JP4333377B2 - GaN single crystal substrate, manufacturing method thereof, and light emitting device - Google Patents

Description

  The present invention relates to a GaN single crystal substrate having a small light absorption coefficient, a method for manufacturing the same, and a light emitting device.

  As a substrate of a light emitting device such as a light emitting diode (hereinafter referred to as LED) or a laser diode (hereinafter referred to as LD), a sapphire substrate, a GaN substrate, or the like is used.

  However, since the sapphire substrate is highly insulating, an electrode cannot be provided on the back surface of the sapphire substrate (the surface on which the semiconductor layer having a light-emitting layer is not formed; the same applies hereinafter). It is necessary to form an electrode on the formed semiconductor layer (for example, n-type GaN layer), and there is a problem that the driving voltage of the light emitting device is increased by passing a current through the semiconductor layer having a small thickness.

  On the other hand, the GaN substrate can be provided with an electrode on the back surface of the GaN substrate, so that the driving voltage of the light emitting device can be reduced. There is a problem in that part of the emitted light is absorbed by the GaN substrate and the light output is reduced. A GaN substrate having a high transparency and a small light absorption coefficient and a method for manufacturing the same have been proposed, but the light absorption coefficient of the GaN substrate is not sufficiently small (see, for example, Patent Document 1). Therefore, there has been a demand for the development of a GaN single crystal substrate having a small light absorption coefficient, a method for manufacturing the same, and a light emitting device having a large light output.

In addition, it has been proposed to increase the light extraction efficiency from the side surface of the substrate by providing irregularities on the back surface of the sapphire substrate or GaN substrate and reflecting the light toward the side surface of the substrate. The improvement was not sufficiently large (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 2000-12900 JP 2002-368261 A

  In view of the above situation, an object of the present invention is to provide a GaN single crystal substrate having a small light absorption coefficient, a method for manufacturing the same, and a light emitting device having a large light output.

The present invention is a GaN single crystal substrate having a thickness of 70 μm to 450 μm, the GaN single crystal substrate including at least one element selected from the group consisting of oxygen, sulfur and silicon as a dopant, and having a wavelength of 375 nm absorption coefficient is 34cm ^-1 ~68cm ^-1, and a GaN single crystal substrate, wherein the absorption coefficient of light of wavelength 500nm is 7cm ^-1 ~10cm ^-1.

The carrier concentration of the GaN single crystal substrate according to the present invention is preferably 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ . The surface roughness Ra of the main surface of the GaN single crystal substrate according to the present invention is preferably 10 nm or less.

The present invention is also a method for producing the GaN single crystal substrate, comprising: forming a mask layer having a dotted or striped opening window on a GaAs substrate; and at least two GaN buffer layers on the opening window. a step of times grown epitaxially growing a GaN single crystal layer by HVPE on a GaN buffer layer, viewed at least containing a step of removing the GaAs substrate, and in the step of epitaxially growing a GaN single crystal layer, as a raw material gas , NH ₃ reacts with the gas and the Ga melt in addition to the HCl gas as a GaCl gas, a mixed gas of O ₂ and N _2, a mixed gas of SiH ₄ and H ₂ or a gas mixture of H ₂ S and H _2, This is a method of manufacturing a GaN single crystal substrate using

  Furthermore, the present invention is a light emitting device in which at least one group III nitride semiconductor layer is formed on the GaN single crystal substrate.

  As described above, according to the present invention, it is possible to provide a GaN single crystal substrate having a small light absorption coefficient, a manufacturing method thereof, and a light emitting device having a large light output.

One GaN single crystal substrate according to the present invention is a GaN single crystal substrate having a diameter of 20 mm or more and a thickness of 70 μm to 450 μm, and absorbing light in a wavelength region of 375 nm to 500 nm of the GaN single crystal substrate. coefficient α is 7cm ^-1 ~68cm ^-1.

  If the diameter of the GaN single crystal substrate is less than 20 mm, the productivity of the substrate is reduced. If the thickness is less than 70 μm, the mechanical strength of the substrate is reduced. If the thickness exceeds 450 μm, the amount of light absorbed by the substrate. Becomes larger. Further, when the thickness is 200 μm or more, the mechanical strength of the substrate is improved and the handling of the substrate becomes easy. Therefore, the thickness of the GaN single crystal substrate is preferably 200 μm to 450 μm.

