JPH1022568A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing the defective density of a nuclear crystal layer constituting an electronic device and an optical device, which are composed of nitride materials, and to provide a semiconductor device which realizes the stripe structure of basic lateral mode control required by means of a semiconductor laser element, and which is applied as the light source of an applied field represented by an optical disk system and the like. SOLUTION: An insulating film is provided on the whole face on a silicon carbide (α-SiC) substrate 1, the surface is nitrided and a GaN buffer layer 4 and an n-type GaN optical waveguide layer 5 are crystal-grown. Then, insulating film masks 16 are formed and the layers from the layer 5 to the layer 12 are selectively grown. The insulating film 13 narrowing current is provided, a p-side electrode and an n-side electrode are evaporated and are split/opened. The face of a resonator is cut and the element is separated by a scriber. Thus, crystal defective density in the optical waveguide layer and the emission active layer in the semiconductor laser element is reduced compared with a conventional case and an inner light loss owing to a scattering loss can considerably be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device which is particularly useful when applied to a semiconductor laser device suitable for optical information processing or an optical measurement light source.

[0002]

2. Description of the Related Art In the prior art, after a buffer layer made of a nitride material is provided on a sapphire substrate, a nitride semiconductor GaIn
Known example 1 of producing a semiconductor laser diode in the blue-violet wavelength region composed of N / GaN / AlGaN system 1) Japan Journal
Applied Physics 1996, 35, L74-L76 (Jpn
J. Appl. Phys., 35, L74-L76 (1996).).

[0003]

In the above prior art, on a substrate on which a substrate material on which a nitride material is provided is limited,
A light emitting active layer and an optical waveguide layer of a nitride-based material constituting a semiconductor laser diode are provided by crystal growth, and there is no mention of a method of providing an element on another substrate. In addition, there is no mention of a method for forming a crystal layer with a reduced crystal defect density compared to the prior art. Further, in the above prior art, the resonator surface is manufactured by dry processing.
It does not describe the fabrication of a resonator surface by a cleavage method that is easy to process, or a waveguide resonant structure that controls the transverse mode of a laser device.

It is an object of the present invention to firstly expand a selection range of a substrate material on which a crystal of a nitride material can be grown.
Another object of the present invention is to provide a method for providing a crystal layer with a low defect density on an insulating film, and to favorably form electronic devices such as field-effect transistors and optical devices typified by light-emitting diodes and laser devices. Furthermore, the laser device achieves a stripe structure capable of controlling the fundamental transverse mode, improves the device characteristics of a semiconductor laser made of a nitride material, and is represented by an optical disk system or the like that requires a near-field image of the fundamental transverse mode. Enables application of nitride semiconductor lasers as light sources to application fields.

[0005]

Means for achieving the above object will be described below.

[0006] In the present invention, any substrate can be used as long as it is a robust substrate having a melting point higher than the growth temperature of the crystal layer provided on the substrate. It has been devised that crystal growth can be achieved. The composition of the substrate material is diamond structure represented by Si substrate, β
It may have a zinc blende Zinc Blende structure typified by a -SiC silicon carbide substrate or a hexagonal Wurtzite structure typified by α-Al ₂ O ₃ sapphire or α-SiC silicon carbide. In common with providing an insulating film on at least these substrates, the surface of the insulating film is modified by nitriding using a nitrogen source, and a buffer layer or an epitaxial crystal layer of a nitride material is provided thereon. According to the present technology, even when the lattice constant of the growing crystal layer is significantly different from the substrate material and the lattice constant difference is large, the crystal can be grown on the insulating film and an epitaxial crystal layer with a low crystal defect density can be formed. It is.

