JPH11330550A - Group iii-v compound semiconductor element, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a group III-V compound semiconductor element which can form hetero junction structure in a group III-V compound semiconductor suitable to constitute the quantum structure consisting of plural group III-V compound semiconductor crystal regions different in nitrogen composition ratio, and also can easily obtain low dimensional quantum structure selectively having regions different in forbidden band width within a group III-V compound semiconductor layer, without using a complicated method, thereby obtaining the group III-V compound semiconductor element. SOLUTION: The selected region within the first crystal region 24 consisting of a group III-V compound semiconductor is made the second layer region 24a being made by replacing a part or the whole of the group V atoms with nitrogen atoms. There, hetero junction structure is made of the second crystal region 24a and the first crystal region 24 surrounding this second crystal region 24a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a group III-V compound semiconductor device having a heterojunction structure composed of group III-V compound semiconductor crystal regions having different nitrogen composition ratios and a method of manufacturing the same. The present invention relates to a group III-V compound semiconductor device suitable for a semiconductor quantum effect device having a heterojunction structure suitable for a three-dimensional quantum structure, and a method for manufacturing the same.

[0002]

2. Description of the Related Art An element (device) utilizing characteristics exhibited by quantized carriers expressed by a quantum well structure in which two types of semiconductor ultrathin films are artificially stacked is a quantum effect device. It is called. This quantum effect device is roughly classified into an optical device and an electronic device. As the optical device, for example, a single quantum well (SQ)
An SQW or MQW type laser diode (LD) having a light emitting layer having a W (Single Quantum Well) structure or a Multi Quantum Well (MQW) structure is known. As an electronic device, two-dimensional electron gas is used.
Schottky Junction Field-Effect Transistor (MESFET: Metal Semiconductor)
Field Effect Transistor) and the like are known. This M
The ESFET utilizes the characteristics of two-dimensional electrons resulting in high mobility, and has a reduced noise figure (NF).

Recently, in addition to the above-described devices using quantized carriers that behave two-dimensionally, devices using low-dimensional quantized carriers that behave one-dimensionally have also been proposed (for example, Japanese Patent Application Laid-Open No. H10-157572). Kaihei 9-64476
Reference). This device is a gallium arsenide (GaAs) / GaInAs heterojunction light-emitting device using a gallium indium arsenide (GaInAs) semiconductor microcrystal having a small volume and a small volume and having a small dot structure. This is based on the fact that when the size is reduced, the electrostatic energy greatly changes compared to the thermal fluctuation due to the increase or decrease of one electron.

In general, a light emitting layer having a quantum well structure that provides quantized carriers has an advantage that narrow band light having a narrow half width is emitted. Recently, a quantum dot laser (quantum LD) using a quantum dot having an ultimate quantum confinement structure has been proposed (see, for example, Motokoji: Applied Physics 65 (2), 172 (1998)). This quantum LD has a ridge mesa structure in which a quantum well layer made of indium arsenide (InAs) / GaAs is used as a quantum dot active layer, and a light emission having a narrow half-value width is actually concluded. Reduction of voltage and improvement of luminous efficiency are expected.

The conventional quantum well structure is formed by a method of sequentially stacking ultra-thin semiconductor crystal layers. FIG.
FIG. 4 is a cross-sectional view illustrating an example of a light emitting unit having a conventional DH (double hetero) structure having an MQW structure. The light emitting unit includes a barrier layer 2 and a well on a lower clad layer 1.
l) Layers 3 are alternately stacked to form an MQW structure 4 having two well layers 3 and an upper cladding layer 5 formed on the uppermost barrier layer 2. In order to form the MQW structure 4, a deposition operation is required in which a barrier layer 2 is formed on the lower cladding layer 1 and then the well layer 3 and the barrier layer 2 are sequentially laminated. Thus, GaAs or aluminum gallium arsenide (Al _X G
a _Y As: general II such as 0 <X ≦ 1, X + Y = 1)
An SQW structure or an MQW structure can be formed relatively easily using an IV group compound semiconductor. This uses indium phosphide (InP) as a barrier layer and uses a gallium-indium arsenide mixed crystal (for example, Ga _0.47 In _0.53 A
This is because, as in the case of forming the SQW structure or the MQW structure using s) as a well layer, a significant change in the film formation temperature is not required.