Also, at a low carrier concentration such that the light absorption coefficient α in the wavelength region of 375 nm to 500 nm is less than 7 cm ⁻¹ , the GaN substrate electrical resistance increases, and an electrode is provided on the back side of the GaN single crystal substrate. When the light emitting device having the structure is configured, the driving voltage is increased. On the other hand, when the light absorption coefficient α in the wavelength region of 375 nm to 500 nm exceeds 68 cm ⁻¹ , the light absorption coefficient of the GaN single crystal substrate increases and the light output of the light emitting device decreases. In addition, since the light has higher energy as the wavelength of light is smaller, the light absorption coefficient of the GaN single crystal substrate becomes larger.

  Here, the light absorption coefficient α is defined by the following equation (1).

α = − (1 / H) In (I / I ₀ ) (1)
(In formula (1), I ₀ represents the intensity of incident light, I represents the intensity of observation light, H represents the thickness of the substrate, and In represents the natural logarithm.)
The carrier concentration of the GaN single crystal substrate according to the present invention is preferably 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ . When the carrier concentration of the GaN single crystal substrate is less than 5 × 10 ¹⁷ cm ⁻³ , the electrical resistance of the GaN single crystal substrate increases, and a light emitting device having a structure in which an electrode is provided on the back side of the GaN single crystal substrate is configured. I can't. On the other hand, when the carrier concentration of the GaN single crystal substrate exceeds 2 × 10 ¹⁹ cm ⁻³ , the level other than the donor level in the forbidden band increases, and the light absorption coefficient increases.

  The GaN single crystal substrate according to the present invention preferably contains at least one element selected from the group consisting of O, C, S and Si as a dopant. By doping the GaN single crystal substrate, O or S enters the N position of the GaN single crystal, and C or Si enters the Ga position of the GaN single crystal, both exhibiting n-type conductivity. The electrical resistance can be lowered.

  The surface roughness Ra of the main surface of the GaN single crystal substrate according to the present invention is preferably 10 nm or less. When the surface roughness Ra is less than 10 nm, the crystallinity of the semiconductor layer formed on the surface is lowered, which is disadvantageous for manufacturing a light emitting device. Here, the surface roughness Ra means the arithmetic average roughness Ra in JIS B 0601. That is, Ra is the average of the absolute values of Z (x) at the reference length L as defined by the following equation (2). Here, Z (x) indicates the height of the roughness curve at an arbitrary position x. The surface roughness Ra of the main surface of the GaN single crystal substrate is reduced by polishing the main surface by an MP (Mechanical Polishing) method or a CMP (Chemical Mechanical Polishing) method. Can do.

  A method of manufacturing a GaN single crystal substrate according to the present invention is described with reference to FIG. 1 in which a mask layer having a dotted or striped opening window 21 is formed on a GaAs substrate 1 as shown in FIG. A step of forming (hereinafter referred to as a mask layer forming step) and a step of growing the first GaN buffer layer 3a on the opening window 21 as shown in FIG. 1B (hereinafter referred to as the first GaN buffer layer forming step). 1), a step of growing the second buffer layer 3b on the first GaN buffer layer 3a to form the GaN buffer layer 3 (hereinafter referred to as a second buffer layer forming step), as shown in FIG. 1D), as shown in FIG. 1D, a step of epitaxially growing the GaN single crystal layer 4 on the GaN buffer layer 3 by the HVPE method (hereinafter referred to as GaN single crystal layer forming step), and FIG. Ga as shown s substrate 1, the step of removing the mask layer 2 and the GaN buffer layer 3 (hereinafter, GaAs substrate removing step) comprising at least a.

  By growing the GaN buffer layer 3 in two or more times, the crystallinity of the GaN single crystal layer 4 formed on the GaN buffer layer 3 is further improved, and the concentration of the internal level that absorbs light is reduced. Thus, it is considered that the light absorption coefficient of the GaN single crystal substrate is remarkably reduced. Here, when the GaN buffer layer is formed twice, there is no distinction between the first GaN buffer layer 3a and the second buffer layer 3b in FIG. 1D, and one GaN buffer layer 3 is formed as a whole. To do. Hereinafter, each step will be described in more detail.

