JP2011233689A - Semiconductor light emitting device and liquid crystal display device using the same - Google Patents

Abstract

A semiconductor light emitting device capable of improving the light utilization efficiency by increasing the TE / TM polarization ratio is realized, and a liquid crystal display device using the semiconductor light emitting device as a backlight light source and requiring no polarizing plate can be realized. Like that.
A semiconductor light emitting device includes an active layer formed on a substrate and a ridge waveguide 107a formed on the active layer, and emits light from at least one of a front end surface and a rear end surface. A semiconductor laminate. The ridge waveguide 107a has a groove 113 serving as at least one unconnected portion between the front end surface and the rear end surface, and is formed from a plurality of waveguide portions 107a1, 107a2, and 107a3 separated by the groove 113. .
[Selection] Figure 1

Description

  The present invention relates to a semiconductor light emitting element and a liquid crystal display device using the same, and more particularly to a semiconductor light emitting element that controls the polarization of emitted light and a liquid crystal display device using the same.

  Since it has excellent features such as small size and high output, a light emitting diode (LED: Light Emitting Diode) element and a semiconductor light emitting element of a semiconductor laser element are used in addition to IT (Information Technology) technologies such as communication and optical disks, Used in a wide range of technical fields such as lighting. In recent years, the use of LED elements as a light source of a display device using a liquid crystal panel such as a thin television has been increasing rapidly. The liquid crystal display device uses a liquid crystal panel as a transmissive light modulation element, and a light source device is disposed on the back surface of the liquid crystal panel to irradiate the liquid crystal panel with light. The liquid crystal panel forms an image by controlling the transmittance of light emitted from the light source device. Conventionally, a cold cathode fluorescent lamp (CCFL) has been used as a light source of a light source device, but in recent years, development of LED backlight light sources using LED chips has progressed in the trend of energy saving. Yes.

  Current LED backlight light sources generally use a white LED element in which a yellow phosphor is combined with a blue LED element, and are broadly classified into a direct type and an edge type according to the arrangement method of the LED elements. In the direct type, LED light sources are arranged in a grid pattern on the back side of the liquid crystal panel, and the brightness of the light source is controlled for each area called local dimming. The direct type can improve the contrast ratio of the image, but has a drawback that it is difficult to reduce the thickness. On the other hand, the edge type has advantages that the LED light source is disposed in the peripheral part of the liquid crystal panel and the entire panel is irradiated by the light guide plate, so that the panel can be easily thinned and has high designability. The edge type has an advantage that the number of LEDs can be reduced in terms of cost.

  The liquid crystal panel uses light polarized by a polarizing plate as a backlight light source. When the light source is non-polarized light, 50% of light is lost. Therefore, optical characteristics such as high directivity and high polarization are originally required for edge-type backlight light sources, but currently used LED light sources do not have these characteristics and are optimal as light sources. It is not in a state that has A small light source having high directivity and high polarization has a semiconductor laser element. However, the semiconductor laser element has a drawback that speckle noise is likely to occur due to high coherence of light.

  Therefore, the present inventor has focused on a super luminescent diode (SLD) element as a light source having both high directivity, high polarization, and low coherence. The SLD element is a semiconductor light emitting element using an optical waveguide as in the semiconductor laser (LD) element. In the SLD element, spontaneous emission light generated by recombination of injected carriers is amplified by receiving a high gain due to stimulated emission while traveling in the direction of the light emission end face, and is emitted from the light emission end face. The difference between the SLD element and the LD element is that the formation of an optical resonator due to end face reflection is suppressed, and laser oscillation in the Fabry-Perot mode is prevented. Therefore, the SLD element can show an incoherent and broadband spectrum shape like a normal LED element, and can obtain an output up to about several tens of mW. In particular, an SLD element using a nitride semiconductor is expected as a high-power incoherent light source in the visible range from ultraviolet to green (for example, see Non-Patent Document 1).

  In this way, by using an SLD element, which is a light source having both high directivity, high polarization, and low coherence, as an edge-type backlight light source, the optical coupling efficiency with the light guide plate is improved, and the number of polarizing plates is reduced. Therefore, it is expected as a backlight light source with higher performance and lower cost.

  FIG. 15 shows a conventional SLD element disclosed in Non-Patent Document 1. As shown in FIG. 15, the conventional SLD element is formed on a substrate 1 made of gallium nitride (GaN), a cladding layer 2 that is a superlattice layer made of AlGaN / GaN having a thickness of 1 μm, and Si-doped GaN. An n-type guide layer 3, a multiple quantum well layer 4 made of InGaN, a barrier layer 5 made of AlGaN, a p-type guide layer 6 made of Mg-doped GaN, a p-type cladding layer 7 made of Mg-doped AlGaN, A p-type contact layer 8 is sequentially stacked.

