JP2022054987A - Method for manufacturing nitride semiconductor laminate, and nitride semiconductor laminate - Google Patents

Abstract

To provide: a method for manufacturing a nitride semiconductor laminate capable of reducing on-resistance and obtaining high breakdown voltage; and the nitride semiconductor laminate.SOLUTION: A method for manufacturing a nitride semiconductor laminate includes forming an AlxGa(1-x) N layer 12 formed in AlxGa(1-x) N (0≤x≤0.2) at a growth rate of 0.7 μm/hr or more by an organic metal vapor phase growth method on a nitride semiconductor substrate 11 having a temperature of 650°C or more and less than 1000°C and including Al so that the coverage of the AlxGa(1-x) N layer to the direct under layer is 80% or more and 100% or less. The relaxation rate of the AlxGa(1-x) N layer 12 in a region of 0.5-5-nm from the nitride semiconductor substrate 11 side is 0-50% to the nitride semiconductor substrate 11, and the relaxation rate of the AlxGa(1-x) N layer 12 in a region of more than 5 nm and 30 nm or less from the nitride semiconductor substrate 11 side is 50-100% to the nitride semiconductor substrate 11.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a method for manufacturing a nitride semiconductor laminate and a nitride semiconductor laminate.

The nitride semiconductor laminate has a structure in which nitride semiconductors having different band gaps are laminated, and a two-dimensional carrier gas is induced at the interface between the nitride semiconductors. Conventionally, a high electron mobility transistor (HEMT) device using such a two-dimensional carrier gas has been manufactured.

A power device made of a general nitride semiconductor laminate has an AlGaN barrier layer provided on a GaN substrate (for example, Patent Document 1). Further, in order to increase the withstand voltage of the power device, a method of growing a nitride semiconductor laminate on an AlN substrate having a wider bandgap to create a power device on the AlN substrate is disclosed (for example, Patent Document). 2).

Japanese Patent Application Laid-Open No. 2009-49121 Public Relations

Sumitomo Electric Technical Review No. 180, page 83 (2012)

Nitride power devices are required to have further improved withstand voltage and lower on-resistance. However, in the above-mentioned power device, the electron mobility of the two-dimensional carrier gas generated at the interface is lowered due to the alloy scattering of AlGaN. Since the on-resistance is determined by the electron mobility of the two-dimensional carrier gas and the concentration of the carrier gas, the on-resistance deteriorates due to the decrease in the electron mobility of the two-dimensional carrier gas.
An object of the present disclosure is to provide a method for manufacturing a nitride semiconductor laminate capable of reducing on-resistance and obtaining a high withstand voltage, and to provide a nitride semiconductor laminate.

In order to solve the above-mentioned problems, the method for producing a nitride semiconductor laminate according to the embodiment of the present disclosure is to use an organic metal-based material on a nitride semiconductor substrate containing Al having a temperature of 650 ° C. or higher and lower than 1000 ° C. The Al _x Ga _(1-x) N layer formed by Al _x Ga _(1-x) N (0 ≦ x ≦ 0.2) at a growth rate of 0.7 μm / hr or more by the phase growth method is directly underneath. It is characterized in that the Al x Ga (1-x) N layer is formed so that the coverage of the Al _x Ga _(1-x) N layer with respect to the layer is 80% or more and 100% or less.

Further, the nitride semiconductor laminate according to the embodiment of the present disclosure includes a nitride semiconductor substrate containing Al and Al _x Ga _(1-x) N (0 ≦ x ≦ 0) arranged on the nitride semiconductor substrate. The Al _{x Ga (1-x) N layer formed in 2.) is provided, and the coverage of the Al x Ga ( 1-x)} N layer with respect to the layer immediately below is 80% or more and 100% or less. It is characterized by.

According to the present disclosure, it is possible to obtain a method for manufacturing a nitride semiconductor laminate and a nitride semiconductor laminate that can reduce on-resistance and obtain a high withstand voltage.

It is sectional drawing which shows one structural example of the nitride semiconductor laminate which concerns on 1st Embodiment of this disclosure. It is sectional drawing which shows the other structural example of the nitride semiconductor laminate which concerns on 1st Embodiment of this disclosure. It is sectional drawing which shows the other structural example of the nitride semiconductor laminate which concerns on 1st Embodiment of this disclosure.

Hereinafter, the nitride semiconductor laminate according to the present embodiment will be described through the embodiments, but the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential to the means of solving the invention.

1. 1. First Embodiment Hereinafter, the nitride semiconductor laminate 1 according to the first embodiment will be described with reference to FIG.
The nitride semiconductor laminate 1 is a semiconductor element capable of emitting ultraviolet light.

(1.1) Configuration of Nitride Semiconductor Laminate with reference to FIG. 1, the nitride semiconductor laminate 1 according to the first embodiment will be described. The nitride semiconductor laminate 1 is arranged on a nitride semiconductor substrate (hereinafter referred to as a substrate) 11 containing Al and the substrate 11, and is Al _x Ga _(1-x) N (0 ≦ x ≦ 0.2). The Al _x Ga _(1-x) N layer 12 is provided, and the coverage of the Al _x Ga _(1-x) N layer with respect to the layer immediately below is 80% or more and 100% or less. Such a _nitride semiconductor laminate 1 _is formed on a substrate 11 containing Al having a temperature of 650 ° C. or higher and lower than 1000 ° C. at a growth rate of 0.7 μm / hr or higher by an organic metal vapor phase growth method. _1-x) It is formed by forming the Al _x Ga _(1-x) N layer 12 formed by N (0 ≦ x ≦ 0.2).
Hereinafter, each layer will be described in detail.

(substrate)
The substrate 11 contains a nitride semiconductor containing Al. The nitride semiconductor containing Al is, for example, AlN. The nitride semiconductor containing Al is not limited to AlN, and may be, for example, AlGaN. For example, when the substrate 11 is a nitride semiconductor single crystal substrate such as AlN or AlGaN, the lattice constant difference from the nitride semiconductor layer formed on the upper side of the substrate 11 becomes small, and the nitride semiconductor layer is used in a lattice matching system. Penetration shifts can be reduced by growing.

Here, "contains" in the expression "the substrate 11 includes ... a nitride semiconductor" means that the nitride semiconductor is mainly contained in the layer, but the expression also includes other elements. Is done. Specifically, minor changes to the composition of this layer are made by adding a small amount of other elements (for example, Ga (when Ga is not the main element), or adding an element such as In, As, P, or Sb to a few percent or less). The case of adding is also included in this expression. In the expression of the composition of other layers, the word "contains" has the same meaning. Further, the small amount of elements contained is not limited to the above.

Further, the substrate 11 may be doped into n-type or p-type by a donor impurity or an acceptor impurity. Further, the substrate 11 may be a mixed crystal of a nitride semiconductor such as AlN and sapphire (Al ₂ O ₃ ), Si, SiC, MgO, Ga ₂ O ₃ , ZnO, GaN or InN.

As an example, the substrate 11 preferably has a film thickness of 100 μm or more and 600 μm or less.
The plane orientation includes c-plane (0001), a-plane (11-20), m-plane (10-10), and the like, but a c-plane substrate is more preferable.