(Mask layer forming process)
In the mask layer forming step, referring to FIG. 1A, a mask layer 2 having dot-like or stripe-like opening windows 21 is formed on a GaAs substrate 1. A dot-shaped opening window refers to an opening window as a circular or polygonal isolated point, and a stripe-shaped opening window refers to a band-shaped opening window. Here, from the viewpoint of uniformly growing the GaN single crystal layer, it is preferable that the dot-shaped or stripe-shaped openings are arranged at equal intervals. GaAs used as a substrate for growing a GaN single crystal layer has a cubic system, and generally uses the (111) A plane and the (111) B plane as crystal growth planes. The A surface is a surface where Ga atoms are exposed, and the B surface is a surface where As atoms are exposed.

Formation of a mask layer having an opening on a GaAs substrate can be performed, for example, by covering the entire GaAs substrate with a mask material and then providing opening windows at equal intervals by photolithography. Here, examples of the mask material include Si ₃ N ₄ and SiO ₂ . The thickness of the mask layer is not particularly limited, but is preferably about 100 nm to 300 nm.

For example, referring to FIG. 2, the dotted aperture windows are formed on the (111) A surface of the GaAs substrate 1 with a constant interval P in the [11-2] direction and in the [−110] direction. Is performed by providing a square-shaped opening window 21 shifted by a half pitch. Here, the interval Q in the [−110] direction is preferably 3 ^1/2 × P / 2. At this time, the dotted aperture windows 21 are arranged so as to be positioned at the vertices of an equilateral triangle having a side length of P. With such an arrangement of the aperture windows, when the GaN buffer layer is grown twice or more in the aperture window 21 and then the GaN single crystal layer 4 is grown, GaN is hexagonal, so that FIG. As shown in FIG. 4, the GaN single crystal 4 grows in a substantially hexagonal shape, and as shown in FIG. 4, the hexagonal GaN single crystal 4 comes into contact with the adjacent GaN single crystal almost simultaneously and thereafter grows with a uniform thickness. The stripe-shaped opening window is formed by, for example, providing a stripe-shaped opening window extending in the [11-2] direction or the [−110] direction.

(GaN buffer layer formation process)
Next, referring to FIG. 1B and FIG. 1C, a GaN buffer layer is grown in the opening window 21 twice or more. In the present invention, it is preferable to form the GaN buffer layer twice or more from the viewpoint of improving the crystallinity of the GaN single crystal layer. In the case of forming the GaN buffer layer twice or more, a method for forming the first GaN buffer layer, the second GaN buffer layer, and the nth GaN buffer layer (where n is an integer of 2 or more) There is no limitation, HVPE (Hydride Vapor Phase Epitaxy) method, MOCVD (Metal Organic Chemical Vapor Deposition) method, MOC (Metal Organic Chloride Vapor Deposition; Metal Organic Chloride) Vapor phase growth such as Method) can be used. Here, the GaN buffer layer is an amorphous layer of GaN, and is generally grown in a low temperature atmosphere of 400 ° C. to 600 ° C. in the above vapor phase growth method. Further, by setting the total thickness of the GaN buffer layer to about 20 nm to 100 nm, the GaN buffer layer can be formed only in the opening window portion of the mask layer.

In the HVPE method, referring to FIG. 5, HCl gas 113 introduced from a raw material gas inlet 103 provided at the top top of a hot-wall type reactor 101 having a cylindrical heater 102 around is a Ga reservoir 105. It reacts with the Ga melt 106 and becomes GaCl gas 116. An NH ₃ gas 114 introduced from a source gas inlet provided at the top of the reaction furnace 101 is introduced, reacted with the GaCl gas 116 to synthesize GaN, and on the substrate 109 installed on the susceptor 107. Is to be deposited. From the viewpoint of reactivity control, HCl gas and NH ₃ gas, which are raw material gases, are generally used by being mixed with a carrier gas such as H ₂ gas.

In the MOCVD method, TMG (trimethyl gallium) or another Ga organometallic compound gas such as TMG (trimethylgallium) gas and NH ₃ gas are sprayed onto a heated substrate together with H ₂ gas as a carrier gas in a cold wall type reactor. GaN produced by the reaction of NH ₃ and NH ₃ is grown on the substrate.

  In the MOC method, a Ga organometallic gas such as TMG and HCl gas are reacted in a hot-wall type reactor to synthesize GaCl, and this is reacted with NH 3 gas flowed in the vicinity of the substrate to heat the substrate. GaN is grown on top.