The p-type cladding layer 7 is formed with a ridge portion having a convex cross section at the top for forming an optical waveguide, and an insulating film 9 made of silicon oxide (SiO ₂ ) is formed on both sides of the ridge portion. ing. An n-type contact 10 is formed on the back surface of the substrate 1.

  Further, the end surface on the light emission side in the p-type contact layer 8 including the insulating film 9 is inclined with respect to the plane perpendicular to the extending direction of the waveguide. Thereby, the SLD operation is enabled by reducing the mode reflectance of light and suppressing laser oscillation. As described above, since the SLD element has an optical waveguide structure similar to that of the laser element, it is possible to output light having low directivity while having high directivity.

E. Feltin et al., Appl. Phys. Lett. 95, 081107 2009.

  However, the SLD element having a general structure has a polarization ratio of about 15, which is lower than 100 or more of the LD element. Therefore, there is a problem that it cannot be said that the change ratio is so high that the number of polarizing plates can be reduced. This is because the high polarization property of the LD element depends on the dependence of the optical gain on the TE (Transverse-Electric) polarization / TM (Transverse-Magnetic) polarization and the dependence of the reflectance on both ends of the resonator on the TE-polarization / TM polarization. Because. In the case of a general SLD element, there is almost no reflection by the end face of the resonator, and as a result, the polarization ratio is lower than that of the LD element.

  The present invention has been made in view of the above problems, and an object of the present invention is to realize a semiconductor light emitting device capable of improving the light use efficiency by increasing the polarization ratio (TE / TM polarization ratio), and using the semiconductor light emitting device as a backlight light source. The object is to realize a liquid crystal display device that does not require a polarizing plate.

  In order to achieve the above object, according to the present invention, a semiconductor light emitting device is configured such that a non-connection portion for dividing the optical waveguide is provided in the middle of the optical waveguide.

  Specifically, a semiconductor light emitting device according to the present invention has a light emitting layer formed on a substrate and an optical waveguide including the light emitting layer, and emits light from at least one of a front end face and a rear end face. The optical waveguide has at least one unconnected portion between the front end surface and the rear end surface, and is formed of a plurality of waveguide portions separated by the unconnected portion.

  According to the semiconductor light emitting device of the present invention, the optical waveguide has at least one non-connected portion between the front end surface and the rear end surface, and is formed of a plurality of waveguide portions separated by the non-connected portion. For this reason, polarization selectivity can be provided in the non-connected portion of the optical waveguide, and the TE / TM polarization ratio of the emitted light can be increased, so that the light utilization efficiency can be improved.

  In the semiconductor light emitting device of the present invention, the non-connection portion may be a recess that divides the optical waveguide.

  In this way, the difference between the refractive index of the light in the optical waveguide and the refractive index in the non-connection portion can be increased, so that the polarization selectivity can be increased and the TE / TM polarization ratio of light emission can be increased.

  In the semiconductor light emitting device of the present invention, it is preferable that the normal direction of the interface between the optical waveguide and the recess is inclined from the extending direction of the optical waveguide, and light is guided through the non-connection portion by refraction at the interface.

  This makes it possible to increase the polarization selectivity of the waveguide by utilizing the fact that the ratio of refraction (transmission) and reflection at the interface between the optical waveguide and the recess is different between the TE wave and the TM wave. The TE / TM polarization ratio of light can be increased.

In this case, the angle theta formed by the extending direction of the normal direction and the optical waveguide of the interface at the interface between the optical waveguide and the recess, the critical angle is taken as _{θ c, θ c / 2 ≦} θ <θ c It is preferable that this relationship is established.

  In this way, the difference in the ratio between the refraction (transmission) and reflection of the TE wave and TM wave at the interface between the optical waveguide and the recess can be increased, so that the TE / TM polarization ratio of the emitted light is increased. be able to.

  In this case, the plurality of waveguide portions may be formed such that the central axes in the extending direction of the adjacent waveguide portions are shifted from each other.

  In the semiconductor light emitting device of the present invention, the semiconductor laminate preferably constitutes a super luminescence diode (SLD) device that emits stimulated emission light from the front end surface or the rear end surface.

In the semiconductor light emitting device of the present invention, the semiconductor stacked body is a group III represented by Al _x Ga _y In _1-xy N (where 0 ≦ x, y ≦ 1, 0 ≦ x + y ≦ 1). It may be made of a nitride semiconductor.

  Thus, the semiconductor light emitting device can be used as a blue or green light source having high directivity, high polarization, and low coherence. In particular, the blue SLD light source can be used as a white light source by combining yellow or a green phosphor and a red phosphor.

In the semiconductor light emitting device of the present invention, the semiconductor stacked body may be Al _x Ga _y In _1-xy As _z P _1-z (where 0 ≦ x, y, z ≦ 1, 0 ≦ x + y ≦ 1. A group III-V compound semiconductor represented by

  If it does in this way, it can utilize as a red light source which has high directivity, high polarization property, and low coherence. Further, the blue, green and red SLD light sources can be used as backlight light sources or display light sources with higher color reproducibility.

