JP4535935B2 - Nitride semiconductor thin film and manufacturing method thereof - Google Patents

Description

  The present invention relates to a nitride semiconductor thin film containing a group III element and a method for producing the same.

A nitride semiconductor is a compound of at least one element among group III elements such as B, Al, Ga, or In and nitrogen that is a group V element, and has a general formula of Al _1-abc. B _a Ga _b In _c N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1). Nitride semiconductors have been actively researched and developed in recent years as active materials used in electronic devices such as field effect transistors and light emitting devices in the short wavelength band from the visible light region to the ultraviolet region.

  A nitride semiconductor thin film is generally produced on a heterogeneous substrate such as sapphire or silicon nitride (SiC) using a heteroepitaxy technique. However, since the nitride semiconductor and sapphire and SiC have greatly different lattice constants and thermal expansion coefficients, the produced nitride semiconductor thin film has many defects such as cracks and threading dislocations. In recent years, crystal substrates such as GaN and AlN have become commercially available. However, the lattice constants and the thermal expansion coefficients are still greatly different between the nitride semiconductors having various group III elements represented by the general formula and these crystal substrates. For example, the nitride constant shown by the general formula and the AlN crystal substrate have a lattice constant (a-axis) different by 12% at maximum in the case of the wurtzite type.

Therefore, it is very important to reduce the dislocation density in order to improve the quality of nitride semiconductor multilayer films containing various group III elements, such as those used in electronic devices and light-emitting devices. As a method for reducing the dislocation density of a nitride semiconductor, a quantum dot is formed using a lateral growth method by HVPE (Hydride Vapor Phase Epitaxy) (see, for example, Non-Patent Document 1), and a Si—N single layer formed on a substrate. Silicon anti-surfactant method to be formed (for example, see Non-Patent Document 2), a method using an AlN intermediate layer grown at a low temperature (for example, see Non-Patent Document 3), facet-controlled lateral growth in which facet formation is performed using a SiO ₂ mask The law (for example, refer nonpatent literature 4) etc. is proposed. However, in reality, there is still no method that satisfies all of a sufficiently low dislocation density, homogeneity over a wide area, simplicity of the production process, economy, and the like.

A. Usui, et al., “Thick GaN Epitaxial Growth with Low Dislocation Density by Hydride Vapor Phase Epitaxy”, Jpn. J. Appl. Phys. Vol. 36, pp. L899-L902, 1997 S. Tanaka, et al., “Anti-Surfactant in III-Nitride Epitaxy Quantum Dot Formation and Dislocation Termination-”, Jpn. J. Appl. Phys. Vol.39, pp.L831-L834, 2000 M.Iwaya, et al., “High-Quality AlXGa1-XN using Low Temperature Interlayer and its Application to UV Detector”, Mat. Res. Soc. Symp. Vol.595, W1.10.1, 2000 Y. Honda, et al., “Transmission Electron Microscopy Investigation of Dislocations in GaN Layer Grown by Facet-Controlled Epitaxial Lateral Overgrowth”, Jpn. Appl. Phys. Vol.40, pp.L309-L312, 2001 S. Heikman, et al., “Growth of Fe doped semi-insulating GaN by metalorganic chemical vapor deposition”, Appl. Phys. Lett. Vol. 81, No. 3, pp. 439-441, 2002 K. Kumakura, et al., “Novel Buffer Layers of ECR-doposited AlN / AlON / Al2O3 for GaN Grown on Sapphire”, Proceedings of International Workshop on Nitride Semiconductors IWN2004, pp.48

  FIG. 1 shows a cross section of a nitride semiconductor thin film grown on a sapphire substrate. Sapphire is readily available and inexpensive, and is most widely used as a substrate for growing nitride semiconductors. FIG. 1 is a schematic view when GaN is grown on a sapphire substrate by metal organic chemical vapor deposition (MOCVD). Since the sapphire substrate 11 and the GaN 12 have large differences in thermal expansion coefficient and lattice constant, high-density threading dislocations 13 are generated.