On the other hand, when an SQW structure or an MQW structure is formed using a group III-V nitride semiconductor growth layer, a film forming operation is complicated. For example, a light emitting layer having an MQW structure used as a quantum effect light device has been conventionally used.
In general, gallium nitride-indium mixed crystal (Ga _B In _C
N: 0 <C ≦ 1, B + C = 1) as a well layer, and aluminum nitride / gallium mixed crystal (Al _A Ga _B N: 0 ≦ A ≦ 1,
A + B = 1) is used as a barrier layer, so that Ga _B In _C N
In the mixed crystal and the Al _A Ga _B N mixed crystal, there are several hundred degrees of separation between the respective suitable film-forming temperature (J.Crystal Growt
h, 145, pp. 209-213 (1994)). Therefore, SQ
In order to form the W structure or the MQW structure, frequent changes in the film forming temperature are required every time a film is formed, and a complicated film forming operation is necessary.

[0007] A half-dimensional quantum well structure such as a quantum wire structure or a quantum dot structure is conventionally formed mainly by a selective epitaxial growth method. For example, a gallium nitride (GaN) layer is deposited on a sapphire (α-Al ₂ O ₃ ) substrate, and then a mask material having a region selectively opened according to the shape of a quantum dot or quantum line to be formed. A method has been proposed in which the surface of the GaN layer is coated with a GaN layer, and then a group III-V nitride semiconductor crystal having a quantum dot shape or a quantum line shape is selectively formed only in the opening region (Proc.
2nd.Int.Conf.on Nitrides Semiconductors (Jpn.So
ciety of Applied Physics), pp. 492-493 (1997)).

FIG. 12 is a cross-sectional view showing a conventional quantum dot structure using a group III-V nitride semiconductor crystal. This quantum dot structure is, for example, a crystal of a conductive group III-V compound semiconductor substrate or the like. on the substrate 11, buffer layer 12, a lower cladding layer 1, the light emitting layer 13 and the upper cladding layer 5 are sequentially laminated, the light emitting layer 13, the quantum dots emitting medium in a short wavelength visible light Ga _B in _C N ( 0 <C ≦ 1, B + C =
1) crystal 14, is constituted by the Ga _B In _C N crystal _{14 Al A Ga B N (0} ≦ A ≦ 1, A + B = 1) barrier layer 15 of which surrounds the lower cladding layer 1, the light-emitting layer 13
The light emitting section 16 is constituted by the upper cladding layer 5.

The steps of forming this structure will be described in order. First, the buffer layer 12 and the Al
Sequentially forming a lower cladding layer 1 consisting of _A Ga _B N. After the film formation, the surface of the lower cladding layer 1 is coated with silicon dioxide (Si).
It is covered with a mask material made of a film such as O ₂ ) or silicon nitride (Si ₃ N ₄ ). This mask material is a mask material for selective epitaxial growth and is opened only in a region where quantum dots are desired to be formed. Next, by again depositing operation while bearing the mask material, growing a Ga _B In _C N crystal 14 in a dot pattern on the lower cladding layer 1 on the surface. Next, Al _A Ga _B is formed so as to surround the quantum dot-shaped crystal 14.
A barrier layer 15 made of N is formed to be a light emitting layer 13 in which quantized carriers are provided.

[0010] Finally, bearing the upper cladding layer 5 made of Al _A Ga _B N on the light emitting layer 13, forming a light emitting portion 16 of the quantum well structure made of Group III-V nitride semiconductor crystal.
FIG. 12 shows a dot-shaped crystal 14 grown selectively.
This shows a quantum dot structure having the following. If the shape of the crystal 14 is linear (band), a quantum wire structure is obtained. In this case, the mask material covering the surface of the lower cladding layer 1 may be opened only in the region where the formation of the quantum wires is desired.

As described above, the conventional group III-V nitride semiconductor is used for either a two-dimensional quantum structure such as a quantum well or a one-dimensional quantum structure such as a quantum dot (or quantum wire). The quantum structure depends on a method of forming a desired quantum structure by laminating each layer constituting the quantum structure as described above.

