WO2019039342A1

WO2019039342A1 - Gallium nitride substrate, self-supporting substrate, and functional element

Info

Publication number: WO2019039342A1
Application number: PCT/JP2018/030222
Authority: WO
Inventors: 佳範磯田; 崇行平尾; 中西　宏和; 幹也市村; 孝直下平; 坂井　正宏; 隆史吉野
Original assignee: 日本碍子株式会社
Priority date: 2017-08-24
Filing date: 2018-08-13
Publication date: 2019-02-28
Also published as: JPWO2019039342A1; JP7160815B2

Abstract

This gallium nitride substrate is provided with an upper surface and a bottom surface. When observed using cathode luminescence, the upper surface has: a linear high luminance light emission portion; and a low luminance light emission region disposed next to the high luminance light emission portion. The elastic constant C11 is in the range of 200-290 GPa inclusive.

Description

Gallium nitride substrate, free-standing substrate and functional device

The present invention relates to a gallium nitride substrate, a free standing substrate and a functional device.

As a light emitting element such as a light emitting diode (LED) using a single crystal substrate, one in which various gallium nitride (GaN) layers are formed on sapphire (α-alumina single crystal) is known. For example, on a sapphire substrate, an n-type GaN layer, a multiple quantum well layer (MQW) in which quantum well layers composed of InGaN layers and barrier layers composed of GaN layers are alternately stacked, and p-type GaN layers are sequentially deposited. Those having a different structure are mass-produced.

Patent Document 1 shows that, in a gallium nitride single crystal produced by the HVPE method, the elastic constant C11 is 340 to 380 GPa. Specifically, if the elastic constant C11 is 348 GPa or more and 365 GPa or less and the elastic constant C13 is 90 GPa or more and 98 GPa or less, or the elastic constant C11 is 352 GPa or more and 362 GPa or less and the elastic constant C13 is 86 GPa or more and 93 GPa or less " For example, when growing a gallium nitride single crystal body and when processing the grown gallium nitride single crystal body into a substrate or the like, a semiconductor layer is formed on the substrate-like gallium nitride single crystal body to manufacture a semiconductor device. At the same time, it is possible to suppress the occurrence of cracks.

Further, Patent Document 2 shows that the elastic constant C11 of gallium nitride is 296 to 396 GPa from calculation and experiment.

Patent No. 4957751 Appl. Phys. Lett., Vol. 70, No. 9, 3 March 1997

In recent technological trends, it is required to use a semiconductor light emitting element as a high luminance light source such as a headlamp for a car or a light source for a projector. For this reason, when a laser diode (LD) element or an LED element is manufactured on a gallium nitride substrate, further improvement of the light emission efficiency is required. However, when the light emitting element is formed on the conventional gallium nitride substrate, improvement of the light emission efficiency is still limited, and a breakthrough is required. Further, also in semiconductor-based functional elements other than light-emitting elements, such as rectifying elements, further improvement of the function is required.

An object of the present invention is to further improve functions such as luminous efficiency in a semiconductor functional element provided on a gallium nitride substrate.

The present invention is a gallium nitride substrate having a top surface and a bottom surface, wherein
When the upper surface is observed by cathode luminescence, it has a linear high luminance light emitting portion and a low luminance light emitting region adjacent to the high luminance light emitting portion, and the elastic constant C11 is 200 GPa or more and 290 GPa or less It is characterized by

Further, the present invention relates to a self-supporting substrate comprising the above-mentioned gallium nitride substrate.

Further, the present invention relates to a functional element characterized by having a functional layer provided on the free-standing substrate and the upper surface of the gallium nitride substrate.

The present invention also relates to a composite substrate comprising a support substrate and the gallium nitride substrate provided on the support substrate.

In addition, the present invention relates to a functional device including the composite substrate and a functional layer provided on the upper surface of the gallium nitride substrate.

The gallium nitride substrate of the present invention has a linear high luminance light emitting portion and a low luminance light emitting region adjacent to the high luminance light emitting portion when the upper surface is observed by cathode luminescence, and the elastic constant C11 is 200-290 GPa, lower than conventional ones. By forming a functional layer such as a light emitting layer on the upper surface of such a gallium nitride substrate, it was found that the stress of the functional layer is reduced and the function is improved by the reduction of the piezoelectric polarization. In particular, this can increase the probability of recombination of holes and electrons and improve the light emission efficiency.

(A) shows the state which provided the alumina layer 2, the seed-crystal layer 3, and the gallium nitride board | substrate 13 on the support substrate 1, (b) shows the gallium nitride board | substrate 13 isolate | separated from the support substrate. FIG. 5 is a schematic view for explaining a cathode luminescence image of the upper surface 13 a of the gallium nitride substrate 13. It is a photograph which shows the cathode luminescence image of upper surface 13a of gallium nitride substrate 13. It is a partial enlarged photograph of FIG. It is a schematic diagram corresponding to the cathode luminescence image of FIG. It is a photograph which shows the cathode luminescence image of the cross section of the gallium nitride board | substrate 13. FIG. 5 is a scanning electron micrograph showing a cross section of a gallium nitride substrate 13; It is a schematic diagram which shows the functional element 21 which concerns on this invention. It is a photography picture by a scanning electron microscope of the upper surface of a gallium nitride substrate. 2 shows a gray scale histogram generated from a CL image.

Hereinafter, the present invention will be described in more detail.
(Gallium nitride substrate)
The gallium nitride substrate of the present invention is made of gallium nitride and has top and bottom surfaces. For example, as shown in FIG. 1B, in the gallium nitride substrate 13, the top surface 13a and the bottom surface 13b face each other.

The gallium nitride constituting the gallium nitride substrate may be doped with zinc, calcium or other n-type dopant or p-type dopant, in which case the gallium nitride substrate is a p-type electrode, an n-type electrode, p It can be used as a member or layer other than a substrate such as a mold layer and an n-type layer. Preferred examples of the p-type dopant include one or more selected from the group consisting of beryllium (Be), magnesium (Mg), strontium (Sr), and cadmium (Cd). Preferred examples of the n-type dopant include one or more selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn) and oxygen (O).