(Al _x Ga _(1-x) N layer)
The Al _x Ga _(1-x) N layer 12 is formed by Al _x Ga _(1-x) N (0 ≦ x ≦ 0.2), that is, Al _x Ga ₍ 1-x) having an Al composition of 0% or more and 20% or less. ₎ It is a nitride semiconductor layer formed by N. The Al _x Ga _(1-x) N layer 12 is formed on the substrate 11. Here, for example, the word "on" in the expression "Al _x Ga _(1-x) N layer 12 is formed on the substrate 11" means Al _x Ga _(1-x) N on the substrate 11. It means that the layer 12 is formed. Further, the case where another layer is further present between the substrate 11 and the Al _x Ga _(1-x) N layer 12 is also included in the above expression. The word "above" has the same meaning in the relationships between other layers. For example, the case where a buffer layer is formed between the substrate 11 and the Al _x Ga _(1-x) N layer 12 is also included in the expression “formed on the substrate 11”.

Consider the case where Al _x Ga _(1-x) N is grown on a substrate containing Al (for example, an AlN substrate). Al N and Al _x Ga _(1-x) N each have spontaneous polarization and are polarized in the c-axis direction. When layers with different polarizations are laminated, charges are generated at the interface by the difference in polarization. Piezopolarization also occurs due to the distortion of the lattice. Carriers in the semiconductor layer are induced by this piezo polarization and spontaneous polarization, and a high-concentration sheet-like two-dimensional carrier layer is formed at the interface.

When, for example, GaN (Al _x Ga _(1-x) N having an Al composition of 0%) is formed on AlN, a two-dimensional whole gas is formed at the interface between AlN and GaN. When an Al _0.2 Ga _0.8 N layer or the like is laminated on GaN as an electron barrier layer, a two-dimensional electron gas (2DEG) is formed at the interface between GaN and Al _0.2 Ga _0.8 N. To.
Since the two-dimensional carrier gas has high saturated electron mobility, high frequency characteristics can be obtained. In addition, a power device having both low on-resistance due to high electron mobility and high withstand voltage characteristics due to a wide band gap can be obtained. Here, the on-resistance is determined by the electron mobility of the two-dimensional carrier gas and the concentration of the two-dimensional carrier gas. Lower sheet resistance, including both electron mobility and concentration parameters described above, is advantageous for reducing on-resistance. The withstand voltage is determined by the band gap of the nitride semiconductor constituting the HEMT.

The formation of such a two-dimensional carrier gas is affected by polarization or strain. When forming this 2DEG at a higher concentration and higher electron mobility, it is necessary to consider the influence of alloy scattering. This is because if the Al composition x in the Al _x Ga _(1-x) N layer 12 is too high, the electron mobility is significantly reduced due to alloy scattering.

The Al _x Ga _(1-x) N layer 12 is a layer of a nitride semiconductor containing Al and Ga or Ga, and may be, for example, AlGaN or GaN. From the viewpoint of alloy scattering, the Al _x Ga _(1-x) N layer is preferably Al _x Ga _(1-x) N (0 ≦ x ≦ 0.2). When the nitride semiconductor laminate 1 is used in a power device, it is more preferably GaN (x = 0) from the viewpoint of achieving both 2DEG concentration and electron mobility.
Further, a buffer layer that alleviates the lattice mismatch may exist between the substrate 11 and the Al _x Ga _(1-x) N layer 12. However, from the viewpoint of increasing the concentration of 2DEG, it is preferable that no buffer layer is provided at the interface between the substrate 11 and the Al _x Ga _(1-x) N layer 12. Here, examples of the buffer layer include a composition gradient layer in which the Al composition decreases in the direction away from the substrate 11.

The steepness of the interface is important for increasing the concentration of 2DEG, and from this viewpoint, the film thickness of the Al _x Ga _(1-x) N layer 12 is preferably 0.5 nm or more and 30 nm or less.
Further, the relaxation rate in the region of 0.5 nm or more and 5 nm or less from the Al _x Ga _(1-x) N layer 12 substrate 11 side is preferably 0% or more and 50% or less. Further, if the Al _x Ga _(1-x) N layer 12 is distorted by 5 nm or more from the substrate 11 side, the crystal quality is impaired. Therefore, the relaxation rate in the region of more than 5 nm and 30 nm or less from the substrate 11 side of the Al _x Ga _(1-x) N layer 12 is preferably distorted by 50% or more and 100% or less with respect to the substrate 11.

From the viewpoint of distorting the Al _x Ga _(1-x) N layer 12 from the original lattice constant, the a-axis in the region of 0.5 nm or more and 5 nm or less from the substrate 11 side of the Al _x Ga _(1-x) N layer 12. The in-plane lattice constant in the direction is preferably distorted by 0.5% or more and 2.5% or less, and more preferably 1.0% or more and 2.5% or less with respect to the lattice constant of the substrate 11.
However, if the Al _x Ga _(1-x) N layer 12 is distorted by 5 nm or more from the substrate 11 side, the crystal quality is impaired. Therefore, the in-plane lattice constant in the a-axis direction in the region of more than 5 nm and 30 nm or less from the substrate 11 side of the Al _x Ga _(1-x) N layer 12 is 0% or more and 1% or less with respect to the lattice constant of the substrate 11. It is preferable that it is distorted by.

Similarly, from the viewpoint of distorting the Al _x Ga _(1-x) N layer 12 from the original lattice constant, in the region of 0.5 nm or more and 5 nm or less from the substrate 11 side of the Al _x Ga _(1-x) N layer 12. Is preferably free of misfit dislocations or stacking defects. Here, "there is no misfit dislocation or stacking defect" in the present disclosure means that the dislocation density measured by the method described later is less than 1 × 10 ⁴ cm ^-3 . Further, "misfit dislocation" and "stacking defect" will be described in detail later.
However, as described above, if the Al _x Ga _(1-x) N layer 12 is distorted by 5 nm or more, the crystal quality is impaired. Therefore, it is preferable that misfit dislocations or stacking defects are present in the region of the Al _x Ga _(1-x) N layer 12 from the substrate 11 side to more than 5 nm and 30 nm or less. Here, in the present disclosure, "there is a misfit dislocation or a stacking defect" means that the dislocation density measured by the method described later is 1 × 10 ⁴ cm ^-3 or more.
Since 2DEG has high mobility, a power device using the nitride semiconductor laminate 1 can obtain high frequency characteristics. Therefore, high-quality crystallinity and steepness of the interface in the nitride semiconductor laminate 1 are desired.

From the viewpoint of increasing the electron mobility of the 2DEG, the coverage of the Al _x Ga _(1-x) N layer 12 with respect to the layer directly below is 80% or more and 100% or less.
From the viewpoint of high crystal quality, the dislocation density contained in the Al _x Ga _(1-x) N layer 12 is preferably 1 × 10 ⁴ cm ^-3 or less.
From the viewpoint of the steepness of the interface, the surface roughness of the surface of the Al _x Ga _(1-x) N layer 12 is preferably 0.9 nm or less. Here, the surface-squared roughness of the surface of the Al _x Ga _(1-x) N layer 12 is the surface-squared roughness of the Al _x Ga _(1-x) N layer 12 on the surface opposite to the substrate 11.
As a result, 2DEG with high concentration and high electron mobility is realized.