In the conventional method of forming a quantum structure by lamination, the temperature at the time of lamination may be as high as over 1000 ° C. (optical, 22 (11), 670-675 (19
93)). For this reason, a crystal material having excellent heat resistance, such as sapphire (α-Al ₂ O ₃ single crystal), is suitably used as a substrate serving as a base for forming a quantum structure.

[0013]

When an SQW structure or an MQW structure is formed by using the conventional group III-V nitride semiconductor growth layer, frequent changes in the film formation temperature are required every time the film is formed. Therefore, there is a problem that a complicated film forming operation is required. Further, when a low-dimensional group III-V nitride semiconductor quantum structure is formed by using the selective epitaxial growth method, the band gap is further increased around the group III-V nitride semiconductor crystal having a quantum wire structure or a quantum dot structure. Must be surrounded by a different group III-V nitride semiconductor crystal, and there is a problem that film formation is difficult.

Since sapphire, which is a substrate material, does not exhibit clear cleavage like hexagonal silicon carbide (SiC) or many oxide crystals, the end face of the element to be formed is made smooth and flat. There was a problem that it was difficult to do. This means that, for example, in an LD having a quantum well structure, an optical resonance surface requiring smoothness and flatness cannot be formed by using cleavage of a substrate crystal. Therefore, short-wavelength I
In the case of the II-V nitride semiconductor LD, a method utilizing fine etching (see Japanese Patent Application Laid-Open No. 9-283861), or a cutting direction for changing the crystal plane orientation of the sapphire substrate or forming a chip is used. At present, the optical resonance surface is formed by a complicated method such as a method of precisely controlling (see Japanese Patent Application Laid-Open No. 9-275243).

The present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances, and is directed to a III-V semiconductor device suitable for forming a quantum structure including a plurality of III-V compound semiconductor crystal regions having different nitrogen composition ratios. It is possible to form a group III compound semiconductor heterojunction structure, and to form a low-level region having a region in which a band gap is selectively different inside a group III-V compound semiconductor layer without using a complicated method as in the related art. It is an object of the present invention to provide a group III-V compound semiconductor device capable of easily obtaining a three-dimensional quantum structure and a method for manufacturing the same.

[0016]

In order to solve the above-mentioned problems, the present invention provides the following group III-V compound semiconductor device and a method for manufacturing the same. That is, the group III-V compound semiconductor device according to claim 1 is a semiconductor device having a heterojunction structure made of a group III-V compound semiconductor, and includes a first crystal region made of a group III-V compound semiconductor. The selected region is a second crystal region obtained by substituting a part or all of the group V atoms with nitrogen atoms, and the second crystal region and the first crystal region surrounding the second crystal region. Is characterized in that a heterojunction structure is formed by the above crystal region.

The III-V compound semiconductor device according to claim 2 is the III-V compound semiconductor device according to claim 1, wherein the first crystal region surrounding the second crystal region is formed by: Part or all of the Group V atoms are replaced with nitrogen atoms, and the band gap of the first crystal region replaced with the nitrogen atoms is different from the band gap of the second crystal region. Features.

Further, in the III-V compound semiconductor device according to the third aspect, in the III-V compound semiconductor device according to the first or second aspect, the nitrogen composition ratio of the first crystal region is equal to the second composition ratio. 3% compared to the nitrogen composition ratio in the crystal region of
It is characterized by having the above differences.

The III-V compound semiconductor device according to the fourth aspect is the III-V compound semiconductor device according to the first, second or third aspect.
In the group III compound semiconductor device, the group III-V compound semiconductor is formed of gallium arsenide (GaAs), gallium arsenide.
Indium (Ga _X In _Y As: 0 <Y ≦ 1, X + Y =
1) Aluminum gallium arsenide (Al _W Ga _X As:
0 <W ≦ 1, W + X = 1).

A method of manufacturing a III-V compound semiconductor device according to claim 5 is a method of manufacturing a semiconductor device having a heterojunction structure made of a III-V compound semiconductor. A second crystal region is formed by subjecting a selected region in the first crystal region consisting of: to a nitrogen substitution treatment for substituting a part or all of the Group V atoms with nitrogen atoms; and forming a second crystal region. A heterojunction structure is formed by the region and the first crystal region surrounding the second crystal region.

