JP2011114155A - Surface-emitting laser, method of manufacturing surface-emitting laser, surface-emitting laser array element, optical scanning device, and image forming device - Google Patents

Abstract

The present invention provides a highly reliable surface-emitting laser in which oxidation from the wall surface of an element isolation groove is difficult.
A lower reflector formed by alternately laminating semiconductor films having different refractive indexes on a surface of a semiconductor substrate, an active layer made of a semiconductor film, and a current confinement layer made of a semiconductor film are different. By etching a part of the semiconductor film formed by the semiconductor layer forming step of forming the upper reflecting mirror formed by alternately laminating the semiconductor films of refractive index by epitaxial growth and the semiconductor layer forming step, A mesa structure forming step for forming a mesa structure, an element isolation groove forming step for forming an element isolation groove by etching the semiconductor film formed by the semiconductor layer formation step to the surface of the semiconductor substrate, and the element isolation groove A regrowth layer forming step of forming a regrowth layer made of a semiconductor material on the wall surface and the side surface of the mesa structure, and an insulator on the regrowth layer To solve the above problem by providing a protective film forming step of forming a protective film that, the method for manufacturing a surface-emitting type laser which is characterized by having a.
[Selection] Figure 3

Description

  The present invention relates to a surface emitting laser manufacturing method, a surface emitting laser, a surface emitting laser array element, an optical scanning device, and an image forming apparatus.

  A VCSEL (Vertical Cavity Surface Emitting Laser) is a semiconductor laser that emits light in a direction perpendicular to the substrate to be formed. It is less expensive than an edge-emitting semiconductor laser and can be two-dimensionally arrayed. Since it can be performed relatively easily and has high performance, it is used in applications such as light sources for optical communication such as optical interconnection, light sources for optical pickups, and light sources for image forming apparatuses such as laser printers. .

  Specifically, the surface emitting laser has a pair of high-reflectance multilayered DBR (Distributed Bragg Reflector) reflecting mirrors on the surface of the substrate, and between the pair of DBR reflecting mirrors. Is provided with an active layer. A spacer layer is provided between the active layer and the DBR reflector.

  Such a surface emitting laser can be driven with a low threshold current and low power consumption since the volume of the active layer can be reduced. Further, since the mode volume in the resonator is small, modulation of several tens of GHz is possible, which is advantageous for high-speed transmission. Further, the spread angle of the emitted light is small, and the coupling to the optical fiber is easy. Furthermore, it can be manufactured without cleaving, has an advantage that the device area is small, and parallelization and two-dimensional arrangement can be performed at high density.

  Because of such advantages, the surface emitting laser (VCSEL) is not limited to the application to a light transmission light source such as a LAN (Local Area Network), but between boards, in a board, between LSI chips, Application to a light source for optical transmission in a chip is expected.

  Patent Documents 1 and 2 describe surface-emitting lasers having such a configuration. FIG. 1 shows a cross-sectional structure of a conventional general surface emitting laser. A conventional general surface emitting laser has a lower DBR reflecting mirror 312, a lower spacer layer 313, an MQW active layer 314, an upper spacer layer 315, which are formed by epitaxial growth on an n-type GaAs substrate 311 which is a single crystal substrate. It has a current confinement layer 316 having a current confinement structure that is oxidized at the periphery, an upper DBR reflector 317, and a contact layer 318. The lower spacer layer 313, the MQW active layer 314, the upper spacer layer 315, the current confinement layer 316, the upper DBR reflector 317, and the contact layer 318 have a mesa structure formed by etching, and a protective film 319 is formed on the side surface of the mesa structure. The contact layer 318 is formed and connected to the p-side electrode 321, and the n-side electrode 322 is connected to the back surface of the n-type GaAs substrate 311.

  Next, a method for manufacturing the conventional general surface emitting laser shown in FIG. 1 will be described with reference to FIG.

  First, as shown in FIG. 2A, the lower portion is formed on an n-type GaAs substrate 311 by MOCVD (Metal Organic Chemical Vapor Deposition) or MBE (Molecular Beam Epitaxy). The DBR reflecting mirror 312, the lower spacer layer 313, the MQW active layer 314, the upper spacer layer 315, the current confinement layer 316, the upper DBR reflecting mirror 317, and the contact layer 318 are formed by epitaxial growth sequentially.

  The lower DBR reflecting mirror 312 changes the refractive index by changing the composition of n-type AlGaAs, and tens of pairs of n-type AlGaAs serving as a high-refractive index layer and n-type AlGaAs serving as a low-refractive index layer are alternately stacked. To form. The lower spacer layer 313 is formed of AlGaAs, the MQW active layer 314 is formed of AlGaAs having different compositions alternately to form a multiple quantum well structure, the upper spacer layer 315 is formed of AlGaAs, and the current confinement layer 316 is formed. Is formed of AlAs. Further, the upper DBR reflecting mirror 317 is formed by stacking several tens of pairs of p-type AlGaAs that is a high refractive index layer and p-type AlGaAs that is a low refractive index layer, and the contact layer 318 is made of p-type GaAs. Form.

  Next, as shown in FIG. 2B, the lower spacer layer 313, the MQW active layer 314, the upper spacer layer 315, the current confinement layer 316, the upper DBR reflector 317, and the contact layer 318 in a predetermined region are etched. Thus, the mesa structure 330 is formed. By forming the mesa structure 330, light and current can be confined in the MQW active layer 314, laser oscillation can be efficiently performed, and parasitic capacitance in high-speed modulation can be reduced.