  Further, the sapphire substrate is etched at a temperature of about 1000 ° C. which is a typical condition of MOCVD. Since the sapphire substrate is a compound of aluminum and oxygen, the decomposed / generated oxygen is taken into the nitride semiconductor layer near the substrate interface. As a result, the incorporated oxygen works as a donor impurity, and the nitride semiconductor layer 14 near the sapphire substrate interface is difficult to control valence electrons, and in particular, a high resistance layer cannot be obtained, that is, the residual carrier concentration is high. was there. Due to this problem, for example, the performance of a field effect transistor using a nitride semiconductor has been limited.

  As a method for increasing the resistance of the nitride semiconductor layer near the sapphire substrate interface, a method of doping the nitride semiconductor layer 14 near the sapphire substrate interface with iron serving as an acceptor (see, for example, Non-Patent Document 5) has been proposed. Yes. However, there is a problem of the memory effect that the iron content cannot be strictly controlled in the film thickness direction.

  Further, in the above-described silicon anti-surfactant method, since Si is doped during crystal growth, residual carriers increase and it is difficult to realize a high-resistance thin film. Furthermore, in the facet-controlled lateral growth method described above, because of selective growth using a mask, the crystallinity of the GaN thin film is different between the opening of the mask and the overgrowth portion of the mask, so that homogeneity cannot be ensured. There was a problem.

  The present invention has been made in view of such problems. The object of the present invention is to satisfy a sufficiently low dislocation density, homogeneity over a wide area, simplicity of the production process, and economic efficiency, and a substrate interface. The object is to provide a nitride semiconductor thin film having high resistance and a method for manufacturing the same.

In order to achieve the above object, according to the present invention, a nitride semiconductor thin film according to claim 1 includes a first nitride semiconductor containing boron and a first nitride formed on a substrate. A second nitride semiconductor formed on the semiconductor and having a boron composition ratio smaller than a boron composition ratio of the first nitride semiconductor; and the first nitride semiconductor and the second nitride semiconductor. The interface between the physical semiconductor and the semiconductor has an average roughness of 0.1 microns or more .
The nitride semiconductor thin film according to claim 2 is formed on the first nitride semiconductor containing boron and the first nitride semiconductor formed on the substrate, and the composition ratio of boron is the first nitride semiconductor thin film. A first nitride semiconductor having a plurality of island-like crystals having side facets formed on the substrate. The average height is 0.1 micron or more, and the surface orientation of the side facet is {11-20}, {1-100}, {11-22} or {1-101}.

The boron composition of the first nitride semiconductor is preferably 0.001 or more and 0.2 or less .

  At least one or more sets of the first nitride semiconductor and the second nitride semiconductor may be further stacked. The substrate is preferably a sapphire substrate, and the substrate may contain at least one element of carbon, oxygen, sulfur, selenium, tellurium, silicon, germanium, or tin.

Furthermore, an inclined layer having a composition AlO _x N _y (0 ≦ x ≦ 1.5, 0 ≦ y ≦ 1) may be inserted between the substrate and the first nitride semiconductor.

A claims 1 to 7 or nitride manufacturing method of a semiconductor thin film for manufacturing nitride semiconductor thin film according to the, the first nitride semiconductor containing boron, first formed on the substrate And a second step of forming a second nitride semiconductor having a boron composition ratio smaller than the boron composition ratio of the first nitride semiconductor on the first nitride semiconductor. It is characterized by that.

As the nitride material, at least one of borazine derivatives [B ₃ (C _n H _{2n + 1} ) ₃ N ₃ H ₃ ] (n is an integer) and decaborane can be used.

  As described above, according to the present invention, a nitride semiconductor thin film having a sufficiently low dislocation density, homogeneity over a wide area, simplicity of the manufacturing process, economical efficiency, and high resistance near the substrate interface is realized. It becomes possible to do.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the nitride semiconductor thin film according to the present embodiment, a mixed crystal composed of a plurality of nitride semiconductors having different bond lengths with nitrogen is formed on a substrate, and a nitride semiconductor having a composition different from the mixed crystal is formed from the mixed crystal. Formed on top.

FIG. 2 shows a nitride semiconductor thin film according to Example 1 of the present invention. The nitride semiconductor thin film is formed on the sapphire substrate 21 whose main orientation plane is within ± 5 degrees from the (0001) plane using an MOCVD apparatus. On the sapphire substrate 21, a first nitride semiconductor having a composition of Al _1-ab-c B _a Ga _b In _c N (0 <a ≦ 1, 0 ≦ b <1, 0 ≦ c <1). 22 is formed as a large number of island-like crystals. That is, the many crystals of the first nitride semiconductor 22 may have any shape, but it is desirable to have side facets with a plane orientation described later, and over the entire surface of the sapphire substrate 21, It is scattered like an island. The average height of the first nitride semiconductors 22 is 0.3 microns.