According to the present invention, an oxide film or a nitride film or an oxynitride film containing a mixture of oxygen and nitrogen is provided as an insulating film on the substrate, and the surface of the insulating film is nitrided. In addition, a uniform surface required for nucleation of a nitride semiconductor can be formed. The state of the insulating film may be single crystal, polycrystal, or amorphous, and is set to a state in which the surface is nitrided to a depth of at least several atomic layers from the surface by a nitriding treatment. In this case, a uniform nitrided state is preferable. A uniform nucleus can be formed on the surface of the uniform insulating film subjected to the nitriding treatment when the buffer layer of the nitride material is grown, so that an epitaxially grown layer having a lower defect density than in the prior art can be provided. In the prior art, the crystal defect density in the crystal layer is as high as 10 ⁹ to 10 ¹¹ / cm ² , whereas the crystal defect density is 10 ⁴ to 10 ⁵ / cm ² could be reduced to a low level. Thereby, the carrier mobility and the carrier recombination luminescence intensity in the crystal layer were significantly increased.

Further, in the present invention, by applying the selective growth technique, a crystal layer can be homoepitaxially grown laterally on an insulating film mask. According to this method, a waveguide structure with further reduced crystal defect density can be formed. According to the present technology, a single crystal layer having a small crystal defect density can be formed on the insulating film mask by homoepitaxial growth, and the defect density can be further reduced by ^two to ^three orders of magnitude to 10 ² to 10 ³ / c.
It was possible to reduce it to the m ² range. This is particularly important when forming a low-loss waveguide of a semiconductor laser because scattering loss during propagation of laser light can be reduced. That is, the performance of the blue semiconductor laser device made of the nitride semiconductor is improved significantly with respect to the basic characteristics and reliability.

In the waveguide structure by selective growth of the present invention,
In addition to the formation of a waveguide having a low defect density, a waveguide shape that allows propagation of a fundamental transverse mode in a semiconductor laser can be manufactured. An embedded BH (Buried Heterostructure) stripe structure with a real refractive index difference in the lateral direction of the active layer and a ridge stripe structure with a complex refractive index difference are formed, and a refractive index guide that stably secures the basic transverse mode up to high output operation. An element having a corrugated structure can be realized.

Further, by utilizing the characteristics of the substrate to be used, for example, on a Si substrate, it is possible to integrate an electronic device such as a FET or a bipolar transistor manufactured by a conventional technique and an optical device such as the semiconductor laser device. In addition, it is also possible to achieve integration of an optical device with a high-temperature electronic device operating at several hundred degrees on a SiC substrate. Light emitting devices such as light emitting diodes and semiconductor lasers, waveguide devices for optical switches and modulators, PIs
Light receiving elements such as N photodiodes and avalanche photodiodes can be considered.

As described above, according to the method of the present invention, it is possible to grow a crystal layer forming a semiconductor element, particularly a nitride semiconductor, with a low defect density and to improve the performance of an optical device such as an electronic device or a semiconductor laser device. Was possible.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) An embodiment of the present invention will be described with reference to FIG.
In FIG. 1, n-type silicon carbide (α-Si
C) An Al ₂ O ₃ layer 2 is provided on an entire surface of a substrate 1 as an insulating film using an electron cyclotron resonance plasma apparatus. Next, layer 2 was formed using ammonia (NH ₃ ) as a nitrogen raw material.
Is subjected to a nitriding treatment. By using an organometallic vapor composition lengthening apparatus, the temperature is raised to 1030 ° C. in an ammonia (NH ₃ ) atmosphere and exposed to ammonia (NH ₃ ) for several minutes, whereby aluminum is added to the surface layer of the insulating film Al ₂ O ₃ layer 2. A surface nitride layer 3 containing AlN to which nitrogen is bonded is formed. Continuously in the metal organic chemical vapor deposition apparatus, the low-temperature GaN buffer layer 4,
Crystal growth is performed up to the n-type GaN layer 5 by metal organic chemical vapor deposition. Next, the insulating film 6 is provided and processed into a predetermined shape. By performing Si ion implantation using this insulating film as a mask, a high-concentration n + -type GaN layer 7 is formed. Thereafter, a Ti / Al electrode 8 is formed by lithography and electron beam evaporation. The middle Ti / Al electrode in FIG. 1 is a drain electrode of a field effect transistor (FET), and the Ti / Al electrodes at both ends are source electrodes. Also, using lithography,
A polycrystalline Si gate 9 is provided. Thus, a metal oxide film (MOS) FET made of a hexagonal Wurtzite structure nitride semiconductor shown in the cross section of FIG. 1 was produced.