According to a sixth aspect of the present invention, in the method of manufacturing a III-V compound semiconductor device according to the fifth aspect, after forming the second crystal region, The first crystal region surrounding the second crystal region is subjected to a nitrogen substitution treatment for substituting a part or all of the group V atoms with nitrogen atoms, and a nitrogen composition ratio of the first crystal region is reduced. It is characterized in that the nitrogen composition ratio is different from that of the second crystal region.

According to the present invention, a bulk crystal made of a group III-V compound semiconductor and a group III-V compound semiconductor crystal layer deposited on its surface by vapor phase growth or liquid phase growth are collectively referred to as III-V. It is described as a group III compound semiconductor crystal, and is also a target (material) for the nitrogen substitution treatment.
A group III-V compound semiconductor crystal that can be this material is:
B _K Al _L Ga _M In _N (Qn) _1-R N _R (0 ≦ K, L, M,
N ≦ 1, K + L + M + N = 1, 0 <R ≦ 1). Here, the symbol Q is arsenic (As) other than nitrogen (N),
Represents a Group V element such as phosphorus (P) and antimony (Sb). Note that n (where n ≧ 1) is used to represent the number of types of Group V elements other than nitrogen.

In the present invention, the nitrogen composition ratio of the inside of the group III-V compound semiconductor crystal is increased by using the atom substitution technique of substituting the group V element constituting the group III-V compound semiconductor crystal with nitrogen atoms. It is intended to form a region where the height is higher. A group III-V compound semiconductor crystal as a material can be selected. Here, considering the intention to obtain a semiconductor device with stable characteristics with high efficiency, firstly,
The simplicity of formation is the reason for choosing the material. In particular, a material which can be formed as a substrate using a group III-V compound semiconductor crystal having a clear cleavage property, conductivity, and stable supply is preferably used.

Further, according to the present invention, as nitrogen is impregnated into a selected region in the first crystal region made of a group III-V compound semiconductor, the III-V region surrounding the selected region is filled with nitrogen.
The lattice mismatch with the group V compound semiconductor crystal increases. The distortion generated by the lattice mismatch contributes to the formation of quantum levels. Therefore, to form a uniform quantum level,
The condition is that the group III-V compound semiconductor crystal of the material is constituted by a uniform crystal form, and the band structure is constituted by a uniform "field".

Boron arsenide (BAs) and boron phosphide (BP)
In many cases, the boron (B) -containing III-V compound semiconductor crystal layer such as that described above is formed at a relatively high temperature exceeding approximately 800 ° C. Therefore, the material of the substrate is limited to a material which is excellent in heat resistance but is electrically insulating, for example, sapphire (α-Al ₂ O ₃ ), silicon carbide (SiC) and the like. Since these substrate materials are not lattice-matched with the B-containing III-V compound semiconductor crystal, it is difficult to obtain a high-quality B-containing III-V compound semiconductor crystal layer with few crystal defects.

In addition, boron nitride (BN) can have both hexagonal and cubic crystal systems (Yasuharu Suematsu: Optical Device, pp. 28-29).
(Corona Co., Ltd., May 15, 1997, first edition, 8th edition)
Printing). For this reason, it is difficult to unify to one of the crystal systems, and even if a heterojunction structure is formed, it is difficult to form a band that provides a stable quantum level. Therefore, boron (B) is not an essential Group III component in the group III-V compound semiconductor crystal to be subjected to the nitrogen substitution treatment of the present invention.

The GaP growth layer formed by vapor phase growth or liquid phase growth can be converted to GaP _1-R N _R (0 <R ≦ 1) in a selective region by a nitrogen substitution treatment. . That is, in the specified region, GaP /
A GaP _1-R N _R (0 <R ≦ 1) heterojunction structure can be formed.

However, phosphorus (P) is converted to arsenic (A)
In some cases, the heterojunction interface formed becomes disordered due to the thermal diffusion of P, depending on the conditions of the nitrogen replacement treatment involving heating described later, since the diffusion (movement) is easier due to heating as compared with s). The steepness of the interface may be impaired. III-V containing antimony (Sb)
In the case of a group III compound semiconductor, uniform film formation is difficult in the first place. Therefore, II containing Group V elements other than nitrogen
In the IV group compound semiconductor crystal layer, a compound containing As as a constituent element is more preferable as a target of the nitrogen substitution treatment.