The mesa structure 330 is formed by forming a SiO ₂ film or a SiN film (not shown) on the contact layer 318, applying a photoresist on the SiO ₂ film or the SiN film, and on the region where the mesa structure 330 is formed. After the exposure by an exposure apparatus, development is performed so that a resist pattern is formed. Using the formed resist pattern as a mask, the SiO ₂ film or SiN film in the region where the resist pattern is not formed is removed by RIE (Reactive Ion Etching) or the like to form a mesa mask made of the SiO ₂ film or SiN film. . Thereafter, another different etching gas is introduced, and the lower spacer layer 313, the MQW active layer 314, the upper spacer layer 315, the current confinement layer 316, the upper DBR reflector 317, the contact in the region where the mesa mask is not formed by RIE or the like. Layer 318 is removed. Thereafter, the mesa structure 330 is formed by removing the mesa mask made of the SiO ₂ film or the SiN film. Dry etching such as RIE is generally used because it can be etched in a direction perpendicular to the n-type GaAs substrate 311, but can also be formed by wet etching.

  Next, as shown in FIG. 2C, the current confinement layer 316 is selectively oxidized. Specifically, after the mesa structure 330 is formed, heat treatment is performed in a water vapor atmosphere to oxidize the etched surface of the current confinement layer 316 exposed on the side surface of the mesa structure 330. As a result, the peripheral portion of the mesa structure 330 is oxidized to become AlxOy which is an insulator, and the selective oxidation region 316a is formed. A current confinement structure is formed by the selective oxidation region 316a and the current confinement region 316b which is not oxidized in the central portion.

Next, as shown in FIG. 2D, an element isolation groove 331 for element isolation is formed, and a protective film 319 is further formed. Specifically, a resist pattern or the like is formed in a region other than the region where the element isolation groove 331 is formed, and etching is performed by dry etching or wet etching until the surface of the n-type GaAs substrate 311 is exposed. Note that there is a method of separating by chipping or the like when performing chip separation without forming the element isolation groove 331, but in this case, the side surface of the epitaxially grown crystal layer is exposed at the time of element isolation. Absent. After forming the element isolation groove 331, a protective film 319 is formed by forming a SiO ₂ film or a SiN film on the entire surface including the side surface of the mesa structure 330 and the wall surface of the element isolation groove 331 by CVD (Chemical Vapor Deposition). To do.

  Thereafter, the protective film 319 formed on the contact layer 318 is removed by etching to form a p-side electrode 321 connected to the contact layer 318 as shown in FIG. A side electrode 322 is formed. Thereafter, by separating the elements, a surface emitting laser can be manufactured.

By the way, in the case of manufacturing the surface emitting laser described in Patent Documents 1 and 2 described above, the protective film 319 is usually formed of a SiO ₂ film or a SiN film from the viewpoint of insulation. However, the SiO ₂ film or the SiN film is a material different from other III-V compound semiconductors constituting the surface emitting laser, and oxygen, water vapor, or the like can pass through such a protective film 319. It is difficult to form a dense film that does not exist on the side surface of the mesa structure 330 and the wall surface of the element isolation groove 331.

For this reason, even when the protective film 319 made of the SiO ₂ film or the SiN film is formed on the side surface of the mesa structure 330 and the wall surface of the element isolation groove 331, oxygen or water vapor penetrates through the protective film 319 and enters the Al composition. High AlGaAs layer and AlAs layer are gradually oxidized from the side surface of the mesa structure 330 and the wall surface of the element isolation groove 331. In particular, the lower DBR reflecting mirror 312 and the upper DBR reflecting mirror 317 are formed by alternately laminating a low refractive index layer having a high Al composition and a high refractive index layer having a low Al composition, and constitute a DBR. The thickness of each layer is formed so as to be an integral multiple of λ / (4 × n) with respect to the laser oscillation wavelength λ, where n is the refractive index. Since several tens of layers are formed, a low refractive index layer having a high Al composition is particularly susceptible to oxidation.

  In general, surface-emitting lasers are often configured to cause heat generated by laser oscillation from the n-type GaAs substrate 311 side. In this case, the low refractive index layer in the lower DBR reflecting mirror 312 has a thermal conductivity. It is advantageous to use a high AlAs layer. However, when the element isolation trench 331 is formed, the side surface of the AlAs layer in the lower DBR reflecting mirror 312 is exposed by etching, and thus is easily oxidized by oxygen or water vapor that has entered through the protective film 319.

  As described above, when the AlAs layer constituting the surface-emitting laser, particularly the lower DBR reflecting mirror 312 is oxidized, the volume of the oxidized layer is changed to generate stress, so that the element constituting the surface-emitting laser is formed. It is destroyed and adversely affects the reliability of the device using the element constituting the surface emitting laser and the element constituting the surface emitting laser.

  The present invention has been made in view of the above, and provides a surface-emitting laser having a structure in which oxidation from the side of a layer of AlGaAs, AlAs or the like having a high Al composition constituting a lower DBR reflecting mirror or the like is prevented. Furthermore, it is an object of the present invention to provide a highly reliable surface emitting laser, surface emitting laser array, optical scanning device, and image forming apparatus.