In this embodiment, a nitride semiconductor crystal layer having a low defect density, which cannot be achieved by the conventional crystal growth technique, can be formed on the insulating film mask. In the conventional technology, the crystal defect density is in the range of 10 ⁹ to 10 ¹¹ / cm ² , whereas in the crystal growth on the insulating film by this method, the crystal defect density is 10
^It could be reduced to the level of ⁴ to 10 ⁵ / cm ² . Therefore, better drain current saturation characteristics and lower leakage current can be realized as compared with a crystal layer formed by a conventional crystal growth technique. When the gate voltage was −6 V and the drain-source voltage was 3 V, the leakage current below the threshold was 1 μA or less at room temperature, and showed a low value of 100 μA or less even at 400 ° C. When the voltage between the drain and the source is 3 V, the maximum value of the transconductance of the element having a gate length of 5 μm is as high as 0.6 mS / mm at room temperature and 1.8 mS / mm at 400 ° C. This element is 650 ° C
The transistor operation was confirmed up to the high temperature.

(Embodiment 2) Another embodiment of the present invention will be described with reference to FIG. After forming up to the layer 4 in the same manner as in Example 1, an n-type GaN layer 5 is provided as an optical waveguide layer. The well active layer 10, the p-type GaN optical waveguide layer 11, and the p-type GaInN contact layer 12 are sequentially crystal-grown by metal organic chemical vapor deposition. Next, as shown in FIG. 2, the crystal layer is removed by photolithography and etching until the layer 5 is reached. Thereafter, an insulating film 13 is provided, and photolithography and electron beam evaporation are performed.
A Ni / Au electrode 14 and a Ti / Al electrode 15 are formed. By cutting out the element by scribing, the hexagonal crystal shown in FIG.
A light-emitting element cross section made of a Wurtzite nitride semiconductor was obtained.

According to the present embodiment, a nitride semiconductor crystal layer having a low crystal defect density can be obtained in the same manner as in the first embodiment. A blue light emitting diode that operates with high efficiency was realized. In the blue wavelength region, light output of 40 mW or more and 10
Luminance of at least candela was achieved, and light output of at least 25 mW and luminance of at least 20 candela were obtained in the green wavelength region.
The quantum efficiency of the device is 10%, which is more than twice that of the conventional device.
Was achieved. The color purity could be improved as compared with the conventional case, and the half width of the emission spectrum could be reduced to 10 nm or less, which is half or less of the conventional case. The emission wavelength of the device at room temperature can be changed from the blue-violet to red wavelength range by designing the forbidden band width of the light-emitting active layer and changing the material composition and the quantum well layer thickness. A light emitting diode device having a wavelength was produced.

(Embodiment 3) Another embodiment of the present invention will be described with reference to FIG. After crystal growth up to the layer 5 as in the second embodiment, an insulating film mask 16 for selective growth by metal organic chemical vapor deposition is provided. Next, the n-type GaN optical waveguide layer 5, AlG
Compression strained multiple quantum well active layer 10, consisting of aN optical isolation confinement layer, GaN quantum barrier layer and GaInN compression strained quantum well layer, p-type
A GaN optical waveguide layer 11 and a p-type GaInN contact layer 12 are crystal-grown. Thereafter, through the same process as in Example 2, an element longitudinal section shown in FIG. 3 was obtained.

According to this embodiment, the width of the light emitting active layer is 1 to 4
By setting it in the range of μm, it was possible to provide a BH stripe refractive index waveguide type structure that guides light at the actual refractive index difference. This device achieves a laser characteristic that operates continuously with low threshold and high efficiency, and the threshold current can be reduced to 1/3 to 1/4 from 300 to 600 mA in the conventional gain-guided device.
A threshold current of 00 mA or less was obtained. The quantum efficiency was at least five times that of the conventional device, and an internal quantum efficiency of 50 to 60% was obtained. This device has an oscillation wavelength of 410 to 43 at room temperature.
Although the laser operated in the range of 0 nm, it is possible to change the band gap of the light emitting active layer from the blue-violet to green wavelength range by designing the material band gap and the quantum well layer thickness,
Semiconductor lasers having each oscillation wavelength could be manufactured.