  A liquid crystal display device according to the present invention includes the semiconductor light emitting element of the present invention, a light guide plate that receives light from the semiconductor light emitting element, and a liquid crystal panel that receives light transmitted through the light guide plate. A polarizing plate is not provided in the light waveguide path to the panel.

  According to the liquid crystal display device of the present invention, since no polarizing plate is provided in the light guide path from the semiconductor light emitting element to the liquid crystal panel, a light source with low power consumption and low cost can be realized. .

  According to the semiconductor light emitting device and the liquid crystal display device using the semiconductor light emitting device according to the present invention, the polarization ratio of the semiconductor light emitting device can be increased, and as a result, a thin liquid crystal display device with low power consumption and low cost can be realized.

FIG. 1A to FIG. 1C are semiconductor light emitting devices according to a first embodiment of the present invention, FIG. 1A is a plan view, and FIG. 1B is FIG. ) Taken along line Ib-Ib, and FIG. 1C is a sectional view taken along line Ic-Ic in FIG. FIG. 2 is a schematic plan view showing a ridge waveguide and an optical waveguide path according to the first embodiment of the present invention. FIG. 3 is a cross-sectional view in the direction perpendicular to the ridge waveguide of the semiconductor light emitting device according to the first modification of the first embodiment of the present invention. FIG. 4 is a plan view of a semiconductor light emitting device according to a second modification of the first embodiment of the present invention. FIG. 5A is a cross-sectional view schematically showing the reflection / transmission refraction phenomenon by the Fresnel equation, and FIGS. 5B and 5C are semiconductors according to the first embodiment of the present invention. FIG. 5B is a graph showing the dependency of the reflectance on the incident angle, and FIG. 5C is a graph showing the dependency of the transmittance on the incident angle. It is a graph to show. FIG. 6 is a schematic plan view showing an FDTD simulation model of polarization selectivity in the non-connected portion of the optical waveguide of the semiconductor light emitting device according to the first embodiment of the present invention. FIG. 7 is a diagram showing an example of the FDTD simulation result of the polarization selectivity in the non-connected portion of the optical waveguide of the semiconductor light emitting device according to the first embodiment of the present invention. FIG. 8 is a graph showing the dependence of the polarization ratio selectivity on the end face angle in the non-connected portion of the optical waveguide of the semiconductor light emitting device according to the first embodiment of the present invention. FIG. 9 is a schematic plan view of a semiconductor light emitting device according to a third modification of the first embodiment of the present invention. FIG. 10 is a schematic plan view of a semiconductor light emitting device according to a fourth modification of the first embodiment of the present invention. 11 (a) to 11 (c) are semiconductor light emitting devices according to a fifth modification of the first embodiment of the present invention, in which FIG. 11 (a) is a plan view and FIG. 11 (b). FIG. 11A is a cross-sectional view taken along line XIb-XIb in FIG. 11A, and FIG. 11C is a cross-sectional view of region C in FIG. 12 (a) and 12 (b) are semiconductor light emitting devices according to a sixth modification of the first embodiment of the present invention. FIG. 12 (a) is a plan view, and FIG. 12 (b). These are sectional drawings in the XIIb-XIIb line of Drawing 12 (a). 13 (a) to 13 (c) are semiconductor light emitting devices according to comparative examples of the present invention, in which FIG. 13 (a) is a plan view and FIG. 13 (b) is XIIIb in FIG. 13 (a). FIG. 13C is a cross-sectional view taken along line XIIIc-XIIIc in FIG. 13A. FIG. 14A to FIG. 14C are liquid crystal display devices according to the second embodiment of the present invention. FIG. 14A is an exploded sectional view of the display mechanism, and FIG. FIG. 14C is a right side (cross section) view, and FIG. 14C is a front view. FIG. 15 is a schematic perspective view showing a conventional GaN-based SLD element.

  Embodiments according to the present invention will be described with reference to the drawings. In addition, each embodiment shown below is an example, Comprising: This invention is not limited to these embodiment.

(First embodiment)
In the first embodiment of the present invention, a blue SLD element using a nitride semiconductor and outputting blue light having a wavelength of 450 nm will be described.

  In the blue SLD element according to the first embodiment, the ridge waveguide has a non-connection portion formed by at least one groove portion provided in the middle thereof, and light guided through the waveguide portion divided by the non-connection portion is transmitted. It is an SLD element designed to be transmitted and refracted at a non-connecting portion and smoothly guided to adjacent waveguide portions separated by the non-connecting portion. Thus, the polarization ratio can be increased by transmission refraction through the non-connection portion.