Here, when the upper surface 13 a of the gallium nitride substrate 13 is observed by cathode luminescence (CL), it is adjacent to the linear high luminance light emitting portion 5 and the high luminance light emitting portion 5 as schematically shown in FIG. And a low luminance light emitting area 6.

Furthermore, in the present invention, the elastic constant C11 of the gallium nitride substrate is set to 200 GPa or more and 290 GPa or less. By setting the elastic constant C11 to 290 GPa or less, the stress on the functional layer provided on the gallium nitride substrate is reduced, and the function of the functional layer is significantly improved over the whole. From this viewpoint, it is more preferable to set the elastic constant C11 of the gallium nitride substrate to 270 GPa or less. Further, since it is practically difficult to set the elastic constant C11 of the gallium nitride substrate to less than 200 GPa, it is set to 200 GPa or more, and more preferably to 210 GPa or more.

The elastic constant C11 of the gallium nitride substrate is measured as follows. That is, a test piece of 35 mm long × 5 mm wide × 0.3 mm thick (c axis in the thickness direction) is prepared, and the test piece is subjected to a three-point bending test by strain gauge method in air at room temperature, load-strain diagram Obtain and determine the flexural modulus. The test speed is 0.5 mm / min, and the distance between fulcrums is 30 mm.

In a preferred embodiment, the density of gallium nitride constituting the gallium nitride substrate is 6.0 g / cm ³ or more and 6.2 g / cm ³ or less. By setting the density of gallium nitride to 6.0 g / cm ³ or more, the crystallinity of the functional layer can be further improved. When the density of gallium nitride exceeds 6.2 g / cm ³ , the impurity concentration is high and the crystallinity is lowered.
The density of gallium nitride is calculated by geometrical measurement according to JIS Z 8807.

In a preferred embodiment, the dislocation density on the upper surface of the gallium nitride substrate is 1 × 10 ⁶ / cm ² or less, thereby reducing defects in the functional layer provided on the gallium nitride substrate. From such a viewpoint, it is particularly preferable to set the transition density on the upper surface of the gallium nitride substrate to 1 × 10 ⁴ / cm ² or less from the viewpoint of improving the characteristics of the functional element. Also, the dislocation density is often 1 × 10 ² / cm ² or more.

For measurement of dislocation density, a scanning electron microscope (SEM) with a CL detector can be used. For example, when CL observation is carried out using a Hitachi High-Technologies S-3400N scanning electron microscope with a MiniCL system manufactured by Gatan, dislocation sites are observed as black spots (dark spots) without light emission. Dislocation density is calculated by measuring the dark spot density. As the measurement conditions, while the CL detector is inserted between the sample and the objective lens, it is preferable to observe at an acceleration voltage of 10 kV, a probe current of "90", a working distance (W.D.) 22.5 mm, and a magnification of 1200 times. preferable.

In a preferred embodiment, the absorption coefficient of gallium nitride constituting the gallium nitride substrate for light with a wavelength of 400 to 1500 nm is 4 cm ⁻¹ or less.
With such a gallium nitride substrate, for example, when used in a light emitting element, the absorption of light of the light emission wavelength is small, so that a highly efficient light emitting element can be obtained. From such a viewpoint, it is more preferable to set the absorption coefficient of gallium nitride to light having a wavelength of 400 to 1,500 nm at 3 cm ^-1 or less. In addition, the absorption coefficient of gallium nitride for light with a wavelength of 400 to 1500 nm is often 3 cm ^-1 or more.

The absorption coefficient of gallium nitride is calculated by measuring the total transmittance and total reflectance of the light of the target wavelength using a spectrophotometer. The measurement conditions are as follows.

Measuring device: SolidSpec-3700DUV UV-visible near-infrared spectrophotometer (manufactured by Shimadzu Corporation)
Slit width: 8 nm (250 to 720 nm) 20 nm (720 to 1600 nm)
Light source: Halogen lamp detector: PMT (870 nm or less)
InGaAs (870 nm to 1650 nm)
Accessories: Large-sized sample chamber Integral sphere (60 mmφ) Spectralon incidence angle: Transmission measurement: 0 ° Total reflection measurement: 8 °
Reference: Total Reflection Measurement: Al Mirror

In a preferred embodiment, the resistivity of gallium nitride constituting the gallium nitride substrate is 1 × 10 ² Ωcm or less, whereby a substrate with high conductivity can be obtained. From such a viewpoint, it is more preferable to set the resistivity of gallium nitride to 5 × 10 ⁻¹ Ωcm or less.
The specific resistivity of gallium nitride is determined from a hall measurement (a hall measuring instrument manufactured by Toyo Technology Co., Ltd.).

According to the present invention, when the upper surface of the gallium nitride substrate is observed by cathodoluminescence, it has a linear high luminance light emitting portion and a low luminance light emitting region adjacent to the high luminance light emitting portion. This means that a linear high-intensity light emitting part appears in the upper surface, so that a linear high-intensity light emitting part in which the dopant component and the trace component contained in the gallium nitride crystal are dark is generated. ing.

In a preferred embodiment, the high brightness light emitting portion includes a portion extending along the m-plane of the gallium nitride crystal. The fact that the linear high-intensity light emitting portion extends along the m-plane means that the dopants gather along the m-plane during crystal growth, and as a result, the dark linear high-intensity light emitting portion along the m-plane It means to appear.

Gallium nitride substrates having a novel microstructure such as these can reduce dislocation density even if the size is increased (eg, even if the diameter is 6 inches or more), and the variation in characteristics can be reduced overall Can be provided.

However, observation by CL shall be performed as follows.
For CL observation, a scanning electron microscope (SEM) with a CL detector is used. For example, when using Hitachi High-Technologies S-3400N scanning electron microscope with Gatan MiniCL system, measurement conditions are: acceleration voltage 10 kV, probe current “90” with CL detector inserted between sample and objective lens The working distance (W.D.) is preferably 22.5 mm and observed at a magnification of 50 times.

Further, the high luminance light emitting portion and the low luminance light emitting region are distinguished as follows from the observation by cathode luminescence.
Image analysis software (for example, Mitani Shoji Co., Ltd. WinROOF Ver. 6) against the luminance of the image observed with CL at a magnification of 50 × with an acceleration voltage of 10 kV, a probe current of “90”, a working distance (W.D.) of 22.5 mm. Using .1.3), create a 256-step gray scale histogram with the vertical axis as frequency and the horizontal axis as luminance (GRAY). In the histogram, as shown in FIG. 10, two peaks are confirmed, and the high side is defined as a high brightness light emitting portion and the low side as a low brightness light emitting region with the brightness at which the frequency is minimum between the two peaks as a boundary. Do.