FIG. 3 shows the first nitride semiconductor 22 grown on the sapphire substrate. A bird's eye electron micrograph of the island-like crystals of the composition _{Al 1-a-b-c} B a Ga b In c N (0 <a ≦ 1,0 ≦ b <1,0 ≦ c <1). Each island-like crystal has a wurtzite-type crystal structure, grows in an epitaxial relationship on the sapphire substrate 21, and has an upper surface composed of (0001) planes and a side surface composed of facets. This facet plane has a plane orientation of {11-20}, {1-100}, {11-22}, or {1-101} depending on the growth conditions of MOCVD.

AlN, GaN, InN, or a mixed crystal thereof has a relatively long bond bond length and a wurtzite crystal structure is a stable phase. On the other hand, BN has a remarkably short bond bond length and has a stable crystal structure of graphite type and zinc blende type. Thus, a mixed crystal composed of a plurality of nitride semiconductors having different bond lengths is formed as the first nitride semiconductor 22. The first nitride semiconductor 22 having the composition Al _{1 -a-b-c} B _a Ga _b In _c N contains a suitable amount of B, thereby inhibiting uniform two-dimensional growth and causing three-dimensional growth. An island-shaped thin film having side facets is obtained. In the growth process of such island-shaped thin films, the propagation direction of threading dislocations 24 is twisted and bent as the side facets grow.

_{Subsequently, Al 1-d-e-} f B d Ga e In f N (0 ≦ d <1,0 ≦ e ≦ 1,0 ≦ f ≦ 1, d <a) second nitride having a composition of In the growth process of the semiconductor 23, two dislocations having Burgers vectors opposite to each other may form a half loop 25 and disappear. As a result, the threading dislocation density of the nitride semiconductor is reduced. In this case, the first nitride semiconductor 22 preferably has an average height of island-shaped thin films of 0.1 microns or more (described later with reference to FIG. 7).

FIG. 4 shows the relationship between the value of the boron (B) composition a and the threading dislocation density. If the value of the B composition a of the first nitride semiconductor 22 having the composition Al _1-a-b-c B _a Ga _b In _c N is too small, three-dimensional growth is difficult to occur. Will deteriorate. The average height is 0.3 microns, the first nitride semiconductor 22 having the composition _{Al 0.09 B a Ga 0.9-a} In 0.01 N, an average thickness of 2.5 microns, the composition Al _0.09 Ga _0.9 In _0.01 N Using the second nitride semiconductor 23, the relationship between the value of the B composition a of the nitride semiconductor 22 and the threading dislocation density was measured. As shown in FIG. 4, it can be seen that the threading dislocation density is remarkably reduced when the value a is in the range of 0.001 to 0.2.

The composition _{Al 1-d-e-f} B d Ga e In f the second nitride semiconductor 23 N, given the application to the device, it is necessary to make as uniform as possible two-dimensional growth. Therefore, the value of the B composition d is preferably small, and it is desirable that at least the condition of d <a is satisfied. As shown in FIG. 2, the island-shaped thin film of the first nitride semiconductor 22 can be further reduced in dislocation density by repeatedly inserting not only one layer but also two or more layers.

FIG. 5 shows a first nitride semiconductor in which island-shaped thin films are continuously formed. The first nitride semiconductor 52 is not necessarily a discontinuous island-shaped thin film. On a sapphire substrate _51, the first nitride semiconductor having a composition of _{Al 1-a-b-c} B a Ga b In c N (0 <a ≦ 1,0 ≦ b <1,0 ≦ c <1) 52 are formed as a number of island-like crystals. At this time, the island-shaped thin film has a shape in which island-shaped crystals are combined with each other. In order to sufficiently perform the twist bending in the propagation direction of dislocation and the formation of the half loop, the average roughness of the surface of the first nitride semiconductor 52 of the composition Al _{1-ab-cB a} Ga _b In _c N That is, it is desirable that either the mean square root roughness or the arithmetic mean roughness is 0.1 microns or more. In other words, the average roughness of the interface between the second nitride semiconductor 53 of the composition as the first nitride semiconductor _{52 Al 1-d-e-} f B d Ga e In f N is 0.1 microns or more It is desirable. Further, it is desirable that the values of the B compositions a and d have the above-described relationship.