  The present invention is different from a lower reflector formed by alternately laminating semiconductor films having different refractive indexes on a surface of a semiconductor substrate, an active layer made of a semiconductor film, and a current confinement layer made of a semiconductor film. By etching a part of the semiconductor film formed by the semiconductor layer forming step of forming the upper reflecting mirror formed by alternately laminating the semiconductor films of refractive index by epitaxial growth and the semiconductor layer forming step, A mesa structure forming step for forming a mesa structure, an element isolation groove forming step for forming an element isolation groove by etching the semiconductor film formed by the semiconductor layer formation step to the surface of the semiconductor substrate, and the element isolation groove A regrowth layer forming step of forming a regrowth layer made of a semiconductor material on the wall surface and the side surface of the mesa structure; and And having a protective film forming step of forming a protective film.

In the present invention, the mesa structure forming step forms the mesa structure by performing etching after forming a mesa mask made of SiO ₂ or SiN in a region where the mesa structure is formed, The regrowth layer forming step is performed with the mesa mask left.

  In the invention, it is preferable that the regrowth layer is a group III-V compound semiconductor containing no Al.

  In the present invention, the regrowth layer is GaAs.

  Further, the present invention is characterized in that the regrowth layer is formed by MOCVD or MBE.

  The present invention also provides a lower reflector formed by alternately laminating semiconductor films having different refractive indexes on the surface of a semiconductor substrate, and an active layer made of a semiconductor material on the lower reflector. A current confinement layer in which a current confinement structure is formed by oxidizing a partial region of a semiconductor material on the active layer and a semiconductor film having a different refractive index are alternately laminated on the current confinement layer. A mesa structure is formed by etching a part of the semiconductor layer, and a lower electrode is connected to the semiconductor substrate, and an upper electrode is connected to the upper reflector. In a surface-emitting laser that emits laser light substantially perpendicularly to the semiconductor substrate surface by flowing a current between the upper electrode and the lower electrode, In the partial reflector, the active layer, the current confinement layer, and the upper reflector, an element isolation groove for element isolation is formed, and on the wall surface of the element isolation groove and the side surface of the mesa structure, A regrowth layer made of a semiconductor material, and a protective film is formed on the regrowth layer.

  In the invention, it is preferable that the mesa structure is formed by removing a part of the upper reflecting mirror, the active layer, the current confinement layer, and the lower reflecting mirror.

  Further, the present invention is characterized in that the element isolation trench is formed until the surface of the semiconductor substrate is exposed.

  The regrowth layer may be formed by MOCVD or MBE.

  In the invention, it is preferable that the regrowth layer is a group III-V compound semiconductor containing no Al.

  In the present invention, the regrowth layer is GaAs.

In addition, the present invention is characterized in that the protective film has a configuration in which SiN, SiO ₂ or a combination of SiN and SiO ₂ is used.

  In the present invention, the lower reflecting mirror is characterized in that the low refractive index layer is made of AlAs.

  The present invention is characterized in that a plurality of the surface emitting lasers described above are arranged on the same semiconductor substrate.

  The present invention also provides an optical scanning device that scans a surface to be scanned with a light beam, the light source unit having the surface-emitting laser array element described above, and a deflecting unit that deflects the light beam from the light source unit; And a scanning optical system for condensing the light beam deflected by the polarizing means on the surface to be scanned.

  According to another aspect of the present invention, there is provided an optical scanning device that scans a surface to be scanned with a plurality of light beams, the light source unit having the surface-emitting laser array element described above, and the plurality of light beams from the light source unit. A deflecting unit and a scanning optical system for condensing a plurality of light beams deflected by the polarizing unit on a surface to be scanned are provided.

  In addition, the present invention includes at least one image carrier and at least one optical scanning device according to claim 15 that scans the at least one image carrier with a light beam including image information. It is characterized by that.

  Further, the present invention provides at least one image carrier, and at least one optical scanning device according to claim 16 that scans a plurality of light beams including image information with respect to the at least one image carrier. It is characterized by having.

  According to the present invention, the image is a color image.

  According to the present invention, it is possible to provide a surface emitting laser having a structure in which oxidation from the side of a layer of AlGaAs, AlAs or the like having a high Al composition constituting the lower DBR reflector is prevented, and further, reliability Surface emitting laser, surface emitting laser array, optical scanning device, and image forming apparatus can be provided.

Sectional view of a conventional surface emitting laser Process diagram of a conventional surface emitting laser manufacturing method Sectional drawing of the surface emitting laser in 1st Embodiment Manufacturing process diagram of surface emitting laser according to the first embodiment (1) Manufacturing process diagram of surface-emitting type laser according to the first embodiment (2) Configuration of an image forming apparatus according to a second embodiment Schematic diagram of an optical scanning device according to the second embodiment Schematic diagram of surface-emitting laser array element in the second embodiment Configuration of an image forming apparatus capable of color printing according to the second embodiment

Embodiments of the present invention will be described [First Embodiment]
The surface emitting laser according to the first embodiment will be described. The surface emitting laser according to the present embodiment is a surface emitting semiconductor laser formed of a III-V group compound semiconductor.

(Surface emitting laser)
The surface-emitting laser in the present embodiment will be described based on FIG. The surface emitting laser according to the present embodiment includes a lower DBR reflecting mirror 12, a lower spacer layer 13, an MQW active layer 14, an upper spacer layer 15, a current confinement layer 16, an upper portion formed on an n-type GaAs substrate 11 by epitaxial growth. A DBR reflecting mirror 17 and a contact layer 18 are provided.