Further, on the upper surface of the gallium nitride substrate, the low luminance light emitting region is adjacent to the linear high luminance light emitting portion. By this, adjacent low-intensity light emission areas are divided by the linear high-intensity light emission parts located between them. Here, that the high brightness light emitting portion is linear means that the high brightness light emitting portion is elongated and elongated between adjacent low brightness light emitting regions to form a boundary line.

Here, the line made by the high-intensity light emitting portion may be a straight line, a curved line, or a combination of a straight line and a curved line. The curve may include various forms such as arc, ellipse, parabola, hyperbola and the like. Moreover, although the high-intensity light emission part from which a direction mutually differs may be continuous, the terminal of the high-intensity light emission part may be cut off.

On the upper surface of the gallium nitride substrate, the low luminance light emitting region may be an exposed surface of the gallium nitride crystal grown therebelow, and is two-dimensionally spread in a planar manner. On the other hand, the high brightness light emitting portion is linear, but extends in a one-dimensional manner as a boundary that divides adjacent low brightness light emitting regions. This is because, for example, a dopant component, a trace component and the like are discharged from a gallium nitride crystal grown from the bottom, gathered between adjacent gallium nitride crystals in the growth process, and a line between adjacent low brightness light emitting regions on the top surface It is considered that a portion that emits strong light in a shape is generated.

For example, FIG. 3 shows a photograph by CL observation of the top surface of the gallium nitride substrate obtained in the example. 4 is a partial enlarged view of FIG. 3, and FIG. 5 is a schematic view corresponding to FIG. The low brightness light emitting area is two-dimensionally spread in a plane, and the high brightness light emitting portion is linear, and is one-dimensionally stretched like a boundary dividing the adjacent low brightness light emitting areas. I understand that.

From this, the shape of the low luminance light emitting region is not particularly limited, and usually extends two-dimensionally in a planar shape. On the other hand, the line formed by the high luminance light emitting portion needs to be elongated. From such a viewpoint, the width of the high brightness light emitting portion is preferably 100 μm or less, more preferably 20 μm or less, and particularly preferably 5 μm or less. In addition, the width of the high brightness light emitting portion is usually 0.01 μm or more.

From the viewpoint of the present invention, the ratio (length / width) of the length to the width of the high luminance light emitting portion is preferably 1 or more, and more preferably 10 or more.

From the viewpoint of the present invention, the ratio of the area of the high luminance light emitting portion to the area of the low luminance light emitting region on the upper surface (area of high luminance light emitting portion / area of low luminance light emitting region) is 0.001 or more Is more preferably 0.01 or more.
From the viewpoint of the present invention, the ratio of the area of the high luminance light emitting portion to the area of the low luminance light emitting region on the upper surface (area of high luminance light emitting portion / area of low luminance light emitting region) is 0.3 or less Is more preferably 0.1 or less.

In a preferred embodiment, the high brightness light emitting portion includes a portion extending along the m-plane of the gallium nitride crystal. For example, in the example of FIG. 2, FIG. 5, the high-intensity light emission part 5 is extended in elongate linear form, and contains

many parts

5a, 5b, 5c extended along m surface. Specifically, the directions along the m-plane of the hexagonal gallium nitride crystal are [-2110], [-12-10], [11-20], [2-1-10], and [1]. The high-intensity light emitting unit 5 includes a part of the side of a substantially hexagonal shape reflecting hexagonal crystals. The linear high-intensity light emitting portion extending along the m-plane means that the longitudinal direction of the high-intensity light emitting portion is [-2110], [-12-10], [11-20], [2- It means extending along one of 1-10 directions, [1-210] and [-1-120] directions. Specifically, the case where the longitudinal direction of the linear high luminance light emitting part is preferably within ± 1 °, more preferably within ± 0.3 ° with respect to the m-plane is included.

In a preferred embodiment, at the top, linear high-intensity light emitting portions extend generally along the m-plane of the gallium nitride crystal. This means that the main part of the high luminance light emitting part extends along the m plane, and preferably the continuous phase of the high luminance light emitting part extends along substantially the m plane. At this time, the portion extending in the direction along the m-plane preferably occupies 60% or more, more preferably 80% or more, of the total length of the high brightness light emitting portion, and substantially high brightness It may occupy the whole of the light emitting part.

In a preferred embodiment, on the upper surface of the gallium nitride substrate, the high brightness light emitting portion forms a continuous phase, and the low brightness light emitting region forms a discontinuous phase partitioned by the high brightness light emitting portion. For example, in the schematic views of FIGS. 2 and 5, the linear high brightness light emitting portion 5 forms a continuous phase, and the low brightness light emitting region 6 forms a discontinuous phase partitioned by the high brightness light emitting portion 5. ing.

However, the continuous phase means that the high brightness light emitting portion 5 is continuous on the upper surface, but it is not essential that all the high brightness light emitting portions 5 are completely continuous, and the whole It is to be allowed that a small amount of the high luminance light emitting portion 5 is separated from the other high luminance light emitting portions 5 without affecting the pattern.

Further, the dispersed phase means that the low brightness light emitting region 6 is divided by the high brightness light emitting portion 5 and divided into a large number of regions which are not connected to each other. In addition, even if the low brightness light emitting region 6 is separated by the high brightness light emitting portion 5 on the upper surface, it is acceptable that the low brightness light emitting region 6 is continuous inside the gallium nitride substrate.

In a preferred embodiment, the half width of (0002) plane reflection of the X-ray rocking curve on the upper surface of the gallium nitride substrate is 3000 seconds or less and 20 seconds or more. This indicates that the top surface has a small surface tilt angle, and the crystal orientation as a whole is highly oriented like a single crystal. In addition to having the cathode luminescence distribution as described above, the characteristic distribution on the upper surface of the gallium nitride substrate can be made smaller if such a microstructure having a crystal orientation at the surface as a whole as described above is highly oriented. The characteristics of various functional elements provided thereon can be made uniform, and the yield of functional elements is also improved.