(Embodiment 4) Another embodiment of the present invention will be described with reference to FIG. After crystal growth up to the layer 5 as in the third embodiment, an insulating film mask 16 for selective growth by metal organic chemical vapor deposition is provided. At this time, an insulating film mask is provided in a region corresponding to the center of the stripe, and two openings are formed as shown in FIG. Thereafter, through the same process as in Example 3, an element cross section shown in FIG. 4 was obtained.

In this embodiment, in the optical waveguide layer 5 that has been selectively grown, homoepitaxial growth can be performed in the lateral direction on the insulating film mask in the central portion, and one crystal layer is formed by being united. . In the optical waveguide layer in the region on the insulating film in the central part, it could be formed with a further lower defect density and could be reduced to a level of 10 ² to 10 ³ / cm ² . This allows
The laser light can be guided with a low loss, and the internal light loss can be significantly reduced. Compared with Example 3, at least the threshold current can be reduced to half or less, and an element of 30 to 50 mA was obtained. The quantum efficiency also showed a higher value than the device of Example 3, and an internal quantum efficiency of 70 to 80% was obtained. This element is
Laser operation was performed at room temperature within the oscillation wavelength range of 410 to 430 nm. However, the bandgap of the light emitting active layer can be designed to change the wavelength from blue-violet to green depending on the material composition and the quantum well layer thickness. Thus, a semiconductor laser having each oscillation wavelength could be manufactured.

(Embodiment 5) Another embodiment of the present invention will be described with reference to FIG. An element is manufactured in the same manner as in Example 4, except that the layer 1
After the formation of 2, the ridge stripe shown in FIG. 5 is formed at the center by lithography and etching. Next, an n-type GaN current confinement layer or a dielectric insulating film 17 is selectively grown. Thereafter, through the same process as in Examples 3 and 4, the element cross section shown in FIG. 5 was obtained.

In this embodiment, by forming the ridge stripe in the lateral direction of the active layer, the current can be effectively injected only into the low defect density region in the embodiment 4, and the leakage current can be extremely suppressed. As a result, it was possible to reduce internal light loss caused by gain loss and the like. Compared with Example 4, the threshold current can be further reduced to 1/2 or less, and an element of 5 to 10 mA was obtained. The quantum efficiency also showed a higher value than the device of Example 4, and an internal quantum efficiency of 80 to 90% was obtained. In this element, a high-output operation in which an optical output three to five times higher than that in Examples 3 and 4 is achieved by the stripe structure in which the refractive index waveguide structure in which the complex refractive index difference is provided in the lateral direction of the active layer is achieved. did it. This device operated with laser at room temperature in the oscillation wavelength range of 410 to 430 nm. However, the bandgap of the light emitting active layer was designed to change from blue-violet to green depending on the material composition and quantum well layer thickness. It was possible to produce a semiconductor laser having each oscillation wavelength.

(Embodiment 6) Another embodiment of the present invention will be described. The devices of Examples 1 to 5 are manufactured in the same manner, except that a silicon substrate is used instead of the silicon carbide substrate 1, and the devices are manufactured thereon. Through the device fabrication processes of Examples 1 to 5, similar devices could be fabricated.

In the present embodiment, a nitride semiconductor having a hexagonal Wurtzite structure could be grown on a diamond-structured Si substrate via an insulating film. In this method, the first embodiment
To 5 were able to achieve the same characteristics. In addition, since integration with an electronic device provided on a Si substrate can be performed, a circuit for driving a semiconductor laser or a light receiving element can be integrated and operated.

(Embodiment 7) Another embodiment of the present invention will be described. The devices of Examples 1 to 5 are manufactured in the same manner, except that the sapphire (α-Al ₂ O ₃ ) substrate is used instead of the silicon carbide substrate 1 to manufacture the devices thereon. Through the device fabrication processes of Examples 1 to 5, similar devices could be fabricated.

