JP2004096131A - Gallium nitride-based compound semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gallium nitride-based compound semiconductor light emitting element having a low threshold value current and a low operating voltage, free from deterioration, and highly reliable by employing a p-type gallium nitride-based compound semiconductor structure, in which a low-resistance p-side electrode can be easily formed and which has a high carrier concentration that realizes a highly efficient and uniform carrier injection to an active layer. <P>SOLUTION: In the gallium nitride-based compound semiconductor light emitting element, a hole conductive type semiconductor layer has a p-electrode contact layer (9) doped with Mg and at least a Ga<SB>x2</SB>In<SB>y2</SB>Al<SB>z2</SB>N(x2+y2+z2=1, 0≤x2, z2≤1, 0<y2≤1) smoothing layer is formed on the side nearer to an active layer (6) than to the p-electrode contact layer. At the same time, on the surface of the p-electrode contact layer, a laminated structure having a Pt layer (10), TiN layer (11a) and Ti layer (11) laminated in this order is formed and between the p-electrode contact layer and the Pt layer, an alloy layer (15) consisting of Pt and semiconductor is formed. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a gallium nitride-based compound semiconductor light-emitting device such as a gallium nitride-based blue-violet semiconductor laser (hereinafter, also referred to as LD) or a gallium nitride-based high-brightness blue / green light-emitting diode (hereinafter, also referred to as LED). .

Conventionally, short-wavelength semiconductor lasers have already been put into practical use with a 600 nm-band light source using an InGaAlP material whose characteristics have been improved to a level that allows both reading and writing of a disk.

Therefore, blue semiconductor lasers with shorter wavelengths are being actively developed with the aim of further improving the recording density. This is because laser light having a short oscillation wavelength can reduce the size of condensed light and is effective in increasing the recording density.

Therefore, in recent years, gallium nitride-based compound semiconductors such as GaN, InGaN, GaAlN, and InGaAlN have been attracting attention as materials for short-wavelength semiconductor lasers for application to high-density optical disk systems and the like.

For example, room-temperature pulse oscillation at a wavelength of 380 to 417 nm has been confirmed in a semiconductor laser using a GaN-based material. However, a semiconductor laser using a GaN-based material cannot provide satisfactory characteristics, and the threshold voltage at room temperature pulse oscillation is as high as 10 to 40 V and has large variations.

This is due to the difficulty of crystal growth of the gallium nitride based compound semiconductor layer and the high device resistance. In other words, the inability to form a p-type gallium nitride-based compound semiconductor layer with a smooth surface and a high carrier concentration and a high p-side electrode contact resistance cause a large voltage drop, and generate heat and metal reaction even in pulse oscillation operation. This causes deterioration. Note that continuous oscillation at room temperature cannot be achieved unless the operating voltage is reduced to 10 V or less in consideration of the amount of heat generated.

Also, when a current required for laser oscillation is injected, the p-type gallium nitride-based compound semiconductor layer is not a good crystal and has a defect having a plurality of fine holes along a growth direction from a lower layer to an upper layer. Since a locally high current flows, carriers cannot be uniformly injected into the active layer, and instantaneous device breakdown occurs, continuous oscillation does not occur.

As described above, in order to realize a highly reliable gallium nitride-based blue-violet semiconductor laser that operates at a low threshold current and a low threshold voltage for practical use in an optical disk or the like, carrier injection into the active layer is required. It is important to perform the process efficiently and uniformly and to suppress the voltage drop at the electrode contacts, but it is extremely difficult at present.

As described above, in the gallium nitride-based compound semiconductor laser, it is difficult to obtain a high-quality p-type gallium nitride-based compound semiconductor without a plurality of fine hole-shaped defects, and the p-side electrode contact resistance is high. In addition, a large voltage drop occurs at the electrode contact, and further, uniform carrier injection into the active layer cannot be performed, which makes it difficult to realize a device having a low threshold current and a low operating voltage.