  Specifically, as shown in FIGS. 1A to 1C, the blue SLD element according to the present embodiment has a buffer layer (made of n-type GaN) on a substrate 101 made of n-type GaN. (Not shown), n-type cladding layer 102, n-type guide layer 103, active layer 104, p-side guide layer 105, carrier overflow suppression (OFS) layer 106 made of p-type AlGaN, p-type cladding layer 107, and p-type GaN A semiconductor stacked body in which contact layers (not shown) are sequentially formed is provided.

The upper portion of the p-type cladding layer 107 is processed into a ridge stripe to form a ridge waveguide 107a. On the p-type cladding layer 107, a dielectric block layer 110 made of SiO ₂ having an opening exposing the top surface of the ridge stripe portion is formed. A p-side electrode 108 is formed on the top surface of the ridge stripe portion.

  A wiring electrode 109 connected to the p-side electrode 108 is formed on the dielectric block layer 110 including the p-side electrode 108. An n-side electrode 111 is formed on the surface (back surface) opposite to the n-type cladding layer 102 of the substrate 101.

  The ridge waveguide 107a is provided with at least one groove portion which is a non-connection portion in the light waveguide path, here two groove portions 113 are provided. That is, as shown in FIG. 2, the ridge waveguide 107a is divided into a first waveguide section 107a1, a second waveguide section 107a2, and a third waveguide section 107a3 from the reflection end face side. Furthermore, the second waveguide portion 107a2 sandwiched between the two groove portions 113 is arranged in a zigzag shape in plan view so that the loss of light can be minimized in consideration of the refraction angle. As described above, the ridge waveguide 107a according to the first embodiment includes the waveguide portions 107a1 to 107a3 and the two groove portions 113.

  Further, as shown in FIG. 1A, the light emission end face 112 has a surface inclined by about 5 ° to 25 ° from a plane perpendicular to the extending direction (longitudinal direction) of the ridge waveguide 107a. It is formed as an extremely low reflection end face.

  In FIG. 1A, the plane orientation of the hexagonal GaN-based crystal is indicated by c, a, m. c represents the normal vector of the (0001) plane, that is, the c axis, a represents the normal vector of the (11-20) plane and its equivalent plane, that is, the a axis, and m represents the plane direction. Represents the normal vector of the (1-100) plane and its equivalent plane, that is, the m-axis. Here, in this specification, the minus sign “−” attached to the Miller index in the plane orientation represents the inversion of one index following the minus sign for convenience.

  Hereinafter, a method for manufacturing the blue SLD element configured as described above will be described.

(Crystal growth process)
First, for example, by metal organic chemical vapor deposition (MOCVD) method, the n-type hexagonal GaN whose principal plane is the (0001) plane and the carrier concentration is about 1 × 10 ¹⁸ cm ^−3. An n-type cladding layer 102 made of n-type Al _0.03 Ga _0.97 N having a thickness of 2 μm is grown on the main surface of the substrate 101 made of the above. Subsequently, an n-type guide layer 103 made of n-type GaN having a thickness of 0.10 μm, a barrier layer made of In _0.02 Ga _0.98 N, and In _0.16 Ga on the n-type cladding layer 102. A quantum well (MQW) active layer 104 including three periods of _0.84 N quantum well layers is sequentially grown.

Subsequently, a p-side guide layer 105 made of undoped or p-type GaN having a thickness of 0.05 μm is grown on the MQW active layer 104. Subsequently, a carrier overflow suppression layer (OFS layer) 106 made of Al _0.20 Ga _0.80 N having a thickness of 20 nm is grown on the p-side guide layer 105. Subsequently, a strained superlattice having a thickness of 0.50 μm is formed by repeating 160 p-type Al _0.06 Ga _0.94 N layers and GaN layers each having a thickness of 2 nm on the OFS layer 106. A p-type cladding layer 107 as a layer and a p-type contact layer (not shown) made of p-type GaN having a thickness of 0.1 μm are sequentially grown.

Each n-type semiconductor layer is doped with silicon (Si) as a donor impurity at a concentration of about 5 × 10 ¹⁷ cm ⁻³ . Each p-type semiconductor layer is doped with magnesium (Mg) as an acceptor impurity at a concentration of about 1 × 10 ¹⁹ cm ⁻³ . The uppermost p-type contact layer is doped with Mg at a high concentration of about 1 × 10 ²⁰ cm ⁻³ . The OFS layer 106 has a large band gap by setting the Al composition as high as 20%. Therefore, due to the OFS layer 106 having a large band gap, the electrons flowing through the conduction band have higher mobility than the holes flowing through the valence band, and thus pass through the MQW active layer 104, and semiconductors other than the active layer 104 It is possible to suppress non-radiative recombination in the layer.