From such a viewpoint, the half value width of (0002) plane reflection of the X-ray rocking curve on the upper surface of the gallium nitride substrate is preferably 1000 seconds or less and 20 seconds or more, more preferably 500 seconds or less and 20 seconds or more More preferred. It is practically difficult to reduce the half width of (0002) plane reflection of the X-ray rocking curve on the upper surface of the gallium nitride substrate to less than 20 seconds.

However, X-ray rocking curve (0002) surface reflection is measured as follows. Measurement conditions are: tube voltage 40 kV, tube current 40 mA, collimator diameter 0.1 mm, anti-scattering slit 3 mm, using an XRD apparatus (for example, D8-DISCOVER manufactured by Bruker-AXS), ω = peak position angle ± 0.3 ° And the ω step width of 0.003 ° and the counting time of 1 second. In this measurement, it is preferable to parallelize CuKα rays (half-width 28 seconds) with a Ge (022) asymmetric reflection monochromator and measure the axis after setting the axis at a tilt angle CHI of about 0 °. The half width of the X-ray rocking curve (0002) surface reflection can be calculated by performing peak search using XRD analysis software (LEPTOS 4.03 manufactured by Bruker-AXS). The peak search conditions are preferably Noise Filter “10”, Threshold “0.30”, and Points “10”.

When a cross section substantially perpendicular to the upper surface of the gallium nitride substrate is observed by CL, as shown in FIG. 6, a linear high-intensity light emitting portion that emits white light may be observed. In FIG. 6, the low brightness light emitting area is two-dimensionally spread in a planar manner, and the high brightness light emitting portion is linear, and extends like a boundary line which divides adjacent low brightness light emitting areas. Know that The observation method of such a high luminance light emitting portion and the low luminance light emitting region is the same as the observation method of the high luminance light emitting portion and the low luminance light emitting region on the upper surface.

There is no particular limitation on the shape of the low luminance light emitting region in the cross section of the gallium nitride substrate, and it usually extends two-dimensionally in a planar shape. On the other hand, the line formed by the high luminance light emitting portion needs to be elongated. From such a viewpoint, the width of the high brightness light emitting portion is preferably 100 μm or less, and more preferably 20 μm or less. In addition, the width of the high brightness light emitting portion is usually 0.01 μm or more.

Further, from the viewpoint of the present invention, the ratio (length / width) of the length to the width of the light emitting portion in the cross section of the gallium nitride substrate is preferably 1 or more, and more preferably 10 or more.

In a preferred embodiment, in the cross section substantially perpendicular to the upper surface of the gallium nitride substrate, the linear high luminance light emitting portion forms a continuous phase, and the low luminance light emitting region is partitioned by the high luminance light emitting portion. It forms a continuous phase. For example, in the CL photograph of FIG. 6, the linear high-intensity light emitting portion forms a continuous phase, and the low-intensity light emitting region forms a discontinuous phase partitioned by the high-intensity light emitting portion.

However, the continuous phase means that the high brightness light emitting portion is continuous in the cross section, but it is not essential that all the high brightness light emitting portions are completely continuous, and the whole pattern It is acceptable that a small amount of high-intensity light emitting portions are separated from other high-intensity light emitting portions without affecting the above.

Further, the dispersed phase means that the low brightness light emitting region is divided by the high brightness light emitting portion and divided into many regions which are not connected to each other.

In a preferred embodiment, no voids are observed in a cross section substantially perpendicular to the top surface of the gallium nitride substrate. That is, in the SEM photograph shown in FIG. 7 which is the same field of view as the CL photograph in FIG. 6, different crystal phases other than the void (void) and the gallium nitride crystal phase are not observed. However, observation of void is performed as follows.

A void is observed when a cross section substantially perpendicular to the upper surface of the gallium nitride substrate is observed with a scanning electron microscope (SEM), and a void having a maximum width of 1 μm to 500 μm is a “void”. For this SEM observation, for example, S-3400N scanning electron microscope manufactured by Hitachi High-Technologies Corporation is used. Measurement conditions are preferably observed at an acceleration voltage of 15 kV, a probe current of "60", a working distance (W.D.) of 6.5 mm, and a magnification of 100 times.
Further, in a scanning electron microscope (observation conditions described above), when observing a cross section substantially perpendicular to the top surface of the gallium nitride substrate, no apparent grain boundary accompanied by structural macro defects such as voids is observed. With such a fine structure, when a functional element such as a light emitting element is fabricated on a gallium nitride substrate, it is considered that the increase in resistance and the variation in characteristics due to apparent grain boundaries can be suppressed.

In a preferred embodiment, the half width of (0002) plane reflection of the X-ray rocking curve on the upper surface of the gallium nitride substrate is 3000 seconds or less, 20 seconds or more, and the half width of (1000) plane reflection is 10000 seconds. Below, it is 20 seconds or more. This indicates that both the surface tilt angle and the surface twist angle at the upper surface are small, and the crystal orientation is highly oriented as a whole, like a single crystal. With such a fine structure in which the crystal orientation at the surface as a whole is more highly oriented, the characteristic distribution on the upper surface of the gallium nitride substrate can be made smaller, and the characteristics of various functional elements provided thereon become uniform. It also improves the yield of functional devices.

In a preferred embodiment, the half value width of (1000) plane reflection of the X-ray rocking curve on the upper surface of the gallium nitride substrate is 10000 seconds or less and 20 seconds or more. This indicates that the surface twist angle at the top surface is very low, and the crystal orientation as a whole is highly oriented like a single crystal. In addition to having the cathode luminescence distribution as described above, the characteristic distribution on the upper surface of the gallium nitride substrate can be made smaller if such a microstructure having a crystal orientation at the surface as a whole as described above is highly oriented. The characteristics of various functional elements provided thereon can be made uniform, and the yield of functional elements is also improved.

From such a viewpoint, the half value width of (1000) plane reflection of the X-ray rocking curve on the upper surface of the gallium nitride substrate is preferably 5000 seconds or less, more preferably 1000 seconds or less, further 20 seconds or more. More preferred. It is practically difficult to reduce this half-width to less than 20 seconds.