(GaN single crystal formation process)
Next, referring to FIG. 1D, a GaN single crystal layer 4 is epitaxially grown on the GaN buffer layer 3. In the present invention, the HVPE method is preferably used as a method for epitaxially growing a GaN single crystal on the GaN buffer layer. As described above, the vapor phase growth method includes the MOCVD method and the MOC method in addition to the HVPE method. However, in the MOCVD method and the MOC method, a Ga organometallic compound such as TMG is used as a raw material. Although a large amount of C is mixed in the crystal to increase the light absorption coefficient of the GaN single crystal, Ga organic metal compound is not used in the HVPE method, so that the mixing of C into the GaN single crystal can be reduced. it can. In addition, since the HVPE method has a higher crystal growth rate than the MOCVD method and the MOC method, a GaN single crystal can be produced more efficiently. In the HVPE method, the GaN single crystal is epitaxially grown at an atmospheric temperature of about 800 ° C. to 1050 ° C. At this time, the GaN buffer layer is crystallized.

(GaAs substrate removal process)
Next, referring to FIGS. 1D and 1E, the GaAs substrate 1 is removed. The method for removing the GaAs substrate 1 is not particularly limited, but can be etched with aqua regia, for example. The mask layer 2 and the GaN buffer layer 3 with insufficient crystallization can be removed by polishing or the like. In this way, the GaN single crystal layer 4 is obtained. The GaN single crystal layer thus obtained usually has n-type conductivity without the addition of a dopant such as O, C, S, or Si. The electric resistance of the crystal layer can be further reduced. Furthermore, a GaN single crystal substrate is obtained by processing the GaN single crystal layer to a predetermined thickness.

Referring to FIG. 6, one light emitting device according to the present invention has five stages of n-type GaN layers 61, In _0.2 Ga _0.8 N layers and GaN layers alternately arranged on one main surface of the GaN single crystal substrate 60. The stacked multiple quantum well active layer 62, p-type Al _0.15 Ga _0.85 N layer 63, p-type GaN layer 64, and p-side electrode 65 are sequentially stacked, and an n-side electrode 66 is formed on the other main surface of the GaN single crystal substrate 60. It is the formed light emitting device. Thus, by using a GaN single crystal substrate having a small light absorption coefficient as the substrate of the light emitting device, a light emitting device having a low driving voltage and a high light output can be obtained.

Example 1
1. 1. Production of GaN single crystal substrate (1) Mask layer forming step Referring to FIG. 1A, a Si ₃ layer having a thickness of 100 nm is formed as a mask layer 2 on a GaAs substrate 1 having a diameter of 50 mm by a CVD method under atmospheric pressure. N ₄ layer was formed. Next, by photolithography, opening windows 21 (opening window is a square having a side of 1 μm) are arranged at the vertices of an equilateral triangle having P of 4 μm and Q of 3.5 μm in FIG.

(2) GaN buffer layer forming step Referring to FIG. 1B, HCl gas (partial pressure 60.8 Pa) and NH ₃ gas (partial pressure 1. 31 × 10 ⁴ Pa) was used to grow a first GaN buffer layer 3a having a thickness of 40 nm at an atmospheric temperature of 475 ° C. (first GaN buffer layer forming step).

Subsequently, referring to FIG. 1C, HCl gas (partial pressure 60.8 Pa) and NH ₃ gas (partial pressure 1.31) are formed on the first GaN buffer layer 3a by HVPE as source gases. The second GaN buffer layer 3b having a thickness of 40 nm is grown at the atmospheric temperature of 500 ° C. using the × 10 ⁴ Pa) (second GaN buffer layer forming step), and the GaN buffer layer 3 having a thickness of 80 nm is formed. Formed. Here, since the thickness (80 nm) of the GaN buffer layer is smaller than the thickness (100 nm) of the mask layer, the GaN buffer layer 3 was formed only in the opening window 21 portion of the mask layer 2.

(3) GaN Single Crystal Layer Formation Step Next, referring to FIG. 1D, HCl gas (partial pressure 1.25 × 10 ³ Pa) is formed on the GaN buffer layer 3 as a source gas by HVPE. Using an NH ₃ gas (partial pressure 1.31 × 10 ⁴ Pa) and a mixed gas of O ₂ and N ₂ containing 0.1% by mass of O ₂ (partial pressure 23.4 Pa), the ambient temperature is 1000 ° C. Thus, a GaN single crystal layer 4 having a thickness of 450 μm was formed.