  Note that the semiconductor multilayer structure according to this embodiment is an example, and the semiconductor multilayer structure and the growth method are not limited thereto. For example, a crystal growth method for forming a semiconductor stacked body includes a GaN-based method such as a molecular beam epitaxy (MBE) method or a chemical beam epitaxy (CBE) method in addition to the MOCVD method. A method capable of growing a semiconductor stacked structure may be used.

As raw materials when using the MOCVD method, for example, trimethyl gallium (TMG) is used as a Ga raw material, trimethyl indium (TMI) is used as an In raw material, and trimethyl aluminum (TMA) is used as an Al raw material, and ammonia (NH ₃ ) is used as an N raw material. Use it. Further, silane (SiH ₄ ) gas may be used for the Si raw material that is an n-type impurity, and biscyclopentadienyl magnesium (Cp ₂ Mg) may be used for the Mg raw material that is a p-type impurity.

(Ridge waveguide formation process)
Next, a first SiO ₂ film (not shown) having a thickness of 200 nm is deposited on the entire surface of the p-type contact layer by CVD. Thereafter, the substrate 101 is heat-treated in a nitrogen (N ₂ ) atmosphere at a temperature of 850 ° C. for 30 minutes to activate Mg of each p-type semiconductor layer. Subsequently, the first SiO ₂ film is etched by dry etching such as lithography and RIE (Reactive Ion Etching) method, and the ridge waveguide formation region on the p-type contact layer is made of SiO _2. A first mask film is formed. Thereafter, by using the first mask film, ICP (Inductively Coupled Plasma) dry etching with chlorine (Cl ₂ ) gas or silicon tetrachloride (SiCl ₄ ) gas is used to form the p-type contact layer and the p-type cladding layer 107 therebelow. Etching is performed on the upper portion of the substrate by about 0.5 μm to form a planar zigzag ridge stripe portion. At this time, it is common to accurately control the etching digging amount by monitoring the interference waveform using an ultraviolet light source. Here, the width of the bottom side of the ridge waveguide 107a is about 1.5 μm.

  As shown in FIG. 3, as a first modification, in the present ridge waveguide forming step, a groove is formed on both sides of the ridge waveguide 107a, thereby making the base equal in height to the top surface of the ridge waveguide 107a. The portion 107b may be formed. With such a structure, only the ridge waveguide 107a becomes a convex portion, and it is possible to prevent the SLD element from being mechanically damaged during mounting or the like. The distance between the ridge waveguide 107a and the pedestal 107b is preferably about 5 to 15 μm. In this modification, the distance is 7 μm.

(Groove formation process)
Next, the first mask film is removed with a buffered hydrofluoric acid solution (BHF). Thereafter, a second SiO ₂ film (not shown) having a thickness of 800 nm is deposited on the p-type cladding layer 107 including the p-type contact layer and having the ridge waveguide 107a formed thereon by the CVD method again. . Subsequently, the second SiO ₂ film is selectively etched by a lithography method and a dry etching method by RIE, and an opening having an exposed portion in which a plurality of recesses for dividing the ridge waveguide 107a are exposed is formed. 2 mask film is formed. Subsequently, by using the second mask film, the semiconductor stacked body is etched to a depth of about 3 μm from the upper surface of the p-type contact layer by ICP dry etching using Cl ₂ gas or SiCl ₄ gas. A recess is formed. At this time, the plurality of concave portions can simultaneously form the groove 113 serving as a non-connecting portion of the ridge waveguide 107a and the ultra-low reflection end surface 112 which is a light emitting end surface. When the depths of these recesses are set separately, they may be formed in two steps.

Here, in the first embodiment, the angle θ _B formed by each groove 113 with the surface in the direction perpendicular to the extending direction of the ridge waveguide 107a is set to 19.5 °. Further, the width of each groove 113 is set to 1 μm, and the angle θ _F formed by the extremely low reflection end face 112 and the plane perpendicular to the extending direction of the ridge waveguide 107a is set to 10 °.

  As shown in FIG. 4, as a second modification, in the present groove portion forming step, a cleavage assisting groove 115 for dividing and obtaining a plurality of semiconductor light emitting elements from one wafer is simultaneously formed around each element. May be. By forming the cleavage assisting groove 115 in the wafer, the yield at the time of element division can be improved.

(Dielectric block layer and p-side electrode forming step)
Subsequently, the second mask film is removed with a buffered hydrofluoric acid solution (BHF). Thereafter, a third SiO ₂ film (not shown) having a thickness of 300 nm is again deposited on the entire surface of the wafer by CVD. Subsequently, a plurality of openings exposing the top surface of the ridge waveguide 107a, that is, the p-type contact layer, are formed in the third SiO ₂ film by a lithography method and a wet etching method using a buffered hydrofluoric acid solution, A dielectric block layer 110 is formed. In order to form a plurality of openings in the dielectric block layer 110, the openings may be formed by etching back the formed resist film instead of using the lithography method.