However, X-ray rocking curve (1000) surface reflection is measured as follows. Measurement conditions are: tube voltage 40 kV, tube current 40 mA, no collimator, anti-scattering slit 3 mm, range of ω = peak position angle ± 0.3 °, using an XRD apparatus (for example, D8-DISCOVER manufactured by Bruker-AXS) The ω step width may be set to 0.003 ° and the counting time to 4 seconds. In this measurement, it is preferable to measure CuKα rays in parallel monochromatization (half-width 28 seconds) with a Ge (022) asymmetric reflection monochromator and centering around a tilt angle CHI = 88 °. And the half value width of X-ray rocking curve (1000) surface reflection can be calculated by performing peak search using XRD analysis software (manufactured by Bruker-AXS, LEPTOS 4.03). The peak search conditions are preferably Noise Filter “10”, Threshold “0.30”, and Points “10”.

(Example of suitable manufacturing method)
Hereafter, the suitable manufacturing method of a gallium nitride board | substrate is illustrated.
The gallium nitride substrate of the present invention can be manufactured by forming a seed crystal layer on a base substrate and forming a substrate composed of gallium nitride crystals thereon.

For example, as illustrated in FIG. 1, the base substrate may be a single crystal substrate 1 on which an alumina layer 2 is formed. Single crystal substrate 1 is a perovskite such as sapphire, AlN template, GaN template, GaN freestanding substrate, SiC single crystal, MgO single crystal, spinel (MgAl ₂ O ₄ ), LiAlO ₂ , LiGaO ₂ , LaAlO ₃ , LaGaO ₃ , NdGaO _{3 and the} like Type composite oxide, SCAM (ScAlMgO ₄ ) can be exemplified. The composition formula _{_{[A 1-y (Sr 1-}} x Ba x) y ] _{_{_{[(Al 1-z Ga z)}}} 1-u · D u ] _O 3 (A is a rare earth element; D is niobium and One or more elements selected from the group consisting of tantalum; y = 0.3 to 0.98; x = 0 to 1; z = 0 to 1; u = 0.15 to 0.49; x + z = 0 The cubic perovskite structure complex oxide of 1) to 2) can also be used.

The alumina layer 2 can be formed by a known technique, and is prepared by sputtering, MBE (molecular beam epitaxy) method, vapor deposition, mist CVD method, sol gel method, aerosol deposition (AD) method, or tape forming. The method of bonding an alumina sheet to the said single crystal substrate is illustrated, and especially the sputtering method is preferable. It is possible to use one to which heat treatment, plasma treatment, or ion beam irradiation has been added after forming the alumina layer, if necessary. The method of heat treatment is not particularly limited, but heat treatment may be performed in an air atmosphere, vacuum, a reducing atmosphere such as hydrogen, or an inert atmosphere such as nitrogen / Ar, a hot press (HP) furnace, a hot isostatic press (HIP) Heat treatment may be performed under pressure using a furnace or the like.

Further, a sapphire substrate to which the same heat treatment, plasma treatment, or ion beam irradiation as described above is added can be used as a base substrate.

Then, for example, as shown in FIG. 1A, the seed crystal layer 3 is formed on the alumina layer 2 prepared as described above or on the single crystal substrate 1 to which the heat treatment, plasma treatment and ion beam irradiation are applied as described above. Set up. The material constituting the seed crystal layer 3 is a nitride of one or two or more kinds of Group 13 elements specified by IUPAC. The group 13 element is preferably gallium, aluminum or indium. Further, specifically, group 13 element nitride crystals are GaN, AlN, InN, Ga _x Al _{1 -x} N (1>x> 0), Ga _x In _1-x N (1>x> 0) And Ga _x Al _y InN _{1 -x-y} (1>x> 0, 1>y> 0).

The method of producing the seed crystal layer 3 is not particularly limited, but MOCVD (organic metal vapor phase growth method), MBE (molecular beam epitaxy method), HVPE (hydride vapor phase growth method), vapor phase method such as sputtering, Na flux method Liquid phase methods such as ammonothermal method, hydrothermal method, sol-gel method, powder method utilizing solid phase growth of powder, and combinations thereof are preferably exemplified.
For example, a seed crystal layer is formed by depositing a low-temperature growth buffer GaN layer at 450 to 550 ° C. for 20 to 50 nm and then laminating a GaN film having a thickness of 2 to 4 μm at 1000 to 1200 ° C. Preferably by

The gallium nitride substrate 13 is formed to have a crystal orientation substantially following the crystal orientation of the seed crystal layer 3. The method for forming the gallium nitride substrate is not particularly limited as long as it has a crystal orientation substantially following the crystal orientation of the seed crystal film, and a vapor phase method such as MOCVD or HVPE, Na flux method, ammonothermal method, hydrothermal method, A liquid phase method such as a sol-gel method, a powder method utilizing solid phase growth of powder, and a combination thereof are preferably exemplified, but the Na flux method is particularly preferable.

When forming a gallium nitride substrate by the Na flux method, it is preferable to strongly stir the melt and mix the melt sufficiently uniformly. As such a stirring method, a swing, rotation, vibration method may be mentioned, but the method is not limited.

Formation of a gallium nitride substrate by the Na flux method is carried out by using a group 13 metal, metal Na and optionally a dopant (eg, germanium (Ge), silicon (Si), oxygen (O), etc.) n-type Or a melt composition containing p-type dopants such as beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), cadmium (Cd), etc., in a nitrogen atmosphere Preferably, the temperature is raised to 830 ° C. to 910 ° C. and 3.5 to 4.5 MPa, followed by rotation while maintaining the temperature and pressure. The holding time varies depending on the target film thickness, but may be about 10 to 100 hours.

Here, from the viewpoint of the present invention, the pressure increase rate in a nitrogen atmosphere is preferably 0.01 MPa / min or more and 0.1 MPa / min or less, and is 0.02 MPa / min or more and 0.05 MPa / min or less Is more preferred. Further, it is preferable to set the temperature increase rate in a nitrogen atmosphere to 5 ° C./min or more and 20 ° C./min or less, and more preferably 7 ° C./min or more and 12 ° C./min or less.

Further, it is preferable to flatten the plate surface by grinding the gallium nitride crystal thus obtained by the Na flux method with a grindstone, and then to smooth the plate surface by lapping using diamond abrasive grains.