In a GaN-based light emitting device, not only does the operating voltage increase due to the high p-side electrode contact resistance, but also nickel, which is the p-side electrode metal, and gallium, which forms the p-type semiconductor layer, react, melt, and deteriorate when energized. In addition, continuous oscillation of the laser was difficult.

The present invention has been made in view of the above circumstances, and has a high carrier concentration p-type gallium nitride-based compound semiconductor structure capable of easily forming a low-resistance p-side electrode and efficiently and uniformly injecting carriers into an active layer. Accordingly, it is an object of the present invention to provide a gallium nitride-based compound semiconductor light emitting device having a low threshold current, a low operating voltage, no deterioration, and excellent reliability.

The invention according to claim 1 comprises a gallium nitride-based compound semiconductor (Ga _x1 In _y1 Al _z1 N: x1 + y1 + z1 = 1, 0 ≦ x1, y1, z1 ≦ 1), and the active layer is a semiconductor layer having a different conductivity type. In the sandwiched gallium nitride-based compound semiconductor light emitting device, the hole conduction type semiconductor layer has a p-electrode contact layer to which Mg is added, and Ga _x2 In _y2 Al _z2 N is closer to the active layer than the p-electrode contact layer. (X2 + y2 + z2 = 1, 0 ≦ x2, z2 ≦ 1, O <y2 ≦ 1) A smoothing layer is formed, and a stacked structure of a Pt layer, a TiN layer, and a Ti layer is formed on the surface of the p-electrode contact layer. This is a gallium nitride-based compound semiconductor light emitting device in which an alloy layer made of a Pt-semiconductor is formed between the p-electrode contact layer and the Pt layer.

According to a second aspect of the present invention, in the gallium nitride-based compound semiconductor light-emitting device according to the first aspect, a gallium nitride-based compound semiconductor light emitting device includes an Au layer formed on the Ti layer via a second Pt layer. It is a compound semiconductor light emitting device.

Further, the invention corresponding to claim 3 is the gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein the p-electrode contact layer contains carbon, and the interface between the TiN layer and the Pt layer is This is a gallium nitride-based compound semiconductor light emitting device having a higher carbon concentration than a p-electrode contact layer.

According to a fourth aspect of the present invention, in the gallium nitride based compound semiconductor light emitting device according to the first aspect, the p-electrode contact layer contains carbon and oxygen, and an interface between the TiN layer and the Pt layer is A gallium nitride-based compound semiconductor light emitting device having a carbon concentration and an oxygen concentration higher than those of the p-electrode contact layer.

Further, according to a fifth aspect of the present invention, in the gallium nitride-based compound semiconductor light emitting device according to the first aspect, the p-electrode contact layer contains hydrogen and an interface between the second Pt layer and the Au layer. Is a gallium nitride-based compound semiconductor light emitting device having a higher hydrogen concentration than the p-electrode contact layer.

The inventions corresponding to claims 1 to 5 are more preferable embodiments as the following (1) to (5) are individually satisfied.

(1) The amount of Mg added to the p-electrode contact layer has a high concentration distribution near the surface.

(2) The p-electrode contact layer is composed of two or more gallium nitride-based compound semiconductors having different compositions.

(3) The GaInAlN smoothing layer has an active layer formed in a multiple quantum well structure.

(4) When an n-type conductive layer exists below the p-electrode contact layer, at least one GaInAlN smoothing layer is inserted between the p-type conductive layer and the n-type conductive layer. In other words, the positional relationship of forming the p-electrode contact layer above the GaInAlN smoothing layer is important. The cladding layer, the waveguide layer, and the like may or may not be provided between the GaInAlN smoothing layer and the p-electrode contact layer.

(5) In the electrode structure in contact with the p-electrode contact layer, Ti / Pt / Au is laminated on a thin Pt layer having a thickness of 10 nm or less.