FIG. 6 shows a nitride semiconductor thin film according to Example 2 of the present invention. The nitride semiconductor thin film is formed using a MOCVD apparatus on the sapphire substrate 61 whose main azimuth plane is a plane within ± 5 degrees from the (0001) plane. On the sapphire substrate 61, the first nitride semiconductor 62 having a composition of B _0.02 Ga _0.98 N is formed as a large number of island-shaped crystals. Next, a second nitride semiconductor 63 having a GaN composition is formed. Due to the same effect as in Example 1, a part of the threading dislocation 64 disappeared by forming the half loop 65, and the threading dislocation density of the second nitride semiconductor 63 was significantly reduced. As a result of cross-sectional observation with a transmission electron microscope, the threading dislocation density of the second nitride semiconductor 63 was 5 × 10 ⁷ cm ⁻² . This value is two orders of magnitude lower than that of a nitride semiconductor (FIG. 1) in which a GaN thin film is formed on a conventional sapphire substrate.

  Here, the average thickness of the first nitride semiconductor 62 is 0.5 microns, the average thickness of the second nitride semiconductor 63 is 2 microns, and the average roughness of the interface between them is 0.15 microns. FIG. 7 shows the relationship between the average roughness of the interface and the threading dislocation density. It can be seen that the threading dislocation density can be reduced by two orders of magnitude or more by setting the average roughness of the interface to 0.1 microns or more.

Furthermore, when the electrode was formed on the nitride semiconductor thin film shown in FIG. 6 and the sheet resistance was measured, the resistance was as extremely high as 2.3 × 10 ¹⁰ Ω / □ at room temperature. This value is five orders of magnitude higher than that of a nitride semiconductor (FIG. 1) in which a GaN thin film is formed on a conventional sapphire substrate. This is because the low resistance layer near the substrate interface due to oxygen mixed from the sapphire substrate disappears during MOCVD growth, which is a conventional problem, and the residual carrier density is significantly reduced.

As mentioned above, under typical growth conditions of MOCVD, BN can take both zincblende and graphite types as crystal structures. The zinc blende type crystal structure has sp3 hybrid orbitals, like the wurtzite type crystal structure that can be taken by AlN, GaN, InN, or a mixed crystal thereof, and the B atom and the N atom are bonded to each other. ing. However, the graphite-type crystal structure has sp2 hybrid orbitals, and B atoms and N atoms are bonded. In the first nitride semiconductor 62 having the composition B _0.02 Ga _0.98 N, most BN bonds are sp3 hybrid orbitals. However, a very small part of BN bonds are sp2 hybrid orbitals, and as a result, deep levels acting as acceptors are formed in the band gap of B _0.02 Ga _0.98 N. For this reason, the donor by the oxygen mixed from the sapphire substrate 61 is compensated, and the nitride semiconductor near the interface also has an extremely high resistance.

  The distribution in the film thickness direction of the B composition of the nitride semiconductor thin film shown in FIG. 6 was measured with a secondary ion mass spectrometer. The B composition is 0.02 from the interface with the sapphire substrate 61 to the position of 0.5 micron, and the B composition decreases sharply beyond that, and the B composition at the position of 0.6 micron from the interface is the detection limit. It was the following. Therefore, the problem of the memory effect in the technique of doping iron as an acceptor, which has been conventionally used as a technique for increasing resistance, can be overcome by this embodiment.

A nitride semiconductor slightly doped with Si atoms was produced on the second nitride semiconductor 63 having a GaN composition, and after the electrodes were formed, hole measurement was performed. The electron concentration was 6.7 × 10 ¹⁶ cm ⁻³ and the hole electron mobility was 874 cm ² V ⁻¹ s ⁻¹ . This is a result showing that the nitride semiconductor obtained in the present embodiment is extremely high in electrical quality. Even when the nitride semiconductor thin film according to Example 2 was formed using a 3-inch diameter sapphire substrate, similar results were obtained over the entire surface of the substrate.