According to the present embodiment, the defect density of the crystal layer can be reduced by 4 to 5 orders of the prior art, and 10 ² to 10 ² , as compared with the conventional sapphire (α-Al ₂ O ₃ ) substrate. Reduced to the ³ / cm ² range. Thereby, the same characteristics as those of the devices of Examples 1 to 5 could be achieved. Compared to the prior art, as shown in Examples 1 to 5, in the electronic device, the leakage current can be reduced and the transconductance can be increased. In the optical device, the quantum efficiency and light output of the light emitting diode can be increased. In semiconductor lasers, the threshold current was significantly reduced, and quantum efficiency and light output were able to be dramatically increased.

[0026]

According to the present invention, a nitride semiconductor crystal having a low defect density, which cannot be achieved by the prior art, is formed on an insulating film provided on an arbitrary substrate having a melting point higher than the growth temperature of the nitride semiconductor. The provision of layers was realized. In the prior art, the defect density in the crystal layer was in the range of 10 ⁹ to 10 ¹¹ / cm ² , whereas in the present method, the defect density was as low as 10 ⁴ to 10 ⁵ / cm ² due to crystal growth on the insulating film. Reduced to the level. This makes it possible to reduce leakage current and increase transconductance in electronic devices, and to improve quantum efficiency and optical output in optical devices.
The effect of improving the performance of the device was remarkable.

According to the selective growth technique of the present invention, it was possible to further reduce the crystal defect density in the optical waveguide layer and the light emitting active layer of the semiconductor laser device, and to significantly reduce the internal light loss due to scattering loss. Defect density was reduced to a level in the range of 10 ² to 10 ³ / cm ² by lateral homoepitaxial growth by crystal growth and selective growth on the insulating film. As a result, internal light loss caused by gain loss due to crystal defects can be significantly reduced. At the same time, a BH stripe refractive index waveguide structure capable of stably guiding the fundamental transverse mode by providing a real refractive index difference in the lateral direction of the active layer by the insulating film mask pattern for selective growth was produced. Also, it was possible to produce a ridge stripe refractive index waveguide structure capable of stably guiding the fundamental transverse mode by providing a complex refractive index difference by processing the waveguide. In these semiconductor laser device structures, the threshold current can be reduced from 1/10 to 1/20 that of the device according to the prior art, and the quantum efficiency and the optical output can be increased more than 5 times. It was possible to set the threshold current and the operating current to 100 mA or less, which is required for practical use. In the device of the present invention, a nitride semiconductor laser having a low threshold value and a high efficiency operation that oscillates at a short wavelength in a blue-violet to green wavelength region has been achieved.

Further, according to the present invention, a substrate material can be selected and used depending on the use of a single device or an integrated device. Using a Si substrate makes it possible to integrate a conventional Si electronic device and a nitride semiconductor optical device. In addition, by using the SiC substrate, an electronic device and an optical device that operate even at a high temperature of several hundred degrees can be integrated, and a semiconductor laser device in which a resonator surface is formed by cleavage in a single device can be easily realized. Sapphire substrates and other ceramic substrates with high melting points can also be used depending on the application, and can be used for electronic devices due to their high resistance or used for optical devices due to their transparency. Enabled.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an element structure according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of an element structure according to another embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of an element structure according to another embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of an element structure according to another embodiment of the present invention.

FIG. 5 is a longitudinal sectional view of an element structure according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... (0001) C-plane alpha-SiC single crystal substrate, 2 ... insulating film, 3 ... insulating film surface nitride layer, 4 ... GaN buffer layer, 5 ... n-type GaN layer,
6 ... insulating film mask, 7 ... Si ion implanted n + type GaN layer,
8 Ti / Al electrode, 9 Polycrystalline Si, 10 GaInN / GaN / AlGaN
Multiple quantum well structure active layer, 11 ... p-type GaN optical waveguide layer, 1
2 ... p-type GaInN contact layer, 13 ... insulating film, 14 ... Ni /
Au electrode, 15: Ti / Al electrode, 16: insulating film mask for selective growth, 17: n-type GaN current confinement layer or dielectric insulating film.