Al _x Ga _(1-x) N layer 12 is mixed with group V elements other than N such as P, As and Sb, and impurities such as C, H, F, O, Be, Mg, Zn and Si. It is good, but the type of impurity element is not limited to this.

(1.2) Modification Example of Nitride Semiconductor Laminate (1.2.1) First Example of Modification In the above-mentioned nitride semiconductor laminate 1, the Al _x Ga _(1-x) N layer 12 emits light. It may be a light emitting device used as a p-type semiconductor layer of the device. For example, as shown in FIG. 2, the nitride semiconductor laminate 1A includes a light emitting layer 14 provided between the substrate 11 and the Al _x Ga _(1-x) N layer 12. That is, the nitride semiconductor laminate 1A as a light emitting element is, for example, a substrate 11, an n-type semiconductor layer 13, a light emitting layer 14 including a nitride semiconductor active layer, and Al _x Ga _(1-x) N as a p-type semiconductor layer. The layers 12 are laminated in this order. At this time, the Al _x Ga _(1-x) N layer 12 is formed of, for example, p-type GaN (x = 0). Further, the nitride semiconductor laminate 1A may have an Al _x Ga _(1-x) N layer 12 grown on an electron block layer (not shown) formed of, for example, AlN or AlGaN. In this case, the electron block layer is provided between the light emitting layer 14 and the Al _x Ga _(1-x) N layer 12.
When the Al _x Ga _(1-x) N layer 12 is used as the p-type semiconductor layer, the Al _x Ga _(1-x) N layer 12 preferably contains Mg, Zn or Be as a dopant atom. The concentration of the dopant atom (p-type doping concentration) is preferably 1 × 10 ¹⁸ cm ^-3 or more and 5 × 10 ¹⁹ cm ^-3 or less from the viewpoint of achieving both crystal quality and carrier concentration.

(1.2.2) Second Example of Modification In the above-mentioned nitride semiconductor laminate 1, the Al N layer 15 provided between the substrate 11 and the Al _x Ga _(1-x) N layer 12 is provided. Alternatively, the electron barrier layer 17 provided on the Al _x Ga _(1-x) N layer 12 may be provided.
Hereinafter, the AlN layer 15, the composition gradient layer 16 and the electron barrier layer 17, which are examples of the buffer layer, will be described in detail with reference to FIG.

(Electronic barrier layer)
The nitride semiconductor laminate 1B may be provided with an electron barrier layer 17 on the Al _x Ga _(1-x) N layer 12. The electron barrier layer 17 is a layer provided for forming a two-dimensional electron gas (2DEG) at an interface with, for example, an Al _x Ga _(1-x) N layer 12.
The electron barrier layer 17 is a layer of a nitride semiconductor containing Al and Ga or Ga. The electron barrier layer 17 is formed by Al _y Ga ₍ 1- _{y )} N (0 ≦ y ≦ 1) from the viewpoint of lattice matching with Al _x Ga _(1-x) N layer 12. _{-Y) The} N layer is preferable. Further, the electron barrier layer 17 includes Group III atoms other than Al and Ga such as In, Group V elements other than N such as P, As and Sb, C, H, F, O, Be, Mg, Zn, Si and the like. It may contain impurities of, but the type of impurity elements is not limited to this.

A two-dimensional carrier layer is formed at the interface between the electron barrier layer 17 and the Al _x Ga _(1-x) N layer 12 in the same manner as the interface between the substrate 11 and the Al _x Ga _(1-x) N layer 12. Therefore, it is preferable that the Al composition x in the Al _x Ga _(1-x) N layer 12 and the Al composition y in the electron barrier layer 17 are different (that is, x ≠ y).

From the viewpoint of forming two-dimensional electron gas, it is preferable that the Al composition x in the Al _x Ga _(1-x) N layer 12 is smaller (x <y) than the Al composition y in the electron barrier layer 17. Further, if the difference between the Al composition x and y in each layer is too large, cracks may occur in the Al _x Ga _(1-x) N layer 12 and the electron barrier layer 17. Therefore, the difference between the Al composition x in the Al _x Ga _(1-x) N layer 12 and the Al composition y in the electron barrier layer 17 is preferably 0.5 or less. Further, the Al composition x in the Al _x Ga _(1-x) N layer 12 is preferably 0 ≦ x ≦ 0.2, and the Al composition y in the electron barrier layer 17 is 0.2 <y ≦ 0. 5 is more preferable.

(Composition inclined layer)
The composition gradient layer 16, which is an example of the buffer layer described above, may be provided between the substrate 11 and the Al _x Ga _(1-x) N layer 12, but from the viewpoint of increasing the concentration of 2DEG, the composition may be provided. It is preferable that the inclined layer 16 is not provided.
When the composition inclined layer 16 is provided, the composition inclined layer 16 is formed of Al _z Ga _(1-z) N (0 ≦ z ≦ 1.0), and the Al composition z changes in the direction away from the substrate 11. ing. It is preferable that the Al composition z of the composition inclined layer 16 decreases in the direction away from the substrate 11.

The profile (inclination) of Al composition z in the composition inclined layer 16 may change continuously or intermittently. Here, "intermittently changing" means that the film of the composition gradient layer 16 includes a portion having the same Al composition z. That is, the composition inclined layer 16 may include a portion where the Al composition z does not change in the direction away from the substrate 11.

The composition inclined layer 16 may be in contact with the substrate 11, or another layer may be present between the composition inclined layer 16 and the substrate 11. Further, the composition inclined layer 16 may be in contact with the Al _x Ga _(1-x) N layer 12, and another layer is present between the composition inclined layer 16 and the Al _x Ga _(1-x) N layer 12. May be good.

(AlN layer)
The AlN layer 15 is an example of a base layer, and is formed on the entire surface of the substrate 11. That is, the AlN layer 15 is provided between the substrate 11 and the Al _x Ga _(1-x) N layer 12.
The AlN layer 15 can recover pits and polishing marks formed on the surface of the substrate. Further, the difference in lattice constant and the difference in coefficient of thermal expansion between the Al _x Ga _(1-x) N layer 12 is small, and a nitride semiconductor layer having few defects can be grown on the Al N layer 15. Further, the Al N layer 15 can grow the Al _x Ga _(1-x) N layer 12 under compressive stress, and can suppress the generation of cracks in the Al _x Ga _(1-x) N layer 12. .. Therefore, even when the substrate 11 is formed of a nitride semiconductor such as AlN or AlGaN, a nitride semiconductor layer having few defects can be grown above the substrate 11 via the AlN layer 15.

Impurities such as C, B, O, H, Si, Fe, and Mg may be mixed in the AlN layer 15.
When AlN is used as the material for forming the substrate 11, the boundary between the AlN layer 15 and the substrate 11 becomes unclear because the AlN layer 15 and the substrate 11 are formed of the same material. When the substrate 11 is made of AlN, it may be considered that the substrate 11 constitutes the substrate 11 and the AlN layer 15.

The AlN layer 15 has a thickness of, for example, several μm. Specifically, the thickness of the AlN layer 15 is preferably thicker than 10 nm and thinner than 1 μm. When the thickness of the AlN layer 15 is thicker than 10 nm, the recovery of the substrate surface proceeds and the crystallinity of AlN becomes high. Further, from the viewpoint of raw material cost, it is preferable that the thickness of the AlN layer 15 is thinner than 1 μm.