(Separation method of gallium nitride substrate)
Then, the gallium nitride substrate is separated from the single crystal substrate to obtain a freestanding substrate including the gallium nitride substrate.

Here, the method of separating the gallium nitride substrate from the single crystal substrate is not limited. In a preferred embodiment, the gallium nitride substrate is naturally peeled from the single crystal substrate in the temperature lowering step after growing the gallium nitride substrate.

Alternatively, the gallium nitride substrate can be separated from the single crystal substrate by chemical etching.
As an etchant at the time of chemical etching, a strong acid such as sulfuric acid or hydrochloric acid, a mixed solution of sulfuric acid and phosphoric acid, or a strong alkali such as sodium hydroxide aqueous solution or potassium hydroxide aqueous solution is preferable. Moreover, as for the temperature at the time of performing chemical etching, 70 degreeC or more is preferable.

Alternatively, the gallium nitride substrate can be peeled off from the single crystal substrate by a laser lift-off method.
Alternatively, the gallium nitride substrate can be peeled off from the single crystal substrate by grinding.
Alternatively, the gallium nitride substrate can be peeled off from the single crystal substrate with a wire saw.

(Self-standing substrate)
A freestanding substrate can be obtained by separating a gallium nitride substrate from a single crystal substrate. In the present invention, the term "self-supporting substrate" means a substrate which can be handled as a solid without deformation or breakage under its own weight. The self-supporting substrate of the present invention can be used as a substrate for various semiconductor devices such as light emitting elements, but in addition to that, it can be an electrode (may be a p-type electrode or an n-type electrode), a p-type layer, an n-type layer, etc. It can be used as a member or layer other than the base material. This freestanding substrate may further be provided with one or more other layers.

When the gallium nitride substrate constitutes a self-supporting substrate, the thickness of the self-supporting substrate needs to be capable of giving self-supporting properties to the substrate, preferably 20 μm or more, more preferably 100 μm or more, and still more preferably 300 μm or more . The upper limit of the thickness of the free-standing substrate should not be defined, but 3000 μm or less is realistic in terms of manufacturing cost.

(Composite substrate)
The gallium nitride substrate can be used as a template substrate for forming another functional layer without separating the gallium nitride substrate in a state where the gallium nitride substrate is provided over a single crystal substrate. In this case, the thickness of the gallium nitride substrate is preferably 20 μm or more, more preferably 100 μm or more, and still more preferably 300 μm or more. The upper limit of the thickness of the gallium nitride substrate should not be defined, but 3000 μm or less is realistic in terms of manufacturing cost.

(Functional element)
The functional element structure provided on the gallium nitride substrate of the present invention is not particularly limited, but can exemplify a light emitting function, a rectifying function or a power control function.

The structure of the light emitting device using the gallium nitride substrate of the present invention and the method of manufacturing the same are not particularly limited. Typically, a light emitting device is manufactured by providing a light emitting functional layer on a gallium nitride substrate. However, the light emitting element may be manufactured using a gallium nitride substrate as a member or layer other than a substrate such as an electrode (which may be a p-type electrode or an n-type electrode), a p-type layer, or an n-type layer.

FIG. 8 schematically shows a layer configuration of a light emitting element according to one embodiment of the present invention. A light emitting element 21 shown in FIG. 8 includes a self-supporting substrate 13 and a light emitting functional layer 18 formed on the substrate. The light emitting functional layer 18 provides light emission based on the principle of a light emitting element such as an LED by appropriately providing an electrode or the like and applying a voltage.

The light emitting functional layer 18 is formed on the substrate 13. The light emitting functional layer 18 may be provided on the entire surface or a part of the substrate 13, or may be provided on the entire surface or a part of the buffer layer when the buffer layer described later is formed on the substrate 13. Good. The light emitting functional layer 18 can adopt various known layer configurations that provide light emission based on the principle of a light emitting element represented by an LED by appropriately providing an electrode and / or a phosphor and applying a voltage. Therefore, the light emitting functional layer 18 may emit visible light such as blue and red, or may emit ultraviolet light without visible light or together with visible light. The light emitting functional layer 18 preferably constitutes at least a part of a light emitting element utilizing a pn junction, and the pn junction includes a p-type layer 18a and an n-type layer 18c as shown in FIG. The active layer 18 b may be included between At this time, a double hetero junction or a single hetero junction (hereinafter collectively referred to as a hetero junction) using a layer having a smaller band gap than the p-type layer and / or the n-type layer may be used as the active layer. In addition, a quantum well structure in which the thickness of the active layer is reduced can be employed as one mode of the p-type layer-active layer-n-type layer. It goes without saying that in order to obtain a quantum well, a double hetero junction in which the band gap of the active layer is smaller than that of the p-type layer and the n-type layer should be employed. Further, a multiple quantum well structure (MQW) in which a large number of these quantum well structures are stacked may be used. With these structures, the light emission efficiency can be enhanced as compared to a pn junction. Thus, the light emitting functional layer 18 is preferably provided with a pn junction and / or hetero junction and / or quantum well junction having a light emitting function. 20 and 22 are examples of electrodes.

Therefore, at least one layer constituting the light emitting functional layer 18 is at least selected from the group consisting of an n-type layer doped with an n-type dopant, a p-type layer doped with a p-type dopant, and an active layer. It can be one or more. The n-type layer, the p-type layer and the active layer (if present) may be composed of the same material as the main component or may be composed of materials different from each other in the main component.

The material of each layer constituting the light emitting functional layer 18 is not particularly limited as long as it is grown substantially in accordance with the crystal orientation of the crystal constituting the gallium nitride substrate and has a light emitting function, but a gallium nitride (GaN) based material It is preferable to be composed of a material mainly composed of at least one or more selected from zinc oxide (ZnO) based materials and aluminum nitride (AlN) based materials, and a dopant for controlling p type to n type is suitably selected It may be included. Particularly preferred materials are gallium nitride (GaN) based materials. Further, the material constituting the light emitting functional layer 18 may be, for example, a mixed crystal in which AlN, InN or the like is solid-solved in GaN in order to control the band gap. In addition, as described in the immediately preceding paragraph, the light emitting functional layer 18 may be a heterojunction made of a plurality of material systems. For example, a gallium nitride (GaN) based material may be used for the p-type layer, and a zinc oxide (ZnO) based material may be used for the n-type layer. Further, a zinc oxide (ZnO) based material may be used for the p-type layer, and a gallium nitride (GaN) based material may be used for the active layer and the n-type layer, and the combination of materials is not particularly limited.