Claims (18)

[Claims] 1. A semiconductor device comprising: a predetermined substrate having an insulating layer subjected to a nitriding treatment; and a semiconductor layer containing nitrogen provided so as to cover the insulating layer. A semiconductor device provided with one of an element part and an optical element part. 2. The semiconductor device according to claim 1, wherein at least both an electronic element portion and an optical element portion are provided in said nitrogen-containing semiconductor layer. 3. The semiconductor device according to claim 1, wherein the nitrided insulating layer has at least one selected from the group consisting of aluminum and gallium as a constituent element. A semiconductor device characterized in that: 4. The semiconductor device according to claim 1, wherein said nitrided insulating layer has at least one surface selected from the group consisting of aluminum nitride and gallium nitride. A semiconductor device comprising: 5. The semiconductor device according to claim 1, wherein said nitrided insulating layer is an oxide or nitride of at least one selected from the group consisting of aluminum and gallium. A semiconductor device having at least one of the following. 6. The semiconductor device according to claim 4, wherein said insulating film provided on said substrate comprises at least aluminum or gallium as a constituent element, and said insulating film comprises an oxide thereof or Made of nitride or oxynitride, AlOx, Al ₂ O ₃ , AlO ₁ -xNx, AlN, GaO
x, Ga ₂ O ₃ , GaO ₁ -xNx, GaN, AlGaOx, (AlGa) ₂ O ₃ , (AlGa)
A semiconductor device provided on an insulating film formed of any one of O ₁ -xNx and AlGaN. 7. The semiconductor device according to claim 1, wherein the substrate on which the insulating film is provided is made of a material having a melting point higher than a growth temperature of at least a nitride material for crystal growth thereon. And a substrate made of a material satisfying the high melting point. 8. The semiconductor device according to claim 7, wherein the melting point or softening point of the substrate is desirably at least 1.5 times the crystal growth temperature of the nitride material. 9. The semiconductor device according to claim 1, wherein said substrate has a diamond structure, a zinc blende zinc blend (Zinc Blende) structure, and a hexagonal wurtzite type.
e) A semiconductor device having any one of the following crystal structures. 10. The semiconductor device according to claim 9, wherein said substrate is a diamond-structured Si substrate or a zinc blende Zi.
nc Blende structure silicon carbide (β-SiC) or gallium nitride
(β-GaN) or aluminum nitride (β-AlN), or single crystal sapphire (α-Al ₂ O ₃ ) having a hexagonal Wurtzite structure or silicon carbide (α-SiC) or gallium nitride (α-GaN) or nitrided A semiconductor device comprising at least one of aluminum (α-AlN). 11. The semiconductor device according to claim 9, wherein said substrate is a single crystal substrate, and has a cleavage property on a specific crystal plane. 12. The semiconductor device according to claim 1, wherein said optical element portion includes a semiconductor laser element having a resonator surface formed by cleavage. 13. The semiconductor device according to claim 1, wherein an insulating film mask pattern is provided on a crystal layer provided on said substrate, and selective growth is applied. A semiconductor laser device having a heterojunction structure comprising a light emitting active layer and an optical waveguide layer formed in the optical waveguide. 14. The semiconductor device according to claim 13, wherein said semiconductor laser device has a refractive index waveguide structure capable of stably guiding only a fundamental transverse mode, and has an embedded real refractive index difference in a lateral direction of the active layer. A semiconductor laser device having a BH (Buried Heterostructure) stripe structure. 15. The semiconductor device according to claim 13, wherein a refractive index waveguide structure capable of stably guiding only the fundamental transverse mode of the semiconductor laser element is formed by providing a complex refractive index difference in a lateral direction of the active layer. A semiconductor laser device having a ridge stripe structure that can be used. 16. The semiconductor device according to claim 12, wherein said light emitting active layer of said semiconductor laser device has a single or multiple quantum well structure comprising a quantum well layer. A semiconductor device characterized by the above-mentioned. 17. The semiconductor device according to claim 16, wherein the light emitting active layer of the semiconductor laser device has a single or multiple strained quantum well structure constituted by a strained quantum well layer in which lattice strain is introduced. A semiconductor device characterized by the above-mentioned. 18. The semiconductor device according to claim 1, wherein the crystal layer forming the element is made of a nitride semiconductor AlGaInN material.