(Action)
Therefore, the invention corresponding to claim 1 and claim 2 takes the above measures to form an Mg-added gallium nitride-based semiconductor layer on the GaInAlN smoothing layer containing at least the In element, and further to form Pt. And the formation of the Ti electrode, a p-type semiconductor layer having a small crystal defect such as a fine hole-like defect and a high acceptor concentration can be obtained, and a thin Pt layer as an electrode metal is slightly diffused into the p-type semiconductor layer. As a result, the effective electrode contact area increases, and the Pt element acts as a hydrogen element taken in simultaneously with the addition of Mg and as a catalyst for reducing the surface oxide film due to exposure to the air after crystal growth, improving the activation rate of Mg and improving the effectiveness. The upper acceptor concentration, and the upper Ti layer reacts with the nitrogen element of the gallium nitride based semiconductor layer to form extremely stable TiN, thereby being an upper electrode metal. Since the diffusion of downward second Pt layer and an Au layer can be suppressed, it is possible to result improvement in crystal quality. Therefore, a p-type gallium nitride-based compound semiconductor structure with a high carrier concentration that can easily form a low-resistance p-side electrode and can efficiently and uniformly inject carriers into the active layer can be realized, and a voltage drop at an electrode contact can be reduced. Suppressing, low threshold current, low operating voltage, no deterioration, and excellent reliability can be achieved.

In the invention corresponding to claims 3 and 4, the p-electrode contact layer contains carbon and oxygen, and the interface between the TiN layer and the Pt layer has a lower carbon concentration and oxygen concentration than the p-electrode contact layer. In other words, since the carbon and oxygen in the semiconductor layer are stopped by the TiN layer in the process of being removed to the outside by using Pt as a catalyst, the same operation as the operation corresponding to claim 1 is performed. Can play.

Further, in the invention corresponding to claim 5, the p-electrode contact layer contains hydrogen, and the interface between the second Pt layer and the Au layer has a higher hydrogen concentration than the p-electrode contact layer. Since the carbon and oxygen in the semiconductor layer are stopped by the Au layer in the process of being removed to the outside by using Pt as a catalyst, the same operation as the first embodiment can be achieved.

(Related invention)
A description will be given of related inventions with respect to the inventions corresponding to claims 1 to 5 described above. This related invention reduces the operating voltage and reduces the amount of heat generated by forming a p-type semiconductor layer containing 1% or more of each of palladium (Pd) or Pt and Ti for supplying current to a p-type GaN-based semiconductor. The purpose of the present invention is to improve the reliability by suppressing the diffusion and preventing the diffusion of the constituent elements due to the conduction.

For example, in order to supply a current to a p-type semiconductor layer of a group III-V compound semiconductor device having a hexagonal structure, a p-type semiconductor layer containing 1% or more of each of Pd or Pt and Ti is substantially formed. Not only the electrode contact area can be increased and the electrode resistance can be reduced to about 10 ⁻⁵ Ωcm ² , but also this layer formed in a shallow region from the surface of the GaN-based semiconductor contains a bond between Ti and N and thus has a stable diffusion. It serves as a prevention layer and suppresses element diffusion that occurs at the time of energization, thereby preventing element deterioration.

Further, by making the p-type semiconductor layer a Ga _x In _y Al _z N (0 ≦ x, y, z ≦ 1 and x + y + z = 1) semiconductor containing In, Pd or Pt and Ti are each 1% or more. The electrode resistance with the contained p-type semiconductor layer can be reduced to 10 ⁻⁶ Ωcm ² . Further, Pd or Pt is formed (in a range of 10 nm or less), Ti is formed (in a range of 50 nm or less), and p-type is formed on the surface of the p-type semiconductor layer of the hexagonal structure III-V compound semiconductor device. In a semiconductor device in which an electrode metal for supplying a current to a semiconductor layer is formed, a p-type semiconductor having a thickness of 20 nm or less containing 1% or more of Pd or Pt and Ti each having a chemically strong bond by a heat treatment process of 300 ° C. or more. Layers can be formed.