(4) GaAs Substrate Removal Step Next, referring to FIG. 1 (d) and FIG. 1 (e), the GaAs substrate 1 is removed by etching with aqua regia, and the mask layer 2 and crystallization are insufficient. The GaN buffer layer 3 was removed by the MP method to obtain a GaN single crystal layer 4. Further, after slicing the GaN single crystal layer 4 with a slicing blade or an inner peripheral blade, a GaN single crystal substrate having a surface roughness Ra of 3 nm and a thickness of 200 μm was obtained by CMP. The carrier concentration of the obtained GaN single crystal substrate was 5 × 10 ¹⁷ cm ⁻³ , the absorption coefficient of light with a wavelength of 375 nm was 34 cm ⁻¹ , and the absorption coefficient of light with a wavelength of 500 nm was 7 cm ⁻¹ . Here, the carrier concentration of the GaN single crystal substrate was measured at room temperature (23 ° C.) by the van der Pauw method, and the light absorption coefficient was measured using a spectrophotometer.

2. Production of LED As a light emitting device, the following LED was produced. Referring to FIG. 6, first, a 1.5 μm-thickness is formed on one main surface of GaN single crystal substrate 60 having a diameter of 50 mm, a thickness of 250 μm, and a surface roughness Ra of 3 nm by MOCVD. An n-type GaN layer 61, a multiple quantum well active layer 62 in which an In _0.2 Ga _0.8 N layer having a thickness of 3 nm and a GaN layer having a thickness of 15 nm are alternately stacked in five stages, and a p-type Al _0.15 Ga _0.85 N layer 63 having a thickness of 30 nm Then, a p-type GaN layer 64 having a thickness of 100 nm was sequentially formed. Further, an Au / Ni (p-type GaN layer side is Au layer) layer was formed as a p-side electrode 65 on the p-type GaN layer 64. Next, in order to facilitate chip division, the other main surface of the GaN single crystal substrate 60 was lapped by the CMP method, and the thickness of the GaN single crystal substrate 60 was set to 200 μm. Next, a Ti / Al (GaN single crystal substrate side is Ti) layer having a diameter of 80 μm was formed as an n-side electrode 66 on the center of each 300 μm × 300 μm section on the other main surface of the GaN single crystal substrate 60. . Further, the GaN single crystal substrate 60 on which the semiconductor layer and the p-side electrode are formed is divided into 300 μm × 300 μm chips so that the n-side electrode is located at the center of the other main surface. Obtained. The driving voltage of the obtained LED at 20 mA was 3.3 V, and the light output at an emission wavelength of 460 nm was 4.8 mW. The results are summarized in Table 1.

(Example 2)
During the GaN single crystal formation step, HCl gas (partial pressure 1.25 × 10 ³ Pa), NH ₃ gas (partial pressure 1.31 × 10 ⁴ Pa) and 0.1 mass% O ₂ were used as source gases. A GaN single crystal substrate was produced in the same manner as in Example 1 except that the mixed gas of O ₂ and N ₂ contained (partial pressure 6.55 × 10 ² Pa) was used. The carrier concentration of the obtained GaN single crystal substrate was 2 × 10 ¹⁹ cm ⁻³ , the absorption coefficient of light with a wavelength of 375 nm was 68 cm ⁻¹ , and the absorption coefficient of light with a wavelength of 500 nm was 10 cm ⁻¹ . Further, an LED was produced in the same manner as in Example 1. The driving voltage of the obtained LED at 20 mA was 3.2 V, and the light output at the effective wavelength of 460 nm was 3.5 mW. The results are summarized in Table 1.

(Example 3)
In the GaN single crystal formation step, HCl gas (partial pressure 1.25 × 10 ³ Pa), NH ₃ gas (partial pressure 1.31 × 10 ⁴ Pa) and 0.1% by mass of SiH ₄ are used as source gases. A GaN single crystal substrate was produced in the same manner as in Example 1 except that the mixed gas of SiH ₄ and H ₂ contained (partial pressure 93.5 Pa) was used. The carrier concentration of the obtained GaN single crystal substrate was 5 × 10 ¹⁷ cm ⁻³ , the absorption coefficient of light with a wavelength of 375 nm was 35 cm ⁻¹ , and the absorption coefficient of light with a wavelength of 500 nm was 8 cm ⁻¹ . Further, an LED was produced in the same manner as in Example 1. The driving voltage of the obtained LED at 20 mA was 3.3 V, and the light output at an emission wavelength of 460 nm was 4.7 mW. The results are summarized in Table 1.