In Example 2, the combination of the composition B _0.02 Ga _0.98 N as the first nitride semiconductor 62 and the composition GaN as the second nitride semiconductor 63 was used, but as in Example 1 Alternatively, a nitride semiconductor containing Al, In may be used. That is, as the first nitride semiconductor 62, the composition Al _{1 -abc} B _a Ga _b In _c N (0 <a ≦ 1, 0 ≦ b <1, 0 ≦ c <1), and the second nitride composition as semiconductor _{63 Al 1-d-e-} f B d Ga e in f N of (0 ≦ d <1,0 ≦ e ≦ 1,0 ≦ f ≦ 1, d <a) even in the case of using the Similar results are obtained. At this time, as described above, regarding the values of a and d of the B composition, it is desirable that the value of a is 0.001 or more and 0.2 or less and that the relationship d <a is satisfied.

  Further, the island-shaped thin film of the first nitride semiconductor 62 may be either a large number of island-shaped crystals or a shape in which the island-shaped crystals are combined with each other. Furthermore, by repeatedly using two or more layers of the first nitride semiconductor 62, the dislocation density is further reduced. The substrate is not limited to the sapphire substrate, but if a substrate containing an element that can supply electrons as a donor when mixed into a nitride semiconductor is used, the effect according to the present embodiment can be obtained. These elements include carbon, oxygen, sulfur, selenium, tellurium, silicon, germanium, or tin.

FIG. 8 shows a nitride semiconductor thin film according to Example 3 of the present invention. The nitride semiconductor thin film is formed on the sapphire substrate 81 whose main orientation plane is a plane within ± 5 degrees from the (0001) plane using an MOCVD apparatus. An inclined layer 86 having a composition of AlO _x N _y (0 ≦ x ≦ 1.5, 0 ≦ y ≦ 1) is formed on the sapphire substrate 81, and a composition of B _0.02 Ga _0.98 N is formed thereon. The first nitride semiconductor 82 having the structure is formed as a number of island-shaped crystals. Next, a second nitride semiconductor 83 having a GaN composition is formed. Here, the thickness of the inclined layer 86 is 20 nm, and the x of the O composition and the y of the N composition change smoothly in an inclined manner in the film thickness direction (direction perpendicular to the substrate surface). At the interface with the sapphire substrate 81, x = 1.5 and y = 0 (that is, AlO _1.5 = Al ₂ O ₃ ), and as the film thickness increases, x and y change linearly. Is x = 0 and y = 1 (ie, AlN) at 20 nm.

The gradient layer 86 provides three effects. Boron (B) and oxygen, which is a constituent element of the sapphire substrate 81, react very easily, and the quality of the first nitride semiconductor 82 having the composition B _0.02 Ga _0.98 N is deteriorated in the early stage of growth. In Example 3, since the surface of the graded layer 86 having the composition AlO _x N _y is AlN and does not contain oxygen, such a deterioration in quality can be prevented as a first effect. As described above, the graded layer having the composition AlO _x N _y has a remarkable effect that is not found in the past in combination with a nitride semiconductor containing boron (B).

The second effect is that since the surface of the graded layer 86 with the composition AlO _x N _y does not contain oxygen, mixing of oxygen into the second nitride semiconductor 83 with the composition GaN is further suppressed, and the residual carrier density is reduced. The third effect is that the generation of threading dislocations is further suppressed by smoothly changing the lattice constant of the inclined layer 86 from the value of Al ₂ O _{3 which} is the same as that of the sapphire substrate 81 to the value of AlN which is a nitride semiconductor. Is done. As a result, when an electrode was formed on the nitride semiconductor thin film shown in FIG. 7 and the sheet resistance was measured, it was 4.4 × 10 ¹⁰ Ω / □ at room temperature, which was larger than that in Example 2.

A nitride semiconductor slightly doped with Si atoms was produced on the second nitride semiconductor 83 having a GaN composition, and after forming an electrode, hole measurement was performed. The electron concentration was 7.1 × 10 ¹⁶ cm ⁻³ and the hole electron mobility was 922 cm ² V ⁻¹ s ⁻¹ . Compared with the nitride semiconductor thin film of Example 2, the electrical quality is further improved.