As described above, according to the present invention, a low-resistance p-side electrode can be easily formed, and a high carrier concentration p-type gallium nitride-based compound semiconductor structure capable of injecting carriers with high efficiency and uniformity into the active layer has a low resistance. It is possible to provide a gallium nitride-based compound semiconductor light-emitting device that has excellent reliability at a threshold current and a low operating voltage without causing deterioration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment)
FIG. 1 is a sectional view showing a schematic configuration of a blue semiconductor laser according to a first embodiment of the present invention. This blue semiconductor laser has a GaN buffer layer 2, an n-GaN contact layer 3 (Si-doped, 5 × 10 ¹⁸ cm ⁻³ , 4 μm), an n-Al _0.2 Ga _0.8 N clad on a sapphire substrate 1 by MOCVD. Layer (Si-doped, 5 × 10 ¹⁷ cm ⁻³ , 0.3 μm) 4, GaN waveguide layer (undoped, 0.1 μm) 5, Active layer 6, p-GaN waveguide layer (Mg-doped, 0.1 μm) 7, p-Al _0.2 Ga _0.8 N cladding layer (Mg doped, 5 × 10 ¹⁷ cm ⁻³ , 0.3 μm) 8, p-GaN contact layer (Mg doped, 1 × 10 ¹⁸ cm ⁻³ , 1 μm) 9 It has a multilayer structure formed sequentially.

On this p-type GaN contact layer 9 having a multilayer structure, a Pt layer 10 having a thickness of 10 nm, a TiN layer 11 a to be described later for heat treatment, a Ti layer 11 having a thickness of 30 nm, a Pt layer 12 having a thickness of 10 nm, and an Au electrode pad having a thickness of 1 μm 13 are sequentially laminated to form a p-type electrode.

A part of the outermost surface of the Au electrode pad 13 or the p-type GaN contact layer 9 is removed by a dry etching method to a depth reaching the n-type GaN contact layer 3, and the GaN contact layer 3 exposed by the dry etching is removed. Is formed with an n-side electrode 14.

The active layer 6 is composed of an In _0.05 Ga _0.95 N barrier layer (undoped, 5 nm) sandwiching 10 layers of In _0.2 Ga _0.8 N quantum wells (undoped, 2.5 nm).

Next, a method of manufacturing such a blue semiconductor laser and its operation will be described.

In FIG. 1, each layer from the GaN buffer layer 2 to the p-GaN contact layer 9 on the sapphire substrate 1 is formed by one MOCVD method.

Further, in this blue semiconductor laser, the GaInAIN smoothing layer containing In is used as the InGaN quantum well active layer 6, and the Mg-added gallium nitride based semiconductors 18 and 19 are formed thereon. The GaInAIN smoothing layer suppresses minute hole-like defects and crystal defects such as cracks and dislocations propagated from the substrate, so that smooth p-type semiconductor layers 18 and 19 can be obtained on the p-side electrode side.

According to the experiments of the present inventors, even if the GaInAIN smoothing layer is not provided, when the thickness of the p-GaN contact layer 9 is 0.6 μm or more, the surface of the p-GaN contact layer 9 has a plurality of fine holes. It is considered that the defect can be embedded. That is, in addition to providing the GaInAIN smoothing layer and setting the thickness of the p-GaN contact layer 9 to 0.6 μm or more, it is possible to reliably improve the quality of the p-type semiconductor layer.

Next, Pt (5 nm) / Ti (30 nm) / Pt (10 nm) / Au (1 μm) are sequentially laminated on the surface of the p-GaN contact layer 9 in a region having a width of 10 μm.

Next, when heat treatment is performed in a nitrogen atmosphere at 350 ° C., Pt diffuses down to a depth of about three times the deposited film thickness at the maximum, and undergoes a solid-phase reaction with Ga in the p-GaN contact layer 9 to form an alloy of Pt-semiconductor. A layer 15 is formed, and at the same time, Ti undergoes a solid-phase reaction with N that diffuses upward from the p-GaN contact layer 9 to form a TiN layer 11a at the interface with the Pt layer by being stably bonded. Pt acts as a catalyst to remove the hydrogen element and carbon element that hinder the activation of Mg, which is a p-type dopant, as an acceptor, or the oxygen element that has been bonded to the surface by exposure to the atmosphere before electrode formation, and is removed from the film. It was found that the acceptor concentration increased and the activation rate of Mg became almost 100% (the hydrogen element, the carbon element and the oxygen element were changed before the heat treatment due to various factors during the growth. A multilayer structure consisting of the semiconductor layer in which are distributed at a substantially constant concentration).