(1.3) Method for Manufacturing Nitride Semiconductor Laminate The Nitride Semiconductor Laminate 1 of the present embodiment is formed of Al _x Ga _(1-x) N (0 ≦ x ≦ 0.2) on the substrate 11. It is manufactured through a step of forming an Al _x Ga _(1-x) N layer 12.
The substrate 11 is formed by a vapor phase growth method such as a sublimation method and a hydride Vapor Phase Epitaxy (HVPE) method, and a general substrate growth method such as a liquid phase growth method.

The step of forming the Al _x Ga _(1-x) N layer 12 on the substrate 11 can be performed by a metal organic chemical vapor deposition (MOCVD) method.
Here, the Al _x Ga _(1-x) N layer 12 formed on the substrate 11 contains, for example, an Al raw material containing trimethylaluminum (TMAl), for example, trimethylgallium (TMGa), triethylgallium (TEGa), or the like. It can be formed using a raw material, for example, an N raw material containing aluminum (NH ₃ ).

The Al _x Ga _{(1-x) N} layer 12 is formed on a substrate 11 containing Al having a temperature of 650 ° C. or higher and lower than 1000 ° C. at a growth rate of 0.7 μm / hr or higher by an organic metal vapor phase growth method. The Al _x Ga _(1-x) N layer formed by Ga _(1-x) N (0 ≦ x ≦ 0.2) may be formed, and other conditions are not particularly limited. Further, the growth rate of the Al _x Ga _(1-x) N layer 12 is more preferably less than 2 μm / hr.
By setting the growth rate of Al _x Ga _(1-x) N at the time of forming the Al _x Ga _(1-x) N layer 12 to 0.7 μm / hr or more, the sheet resistance is reduced and the electron mobility is improved. do. The growth rate of the Al _x Ga _(1-x) N layer 12 can be controlled to 0.7 μm / hr or more by appropriately adjusting the temperature of the substrate 11 described later, the degree of vacuum of the chamber, and the flow rate of the raw material gas. ..

At this time, from the viewpoint of improving the sheet resistance and electron mobility of the nitride semiconductor laminate 1, the temperature of the substrate 11 at the time of forming the Al _x Ga _(1-x) N layer 12 shall be 700 ° C. or higher and 950 ° C. or lower. Is preferable, and it is more preferable that the temperature is 750 ° C. or higher and 950 ° C. or lower.
Further, from the viewpoint of removing impurities, it may be preferable to anneal the substrate 11 in a hydrogen atmosphere of 1000 ° C. or higher, preferably 1200 ° C. or higher.

Further, from the viewpoint of improving sheet resistance and electron mobility, the vacuum degree of the chamber at the time of forming the Al _x Ga _(1-x) N layer 12 is preferably 30 mbar or more and 200 mbar or less, and is 30 mbar or more and 100 mbar or less. Is more preferable.

(1.4) Method for Measuring Physical Properties, etc. of Nitride Semiconductor Laminate The physical properties, etc. of the above-mentioned nitride semiconductor laminate 1 can be measured as follows.
(Measurement of coverage of Al _x Ga _(1-x) N layer)
For measuring the coverage of the Al _x Ga _(1-x) N layer 12, for example, a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, FE-SEM "SU9000") and image processing software (manufactured by Asahi Kasei Engineering Co., Ltd.) Image analysis software "A image-kun" (registered trademark) is used. More specifically, at the time of SEM measurement, any three points in the plane are measured in a measurement range of 50 μm × 50 μm at the portion where the surface of the Al _x Ga _(1-x) N layer 12 is exposed. At this time, by acquiring the reflected electron image by the lower detector, an SEM image in which the contrast due to the composition difference is clear can be obtained.

The obtained SEM image is processed using image processing software. The region where the brightness is 50% or more lower than the average brightness in the SEM image is defined as a portion where the Al _x Ga _(1-x) N layer 12 is not covered with respect to the substrate 11 which is the layer directly below. The coverage is the ratio of the covered area, and the average value of any three points is the coverage of the Al _x Ga _(1-x) N layer 12.

An atomic force microscope (AFM) device (manufactured by Seiko Instruments Co., Ltd., "SPA400") is used for measuring the surface roughness. Arbitrary three points in the plane are measured in a measurement range of 4 μm × 4 μm by AFM at the same points as the coverage measurement. The scan frequency at this time was 0.2 Hz. The average value of the three points of the root mean square roughness obtained by the measurement is taken as the surface roughness of the Al _x Ga _(1-x) N layer 12.

(Measurement of Al _x Ga _(1-x) N Layer Doping Atom Concentration)
The concentration of dopants and impurities contained in the Al _x Ga _(1-x) N layer 12 can be measured by secondary ion mass spectrometry (SIMS).
When measuring the concentration of dopants and impurities contained in the Al _x Ga _(1-x) N layer 12 by SIMS after being processed into a device, the electrode should be removed by chemical etching or physical polishing. Can be done. Further, the concentration of the dopant and the impurities contained in the Al _x Ga _(1-x) N layer 12 can be measured by sputtering from the substrate 11 side on which the electrode is not formed.
Specifically, SIMS measurement is performed under the measurement conditions provided by Evans Analytical Group (EAG). A cesium (Cs) ion beam having an energy of 14.5 keV is used for sputtering the sample at the time of measurement.

(Al _x Ga _(1-x) N layer film thickness and through-dislocation measurement method)
The thickness of the Al _x Ga _(1-x) N layer 12 is determined by cutting out a predetermined cross section perpendicular to the substrate 11 and observing this cross section with a transmission electron microscope (TEM) to measure the length of the TEM. Can be measured by using. For TEM measurement, for example, a transmission electron microscope "HD-2300" manufactured by Hitachi High-Technologies Corporation is used.
As a measuring method, first, a TEM is used to observe a cross section perpendicular to the main surface of the substrate 11 of the nitride semiconductor laminate. As an example, the measurement on the a-plane (11-20) is preferable. Specifically, for example, in a TEM image showing a cross section perpendicular to the main surface of the substrate 11 of the nitride semiconductor laminate 1, a range of 2 μm or more is observed in a direction parallel to the main surface of the substrate 11. The width. Since contrast is observed at the interface between the two layers having different compositions within this observation width range, the thickness up to this interface is observed in a continuous observation region having a width of 200 nm. The film thickness of each layer can be obtained by calculating the average value of the thickness of each layer included in the observation region having a width of 200 nm from the five points arbitrarily extracted from the observation width of 2 μm or more described above.

Similarly, for the through-translocations, the number of through-translocations per volume is calculated from the number of through-translocations existing in the cross section perpendicular to the main surface of the substrate 11, the viewing area, and the thickness of the sample. The penetrating dislocations are calculated from 5 samples, and the average value thereof is taken as the number of penetrating dislocations.

(Measurement of strain and misfit dislocations and stacking defects of nitride semiconductor layer)
The atomic arrangement of each layer constituting the nitride semiconductor laminate 1 can be measured by high-resolution TEM measurement. High-resolution TEM measurement is performed with an atomic resolution analysis electron microscope (acceleration voltage: 200 kV) for the sample stripped to 50 nm during the above-mentioned TEM measurement. For high-resolution TEM measurement, for example, an atomic resolution analysis electron microscope "JEM-ARM200F" manufactured by JEOL Ltd. is used.