The lower DBR reflecting mirror 12 is formed by alternately stacking 40.5 pairs of n-type Al _0.3 Ga _0.7 As and n-type AlAs, and Se (selenium) as a dopant is 5 × It is doped with 10 ¹⁷ cm ^{−3 to} 2 × 10 ¹⁸ cm ⁻³ . The lower DBR reflecting mirror 12 is formed by laminating a low refractive index layer and a high refractive index layer, but a layer formed of n-type AlAs becomes a low refractive index layer, and n-type Al _0.3 Ga. A layer formed of _0.7 As becomes a high refractive index layer.

The lower spacer layer 13 is made of non-doped Al _0.6 Ga _0.4 As.

The MQW active layer 14 has a multiple quantum well structure in which Al _0.1 Ga _0.9 As and Al _0.3 Ga _0.7 As are alternately stacked.

The upper spacer layer 15 is made of non-doped Al _0.6 Ga _0.4 As.

  The current confinement layer 16 is formed of p-type AlAs and is selectively oxidized later to form a current confinement structure including a selective oxidation region 16a and a current confinement region 16b.

The upper DBR reflecting mirror 17 is formed by alternately stacking 21 pairs of p-type Al _0.9 Ga _0.1 As and p-type Al _0.3 Ga _0.7 As. The upper DBR reflecting mirror 17 is doped with Zn as a dopant by 5 × 10 ¹⁷ cm ^{−3 to} 6 × 10 ¹⁸ cm ⁻³ . The upper DBR reflecting mirror 17 is formed by laminating a low refractive index layer and a high refractive index layer, but a layer formed of p-type Al _0.9 Ga _0.1 As is a low refractive index layer. The layer formed of p-type Al _0.3 Ga _0.7 As is a high refractive index layer.

  The contact layer 18 is formed of a film made of p-type GaAs.

  Thereafter, the mesa structure 30 is formed by etching the lower spacer layer 13, the MQW active layer 14, the upper spacer layer 15, the current confinement layer 16, the upper DBR reflector 17 and the contact layer 18 in a predetermined region, The AlAs layer that is the current confinement layer 16 is selectively oxidized. A protective film 19 serving as a mesa mask for forming a mesa structure is formed on the upper surface of the mesa structure 30, and a part of the protective film 19 is etched to connect the contact layer 18 and the p-side electrode 22 as will be described later. Has been.

  In the surface emitting laser according to the embodiment, the lower DBR reflector 12, the lower spacer layer 13, the MQW active layer 14, the upper spacer layer 15, the current confinement layer 16, the upper DBR reflector 17 and the contact layer 18 are etched. Thus, an element isolation groove 31 for element isolation is formed, and the regrowth layer 20 and the protective film 21 are formed so as to cover the periphery of the mesa structure 30 and the element isolation groove 31. In the surface emitting laser according to the present embodiment, a part of the lower DBR reflecting mirror 12 may be removed when the mesa structure 30 is formed.

  The p-side electrode 22 is formed on the protective film 21 in contact with the contact layer 18 and is formed in ohmic contact with the contact layer 18.

  The n-side electrode 23 is provided on the back surface of the n-type GaAs substrate 11 and is formed in ohmic contact with the n-type GaAs substrate 11.

  In the surface emitting laser according to the present embodiment, the lower DBR reflecting mirror 12 and the upper DBR reflecting mirror 17 are configured by laminating a high refractive index layer and a low refractive index layer. In order to reduce the electrical resistance at the interface between the low refractive index layer and the low refractive index layer, a composition gradient layer having a thickness of 20 nm in which the composition of AlGaAs is changed is formed at the interface between the high refractive index layer and the low refractive index layer. .

(Method for manufacturing surface-emitting laser)
Next, a method for manufacturing the surface emitting laser according to the present embodiment will be described with reference to FIGS.

  First, as shown in FIG. 4A, the lower portion is formed on the n-type GaAs substrate 11 by MOCVD (Metal Organic Chemical Vapor Deposition) or MBE (Molecular Beam Epitaxy). The DBR reflector 12, the lower spacer layer 13, the MQW active layer 14, the upper spacer layer 15, the current confinement layer 16, the upper DBR reflector 17 and the contact layer 18 are sequentially formed by epitaxial growth.

The lower DBR reflecting mirror 12 is formed by alternately stacking 40.5 pairs of n-type Al _0.3 Ga _0.7 As serving as a high refractive index layer and n-type AlAs serving as a low refractive index layer. The lower spacer layer 13 is made of undoped Al _0.6 Ga _0.4 As, and the MQW active layer 14 is made of Al _0.1 Ga _0.9 As and Al _0.3 Ga _0.7 As alternately. A multi-quantum well structure is formed by stacking, the upper spacer layer 15 is formed of undoped Al _0.6 Ga _0.4 As, and the current confinement layer 16 is formed of p-type AlAs. Further, 21 pairs of p-type Al _0.3 Ga _0.7 As serving as a high refractive index layer and p-type Al _0.9 Ga _0.1 As serving as a low refractive index layer are alternately laminated as the upper DBR reflecting mirror 17. The contact layer 18 is formed of p-type GaAs.

  Next, as shown in FIG. 4B, a part of the lower spacer layer 13, the MQW active layer 14, the upper spacer layer 15, the current confinement layer 16, the upper DBR reflector 17 and the contact layer 18 in a predetermined region is formed. The mesa structure 30 is formed by etching. By forming the mesa structure 30, light and current can be confined in the MQW active layer 14, and laser oscillation can be efficiently performed, and parasitic capacitance in high-speed modulation can be reduced.