Further, the interface between the TiN layer 11a and the Pt layer 10 has a higher carbon concentration and oxygen concentration than the p-GaN contact layer 9, that is, the carbon and oxygen in the semiconductor layer are externalized by using Pt as a catalyst. Is stopped at the TiN layer 11a in the process of being removed.

Further, the interface between the upper Pt layer 12 and the Au layer 13 has a higher hydrogen concentration than the p-GaN contact layer 9, that is, carbon and oxygen in the semiconductor layer are externalized using Pt as a catalyst. Stopped at the Au layer 13 during the removal process.

Next, a mesa shape including a p-side electrode is formed for forming the n-side electrode 14, and the n-side electrode 14 is formed of Ti / Au on the n-GaN contact layer 3 appearing below the mesa. Here, a p-electrode may be formed after the formation of the n-side electrode 14. Further, the sapphire substrate 1 is mirror-polished to 50 μm and cleaved in a direction perpendicular to the longitudinal direction of the p-side electrode, thereby forming a 1 mm long laser chip.

This blue semiconductor laser continuously oscillated at room temperature with a threshold current of 80 mA. The oscillation wavelength was 420 nm, the operating voltage was 7 V, and the device life under driving at 50 ° C. and 30 mW was 5000 hours. In the case of this laser, since the substantial contact area between the Pt layer 10 and the p-GaN contact layer 9 increases, the resistance can be reduced not only to 1 × 10 ⁻⁵ Ωcm ² , but also the p-GaN contact layer 9 Since the Mg activation rate could be improved to almost 100%, a high carrier concentration was obtained, and carriers could be uniformly injected into the active layer 6 via the p-AlGaN cladding layer 8.

Furthermore, the two-step doping in which the amount of Mg added to the p-GaN contact layer 9 according to the first embodiment is doubled in the range of 0.2 μm from the surface and halved in the remaining range of 0.8 μm. The characteristics of the blue semiconductor laser were further improved. That is, in the blue semiconductor laser having this structure, the operating voltage was further reduced to 6.5 V as compared with the first embodiment. By doping the p-type contact layer with two steps, the effect of reducing the electrode contact resistance on the surface and the effect of increasing the resistance under the contact layer to suppress the leakage current in the lateral direction were obtained.

As described above, according to the first embodiment, by forming the Mg-doped gallium nitride-based semiconductor layer on the GaInAlN smoothing layer containing at least In, crystal defects such as minute hole defects are reduced. be able to.

Further, by forming the Pt layer 10 on the p-GaN contact layer 9, the Pt layer slightly diffuses into the p-GaN contact layer 9, thereby increasing the effective electrode contact area. , Acts as a reduction catalyst for the hydrogen element, carbon element, and oxygen element present in the p-type semiconductor layer due to various causes, and acts to remove each of these impurity elements from the p-type semiconductor layer. It is possible to increase the effective acceptor concentration.

Further, by forming the Ti layer 11 on the Pt layer 10, the Ti layer reacts with the N element of the gallium nitride based semiconductor layer to form extremely stable TiN, thereby forming the second Pt layer 12 as the upper electrode metal. And diffusion of Au layer 13 downward.

各 Each effect of the GaInAlN smoothing layer, the Pt layer 10 and the Ti layer 11 can improve the crystal quality as a result.

Therefore, a low-resistance p-side electrode can be easily formed, and a p-type gallium nitride-based compound semiconductor structure having a high carrier concentration that can efficiently and uniformly inject carriers into the active layer can be realized, and a voltage drop at an electrode contact can be suppressed. As a result, excellent reliability can be achieved with low threshold current and low operating voltage without deterioration.