Subsequently, a p-side electrode 108 made of palladium (Pd) / platinum (Pt) is formed in each opening of the dielectric block layer 110 by electron beam evaporation. The electron beam evaporation is performed by heating the substrate 101 to 70 ° C., and the film thicknesses of the Pd film and the Pt film are 40 nm and 35 nm, respectively. Thereafter, a heat treatment at a temperature of 400 ° C. is applied to obtain a good contact resistance of 2 × 10 ⁻⁴ Ωcm ² or less. As a result of the examination, it has become clear that the contact resistance is most improved and the adhesion is improved when heated to about 70 ° C. to 100 ° C. Furthermore, in consideration of the heat resistance of the resist used for patterning, it is an appropriate condition that the deposition is performed at a temperature of about 70 ° C. without decreasing the process yield and improving the contact resistance.

Subsequently, the SiO ₂ film deposited on the sidewall of the groove 113 is removed by lithography and wet etching using a buffered hydrofluoric acid solution (BHF). By this step, the groove 113 can be an air layer only. However, as will be described later, the SiO ₂ film on the side wall may be used as it is as a protective film without being removed.

(Wiring electrode formation process)
Next, by lithography and electron beam evaporation, titanium (Ti) / Ti so that the p-side electrodes 108 are electrically connected to each other on the dielectric block layer 110 including the plurality of p-side electrodes 108. A wiring electrode 109 made of platinum (Pt) / gold (Au) is formed. Here, the film thicknesses of Ti, Pt, and Au are 50 nm, 35 nm, and 500 nm, respectively.

  As described above, the substrate 101 is generally in a wafer state, and a plurality of laser elements are formed in a matrix on the main surface of the substrate 101. Therefore, when the individual laser elements are divided from the substrate 101 in the wafer state by cleavage, if the wiring electrode 109 is continuously formed between the elements, the p-side electrode 108 in close contact with the wiring electrode 109 becomes a p-type contact. There is a risk of peeling from the layer. Therefore, it is desirable that the wiring electrode 109 is formed separately for adjacent chips. Furthermore, when the thickness of the upper Au layer of the wiring electrode 109 is increased to about 3 μm by electrolytic plating and a pad electrode (not shown) is formed, the heat generated from the MQW active layer 104 is effectively dissipated. be able to. That is, the reliability of the SLD element according to the first embodiment can be improved by the pad electrode made of Au having a thickness of about 3 μm.

(Back electrode forming process)
Next, the back surface of the substrate 101 is ground and polished to reduce the thickness of the substrate 101 to about 100 μm. Thereafter, an n-side electrode 111 made of Ti / Pt / Au is formed on the back surface of the thinned substrate 101. Here, the film thicknesses of Ti, Pt, and Au are 15 nm, 35 nm, and 300 nm, respectively. With this configuration, a good contact resistance of 1 × 10 ⁻⁴ Ωcm ² or less can be realized. Here, it is desirable to form an electrode pattern by performing etching only on the upper Au film by lithography and wet etching as a recognition pattern in the subsequent cleavage and assembly processes.

  The substrate 101 may be polished by a mechanical polishing method using diamond slurry or colloidal silica or a chemical mechanical polishing method using an alkaline solution such as a potassium hydroxide (KOH) solution at the same time.

(Cleaving and assembly process)
Next, a cleavage assisting groove is formed at a cleavage position in the wafer. After that, braking is performed along the formed cleavage assisting groove, and primary cleavage is performed to form the resonator end face. Subsequently, a multilayer dielectric reflective film having a reflectivity of about 95% is formed on the end surface (rear end surface) opposite to the light emitting end surface by a CVD method or the like. Thereafter, secondary cleavage is performed in a direction parallel to the longitudinal direction of the resonator, and mounting and wiring in a desired CAN package can produce a GaN-based blue SLD element.

  FIG. 5A schematically shows the reflection / transmission refraction phenomenon by the Fresnel equation, FIG. 5B shows the incident angle dependence of the reflectance, and FIG. 5C shows the incident angle of the transmittance. Indicates dependency. As shown in FIGS. 5 (b) and 5 (c), the TE polarized light (p wave) and the TM polarized light (s wave) have different reflectivities and transmittances, and at an angle called Brewster angle, TE polarized light is 100% transmitted, but TM polarized light is only partially transmitted. This is a zero-order approximation in which light is treated as a straight line having no width, but qualitatively, a similar phenomenon occurs even in a waveguide having a finite width. The inventor of the present application has found that by utilizing this phenomenon, polarization selectivity can be added to the waveguide, and therefore, the value of the polarization ratio of light emission can be increased.

  6, 7, and 8 show an example in which the state of light propagation in the unconnected portion of the ridge waveguide 107 a is calculated using the finite-difference time-domain method (FDTD method). . In the two-dimensional model shown in FIG. 6, it can be seen that TE polarized light and TM polarized light have different transmittances and TE polarized light is preferentially guided as shown in FIG.