Specifically, in the surface emitting laser according to the present embodiment, a SiO ₂ film having a film thickness with an optical length of λ / 4 with respect to the oscillation wavelength λ of the surface emitting laser on the contact layer 18 by CVD or the like. A SiN film is formed, a photoresist is coated on the SiO ₂ film or the SiN film, exposed by an exposure apparatus, and developed to form a resist pattern on a region where the mesa structure 30 is formed. Next, using the resist pattern thus formed as a mask, the SiO ₂ film or SiN film in the region where the resist pattern is not formed is removed by RIE or the like, and the protective film 19 serving as a mesa mask made of the SiO ₂ film or SiN film. Form. Next, with the protective film 19 serving as a mesa mask made of SiO ₂ film or SiN film as a mask, a gas such as Cl ₂ , BCl ₃ , SiCl _4, etc. is introduced and the lower spacer layer 13, MQW active layer 14, upper part is formed by RIE or the like. The spacer layer 15, the current confinement layer 16, the upper DBR reflecting mirror 17, and the contact layer 18 are removed. Thereby, the mesa structure 30 is formed. An etching method for forming the mesa structure 30 may be performed by a dry etching method such as inductively coupled plasma etching other than RIE, a wet etching method, or an etching method that combines dry etching and wet etching. Is possible.

  Next, as shown in FIG. 4C, the current confinement layer 16 is selectively oxidized. Specifically, after the mesa structure 30 is formed, heat treatment is performed in a water vapor atmosphere, so that oxidation proceeds from the side surface of the current confinement layer 16 exposed by the mesa structure 30. As a result, the peripheral portion of the mesa structure 30 is oxidized to form AlxOy, which is an insulator, and the selective oxidation region 16a is formed. A current confinement structure is formed by the selective oxidation region 16a and the non-oxidized current confinement region 16b in the central portion.

  Next, as shown in FIG. 5D, element isolation trenches 31 are formed. Specifically, a resist pattern (not shown) is formed on a region where the element isolation groove 31 is not formed by applying a photoresist, exposing with an exposure apparatus, and developing. Thereafter, the lower DBR reflector 12, the lower spacer layer 13, the MQW active layer 14, the upper spacer layer 15, the current confinement layer 16, the upper DBR reflector 17 and the contact layer 18 in the region where the resist pattern is not formed are RIE or the like. The element isolation trench 31 is formed by etching and removing by the above. The etching method for forming the element isolation trench 31 can be performed by a dry etching method other than RIE, a wet etching method, or an etching method combining dry etching and wet etching.

Next, as shown in FIG. 5E, a regrowth layer 20 is formed. Specifically, it is formed by epitaxially growing a compound semiconductor by MOCVD, MBE or the like. The material for forming the regrowth layer 20 is preferably GaAs or GaInP not containing Al in order to suppress oxidation as much as possible. That is, the regrowth layer 20 is preferably formed of a III-V group compound semiconductor having a low Al composition, and is further formed of GaAs, GaInP, or the like, which is a group III-V compound semiconductor not containing Al. More preferably. In particular, in the case of GaAs, epitaxial growth does not occur on the protective film 19 serving as the mesa mask made of the SiO ₂ film or the SiN film, and the surface in the region where the protective film 19 serving as the mesa mask is not formed, that is, the mesa structure 30. Since the regrowth film 20 can be formed also on the side surface and the wall surface of the element isolation trench 31, it is even more preferable. In addition, the regrowth layer 20 is preferably a method by which the regrowth layer 20 having a desired film thickness can be formed on the side surface of the mesa structure 30 and the wall surface of the element isolation groove 31. Therefore, the regrowth layer 20 is formed by MOCVD. It is preferable to do. Since the regrowth film 20 formed in this way is formed by epitaxial growth, the regrowth film 20 is a dense film and can prevent oxygen from entering from the wall surface of the element isolation trench 31. That is, since the formed regrowth film 20 can prevent oxygen from entering from the end portion of the element constituting the surface emitting laser, reliability can be improved without being broken by stress or the like.

Next, as shown in FIG. 5F, a protective film 21 is formed. Specifically, it is made of a SiO ₂ film or a SiN film having a film thickness with an optical length of λ / 4 or 3 × λ / 4 with respect to the oscillation wavelength λ of the surface emitting laser in the present embodiment by CVD or the like. A protective film 21 is formed.

  Next, as shown in FIG. 5G, the p-side electrode 22 and the n-side electrode 23 are formed. Specifically, a photoresist (not shown) having an opening in a region where the p-side electrode 22 and the contact layer 18 are connected by applying a photoresist on the protective film 21 and performing exposure and development with an exposure apparatus. Form a pattern. Thereafter, the protective film 21 and the protective film 19 serving as a mesa mask in the region where the resist pattern is not formed are removed by performing wet etching with buffered hydrofluoric acid or the like. Thereafter, the p-side electrode 22 connected to the contact layer 18 is formed, and the n-side electrode 23 is formed on the back surface of the n-type GaAs substrate 11. Thereby, the surface emitting laser in this Embodiment can be produced.

The contact layer 18 has a structure in which a protective film 19 and a protective film 21 serving as a mesa mask are laminated, and both are formed of a SiO ₂ film or a SiN film. The total film thickness of the protective film 19 and the protective film 21 serving as a mesa mask with respect to the oscillation wavelength λ is formed by a film thickness with an optical length that is an integral multiple of λ / 2. Will not be affected. In other words, in order not to affect the characteristics of the surface emitting laser, the optical length of the combined thickness of the protective film 19 and the protective film 21 serving as a mesa mask is set to a film thickness that is an integral multiple of λ / 2. There is a need.