(Second embodiment)
Next, a blue semiconductor laser according to a second embodiment of the present invention will be described. FIG. 2 is a cross-sectional view showing a schematic configuration of the blue semiconductor laser. The same portions as those in FIG. 1 are denoted by the same reference numerals, detailed description thereof will be omitted, and only different portions will be described here.

That is, the semiconductor laser according to the present embodiment is intended to further reduce the contact resistance as compared with the first embodiment, and more specifically, as shown in FIG. The structure is such that a p-In _0.1 Ga _0.9 N contact layer 21 is inserted between the Pt electrode 10 and the Pt electrode 10.

Here, the p-In _0.1 Ga _0.9 N contact layer 21 is a semiconductor layer doped with Mg, 1 × 10 ¹⁹ cm ⁻³ and a thickness of 0.2 μm.

The blue semiconductor laser is manufactured in the same manner as in the first embodiment except that the p-In _0.1 Ga _0.9 N contact layer 21 is formed.

The blue semiconductor laser described above continuously oscillated at room temperature with a threshold current of 75 mA. The oscillation wavelength was 420 nm, the operating voltage was 6 V, and the device life at 50 ° C. and 30 mW drive was 5000 hours. In the case of this laser, since the band gap of the p-In _0.1 Ga _0.9 N contact layer 21 in contact with the Pt layer 10 is smaller than that of the p-GaN layer 9, the Schottky barrier is reduced. As a result, not only the electrode contact resistance could be reduced to 7 × 10 ⁻⁶ Ωcm ² , but also the Mg activation rate of the p-In _0.1 Ga _0.9 N contact layer 21 could be improved to almost 100%, so that a high carrier concentration was obtained. Carriers can be uniformly injected into the active layer 6 via the p-AlGaN cladding layer 8.

As described above, according to the second embodiment, the p-In _0.1 Ga _0.9 N contact layer 21 having a narrower band gap than the p-GaN layer 9 is provided between the p-GaN layer 9 and the Pt electrode 10. Since it is inserted, in addition to the effects of the first embodiment, the contact resistance with the p-side electrode can be further reduced, and thus the operating voltage can be reduced.

(Third embodiment)
Next, a blue semiconductor laser according to a third embodiment of the present invention will be described. FIG. 3 is a sectional view showing a schematic configuration of the blue semiconductor laser. The same parts as those in FIG. 1 are denoted by the same reference numerals, detailed description thereof will be omitted, and only different parts will be described here.

That is, unlike the first embodiment, the semiconductor laser according to the present embodiment has an internal current confinement structure. Specifically, as shown in FIG. 3, p-Al _0.2 Ga _0.8 N A plurality of n-GaN current blocking layers 31 (1 × 10 18 cm ⁻³ , 0.5 μm) selectively formed on the cladding layer 8, the p-Al _0.2 Ga _0.8 N cladding layer 8 and each n-GaN A 0.1 μm-thick In _0.1 Ga _0.9 N smoothing layer 32 formed on the current blocking layer 31;

The p-GaN contact layer 9 is formed on the In _0.1 Ga _0.9 N smoothing layer 32 as described above.

This blue semiconductor laser is manufactured in the same manner as in the first embodiment, except that the number of times of growth by the MOCVD method is three due to the current confinement structure. The semiconductor laser as described above continuously oscillated at room temperature with a threshold current of 70 mA. The oscillation wavelength was 420 nm, the operating voltage was 6.5 V, and the device life under driving at 50 ° C. and 30 mW was 5000 hours. In the case of this laser, in addition to the effects described in the first embodiment, the area of the p-side electrode is increased due to the formation of the internal current confinement structure, and the p-side contact resistance is reduced to 5 × 10 ⁻⁶ Ωcm ^2. did it. That is, further lower voltage operation was achieved by the internal structure current confinement structure.

According to the third embodiment, as described above, the contact resistance can be further reduced in addition to the effects of the first embodiment.