At this time, if group III atoms and nitrogen atoms are alternately stacked and a state in which group III atoms are vertically arranged (that is, there is no deviation) is observed, the state of each layer is observed. It can be determined that the atomic arrangement is lattice-matched.

The presence of misfit dislocations and stacking defects can be confirmed from this atomic arrangement. When there is a place where the vertical arrangement of Group III atoms is arranged by skipping one atom, for example, this is called a misfit dislocation. In Group III atoms that are aligned in the horizontal direction without deviation, when two layers are gathered in one layer, this is regarded as a stacking defect. The dislocation density is calculated from the volume obtained from the film thickness and the sample thickness and the number of misfit dislocations and stacking defects.

Next, the distance between adjacent atoms in the horizontal direction of the TEM image of Group III atoms is measured. The distance between adjacent atoms is measured by measuring the distance between the centers of atomic contrast. This distance between adjacent atoms is measured in the Al _x Ga _(1-x) N layer 12 in the vertical direction. Al _x Ga _(1-x) The measurement is performed at a position in the N layer 12 at an arbitrary film thickness to be measured. From the measured interatomic distance, the strain factor can be obtained using Eq. (1).

Lattice distortion rate [%] = [(a1-a2) / a1] × 100 ... Equation (1)
Here, a1 in the equation is the original lattice constant of the Al _x Ga _(1-x) N layer 12 in the in-plane a-axis direction, and a2 is the Al _x after being distorted to match the lattice constant of the substrate 11. Ga _(1-x) Let it be the lattice constant of the N layer 12.
The grid distortion factor obtained by the equation (1) is measured at any three points in the image, and the average value thereof is taken as the grid strain factor.

Here, the original lattice constant a1 is a lattice constant of 3.18 Å in the a-axis direction when the Al _x Ga _(1-x) N layer 12 is GaN, and the Al _x Ga _(1-x) N layer 12 Is Al _x Ga _(1-x) N (0 <x ≦ 0.2), which is the lattice constant of the a-axis in the Al composition x. The lattice constant of the a-axis in the Al composition x is calculated by the Boeing rule using the lattice constant of AlN in the a-axis direction of 3.11 Å and the lattice constant of GaN in the a-axis direction of 3.18 Å. Calculated in (2).

A-axis lattice constant [Å] in Al composition x = 3.18 × (1-x) +3.11 × x ... Equation (2)

(Al _x Ga _(1-x) Method for measuring Al composition and relaxation rate of N layer)
The relaxation rate can be measured, for example, by performing a reciprocal lattice mapping measurement (RSM: Reciprocal Space Mapping) by an X-ray diffraction (XRD: X-Ray Diffraction) method. For XRD measurement, for example, "X'pert3 MRD" manufactured by PANalytical Co., Ltd. is used. In this case, in a state where the tube is 45 kV / 40 mA, a radiation source parallelized using a dicrystal Ge (220) is used, the incident solar slit is 0.04 °, and the detector slit is 1/16 mm. Axialization is performed on the (20-24) plane peak of the substrate 11. After that, the 2θ / ω scan is measured, and the 2θ / ω scan is repeated while changing ω in the range of ± 1.5 ° at 0.05 ° intervals. Spatial coordinates Qx and Qy are calculated from such measurements, and the relaxation rate and Al composition with respect to the substrate 11 are calculated.

(1.5) Effect of First Embodiment The nitride semiconductor laminate according to the first embodiment has the following effects.
(1) The nitride semiconductor laminate 1 is formed of a nitride semiconductor substrate containing Al and Al _x Ga _(1-x) N (0 ≦ x ≦ 0.2) arranged on the nitride semiconductor substrate. It also has an Al _x Ga _(1-x) N layer.
This reduces the influence of alloy scattering of Al _{x Ga (1-x) N constituting the Al x Ga ( 1-x)} N layer, suppresses the decrease in electron mobility of the two-dimensional carrier gas, and lowers the on. A resistance can be obtained, and a high withstand voltage equivalent to that of a nitride semiconductor containing Al can be obtained.
(2) In the nitride semiconductor laminate 1, the coverage of the Al _x Ga _(1-x) N layer with respect to the layer immediately below is 80% or more and 100% or less.
As a result, the electron mobility of the 2DEG can be increased to obtain a lower on-resistance.

(3) In the nitride semiconductor laminate 1, the nitride semiconductor substrate is preferably an AlN single crystal substrate.
As a result, the through-dislocation of the nitride semiconductor layer formed on the upper side of the substrate 11 can be reduced, so that the crystal becomes high quality and the nitride semiconductor laminate 1 suitable for the power device can be obtained.
(4) In the nitride semiconductor laminate 1, the film thickness of the Al _x Ga _(1-x) N layer is preferably 0.5 nm or more and 30 nm or less.
As a result, the lattice constant of the Al _x Ga _(1-x) N layer 12 can be distorted from the original lattice constant to increase the concentration of 2DE, and a lower on-resistance can be obtained.

(5) In the nitride semiconductor laminate 1, the relaxation rate in the region of 0.5 nm or more and 5 nm or less from the substrate 11 side of the Al _x Ga _(1-x) N layer 12 is 0% or more and 50% with respect to the substrate 11. The following is preferable. Further, the relaxation rate in the region of more than 5 nm and 30 nm or less from the substrate 11 side of the Al _x Ga _(1-x) N layer 12 is preferably 50% or more and 100% or less with respect to the substrate 11.
This makes it possible to increase the concentration of 2DE and obtain lower on-resistance.
(6) In the nitride semiconductor laminate 1, the penetration dislocation density contained in the Al _x Ga _(1-x) N layer is preferably 1 × 10 ⁴ cm ^-3 or less.
As a result, the crystal becomes high quality, and the nitride semiconductor laminate 1 suitable for a power device can be obtained.

(7) In the nitride semiconductor laminate 1, there shall be no misfit dislocations or stacking defects in the region of 0.5 nm or more and 5 nm or less from the nitride semiconductor substrate side of the Al _x Ga _(1-x) N layer. preferable.
As a result, the crystal becomes high quality, and the nitride semiconductor laminate 1 suitable for a power device can be obtained.
(8) In the nitride semiconductor laminate 1, it is preferable that misfit dislocations or stacking defects are present in a region of more than 5 nm and 30 nm or less from the nitride semiconductor substrate side of the Al _x Ga _(1-x) N layer.
As a result, the Al _x Ga _(1-x) N layer 12 can be prevented from being distorted by 5 nm or more, and the deterioration of the crystal quality can be suppressed.

(9) In the nitride semiconductor laminate 1, the surface roughness of the Al _x Ga _(1-x) N layer is preferably 0.9 nm or less.
As a result, the steepness of the interface between the Al _x Ga _(1-x) N layer and the electron barrier layer can be improved, and damage to the crystal quality can be suppressed.
(10) In the nitride semiconductor laminate 1, the in-plane lattice constant in the a-axis direction in the region of 0.5 nm or more and 5 nm or less from the nitride semiconductor substrate side of the Al _x Ga _(1-x) N layer is the nitride semiconductor. It is preferably distorted by 0.5% or more and 2.5% or less with respect to the lattice constant of the substrate.
As a result, the Al _x Ga _(1-x) N layer can be distorted from the original lattice constant to increase the concentration of 2DEG.