  In the surface emitting laser according to the present embodiment, the side surfaces of the mesa structure 30 and the wall surfaces of the element isolation trenches 31 are covered with the dense regrowth film 20 formed by epitaxial growth, thereby preventing oxygen from entering from the outside. Therefore, oxidation of the semiconductor layer can be prevented. Accordingly, it is possible to prevent the volume of the semiconductor layer from changing due to the oxidation of the semiconductor layer and applying stress, and the elements constituting the surface-emitting laser from being destroyed, thereby improving the reliability. In particular, it is possible to prevent oxidation in the lower DBR reflecting mirror 12 having a structure using a GaAs layer, and in a surface emitting laser having a structure with a high heat dissipation effect, a highly reliable surface even when the element isolation groove 31 is formed. A light emitting laser can be obtained.

[Second Embodiment]
Next, a second embodiment will be described. The present embodiment is an image forming apparatus using the surface emitting laser array element according to the present invention, that is, the surface emitting laser array element according to the first embodiment as a light source. This embodiment will be described with reference to FIG.

  A laser printer as an image forming apparatus according to the present embodiment includes an optical scanning device 100, a photosensitive drum 101, a charging charger 102, a developing roller 103, a toner cartridge 104, a cleaning blade 105, a paper feed tray 106, and a paper feed roller 107. , A registration roller pair 108, a fixing roller 109, a paper discharge tray 110, a transfer charger 111, a paper discharge roller 112, a charge removal unit 114, and the like.

  Specifically, in the rotation direction of the photosensitive drum 101, the charging charger 102, the developing roller 103, the transfer charger 111, the static elimination unit 114, and the cleaning blade 105 are arranged in the vicinity of the photosensitive drum 101.

  A photosensitive layer is formed on the surface of the photosensitive drum 101. Here, the photosensitive drum 101 is configured to rotate clockwise as shown in the figure. The charging charger 102 has a function of uniformly charging the surface of the photosensitive drum 101.

  The optical scanning device 100 irradiates the surface of the photosensitive drum 101 charged by the charging charger 102 with light modulated based on image information from a host device such as a personal computer. By this light irradiation, a latent image corresponding to the image information is formed on the surface of the photosensitive drum 101. The area where the latent image is formed on the surface of the photosensitive drum 101 moves in the direction in which the developing roller 103 is provided as the photosensitive drum 101 rotates. Details of the optical scanning device 100 will be described later.

  The toner cartridge 104 stores toner, and this toner is supplied to the developing roller 103. The developing roller 103 causes the toner supplied from the toner cartridge 104 to adhere to the latent image formed on the surface of the photoconductive drum 101 to visualize the image information on the surface of the photoconductive drum 101. Thereafter, as the photosensitive drum 101 rotates, the area where the toner is attached to the latent image on the surface of the photosensitive drum 101 moves in the direction in which the transfer charger 111 is provided.

  Recording paper 113 is stored in the paper feed tray 106. A paper feed roller 107 is disposed in the vicinity of the paper feed tray 106, and the paper feed roller 107 takes out the recording paper 113 one by one from the paper feed tray 106 and conveys it to the registration roller pair 108. The registration roller pair 108 is disposed in the vicinity of the transfer charger 111, temporarily holds the recording paper 113 taken out by the paper feeding roller 107, and exposes the recording paper 113 in accordance with the rotation of the photosensitive drum 101. It is sent out toward the gap between the body drum 101 and the transfer charger 111.

  The transfer charger 111 is charged with a reverse polarity to the toner on the surface of the photoconductor 101 in order to electrically attract the toner on the surface of the photoconductor drum 101 to the recording paper 113. The toner on the surface of the photosensitive drum 101 is transferred to the recording paper 113 by this charge, that is, an image formed by the toner is transferred to the recording paper 113. Thereafter, the recording sheet 113 is sent to the fixing roller 109.

  In the fixing roller 109, heat and pressure are applied to the recording paper 113, whereby the toner is fixed on the recording paper 113. Here, the recording paper 113 on which the image is fixed is sent to the paper discharge tray 110 via the paper discharge roller 112, and is sequentially stacked on the paper discharge tray 110.

  The neutralization unit 114 neutralizes the surface of the photosensitive drum 101. The cleaning blade 105 removes toner remaining on the surface of the photosensitive drum 101 (residual toner). The removed residual toner is configured to be reusable. The surface of the photosensitive drum 101 from which the residual toner has been removed moves again in the direction in which the charging charger 102 is provided.

(Optical scanning device)
Next, the optical scanning device 100 will be described with reference to FIG.

  The optical scanning device 100 controls a light source unit 121, a coupling lens 122, an aperture plate (aperture) 123, a cylindrical lens 124, a polygon mirror 125, an fθ lens 126, a toroidal lens 127, two mirrors 128 and 129, and the above-described parts. And a main controller (not shown) for controlling the operation.

  The light source unit 121 includes a surface emitting laser array in which a plurality of surface emitting semiconductor lasers according to the first embodiment are formed.

  The coupling lens 122 is for making the light beam emitted from the light source unit 121 substantially parallel light.

  The aperture plate 123 has an aperture and is for defining the beam diameter of the light beam from the coupling lens 122.

  The cylindrical lens 124 condenses the light beam that has passed through the aperture plate 123 on the reflection surface of the polygon mirror 125 via the mirror 128.