FIG. 8 shows the angle dependency of the transmittance of TE polarized light and TM polarized light and the angle dependency of the polarization ratio. It can be seen that the transmittance of the TE wave is maximized and the polarization ratio is increased in the vicinity of the Brewster angle of the 0th order approximation. It can be seen that an increase in the value of the polarization ratio can be expected in the range of θ _C / 2 ≦ θ <θ _C with respect to the critical angle θ _C = sin ⁻¹ (n2 / n1). However, since it is preferable from the viewpoint of light emission efficiency to use an angle with the least TE wave loss, in this embodiment, θ = 19.5 °.

  Since about half of the TM wave component reflected is radiated to the outside of the waveguide and becomes a loss, it is possible to reduce the overall loss by radiating to the outside of the waveguide before receiving the amplification effect by stimulated emission as much as possible. . Therefore, when two non-connection portions (groove portions 113) are provided in the ridge waveguide 107a, as a third modification shown in FIG. 9, light is emitted only from one end surface and the other end surface is connected to the reflection surface 114. Then, it is desirable that the ratio of the lengths of the regions 107a1, 107a2, and 107a3 of the ridge waveguide 107a is 1: 2: 2. By setting such a ratio, the maximum amplification length in each region can be as short as 2L / 5 (L is the resonator length), so that carrier loss due to stimulated emission of TM waves can be minimized. .

  As shown in FIG. 10, as a fourth modification, when light is emitted from both end faces of the cleavage end face, the ratio of the lengths of the waveguide portions 107a1, 107a2, and 107a3 of the ridge waveguide 107a is set to 1: 1: 1 is desirable. By setting such a ratio, the maximum amplification length in each waveguide portion can be minimized to L / 3 (L is a resonator length).

  By the way, the non-connection part (groove part 113) can be provided in three or more places, and the polarization ratio increases as the number increases. However, since the loss of TE waves at the non-connection portion is not zero, if the number of non-connection portions is too large, the characteristics of the SLD element as a device are deteriorated.

  In the SLD structure in the present embodiment, it is clear that a characteristic with a polarization ratio of about 100 to 500 can be obtained by providing about 2 to 4 non-connection portions.

  In the present embodiment, the groove 113 which is a non-connecting portion of the ridge waveguide 107a is an air layer and has a refractive index of 1, but is transparent to emitted light such as a dielectric film or a resin film. It may be embedded with any material.

  Further, as shown in FIG. 11C, as a fifth modification, the wall surface (end surface) of the groove 113 may be covered with a dielectric protective film 116. Since the optimum inclination angle varies depending on the refractive index of the material used, etc., it is necessary to design it accordingly. In addition, although the polarization selectivity increases as the refractive index difference between the ridge waveguide 107a and the groove 113 increases, it is preferable that some protective film is formed from the viewpoint of reliability as in the fifth modification. . Further, the groove 113 may be embedded with a low refractive index material that does not absorb the emission wavelength.

  In this embodiment, the light emission end face (front end face) is an inclined face by dry etching, and the other end face (reflection end face) is an end face by cleavage. On the contrary, the emission end face is cleaved. There is no problem even if the combination of the forming methods of both end faces is changed, such as forming the reflecting end faces by dry etching.

  Also, as shown in FIGS. 12A and 12B, as a sixth modification, it is possible to make the reflective end face a highly reflective surface by providing a dielectric multilayer film 117 on the reflective surface. .

(Comparative example)
FIG. 13A to FIG. 13C show a blue SLD element according to a comparative example of the present invention.

  As shown in FIG. 13A, the blue SLD element according to this comparative example is not perpendicular to the emitting end face in which the extending direction of the ridge waveguide 107c, that is, the light resonance direction is the cleavage plane, but at a predetermined angle. It is formed by being inclined by (for example, about 7 °).

  Thereby, SLD operation | movement is attained by reducing the mode reflectance of light and suppressing laser oscillation. Thus, even the SLD element according to the comparative example can output light with low coherence.

  However, as in the conventional example, the polarization ratio (TE / TM polarization ratio) at the ultra-low reflection exit surface 112 that is the front end surface and the reflection surface 114 that is the rear end surface is higher than that of the LED element, but the conventional liquid crystal It is not so high that the polarizing plate, which is an essential component of the display device, can be eliminated.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

  In the second embodiment, a liquid crystal display device using a blue SLD element according to the first embodiment and its modification will be described.

  As shown in FIG. 14, the liquid crystal display device according to the second embodiment irradiates a plurality of SLD light sources 201 each composed of a blue SLD element according to the first embodiment and light from each SLD light source 201. From the light guide plate 203 received from the lower end thereof, the reflection plate 202 that reflects light transmitted through the light guide plate 203 forward, the diffusion plate 204 that diffuses light transmitted through the light guide plate 203 forward, and the diffusion plate 204 The liquid crystal panel 205 receives the light from the back surface.