In the third embodiment, the thickness of the inclined layer 86 is 20 nm, but this thickness can be freely set between 1 nm and 100 nm. Further, the combination of the composition B _0.02 Ga _0.98 N as the first nitride semiconductor 82 and the composition GaN as the second nitride semiconductor 83 was used. As in Example 1, Al, In A nitride semiconductor containing may be used. That is, as the first nitride semiconductor 82, the composition Al _{1 -abc} B _a Ga _b In _c N (0 <a ≦ 1, 0 ≦ b <1, 0 ≦ c <1), and the second nitride composition as semiconductor _{83 Al 1-d-e-} f B d Ga e in f N of (0 ≦ d <1,0 ≦ e ≦ 1,0 ≦ f ≦ 1, d <a) even in the case of using the Similar results are obtained. At this time, as described above, regarding the values of a and d of the B composition, it is desirable that the value of a is 0.001 or more and 0.2 or less and that the relationship d <a is satisfied.

  In addition, the island-shaped thin film of the first nitride semiconductor 82 may have either a large number of island-shaped crystals or a shape in which the island-shaped crystals are combined with each other. Furthermore, by repeatedly using two or more layers of the first nitride semiconductor 82, the dislocation density is further reduced.

  A method for manufacturing a nitride semiconductor thin film according to this embodiment will be briefly described. For the nitride semiconductor thin film, a general crystal growth apparatus, that is, a liquid layer growth apparatus or a vapor phase growth apparatus can be used. However, considering crystal quality, thin film thickness controllability, mass productivity, and response to large areas, it is preferable to use an MOCVD apparatus as described in Examples 1 to 3.

As a raw material for nitrogen, ammonia, dimethylhydrazine, borazine derivative [B ₃ (C _n H _{2n + 1} ) ₃ N ₃ H ₃ ] (n is an integer), or the like can be used. As a raw material of boron, trimethylboron, triethylboron, diborane, decaborane, a borazine derivative [B ₃ (C _n H _{2n + 1} ) ₃ N ₃ H ₃ ] (n is an integer) or the like can be used.

When Annimore is used as the nitrogen material and diborane is used as the boron material, before both materials reach the growth substrate, a parasitic reaction occurs in the gas phase to cause heterogeneous nucleation, and the quality of the nitride semiconductor is improved. It will be damaged. Since the borazine derivative [B ₃ (C _n H _{2n + 1} ) ₃ N ₃ H ₃ ] contains both nitrogen and boron, a parasitic reaction in the gas phase can be suppressed, so that a particularly high-quality nitride semiconductor can be formed. In addition, decaborane is less likely to cause a parasitic reaction and is therefore suitable for use with the above nitrogen raw material. Moreover, since the vapor pressure is low, it is very suitable for producing a nitride semiconductor having a relatively low B composition.

  A method for manufacturing the nitride semiconductor thin film according to Example 1 shown in FIG. 2 will be described. (A) The sapphire substrate 21 is inserted into the MOCVD apparatus, and the substrate is cleaned while flowing at least hydrogen. The optimum pressure and substrate temperature at this time are 0.01 to 3 atmospheres and 800 to 1200 ° C. Hereinafter, pressure and temperature are within these ranges.

(B) An organic metal containing Al, an organic metal containing Ga, an organic metal containing In, the borazine derivative or decaborane described above, and ammonia are used as a source gas. Using hydrogen and nitrogen as the carrier gas, the composition on the sapphire substrate _{21 Al 1-a-b-} c B a Ga b In c N (0 <a ≦ 1,0 ≦ b <1,0 ≦ c <1) The island-shaped first nitride semiconductor 22 is formed. At this time, by appropriately adjusting the supply amount of the organic metal containing Al, the organic metal containing Ga, the organic metal containing In, the borazine derivative, or decaborane, the B composition a becomes 0.001 or more and 0.2 or less. To. Further, the average height of the island-shaped first nitride semiconductor 22 is adjusted to 0.1 μm or more by appropriately adjusting the supply time of all source gases. Alternatively, in the case where the island-shaped crystals have a shape that is combined with each other, the average roughness of the interface between the first nitride semiconductor 22 and the second nitride semiconductor 23 is set to 0.1 microns or more.