  The polygon mirror 125 is formed in a regular hexagonal column shape, and a mirror surface is formed so that the six side surfaces are reflective surfaces. The polygon mirror 125 is rotated at a constant speed in a direction indicated by an arrow by a motor (not shown), and the light beam is deflected at a constant angular velocity with this rotation.

  The fθ lens 126 has an image height proportional to the incident angle of the light beam from the polygon mirror 125, and the image surface of the light beam polarized at a constant angular velocity by the polygon mirror 125 is constant in the main scanning direction. Move.

  The toroidal lens 127 forms an image of the light flux from the fθ lens 126 on the surface of the photosensitive drum 101 via the mirror 129.

  As shown in FIG. 8, the light source unit 121 includes a surface emitting laser array LA in which surface emitting laser elements (VCSEL) are two-dimensionally arranged in an array. The surface emitting lasers are arranged with a predetermined sufficient interval in the main scanning direction, and the arrangement of the surface emitting lasers in the main scanning direction is arranged with a gap of d2 in the sub scanning direction. In this way, an array arranged in the main scanning direction while being shifted by an interval d2 in the sub scanning direction is formed for each pitch d1 in the sub scanning direction. By arranging in this way, it is possible to make the interval of the perpendiculars perpendicular to the sub-scanning direction from the center of each surface emitting laser equal (interval d2 is equal). Thus, by controlling the lighting timing of each surface emitting laser, the same configuration as when light sources are arranged on the photosensitive drum 101 at narrow regular intervals in the sub-scanning direction can be obtained. .

  For example, when the pitch d1 of the surface emitting semiconductor lasers in the sub-scanning direction is 26.5 μm and ten surface emitting semiconductor lasers are arranged in the main scanning direction, the distance d2 between the surface emitting semiconductor lasers. Is 2.65 μm. If the magnification in the optical system is set to double, writing dots can be formed on the photosensitive drum 101 at intervals of 5.3 μm. This corresponds to 4800 dpi (dots / inch), and high-density writing of 4800 dpi can be performed.

  Further, by increasing the number of surface emitting semiconductor lasers arranged in the main scanning direction, narrowing the pitch d1, and further narrowing the interval d2, it is possible to perform writing with higher density. Note that the writing interval in the main scanning direction can be easily controlled by controlling the lighting timing of the surface emitting semiconductor laser as the light source.

  In the optical scanning device and the image forming apparatus using the same according to the present embodiment, the surface emitting semiconductor laser according to the first embodiment having high reliability is used as the light source. Thus, it is possible to obtain an optical scanning apparatus and an image forming apparatus that have low power consumption, high speed, and high quality.

(Image forming apparatus for forming a color image)
Next, an image forming apparatus for forming a color image will be described with reference to FIG.

  This image forming apparatus is a color laser printer, which is a dandem color machine having a plurality of photosensitive drums for color images.

  This color laser printer includes a black (K) photosensitive drum K1, a charger K2, a developing unit K4, a cleaning unit K5, a transfer charging unit K6, a cyan (C) photosensitive drum C1, and a charging unit. C2, developing unit C4, cleaning unit C5, transfer charging unit C6, magenta (M) photosensitive drum M1, charging unit M2, developing unit M4, cleaning unit M5, transfer charging unit M6, yellow (Y) photosensitive drum Y1, charger Y2, developing unit Y4, cleaning unit Y5, transfer charging unit Y6, optical scanning device 100, transfer belt 201, fixing unit 202, and the like.

  In this color laser printer, the optical scanning device 100 includes a semiconductor laser for black, a semiconductor laser for cyan, a semiconductor laser for magenta, and a semiconductor laser for yellow. Each semiconductor laser is included in the present invention. It is comprised by the surface emitting semiconductor laser which concerns. The light beam from the black semiconductor laser is irradiated to the black photosensitive drum K1, the light beam from the cyan semiconductor laser is irradiated to the cyan photosensitive drum C1, and the light beam from the magenta semiconductor laser is magenta. The light beam from the yellow semiconductor laser is irradiated to the yellow photosensitive drum Y1, and the light beam from the yellow semiconductor laser is irradiated to the yellow photosensitive drum Y1.

  Each of the photosensitive drums K1, C1, M1, and Y1 rotates in the direction of the arrow, and in the order of the rotation direction, each of the chargers K2, C2, M2, and Y2, the developing devices K4, C4, M4, and Y4, for transfer. Charging means K6, C6, M6, Y6 and cleaning means K5, C5, M5, Y5 are arranged. Each of the chargers K2, C2, M2, and Y2 uniformly charges the surface of the corresponding photosensitive drum K1, C1, M1, and Y1. The charged surface of the photosensitive drums K1, C1, M1, and Y1 is irradiated with a light beam from the optical scanning device 100, and an electrostatic latent image is formed on the surface of the photosensitive drums K1, C1, M1, and Y1. It has become. Thereafter, toner images are formed on the surfaces of the photosensitive drums K1, C1, M1, and Y1 by the developing units K4, C4, M4, and Y4, and the transfer charging units K6, C6, M6, and Y6 corresponding to the toner images are formed. Thus, the toner images of the respective colors are transferred to the recording paper, and the image is fixed on the recording paper by the fixing unit 202. The cleaning means K5, C5, M5, and Y5 remove residual toner remaining on the surfaces of the corresponding photosensitive drums K1, C1, M1, and Y1.

  In this embodiment, the photosensitive drum is described as the image carrier. However, the image carrier may be an image forming apparatus using a silver salt film. In this case, a latent image is formed on the silver salt film by optical scanning, and this latent image can be visualized by a process similar to a developing process in a normal silver salt photographic process. Then, it can be transferred to photographic paper by the same process as the printing process in the ordinary silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.