(11) In the nitride semiconductor laminate 1, in the Al _x Ga _(1-x) N layer, the in-plane lattice constant in the a-axis direction in the region of more than 5 nm and 30 nm or less from the nitride semiconductor substrate side is the nitride semiconductor substrate. It is preferable that the strain is distorted by 0% or more and 1% or less with respect to the lattice constant of.
As a result, the Al _x Ga _(1-x) N layer 12 can be prevented from being distorted by 5 nm or more, and the deterioration of the crystal quality can be suppressed.
(12) In the nitride semiconductor laminate 1, the Al _x Ga _(1-x) N layer contains Mg, Zn or Be as a dopant atom in an amount of 1 × 10 ¹⁸ cm ^-3 or more and 5 × 10 ¹⁹ cm ^-3 or less. Is preferable.
As a result, it is possible to obtain a nitride semiconductor laminate 1 suitable for a power device because the crystal quality and the carrier concentration are compatible with each other.

(13) In the nitride semiconductor laminate 1, it is preferable that the Al _x Ga _(1-x) N layer is formed of GaN.
As a result, it is possible to obtain a device having both 2DEG concentration and electron mobility, and having lower on-resistance and higher withstand voltage.
(14) In the nitride semiconductor laminate 1, a composition gradient layer whose Al composition decreases in the thickness direction of the substrate is provided between the nitride semiconductor substrate and the Al _x Ga _(1-x) N layer. It is preferable that there is no such thing.
This makes it possible to increase the concentration of 2DEG.
(15) The nitride semiconductor laminate 1 further includes a light emitting layer provided between the substrate 11 and the Al _x Ga _(1-x) N layer 12, and the Al _x Ga (1-x ₎ N layer 12 is further provided. It is preferable that the p-type doping concentration is 1 × 10 ¹⁸ cm ^-3 or more and 5 × 10 ¹⁹ cm ^-3 or less.
As a result, the nitride semiconductor laminate 1 can also be used as a light emitting device.

(16) In the method for producing the nitride semiconductor laminate 1, a growth rate of 0.7 μm / hr or more is obtained by an organic metal vapor phase growth method on a nitride semiconductor substrate containing Al having a temperature of 650 ° C or higher and lower than 1000 ° C. The Al _x Ga _(1-x) N layer formed by Al _x Ga _(1-x) N (0 ≦ x ≦ 0.2) is formed.
As a result, the sheet resistance can be reduced and the electron mobility can be improved.

(17) The temperature of the surface of the nitride semiconductor substrate is preferably 750 ° C. or higher and 950 ° C. or lower.
This makes it possible to improve the sheet resistance and electron mobility of the nitride semiconductor laminate 1.
(18) Al _x Ga _(1-x) It is preferable that the degree of vacuum when forming the N layer is 30 mbar or more and 150 mbar or less.
Thereby, the sheet resistance and the electron mobility can be improved.

[Example 1]
A c-plane AlN single crystal substrate having a thickness of 550 μm was annealed using an organic metal vapor phase growth (MOCVD) apparatus. In the annealing treatment, two sets of annealing were performed in an environment of 1300 ° C., with 5 minutes of annealing in the NH ₃ atmosphere and 5 minutes of annealing in the H ₂ atmosphere as one set.

Next, an AlN layer, which is a homoepitaxial layer, was formed on the AlN single crystal substrate. The AlN layer was formed to a thickness of 500 nm in an environment of 1200 ° C. At this time, the ratio (V / III ratio) between the supply rate of the group III element raw material gas and the supply rate of the nitrogen raw material gas was set to 50. Moreover, the degree of vacuum of the chamber was set to 50 mbar. The growth rate of the AlN layer was 0.5 μm / hr. Further, trimethylaluminum (TMAl) was used as an Al raw material. In addition, ammonia (NH ₃ ) was used as the N raw material.

An Al _x Ga _(1-x) N layer was formed on the above-mentioned substrate. The Al _x Ga _(1-x) N layer was formed of GaN (that is, x = 0) having a thickness of 10 nm. The Al _x Ga _(1-x) N layer was formed at a growth temperature (substrate temperature) of 700 ° C. under the conditions that the vacuum degree of the chamber was 50 mbar and the V / III ratio was 1850. Further, the growth rate of GaN at this time was set to 1 μm / hr.
In this way, the nitride semiconductor laminate was formed on the AlN substrate.

When the Al _x Ga _(1-x) N layer formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. rice field. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 3.0 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 90%. Furthermore, the transmission dislocation density observed by cross-sectional TEM measurement was 1 × 10 ⁸ cm ^-3 .

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region less than 2 nm from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of 5 nm or more and 10 nm or less from the interface was 0%.

Subsequently, an electron barrier layer was formed on the Al _x Ga _(1-x) N layer. The electron barrier layer was formed by growing Al _0.25 Ga _0.75 N (that is, y = 0.25) having a thickness of 20 nm. The electron barrier layer was formed at a growth temperature of 700 ° C. under the conditions that the vacuum degree of the chamber was 50 mbar and the V / III ratio was 1850.

The obtained laminate was opened into 15 cm squares, and alloy electrodes (corresponding to n-type electrodes) containing Ti, Al, Ni and Au were formed at the four corners to obtain a nitride semiconductor laminate. When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 10 kΩ / cm ² and the electron mobility was 130 cm ² / Vs.

[Example 2]
A nitride semiconductor laminate was formed in the same manner as in Example 1 except that the growth temperatures of the Al _x Ga _(1-x) N layer and the electron barrier layer were set to 750 ° C.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.7 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 80%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 1.5 kΩ / cm ² and the electron mobility was 600 cm ² / Vs.

[Example 3]
A nitride semiconductor laminate was formed in the same manner as in Example 1 except that the growth temperatures of the Al _x Ga _(1-x) N layer and the electron barrier layer were set to 800 ° C.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.6 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 70%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 1.0 kΩ / cm ² and the electron mobility was 900 cm ² / Vs.

[Example 4]
A nitride semiconductor laminate was formed in the same manner as in Example 1 except that the growth temperatures of the Al _x Ga _(1-x) N layer and the electron barrier layer were set to 850 ° C.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.8 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 65%. Furthermore, no through-transition was observed from the cross-sectional TEM measurement.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 0.8 kΩ / cm ² and the electron mobility was 1100 cm ² / Vs.

[Example 5]
A nitride semiconductor laminate was formed in the same manner as in Example 1 except that the growth temperatures of the Al _x Ga _(1-x) N layer and the electron barrier layer were set to 900 ° C.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.5 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 55%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 0.5 kΩ / cm ² and the electron mobility was 1350 cm ² / Vs.

[Example 6]
A nitride semiconductor laminate was formed in the same manner as in Example 1 except that the growth temperatures of the Al _x Ga _(1-x) N layer and the electron barrier layer were set to 950 ° C.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.8 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 60%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 0.7 kΩ / cm ² and the electron mobility was 1200 cm ² / Vs.

[Example 7]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the growth rate of the Al _x Ga _(1-x) N layer was set to 2 μm / hr.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 1.2 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 70%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 5 kΩ / cm ² and the electron mobility was 330 cm ² / Vs.