(Example 4)
In the GaN single crystal formation step, HCl gas (partial pressure 1.25 × 10 ³ Pa), NH ₃ gas (partial pressure 1.31 × 10 ⁴ Pa) and 1% by mass of H ₂ S are contained as source gases. A GaN single crystal substrate was produced in the same manner as in Example 1 except that a mixed gas of H ₂ S and H ₂ (partial pressure 3.12 × 10 ² Pa) was used. The carrier concentration of the obtained GaN single crystal substrate was 5 × 10 ¹⁷ cm ⁻³ , the absorption coefficient of light with a wavelength of 375 nm was 39 cm ⁻¹ , and the absorption coefficient of light with a wavelength of 500 nm was 10 cm ⁻¹ . Further, an LED was produced in the same manner as in Example 1. The driving voltage at 20 mA of the obtained LED was 3.4 V, and the light output at an emission wavelength of 460 nm was 4.5 mW. The results are summarized in Table 1.

(Comparative Example 1)
Example 1 except that only HC1 gas (partial pressure 1.25 × 10 ³ Pa) and NH ₃ gas (partial pressure 1.31 × 10 ⁴ Pa) were used as source gases during the GaN single crystal formation step. Similarly, a GaN single crystal substrate was produced. The carrier concentration of the obtained GaN single crystal substrate was 1 × 10 ¹⁷ cm ⁻³ , the absorption coefficient of light with a wavelength of 375 nm was 26 cm ⁻¹ , and the absorption coefficient of light with a wavelength of 500 nm was 4 cm ⁻¹ . Further, an LED was produced in the same manner as in Example 1. The driving voltage of the obtained LED at 20 mA was 5.4 V, and the light output at the effective wavelength of 460 nm was 5.0 mW. The results are summarized in Table 1.

(Comparative Example 2)
During the GaN buffer layer forming process, HCl gas (partial pressure 60.8 Pa) and NH ₃ gas (partial pressure 1.31 × 10 ⁴ Pa) are used as source gases on the opening window 21 by HVPE. A GaN single crystal substrate was fabricated in the same manner as in Example 2 except that a GaN buffer layer having a thickness of 80 nm was grown once at an ambient temperature of 500 ° C. and the second and subsequent GaN buffer layers were not grown. . The carrier concentration of the obtained GaN single crystal substrate was 2 × 10 ¹⁹ cm ⁻³ , the absorption coefficient of light with a wavelength of 375 nm was 110 cm ⁻¹ , and the absorption coefficient of light with a wavelength of 500 nm was 25 cm ⁻¹ . Further, an LED was produced in the same manner as in Example 1. The driving voltage of the obtained LED at 20 mA was 3.2 V, and the light output at an emission wavelength of 460 nm was 2.2 mW. The results are summarized in Table 1.

(Comparative Example 3)
The following light-emitting device was manufactured using a sapphire substrate (absorption coefficient of light having a wavelength of 375 nm and a wavelength of 500 nm was 2 cm ⁻¹ ). Referring to FIG. 7, this light emitting device has a thickness of 1.5 μm on one main surface of a sapphire substrate 70 having a size of 400 μm × 300 μm, a thickness of 200 μm, and a surface roughness Ra of 3 nm by MOCVD. N-type GaN layer 61 is formed, and a 3-nm thick In _0.2 Ga _0.8 N layer and a 15-nm thick GaN layer are alternately stacked on a part (300 μm × 300 μm) of this n-type GaN layer 61. The multi-quantum well active layer 62, the p-type Al _0.15 Ga _0.85 N layer 63 having a thickness of 30 nm, and the p-type GaN layer 64 having a thickness of 100 nm are sequentially formed. Further, an Au / Ni (p-type GaN layer side is Au layer) layer is formed on the p-type GaN layer 64 as the p-side electrode 65. In addition, a Ti / Al layer with a diameter of 80 μm (n-type GaN layer side is Ti) is formed as an n-side electrode so that the remaining part (100 μm × 300 μm) of the n-type GaN layer does not come into contact with other semiconductor layers. did. The driving voltage at 20 mA of the obtained LED was 3.7 V, and the light output at an emission wavelength of 460 nm was 4.9 mW. The results are summarized in Table 1.