Further, even in a configuration in which the p-GaN contact layer 9 is formed immediately above the In _0.1 Ga _0.9 N smoothing layer 32, as described above, the In _0.1 Ga _0.9 N smoothing layer 32 prevents propagation of fine hole-like defects. Since this is prevented, the quality of the crystal can be improved.

(Fourth embodiment)
Next, a blue semiconductor laser according to a fourth embodiment of the present invention will be described. FIG. 4 is a cross-sectional view showing a schematic configuration of this blue semiconductor laser. The same parts as those in FIG. 1 are denoted by the same reference numerals, detailed description thereof will be omitted, and only different parts will be described here.

That is, unlike the first embodiment, the blue semiconductor laser according to the present embodiment has a buried-type current confinement structure. Specifically, as shown in FIG. The 5 to p-Al _0.2 Ga _0.8 N cladding layer 8 has a mesa structure with a width of 10 μm (the thickness is as described above), and undoped Al _0.1 Ga _0.9 N block layers 41 are formed on both sides of the mesa structure. A structure in which an InGaAlN smoothing layer 42 is interposed between the p-GaN contact layer 9 and the layers 41 and 8 of the Al _0.1 Ga _0.9 N block layer 41 and the p-Al _0.2 Ga _0.8 N cladding layer 8 is provided. I have.

The blue semiconductor laser is manufactured in the same manner as in the first embodiment, except that the number of times of growth by the MOCVD method is three due to the internal current confinement structure.

The blue semiconductor laser as described above continuously oscillated at room temperature with a threshold current of 60 mA. The oscillation wavelength was 420 nm, the operating voltage was 5 V, and the device life under driving at 50 ° C. and 30 mW was 5000 hours. In the case of this laser, in addition to the effects described in the first embodiment, the area of the p-side electrodes 10 to 13 increases due to the formation of the buried structure current confinement structure, and the p-side contact resistance becomes 5 × 10 ⁻⁶ Ωcm ^2. Could be reduced. In other words, the lower threshold gain by the thin film quantum well active layer having a thickness equal to or less than the critical thickness and the buried structure and the current confinement structure have further reduced the voltage operation.

According to the fourth embodiment, as described above, in addition to the effects of the first embodiment, an internal current confinement structure can be provided.

(Fifth embodiment)
Next, a blue semiconductor laser according to a fifth embodiment of the present invention will be described. FIG. 5 is a cross-sectional view showing a schematic configuration of the blue semiconductor laser. The same parts as those in FIG. 1 are denoted by the same reference numerals, detailed description thereof will be omitted, and only different parts will be described here.

That is, unlike the first embodiment, the blue semiconductor laser according to the present embodiment has a current confinement structure. Specifically, as shown in FIG. The junction with the −Al _0.8 Ga _0.2 N cladding layer 8 has a current confinement structure with the undoped Al _0.1 Ga _0.9 N block layer 51 via the InGaAlN smoothing layer 42.

Here, the GaN waveguide layer 7 is formed on the active layer 6 and is an undoped semiconductor layer having a mesa shape with a width of 10 μm and a thickness of 0.2 μm. The lower portion of the mesa of the GaN waveguide layer 7 has a thickness of 0.1 μm, and an undoped Al _0.1 Ga _0.9 N block layer 51 is formed thereon.

The p-Al _0.8 Ga _0.2 N cladding layer 8 has a window having a width of 10 μm, and the GaN waveguide layer is interposed through the InGaAlN smoothing layer 42 so that the window faces the upper mesa of the GaN waveguide layer 7. 7 and on the undoped Al _0.1 Ga _0.9 N block layer 51. The p-Al _0.8 Ga _0.2 N cladding layer 8 is Mg-doped, 5 × 10 ¹⁷ cm ⁻³ , and 0.3 μm in thickness (at the window), as described above.

The blue semiconductor laser is manufactured in the same manner as in the first embodiment, except that the number of times of growth by the MOCVD method is three due to the current confinement structure.