[Example 8]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the degree of vacuum of the Al _x Ga _(1-x) N layer chamber was set to 30 mbar.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.5 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 75%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 0.5 kΩ / cm ² and the electron mobility was 1300 cm ² / Vs.

[Example 9]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the degree of vacuum of the Al _x Ga _(1-x) N layer chamber was set to 100 mbar.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.6 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 75%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 0.6 kΩ / cm ² and the electron mobility was 1250 cm ² / Vs.

[Example 10]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the degree of vacuum of the Al _x Ga _(1-x) N layer chamber was set to 150 mbar.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 95%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.5 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 70%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 0.6 kΩ / cm ² and the electron mobility was 1250 cm ² / Vs.

[Example 11]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the degree of vacuum of the Al _x Ga _(1-x) N layer chamber was set to 200 mbar.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 85%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 1.6 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 75%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 3.0 kΩ / cm ² and the electron mobility was 510 cm ² / Vs.

[Example 12]
The Al _x Ga _(1-x) N layer is formed of Al _0.1 Ga _0.9 N (that is, x = 0.1), and the electron barrier layer is formed of Al _0.35 Ga _0.65 N (that is, y = 0). A nitride semiconductor laminate was formed in the same manner as in Example 5 except that it was formed in .35).

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.5 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 55%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 2.0 kΩ / cm ² and the electron mobility was 900 cm ² / Vs.

[Example 13]
The Al _x Ga _(1-x) N layer is formed with Al _0.15 Ga _0.85 N (that is, x = 0.15), and the electron barrier layer is formed with Al _0.4 Ga _0.6 N (that is, y = 0). A nitride semiconductor laminate was formed in the same manner as in Example 5 except that 4) was set.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.5 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 55%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 3.0 kΩ / cm ² and the electron mobility was 670 cm ² / Vs.

[Example 14]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the film thickness of the Al _x Ga _(1-x) N layer was set to 2.0 nm.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.5 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 0%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 2.5 kΩ / cm ² and the electron mobility was 700 cm ² / Vs.

[Example 15]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the film thickness of the Al _x Ga _(1-x) N layer was 5.0 nm.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.5 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 0%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 1.3 kΩ / cm ² and the electron mobility was 1000 cm ² / Vs.

[Example 16]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the film thickness of the Al _x Ga _(1-x) N layer was set to 20 nm.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.5 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 60%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 0.4 kΩ / cm ² and the electron mobility was 1400 cm ² / Vs.

[Example 17]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the film thickness of the Al _x Ga _(1-x) N layer was set to 25 nm.
When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.6 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 65%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 1.4 kΩ / cm ² and the electron mobility was 1250 cm ² / Vs.

[Example 18]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the film thickness of the Al _x Ga _(1-x) N layer was 35 nm.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.8. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 80%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 5.0 kΩ / cm ² and the electron mobility was 1000 cm ² / Vs.

[Comparative Example 1]
The Al _x Ga _(1-x) N layer is formed with Al _0.25 Ga _0.75 N (that is, x = 0.25), and the electron barrier layer is formed with Al _0.4 Ga _0.6 N (that is, y = 0). A nitride semiconductor laminate was formed in the same manner as in Example 5 except that it was formed in 4). At this time, the Al _x Ga _(1-x) N layer was formed under the conditions that the growth temperature was 900 ° C., the vacuum degree of the chamber was 50 mbar, and the V / III ratio was 1850. Further, the growth rate of Al _0.25 Ga _0.75 N at this time was set to 1 μm / hr. The electron barrier layer was formed at a growth temperature of 700 ° C. under the conditions that the vacuum degree of the chamber was 50 mbar and the V / III ratio was 1850.

When the Al _x Ga _(1-x) N layer formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 100%. rice field. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 0.5 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 70%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the sheet resistance was 30 kΩ / cm ² and the electron mobility was 90 cm ² / Vs.

[Comparative Example 2]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the growth rate of the Al _x Ga _(1-x) N layer was 0.2 μm / hr.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below was 50%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 13 nm. Moreover, the relaxation rate of the Al _x Ga _(1-x) N layer with respect to the Al N substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 100%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the noise values of both the sheet resistance and the electron mobility were 100%, and the measured values could not be obtained.

[Comparative Example 3]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the growth rate of the Al _x Ga _(1-x) N layer was 0.5 μm / hr.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer immediately below was 60%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 9.0 nm. Moreover, the relaxation rate of the Al _x Ga _(1-x) N layer with respect to the Al N substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 100%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the noise values of both the sheet resistance and the electron mobility were 100%, and the measured values could not be obtained.

[Comparative Example 4]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the substrate was a sapphire substrate.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer immediately below was 60%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 12 nm. Moreover, the relaxation rate of the Al _x Ga _(1-x) N layer with respect to the Al N substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 100%. Further, from the cross-sectional TEM measurement, the dislocation density was 1 × 10 ⁹ cm ^-3 .

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, misfit dislocations and stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 0%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the noise values of both the sheet resistance and the electron mobility were 100%, and the measured values could not be obtained.

[Comparative Example 5]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the growth temperatures of the Al _x Ga _(1-x) N layer and the electron barrier layer were set to 1000 ° C.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer immediately below was 70%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 15 nm. The relaxation rate of the Al _x Ga _(1-x) N layer with respect to the AlN substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 90%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the noise values of both the sheet resistance and the electron mobility were 100%, and the measured values could not be obtained.

[Comparative Example 6]
A nitride semiconductor laminate was formed in the same manner as in Example 5 except that the growth temperatures of the Al _x Ga _(1-x) N layer and the electron barrier layer were set to 1050 ° C.

When the nitride semiconductor laminate formed as described above was observed using SEM, the surface coverage of the Al _x Ga _(1-x) N layer with respect to the layer immediately below was 60%. The surface roughness of the Al _x Ga _(1-x) N layer obtained by AFM measurement was 20 nm. Moreover, the relaxation rate of the Al _x Ga _(1-x) N layer with respect to the Al N substrate measured by the XRD reciprocal lattice mapping measurement performed on the (20-24) plane was 100%. Furthermore, no transmission dislocations were observed from the cross-sectional TEM measurements.

When the region of 5 nm or less from the interface between the AlN substrate and GaN was observed by high-resolution TEM, neither misfit dislocations nor stacking defects were observed. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region 5 nm or less from the interface was 2.2%. On the other hand, when the region of more than 5 nm and 10 nm or less was observed from the interface between the AlN substrate and GaN by high resolution TEM, misfit dislocations and stacking defects were observed, respectively. At this time, the lattice distortion factor of the Al _x Ga _(1-x) N layer in the a-axis direction in the region of more than 5 nm and 10 nm or less from the interface was 0%.
When the obtained nitride semiconductor laminate was Hall-measured by the Van der pauw method, the noise values of both the sheet resistance and the electron mobility were 100%, and the measured values could not be obtained.

Table 1 below shows the configurations and evaluations of each Example and Comparative Example.