Table 1 As is apparent, LED driving voltage in Examples 1 to 4 the absorption coefficient of light is 7cm ^-1 ~68cm ^-1 in the wavelength region of 375nm~500nm is 3.2V~3.4V The light output was as high as 3.5 mW to 4.7 mW. That is, a high output LED with a low driving voltage was obtained. On the other hand, the driving voltage of the LED of Comparative Example 1 having a small absorption coefficient of light with a wavelength of 500 nm on the substrate was as large as 5.4V. This is due to the low carrier concentration of the substrate and the high electrical resistance of the substrate. In addition, the light output of the LED of Comparative Example 2 having a large absorption coefficient of light with a wavelength of 375 nm of the substrate as 110 cm ⁻¹ decreased to 2.2 mW. This is because the light absorption coefficient of the GaN single crystal substrate is large.

  In addition, the drive voltage of LED in Example 1- Example 4 is 3.2V-3.4V, and it should make it still smaller than the drive voltage 3.7V of LED of the comparative example 3 which is a conventional typical LED. I was able to.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  As described above, the present invention can be widely used to provide a GaN single crystal substrate having a small light absorption coefficient, a method for manufacturing the same, and a light emitting device having a large light output.

It is a schematic sectional drawing explaining the manufacturing method of one GaN single crystal substrate concerning this invention. Here, (a) is a mask layer forming step, (b) is a first GaN buffer layer forming step, (c) is a second GaN buffer layer forming step, and (d) is a GaN single crystal forming step. (E) shows a GaAs substrate removal step. It is a figure which shows the arrangement | sequence of the opening window in a mask layer. It is a figure which shows the growth of the GaN single-crystal layer on an opening window. It is a figure which shows the growth of the GaN single-crystal layer following FIG. It is a schematic diagram explaining the HVPE method. It is a schematic sectional drawing which shows one form of a light-emitting device. It is a schematic sectional drawing which shows the other form of a light-emitting device.

Explanation of symbols

1 GaAs substrate, 2 mask layer, 3 GaN buffer layer, 3a first GaN buffer layer, 3b second GaN buffer layer, 4 GaN single crystal layer, 21 aperture window, 60 GaN single crystal substrate, 61 n-type GaN layer , 62 Multiple quantum well active layer, 63 p-type Al _0.15 Ga _0.85 N layer, 64 p-type GaN layer, 65 p-side electrode, 66 n-side electrode, 70 sapphire substrate, 80 output light, 101 reactor, 102 heater, 103 104 source gas inlet, 105 Ga reservoir, 106 Ga melt, 107 susceptor, 108 shaft, 109 substrate, 110 gas outlet, 113 HCl gas, 114 NH ₃ gas, 116 GaCl gas.

Claims (5)

A GaN single crystal substrate having a thickness of 70 μm to 450 μm ,
The GaN single crystal substrates, oxygen as a dopant, wherein at least one of element selected from group consisting of sulfur and silicon, the absorption coefficient of light of wavelength 375nm is 34cm ^-1 ~68cm ^-1, and the wavelength of 500nm light GaN single crystal substrate, wherein the absorption coefficient of a 7cm ^-1 ~10cm ^-1. 2. The GaN single crystal substrate according to claim 1, wherein the GaN single crystal substrate has a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ . 3. The GaN single crystal substrate according to claim 1, wherein a surface roughness Ra of a main surface of the GaN single crystal substrate is 10 nm or less. 4. A method for producing a GaN single crystal substrate according to any one of claims 1 to 3,
A step of forming a mask layer having a dotted or striped opening window on the GaAs substrate, a step of growing a GaN buffer layer on the opening window at least twice, and a GaN single layer by HVPE method on the GaN buffer layer. epitaxially growing a crystal layer, at least it viewed including the step of removing the GaAs substrate, and
In the step of epitaxially growing the GaN single crystal layer, as a source gas, in addition to HCl gas that reacts with NH ₃ gas and Ga melt to become GaCl gas, a mixed gas of O ₂ and N ₂ , SiH ₄ and H ₂ mixed gas or method of manufacturing a GaN single crystal substrate using a mixed gas of H ₂ S and H _2, of. A light emitting device according to the GaN single crystal substrate according to any one of claim 1 to claim 3, and Group III nitride semiconductor layer at least one layer is formed.

Images