The blue semiconductor laser described above continuously oscillated at room temperature with a threshold current of 60 mA. The oscillation wavelength was 420 nm, the operating voltage was 5 V, and the element life under driving at 50 ° C. and 30 mW was 5000 hours. In the case of the present laser, the same effect as in the fourth embodiment was obtained.

(Other embodiments)
The present invention and related inventions are not limited to the above-described first to fifth embodiments, and may have a structure in which the composition and the thickness of the semiconductor layer and the conductivity are reversed. In addition to the light emitting element, the present invention can be applied to a light receiving element and an electronic device such as a transistor.

In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

FIG. 1 is a sectional view showing a schematic configuration of a blue semiconductor laser according to a first embodiment of the present invention. FIG. 4 is a sectional view showing a schematic configuration of a blue semiconductor laser according to a second embodiment of the present invention. FIG. 7 is a sectional view showing a schematic configuration of a blue semiconductor laser according to a third example of the present invention. FIG. 9 is a sectional view showing a schematic configuration of a blue semiconductor laser according to a fourth example of the present invention. FIG. 13 is a sectional view showing a schematic configuration of a blue semiconductor laser according to a fifth example of the present invention.

Explanation of reference numerals

1 ... sapphire substrate, 2 ... GaN buffer layer, 3 ... n-GaN contact _{layer, 4 ... n-Al 0.2 Ga} 0.8 N cladding layer, 5 ... GaN waveguide layer, 6 ... active layer, 7 ... p-GaN waveguiding _{layer, 8 ... p-Al 0.2 Ga} 0.8 N cladding layer, 9 ... p-GaN contact layer, 10 ... Pt layer, 11a ... TiN layer, 11 ... Ti layer, 12 ... Pt layer, 13 ... Au electrode pad, 14 ... n-side electrode, 15 ... alloy layer, 31 ... n-GaN current blocking layer, 32 ... In _0.1 Ga _0.9 n smoothing layer, 41, 51 ... undoped Al _0.1 Ga _0.9 n blocking layer, 42 ... InGaAlN smoothing layer.

Claims (5)

A gallium nitride-based compound semiconductor light-emitting device composed of a gallium nitride-based compound semiconductor (Ga _x1 In _y1 Al _z1 N: x1 + y1 + z1 = 1, 0 ≦ x1, y1, z1 ≦ 1) and having an active layer sandwiched between semiconductor layers of different conductivity types At
The hole conduction type semiconductor layer has a p-electrode contact layer to which Mg is added, and at least Ga _x2 In _y2 Al _z2 N (x2 + y2 + z2 = 1, 0 ≦ x2, z2) on the active layer side of the p-electrode contact layer. .Ltoreq.1, 0 <y2.ltoreq.1) A smoothing layer is formed, and a laminated structure of a Pt layer, a TiN layer and a Ti layer is formed on the surface of the p-electrode contact layer, and the p-electrode contact layer is formed. A gallium nitride-based compound semiconductor light emitting device, wherein an alloy layer made of a Pt-semiconductor is formed between the Pt layer and the Pt layer. The gallium nitride-based compound semiconductor light emitting device according to claim 1,
A gallium nitride-based compound semiconductor light emitting device, wherein an Au layer is formed on the Ti layer via a second Pt layer. The gallium nitride-based compound semiconductor light emitting device according to claim 1,
The p-electrode contact layer contains carbon,
A gallium nitride-based compound semiconductor light emitting device, wherein the interface between the TiN layer and the Pt layer has a higher carbon concentration than the p-electrode contact layer. The gallium nitride-based compound semiconductor light emitting device according to claim 1,
The p-electrode contact layer contains carbon and oxygen;
A gallium nitride-based compound semiconductor light emitting device, wherein the interface between the TiN layer and the Pt layer has a higher carbon concentration and oxygen concentration than the p-electrode contact layer. The gallium nitride-based compound semiconductor light emitting device according to claim 1,
The p-electrode contact layer contains hydrogen;
A gallium nitride-based compound semiconductor light emitting device, wherein the interface between the second Pt layer and the Au layer has a higher hydrogen concentration than the p-electrode contact layer.

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