As shown in Table 1, the nitride semiconductor laminate of each example is 0.7 μm / hr by the organic metal vapor phase growth method on a nitride semiconductor substrate containing Al having a temperature of 650 ° C. or higher and lower than 1000 ° C. By forming the Al _x Ga _(1-x) N layer formed by Al _x Ga _(1-x) N (0 ≦ x ≦ 0.2) at the above growth rate, the nitride semiconductor substrate and Al _x It includes an Al _x Ga _(1-x) N layer formed of Ga _(1-x) N (0 ≦ x ≦ 0.2). The nitride semiconductor laminates of each of these examples are compared using Comparative Example 1 having an Al composition x of more than 0.2, Comparative Examples 2 and 3 having a growth rate of less than 0.7 μm / hr, and a sapphire substrate. Compared with Example 4 and Comparative Examples 5 and 6 having a growth temperature of 1000 ° C. or higher, lower sheet resistance and higher electron mobility can be obtained.

As can be seen from Examples 1 to 6, by setting the growth temperature (substrate temperature) of the Al _x Ga _(1-x) N layer to 750 ° C. or higher and 950 ° C. or lower, the sheet resistance is significantly reduced and the electron mobility is reduced. The degree has improved significantly.
Further, as can be seen from Examples 5 and 7, by setting the growth rate of the Al _x Ga _(1-x) N layer to less than 2 μm / hr, the sheet resistance is remarkably reduced and the electron mobility is remarkably reduced. Improved.

As can be seen from Examples 5 and 8 to 11, the sheet resistance and electron mobility were significantly improved when the vacuum degree of the chamber was 30 mbar or more and 150 mbar or less.
Further, as can be seen from Examples 5, 12, 13 and Comparative Example 1, the smaller the Al composition x of the Al _x Ga _(1-x) N layer, the more suitable it is, and x = 0 (Al _x Ga ₍₁₎ . _-X) The N layer is made of GaN) was the most preferred.

As can be seen from Examples 5 and 14-18, when the film thickness of the Al _x Ga _(1-x) N layer is 0.5 nm or more and 30 nm or less, suitable sheet resistance and electron mobility are obtained, and 10 nm or more and 20 nm. Particularly suitable sheet resistance and electron mobility were obtained in the following cases.

The scope of the present disclosure is not limited to the exemplary embodiments illustrated and described, but also includes all embodiments that provide an equivalent effect to that of the present disclosure. Furthermore, the scope of the present disclosure is not limited to the combination of the features of the invention defined by the claims, but may be defined by any desired combination of the specific features of all the disclosed features.

1,1A, 1B Nitride semiconductor laminate 11 Substrate 12 Al _x Ga _(1-x) N layer 13 n-type semiconductor layer 14 Light emitting layer 15 AlN layer 16 Composition gradient layer 17 Electronic barrier layer

Claims (18)

On a nitride semiconductor substrate containing Al whose temperature is 650 ° C or higher and lower than 1000 ° C, Al _x Ga _(1-x) N (0 ≦ x) at a growth rate of 0.7 μm / hr or higher by the organic metal vapor phase growth method. The Al _x Ga _(1-x) N layer formed in ≦ 0.2) is so that the coverage of the Al _x Ga ₍ 1-x) N layer with respect to the layer immediately below is 80% or more and 100% or less. A method for manufacturing a nitride semiconductor laminate to be formed. The method for manufacturing a nitride semiconductor laminate according to claim 1, wherein an AlN single crystal substrate is used as the nitride semiconductor substrate. The method for manufacturing a nitride semiconductor laminate according to claim 1 or 2, wherein the temperature of the surface of the nitride semiconductor substrate is 750 ° C. or higher and 950 ° C. or lower. The method for producing a nitride semiconductor laminate according to any one of claims 1 to 3, wherein the degree of vacuum when forming the Al _x Ga _(1-x) N layer is 30 mbar or more and 150 mbar or less. Nitride semiconductor substrate containing Al and
An Al _x Ga _(1-x) N layer formed of Al _x Ga _(1-x) N (0 ≦ x ≦ 0.2) arranged on the nitride semiconductor substrate and
Equipped with
A nitride semiconductor laminate in which the coverage of the Al _x Ga _(1-x) N layer with respect to the layer directly below is 80% or more and 100% or less. The nitride semiconductor laminate according to claim 5, wherein the nitride semiconductor substrate is an AlN single crystal substrate. The nitride semiconductor laminate according to claim 5 or 6, wherein the Al _x Ga _(1-x) N layer has a film thickness of 0.5 nm or more and 30 nm or less. The relaxation rate of the Al _x Ga _(1-x) N layer in the region of 0.5 nm or more and 5 nm or less from the nitride semiconductor substrate side is 0% or more and 50% or less with respect to the nitride semiconductor substrate. Claims 5 to 7 that the relaxation rate of the Al _x Ga _(1-x) N layer in the region of more than 5 nm and 30 nm or less from the nitride semiconductor substrate side is 50% or more and 100% or less with respect to the nitride semiconductor substrate. The nitride semiconductor laminate according to any one of the above items. The nitride semiconductor laminate according to any one of claims 5 to 8, wherein the penetration dislocation density contained in the Al _x Ga _(1-x) N layer is 1 × 10 ⁴ cm ^-3 or less. According to any one of claims 5 to 9, there is no misfit dislocation or stacking defect in the region of 0.5 nm or more and 5 nm or less from the nitride semiconductor substrate side of the Al _x Ga _(1-x) N layer. The nitride semiconductor laminate according to the description. The invention according to any one of claims 5 to 10, wherein a misfit dislocation or a stacking defect is present in the region of the Al _x Ga _(1-x) N layer from the nitride semiconductor substrate side to more than 5 nm and 30 nm or less. Nitride semiconductor laminate. The nitride semiconductor laminate according to any one of claims 5 to 11, wherein the surface roughness of the Al _x Ga _(1-x) N layer is 0.9 nm or less. The in-plane lattice constant in the a-axis direction in the region of 0.5 nm or more and 5 nm or less from the nitride semiconductor substrate side of the Al _x Ga _(1-x) N layer is 1 with respect to the lattice constant of the nitride semiconductor substrate. The nitride semiconductor laminate according to any one of claims 5 to 12, which is distorted by% or more and 2.5% or less. In the Al _x Ga _(1-x) N layer, the in-plane lattice constant in the a-axis direction in the region of more than 5 nm and 30 nm or less from the nitride semiconductor substrate side is 0% with respect to the lattice constant of the nitride semiconductor substrate. The nitride semiconductor laminate according to any one of claims 5 to 13, which is distorted by 1% or less. One of claims 5 to 14, wherein the Al _x Ga _(1-x) N layer contains Mg, Zn or Be as a dopant atom in an amount of 1 × 10 ¹⁸ cm ^-3 or more and 5 × 10 ¹⁹ cm ^-3 or less. The nitride semiconductor laminate according to the section. The nitride semiconductor laminate according to any one of claims 5 to 15, wherein the Al _x Ga _(1-x) N layer is formed of GaN. 5. Claim 5 that the nitride semiconductor substrate and the Al _x Ga _(1-x) N layer are not provided with a composition gradient layer in which the Al composition decreases in a direction away from the nitride semiconductor substrate. The nitride semiconductor laminate according to any one of 16 to 16. Further, a light emitting layer provided between the nitride semiconductor substrate and the Al _x Ga _(1-x) N layer is provided.
The nitride according to any one of claims 5 to 17, wherein the p-type doping concentration of the Al _x Ga _(1-x) N layer is 1 × 10 ¹⁸ cm ^-3 or more and 5 × 10 ¹⁹ cm ^-3 or less. Material semiconductor laminate.

Images