The film formation method of the light emitting functional layer 18 and the buffer layer is not particularly limited as long as it is a method of growing substantially in accordance with the crystal orientation of the Group 13 element nitride crystal layer, but a vapor phase method such as MOCVD, MBE, HVPE, sputtering, etc. Preferred examples thereof include liquid phase methods such as Na flux method, ammonothermal method, hydrothermal method and sol-gel method, powder method utilizing solid phase growth of powder, and combinations thereof.

Example 1
(Preparation of a gallium nitride free-standing substrate)
An alumina film 2 of 0.3 μm in thickness is formed on a sapphire substrate 1 with a diameter of 6 inches by sputtering, and then a seed crystal film 3 of 2 μm in thickness made of gallium nitride is formed by MOCVD. Obtained.

The seed crystal substrate was placed in an alumina crucible in a nitrogen atmosphere glove box. Next, metallic gallium and metallic sodium were filled in a crucible so that Ga / Ga + Na (mol%) = 15 mol%, metallic germanium as a dopant was filled with 3 mol% of Ga with respect to Ga, and a lid was covered with an alumina plate. The crucible was placed in a stainless steel inner container and further put in a stainless steel outer container capable of containing it, and the lid was covered. The outer container was placed on a rotary table installed in a heating unit in a crystal manufacturing apparatus which has been vacuum baked in advance, and the pressure resistant container was covered and sealed.

Subsequently, the inside of the pressure resistant container was evacuated to 0.1 Pa or less by a vacuum pump. Subsequently, nitrogen gas was introduced from a nitrogen gas cylinder to 4.0 MPa while heating the temperature of the heating space to 875 ° C. by adjusting the upper heater, middle heater and lower heater. At this time, the pressure increase rate in the nitrogen atmosphere was 0.02 MPa / min, and the temperature increase rate in the nitrogen atmosphere was 8 ° C./min. The outer container was rotated clockwise and counterclockwise at a constant speed of 20 rpm around the central axis. The acceleration time was 12 seconds, the holding time was 600 seconds, the deceleration time was 12 seconds, and the stop time was 0.5 seconds. And it hold | maintained in this state for 40 hours. Thereafter, the vessel was naturally cooled to room temperature and depressurized to the atmospheric pressure, and then the lid of the pressure container was opened and the bale was taken out from the inside. The solidified metallic sodium in the crucible was removed, and the crack-free gallium nitride free-standing substrate peeled off from the seed crystal substrate was recovered.

(Evaluation)
With respect to the obtained gallium nitride substrate, the elastic constant C11, the density, the dislocation density on the upper surface, the absorption coefficient for light with a wavelength of 400 to 1500 nm, and the specific resistivity were measured. The measurement results are shown in Table 1.

Furthermore, the upper surface of the gallium nitride free-standing substrate was polished and CL was observed with a scanning electron microscope (SEM) equipped with a CL detector. As a result, as shown in FIG. 3, a high luminance light emitting portion emitting white light was confirmed inside the gallium nitride crystal in the CL photograph. However, at the same time, as shown in FIG. 9, when the same field of view was observed by SEM, no void etc. were confirmed, and it was confirmed that a homogeneous gallium nitride crystal was grown.

In addition, the gallium nitride free-standing substrate was cut into a cross section perpendicular to the upper surface, and the cut surface was polished and subjected to CL observation with a scanning electron microscope (SEM) equipped with a CL detector. As a result, as shown in FIG. 6, in the CL image, a high brightness light emitting portion emitting white light was confirmed inside the gallium nitride crystal. However, at the same time, as shown in FIG. 7, when the same field of view was observed by SEM, no void etc. were confirmed, and it was confirmed that a homogeneous gallium nitride crystal was grown. That is, even in the cross section of the group 13 element nitride crystal layer, the high brightness light emitting portion exists in CL observation as in the upper surface, but the same shape as the high brightness light emitting portion seen in the same field of view in the SEM There was no microstructure similar to it or that.

(Measurement of surface tilt angle)
It was 73 seconds as a result of measuring the half value width of (0002) plane reflection of the X ray rocking curve in the upper surface of a gallium nitride crystal layer.

(Measurement of surface twist angle)
It was 85 seconds when the half value width of (1000) plane reflection of the X-ray rocking curve in the upper surface of the gallium nitride crystal layer was measured.

(Deposition of light emitting functional layer by MOCVD method)
Using an MOCVD method, an n-type n-type layer was deposited 1 μm as an n-type layer at 1050 ° C. to have a Si atomic concentration of 5 × 10 ¹⁸ / cm ³ as the n-type layer. Next, a multiple quantum well layer was deposited at 750 ° C. as a light emitting layer. Specifically, five layers of 2.5 nm well layers of InGaN and six layers of 10 nm of barrier layers of GaN were alternately stacked. Next, as a p-type layer, 200 nm of p-GaN doped at a temperature of 950 ° C. so that the Mg atom concentration is 1 × 10 ¹⁹ / cm ³ was deposited. Thereafter, it was taken out of the MOCVD apparatus, and heat treatment at 800 ° C. in a nitrogen atmosphere was performed for 10 minutes as activation treatment of Mg ions in the p-type layer.

(Fabrication of light emitting element)
15 nm and 70 nm Ti / Al / Ni / Au film as cathode electrode on the opposite side of n-GaN layer and p-GaN layer of gallium nitride freestanding substrate by photolithography process and vacuum evaporation method It patterned in thickness of 12 nm and 60 nm. Thereafter, heat treatment at 700 ° C. in a nitrogen atmosphere was performed for 30 seconds in order to improve ohmic contact characteristics. Further, a Ni / Au film was patterned to a thickness of 6 nm and 12 nm as a light transmitting anode electrode in the p-type layer using a photolithography process and a vacuum evaporation method. Thereafter, a heat treatment at 500 ° C. was performed for 30 seconds in a nitrogen atmosphere in order to improve ohmic contact characteristics. Furthermore, using a photolithography process and a vacuum evaporation method, the Ni / Au film to be the anode electrode pad has a thickness of 5 nm and 60 nm, respectively, on a partial region of the upper surface of the Ni / Au film as the translucent anode electrode. Patterned. The substrate thus obtained was cut into chips, and then mounted on lead frames to obtain light emitting elements of a vertical structure.

