD of the present invention was close to a Gaussian shape, the wavelength was 1.102 μm, the emission half-value width was 186.3 nm, and the output was 19.6 mW, which was sufficient as a light source for OCT. .

  The semiconductor light emitting device of the present invention can be particularly preferably used for a low coherence light source for an optical image tomography apparatus such as an OCT apparatus. The semiconductor light emitting device of the present invention can be preferably used as a light source for various applications in fields such as communication, measurement, medical care, printing, and image processing in addition to the light source for the optical image tomography apparatus.

1 is a perspective view of a semiconductor light emitting device according to an embodiment of the present invention. A-A 'sectional view in FIG. B-B 'sectional drawing in FIG. The figure which shows the manufacturing process of the semiconductor light-emitting device of FIG. The figure which shows the manufacturing process of the semiconductor light-emitting device of FIG. The figure which shows the manufacturing process of the semiconductor light-emitting device of FIG. The figure which shows the manufacturing process of the semiconductor light-emitting device of FIG. The figure which shows the manufacturing process of the semiconductor light-emitting device of FIG. The figure which shows the manufacturing process of the semiconductor light-emitting device of FIG. 1 is a schematic configuration diagram showing an optical tomographic imaging apparatus according to an embodiment of the present invention.

Explanation of symbols

1 Semiconductor light emitting device (SLD)
DESCRIPTION OF SYMBOLS 11 1st conductivity type (n-type) semiconductor substrate 13 1st conductivity type (n-type) lower clad layer 15 Semiconductor active layer 15a Specific area | region of a semiconductor active layer 17 2nd conductivity type (p-type) upper 1st clad layer 19 1st 2 conductivity type (p type) upper second cladding layer 20 ridge structure portion 21 current blocking layer 23 second conductivity type contact layer 24 current confinement portion 25 second conductivity type (p type) electrode 26 first conductivity type (n type) Electrode 200 Optical tomographic imaging device 210 Light source unit (light source unit)
2, 3 Dividing means 230 Irradiation probe (irradiation optical system)
4 Multiplexing means 250 Image acquisition means S Measurement object La Low coherence light (broadband light)
L1 Measurement light L2 Reference light L3 Reflected light L4 Interference light d Width of ridge structure

Claims (7)

Current confinement for injecting current into a specific region of the semiconductor active layer on one surface of the first conductive type semiconductor substrate from above the semiconductor substrate side to the first conductive type lower cladding layer, the semiconductor active layer, and the semiconductor active layer A semiconductor light emitting device having a first conductive type electrode, a second conductive type contact layer, and a second conductive type electrode, and having a first conductive type electrode below the semiconductor active layer;
The composition and thickness of the semiconductor active layer change stepwise or continuously in the waveguide direction of light emitted from the semiconductor light emitting device,
The current confinement part has a layer width smaller than a layer width of the second conductivity type upper first cladding layer and the upper first cladding layer, and the first conductivity type current blocking layer upward from the semiconductor active layer side And a second conductivity type upper second clad layer embedded in order.   2. The semiconductor light emitting device according to claim 1, wherein at least the semiconductor active layer and the upper first cladding layer form a ridge structure portion.   3. The semiconductor light emitting element according to claim 2, wherein a width of the ridge structure portion is 8 μm or more and 30 μm or less.   4. The semiconductor light emitting element according to claim 1, wherein a layer width of the upper second cladding layer is 2 μm or more and 3 μm or less.   The semiconductor light emitting element according to claim 1, wherein an emission wavelength is 0.95 μm or more and 1.15 μm or less.   6. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is a super luminescent diode or a semiconductor optical amplifier. A light source that emits low coherence light;
A splitting unit that splits the low-coherence light into measurement light and reference light; an irradiation optical system that irradiates the measurement target with the measurement light;
A combining means for combining the reference light and the reflected light from an external measurement object when the reference light or the measurement light is irradiated;
A plurality of measurement objects in which the optical path length of the reference light and the total optical path length of the measurement light and the reflected light substantially match based on the light intensity of the combined reflected light and the interference light of the reference light In an optical tomographic imaging apparatus comprising: an image acquisition means for detecting the intensity of reflected light at a position of a depth and acquiring a tomographic image of a measurement object based on the intensity at these depth positions;
An optical tomographic imaging apparatus, wherein the light source unit includes the semiconductor light emitting element according to claim 1 as a light source of the low coherence light.