  With this configuration, the liquid crystal display device according to the second embodiment includes the blue SLD element according to the first embodiment as the SLD light source, and uses the SLD light source 201 having a high polarization ratio, thereby providing a conventional liquid crystal display. A polarizing plate provided between the light guide plate 203 and the diffusion plate 204, which is an essential component of the apparatus, can be eliminated.

  In addition, since the utilization efficiency of light from the SLD light source 201 is improved, the same brightness can be obtained with less light output and power consumption. In addition, since the SLD element has higher light directivity than the LED, the coupling efficiency with the light guide plate 203 is high, and the light guide plate 203 itself can be made thinner, so that the liquid crystal display device can be further thinned. It becomes possible.

In the first embodiment and the second embodiment, the SLD element that outputs blue light (B) has been described. However, by changing the composition ratio in the compound semiconductor material and the material system, red light can be obtained. The (R) or green light (G) SLD light source 201 can be realized. For example, the semiconductor laminate is represented by the general formula Al _x Ga _y In _1-xy As _z P _1-z (where 0 ≦ x, y, z ≦ 1, 0 ≦ x + y ≦ 1). If a III-V group compound semiconductor is used, a red light source having high directivity, high polarization, and low coherence can be obtained.

  If an SLD light source capable of outputting three colors of RGB is used, it can also be used as a light source for an SLD display device with high color reproducibility, a color filterless liquid crystal display device using RGB backlight, and a mobile projector. .

  The semiconductor light emitting device and the liquid crystal display device using the semiconductor light emitting device according to the present invention can increase the polarization ratio of the semiconductor light emitting device, and as a result, a thin, low power consumption and low cost liquid crystal display device can be realized. Therefore, it is useful as a backlight light source for an ultra-thin liquid crystal display device.

101 Substrate 102 n-type cladding layer 103 n-type guide layer 104 active layer (light emitting layer)
105 p-side guide layer 106 carrier overflow suppression layer 107 p-type cladding layer 107a ridge waveguide (optical waveguide)
107a1 First waveguide portion 107a2 Second waveguide portion 107a3 Third waveguide portion 107b Pedestal portion 107c Ridge waveguide 108 p-side electrode 109 Wiring electrode 110 Dielectric block layer 111 n-side electrode 112 Output end face (very low Reflective light exit surface)
113 Groove (recess)
114 Reflecting surface 115 Cleaving assist groove 116 Dielectric protective film 117 Dielectric multilayer film 201 SLD light source 202 Reflecting plate 203 Light guide plate 204 Diffusing plate 205 Liquid crystal panel

Claims (9)

A light emitting layer formed on a substrate and an optical waveguide including the light emitting layer, and a semiconductor laminate that emits light from at least one of a front end face and a rear end face,
The optical waveguide has at least one non-connected portion between the front end surface and the rear end surface, and is formed from a plurality of waveguide portions separated by the non-connected portion.   The semiconductor light emitting element according to claim 1, wherein the non-connecting portion is a concave portion that divides the optical waveguide. The normal direction of the interface between the optical waveguide and the recess is inclined from the extending direction of the optical waveguide,
The semiconductor light emitting element according to claim 2, wherein the light is guided through the non-connection portion by refraction at the interface. At the interface between the optical waveguide and the concave portion, the angle theta that the extending direction forms of the optical waveguide and the normal direction of the interface, the critical angle when the theta _c,
θ _c / 2 ≦ θ <θ _c
The semiconductor light-emitting element according to claim 3, wherein   5. The semiconductor light emitting element according to claim 3, wherein the plurality of waveguide portions are formed such that central axes in the extending direction of adjacent waveguide portions are shifted from each other.   6. The semiconductor light emitting device according to claim 1, wherein the semiconductor stacked body constitutes a super luminescence diode (SLD) element that emits stimulated emission light from the front end face or the rear end face. 7. element. The semiconductor stacked body is made of a group III nitride semiconductor represented by Al _x Ga _y In _1-xy N (where 0 ≦ x, y ≦ 1, 0 ≦ x + y ≦ 1). The semiconductor light-emitting element according to claim 1, wherein the semiconductor light-emitting element is a light-emitting element. The semiconductor stacked body is represented by Al _x Ga _y In _1-xy As _z P _1-z (where 0 ≦ x, y, z ≦ 1, 0 ≦ x + y ≦ 1). The semiconductor light-emitting device according to claim 1, comprising a group V compound semiconductor. The semiconductor light emitting device according to any one of claims 1 to 8,
A light guide plate that receives light from the semiconductor light emitting element;
A liquid crystal panel for receiving light transmitted through the light guide plate,
A liquid crystal display device, wherein a polarizing plate is not provided in a light waveguide path from the semiconductor light emitting element to the liquid crystal panel.