  Further, an image forming apparatus using a color developing medium (positive photographic paper) that develops color by the heat energy of a beam spot as an image carrier may be used. In this case, a visible image can be directly formed on the image carrier by optical scanning.

  As mentioned above, although the form which concerns on implementation of this invention was demonstrated, the said content does not limit the content of invention.

11 n-type GaAs substrate 12 lower DBR reflector 13 lower spacer layer 14 active layer (multiple quantum well layer)
15 upper spacer layer 16 current confinement layer 16a selective oxidation region 16b current confinement region 17 upper DBR reflector 18 contact layer 19 protective film 20 serving as mesa mask regrown layer 21 protective film 22 p-side electrode 23 n-side electrode

JP 2006-302919 A JP 2007-173513 A

Claims (19)

A lower reflector formed by alternately laminating semiconductor films having different refractive indexes on the surface of a semiconductor substrate, an active layer made of a semiconductor film, a current confinement layer made of a semiconductor film, and a semiconductor having a different refractive index A semiconductor layer forming step of forming an upper reflecting mirror formed by alternately stacking films by epitaxial growth;
A mesa structure forming step of forming a mesa structure by etching a part of the semiconductor film formed by the semiconductor layer forming step;
An element isolation groove forming step of forming an element isolation groove by etching the semiconductor film formed by the semiconductor layer forming step to the surface of the semiconductor substrate;
A regrowth layer forming step of forming a regrowth layer made of a semiconductor material on a wall surface of the element isolation trench and a side surface of the mesa structure;
A protective film forming step of forming a protective film made of an insulator on the regrowth layer;
A method for producing a surface-emitting laser characterized by comprising: The mesa structure forming step forms the mesa structure by performing etching after forming a mesa mask made of SiO ₂ or SiN in a region where the mesa structure is formed,
2. The surface emitting laser manufacturing method according to claim 1, wherein the regrowth layer forming step is performed with the mesa mask left.   3. The surface emitting laser manufacturing method according to claim 1, wherein the regrowth layer is a group III-V compound semiconductor containing no Al.   4. The surface emitting laser manufacturing method according to claim 3, wherein the regrowth layer is GaAs.   5. The surface emitting laser manufacturing method according to claim 1, wherein the regrowth layer is formed by MOCVD or MBE. A lower reflector formed by alternately laminating semiconductor films of different refractive indexes on the surface of a semiconductor substrate;
On the lower reflector, an active layer made of a semiconductor material;
On the active layer, a current confinement layer in which a current confinement structure is formed by oxidizing a partial region of a semiconductor material;
On the current confinement layer, an upper reflector formed by alternately stacking semiconductor films having different refractive indexes;
A mesa structure is formed by etching a part of the semiconductor layer, a lower electrode is connected to the semiconductor substrate, an upper electrode is connected to the upper reflector, and the upper electrode and the lower electrode are connected to each other. In a surface emitting laser that emits a laser beam substantially perpendicular to the semiconductor substrate surface by passing a current between them,
In the lower reflector, the active layer, the current confinement layer, and the upper reflector on the semiconductor substrate, an element isolation groove for element isolation is formed,
A surface-emitting laser comprising a regrowth layer made of a semiconductor material and a protective film formed on the regrowth layer on a wall surface of the element isolation trench and a side surface of the mesa structure.   7. The surface emitting device according to claim 6, wherein the mesa structure is formed by removing a part of the upper reflector, the active layer, the current confinement layer, and the lower reflector. Type laser.   8. The surface emitting laser according to claim 6, wherein the element isolation trench is formed until the surface of the semiconductor substrate is exposed.   The surface emitting laser according to any one of claims 6 to 8, wherein the regrowth layer is formed by MOCVD or MBE.   10. The surface emitting laser according to claim 6, wherein the regrowth layer is a group III-V compound semiconductor that does not contain Al.   The surface emitting laser according to claim 10, wherein the regrowth layer is GaAs. The protective layer, SiN, SiO ₂ or the surface emitting laser according to any one of claims 6 to 11, characterized in that the structure of a combination of a SiN and SiO _2.   The surface emitting laser according to any one of claims 6 to 12, wherein in the lower reflecting mirror, a low refractive index layer is formed of AlAs.   A surface-emitting laser array element, wherein a plurality of surface-emitting lasers according to claim 6 are arranged on the same semiconductor substrate. An optical scanning device that scans a surface to be scanned with a light beam,
A light source unit comprising the surface-emitting type laser array element according to claim 14;
Deflecting means for deflecting the light beam from the light source unit;
A scanning optical system for condensing the light beam deflected by the polarizing means on the surface to be scanned;
An optical scanning device comprising: An optical scanning device that scans a surface to be scanned with a plurality of light beams,
A light source unit comprising the surface-emitting type laser array element according to claim 14;
Deflecting means for deflecting a plurality of light beams from the light source unit;
A scanning optical system for condensing a plurality of light beams deflected by the polarizing means on a surface to be scanned;
An optical scanning device comprising: At least one image carrier;
The optical scanning device according to claim 15, wherein the at least one image carrier is scanned with a light beam including image information;
An image forming apparatus comprising: At least one image carrier;
The optical scanning device according to claim 16, wherein the at least one image carrier is scanned with a plurality of light fluxes including image information;
An image forming apparatus comprising:   The image forming apparatus according to claim 17, wherein the image is a color image.

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