(C) Similarly, the second nitride semiconductor 23 is formed. An organic metal containing Al, an organic metal containing Ga, an organic metal containing In, a borazine derivative or decaborane, and ammonia are used as a source gas. Using hydrogen and nitrogen as the carrier gas, the composition _{Al 1-d-e-f} B d Ga e In f N (0 ≦ d <1,0 ≦ e ≦ 1,0 ≦ f ≦ 1, d <a) of A nitride semiconductor 23 is formed. At this time, the B composition d becomes the B composition a of the first nitride semiconductor 22 by appropriately adjusting the supply amount of the organic metal containing Al, the organic metal containing Ga, the organic metal containing In, the borazine derivative, or decaborane. To be smaller.

  (D) By repeating the steps (b) and (c), the nitride semiconductor thin film shown in FIG. 2 can be produced.

It is sectional drawing which shows the nitride semiconductor thin film grown on the sapphire substrate. It is sectional drawing which shows the nitride semiconductor thin film concerning Example 1 of this invention. It is a bird's-eye electron micrograph which shows the 1st nitride semiconductor grown on the sapphire substrate. It is a figure which shows the relationship between the value of the composition a of boron (B), and a threading dislocation density. It is sectional drawing which shows the 1st nitride semiconductor in which the island-like thin film was formed continuously. It is sectional drawing which shows the nitride semiconductor thin film concerning Example 2 of this invention. It is a figure which shows the relationship between the average roughness of an interface, and a threading dislocation density. It is sectional drawing which shows the nitride semiconductor thin film concerning Example 3 of this invention.

Explanation of symbols

11, 21, 51, 61, 81 Sapphire substrate 12 GaN
13, 24, 64, 84 Threading dislocations 14 Nitride semiconductor layer near the interface 22, 52, 62, 82 First nitride semiconductor 23, 53, 63, 83 Second nitride semiconductor 25, 65, 85 Half loop 86 Tilting layer

Claims (9)

A first nitride semiconductor containing boron formed on the substrate;
A second nitride semiconductor formed on the first nitride semiconductor and having a boron composition ratio smaller than the boron composition ratio of the first nitride semiconductor ;
The nitride semiconductor thin film characterized in that an average roughness of an interface between the first nitride semiconductor and the second nitride semiconductor is 0.1 microns or more . A first nitride semiconductor containing boron formed on the substrate;
A second nitride semiconductor formed on the first nitride semiconductor and having a boron composition ratio smaller than the boron composition ratio of the first nitride semiconductor;
The first nitride semiconductor, a plurality of island-like crystals having a side facets are formed on the substrate, the average height of Ri der than 0.1 microns, the plane orientation of the side facets {11- 20}, {1-100}, {11-22} or {1-101} der nitride compound semiconductor thin characterized Rukoto. 3. The nitride semiconductor thin film according to claim 1, wherein the boron composition of the first nitride semiconductor is 0.001 or more and 0.2 or less. 4. The nitride semiconductor thin film according to claim 1 , wherein at least one or more sets of the first nitride semiconductor and the second nitride semiconductor are further laminated. 5. The substrate, the nitride semiconductor thin film according to any one of claims 1 to 4, characterized in that a sapphire substrate. The nitride semiconductor according to any one of claims 1 to 4 , wherein the substrate contains at least one element of carbon, oxygen, sulfur, selenium, tellurium, silicon, germanium, or tin. Thin film. An inclined layer having a composition AlO _x N _y (0 ≦ x ≦ 1.5, 0 ≦ y ≦ 1) is inserted between the substrate and the first nitride semiconductor. 4. The nitride semiconductor thin film according to 4 or 5 . A method for producing a nitride semiconductor thin film for producing the nitride semiconductor thin film according to claim 1,
A first step of forming a first nitride semiconductor containing boron on a substrate;
A second step of forming on the first nitride semiconductor a second nitride semiconductor having a boron composition ratio smaller than the boron composition ratio of the first nitride semiconductor. A method for producing a nitride semiconductor thin film. 9. The nitride semiconductor according to claim 8, wherein at least one of a borazine derivative [B ₃ (C _n H _{2n + 1} ) ₃ N ₃ H ₃ ] (n is an integer) and decaborane are used as a material for the nitride. Thin film manufacturing method.

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