(Evaluation of light emitting element)
When current was applied between the cathode electrode and the anode electrode, and IV measurement was carried out for 100 individuals arbitrarily selected from the manufactured elements, rectification was confirmed for 90 pieces. In addition, when forward current flowed, emission of wavelength 460 nm was confirmed.

Subsequently, the internal quantum efficiency at the time of 350 mA drive was measured about the produced element, and the measurement result was shown in Table 1.

(Example 2)
A gallium nitride substrate and a light emitting device were produced in the same manner as in Example 1, and various characteristics were measured in the same manner as in Example 1.
However, unlike Example 1, the growth temperature was 870 ° C., the pressure increase rate in a nitrogen atmosphere was 0.04 MPa / min, and the temperature increase rate in a nitrogen atmosphere was 10 ° C./min. The obtained results are shown in Table 1.

(Example 3)
A gallium nitride substrate and a light emitting device were produced in the same manner as in Example 1, and various characteristics were measured in the same manner as in Example 1.
However, unlike Example 1, the crucible is not filled with metallic germanium, the growth temperature is set to 865 ° C., the pressure increase rate in a nitrogen atmosphere is 0.02 MPa / min, and the temperature increase rate in a nitrogen atmosphere is determined. The temperature was 12 ° C./min. The obtained results are shown in Table 1.

(Example 4)
A gallium nitride substrate and a light emitting device were produced in the same manner as in Example 1, and various characteristics were measured in the same manner as in Example 1.
However, unlike Example 1, the growth temperature was 860 ° C., the pressure increase rate in the nitrogen atmosphere was 0.02 MPa / min, and the temperature increase rate in the nitrogen atmosphere was 8 ° C./min. The obtained results are shown in Table 1.

(Comparative example 1)
A gallium nitride substrate was produced by the hydride VPE method as follows.
Specifically, gallium nitride crystal was grown by a hydride VPE method using gallium chloride (GaCl) as a group III raw material and using ammonia (NH ₃ ) gas as a group V raw material. The seed crystal substrate was set in a hydride VPE growth apparatus, and heated to a growth temperature of 1150 ° C. in an ammonia atmosphere. After the growth temperature is stabilized, supply the HCl flow rate at 40 cc / min, grow the n-type GaN crystal with NH ₃ flow rate 1000 cc / min, and silane, (SiH ₄ ) flow rate 0.01 cc / min. The

When held in this state for 4 hours, cooled to normal temperature in an ammonia gas atmosphere and taken out from the growth apparatus, gallium nitride crystals were grown to about 300 microns.

The obtained gallium nitride crystal was separated from the seed crystal substrate in the same manner as in Example 1 to obtain a gallium nitride substrate. The elastic constant C11, the density, the dislocation density on the upper surface, the absorption coefficient for light with a wavelength of 400 to 1500 nm, the content of each atom, and the specific resistivity were measured for the obtained gallium nitride substrate. The measurement results are shown in Table 1. Further, a light emitting element was produced in the same manner as in Example 1, and the measurement result of luminous efficiency is shown in Table 1.

(Comparative example 2)
A gallium nitride substrate and a light emitting device were produced in the same manner as in Comparative Example 1, and various characteristics were measured.
However, unlike the comparative example 1, the growth temperature was set to 1130 ° C. The obtained results are shown in Table 1.

Claims

A gallium nitride substrate having a top surface and a bottom surface,
When the upper surface is observed by cathode luminescence, it has a linear high luminance light emitting portion and a low luminance light emitting region adjacent to the high luminance light emitting portion, and the elastic constant C11 is 200 GPa or more and 290 GPa or less A gallium nitride substrate characterized by
The gallium nitride substrate according to claim 1, wherein the density is 6.0 g / cm 3 or more and 6.2 g / cm 3 or less.
3. The gallium nitride substrate according to claim 1, wherein the dislocation density is 1 × 10 6 cm −2 or less.
The gallium nitride substrate according to any one of claims 1 to 3, which has an absorption coefficient of 4 cm -1 or less for light having a wavelength of 400 to 1,500 nm.
The gallium nitride substrate according to any one of claims 1 to 4, which has a resistivity of 10 2 Ωcm or less.
The nitride according to any one of claims 1 to 5, wherein the high-intensity light emitting portion includes a portion extending along an m-plane of a gallium nitride crystal constituting the gallium nitride substrate. Gallium substrate.
The gallium nitride substrate according to claim 6, wherein the high brightness light emitting portion extends substantially along the m plane of the gallium nitride crystal.
The gallium nitride substrate according to any one of claims 1 to 7, wherein the half width of (0002) plane reflection of the X-ray rocking curve on the upper surface is 3000 seconds or less and 20 seconds or more. .
The gallium nitride substrate according to any one of claims 1 to 8, wherein no void is observed in a cross section substantially perpendicular to the upper surface of the gallium nitride substrate.
10. The high-intensity light emitting portion forms a continuous phase, and the low-intensity light emitting region forms a discontinuous phase partitioned by the high-intensity light emitting portion. A gallium nitride substrate according to any one of the claims.
The gallium nitride substrate according to any one of claims 1 to 10, wherein the half value width of (1000) plane reflection of the X-ray rocking curve on the upper surface is 10000 seconds or less and 20 seconds or more. .
A freestanding substrate comprising the gallium nitride substrate according to any one of claims 1 to 11.
A functional device comprising: the self-supporting substrate according to claim 12; and a functional layer provided on the upper surface of the gallium nitride substrate.
The functional device according to claim 13, wherein the function of the functional layer is a light emitting function, a rectifying function or a power control function.
A composite substrate, comprising: a support substrate; and the gallium nitride substrate according to any one of claims 1 to 11 provided on the support substrate.
A functional element comprising: the composite substrate according to claim 15; and a functional layer provided on the upper surface of the gallium nitride substrate.
The functional device according to claim 16, wherein the function of the functional layer is a light emitting function, a rectifying function or a power control function.