Further, the nitrogen substitution treatment of the present invention can be carried out by the method of III-
By substituting the group V element other than nitrogen in the group V compound semiconductor crystal layer with nitrogen, the group III-V compound semiconductor crystal layer not containing nitrogen as a constituent element can be easily replaced with nitrogen-containing II.
It can be converted to an IV group compound semiconductor crystal layer. Moreover, the exchange ratio of Group V elements other than nitrogen by nitrogen atoms, that is, the nitrogen composition ratio is from several percent to approximately 100%.
It is possible to control in a wide range up to. Therefore, in the present invention, the III-V compound semiconductor crystal layer containing nitrogen (N) can also be subjected to the nitrogen replacement treatment.
It is not always necessary to intentionally perform a nitrogen substitution treatment on the group III-V compound semiconductor crystal layer containing nitrogen in advance.

Therefore, according to the present invention, in the III-V compound semiconductor crystal represented by the above composition formula, Al
_{L Ga M As (0 ≦ L} , M ≦ 1, L + M = 1, Q = A
s), Ga _M In _N As (0 ≦ M, N ≦ 1, M + N = 1,
Q = As) are the main targets of the nitrogen replacement treatment.
Since these crystals have a uniform sphalerite-type crystal structure, they are particularly superior in forming a crystal layer having a uniform and uniform band structure.

The main object of Al _L Ga _M As (0 ≦
L, M ≦ 1, L + M = 1) Crystal layer and Ga _M In _N As
(0 ≦ M, N ≦ 1, M + N = 1) The crystal layer can be formed, for example, by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), halogen, or hydride vapor. A film can be formed by a phase growth method or the like. At the time of film formation, GaAs or InP bulk exhibiting good matching with these crystal layers.
Crystals can be used as substrate materials.

Here, there is no specific plane orientation of the crystal plane constituting the surface. For example, the crystal plane is {001},
A group III-V compound semiconductor crystal represented by {011} or {111} can be used. Also, for example, a bulk crystal having a so-called off-angle plane as a surface, in which the crystal plane is inclined several degrees or several tens degrees from {001}, can be used. Also,
These group III-V compound semiconductors have a bulk single crystal of zinc-blend (zinc-blend) structure.
1] It shows a clear cleavage property in the direction. Therefore, in the LD, there is an advantage that the optical resonance surface can be easily formed by utilizing this cleavage. Furthermore,
If a bulk crystal exhibiting n-type or p-type conductivity instead of semi-insulating (intrinsic: i-type) is used as a substrate, there is the advantage that an ohmic electrode can be formed on this substrate. This is advantageous in forming an electrode of an ohmic device.

In the present invention, in order to form a heterojunction structure exhibiting a quantum effect in a selective region, heat treatment is selectively performed only in a specific region of the group III-V compound semiconductor crystal layer. A nitrogen substitution treatment is performed. As a specific method of performing the nitrogen replacement treatment only in a specific region, for example, a method using a so-called laser annealing technique in which a specific region is irradiated with a laser beam focused in a minute spot shape is considered. Can be However, in this technique, it is necessary to control the irradiation position of the laser light with high precision and scan the laser light for each selected area. However, there occurs a problem that thermal distortion occurs due to a temperature difference between the selected region and a non-irradiation region around the selected region.

Therefore, in the present invention, this laser annealing technique is not adopted, and a specific region to be subjected to the nitrogen substitution treatment is provided with an opening in the film applied on the surface of the III-V compound semiconductor crystal layer. Set by In other words, as a film for performing heat treatment on a selective region of the group III-V compound semiconductor crystal (or crystal layer), an opening for exposing a specific region on the surface of the crystal (or crystal layer) is used. Is an essential requirement.
When the group III-V compound semiconductor crystal layer thus patterned is exposed to an atmosphere for performing a nitrogen substitution process and is heated at a time, a laser beam is irradiated as in the laser annealing technique described above. There is an advantage that nitrogen replacement can be performed collectively without scanning.

As the film, a material that satisfies at least the three requirements of high heat resistance, low volatility, and low decomposition is used. For example, undoped silicon dioxide (SiO ₂ ), undoped silicon nitride (Si ₃ N ₄ )
And the like are preferably used. Arsenic (A
As-doped SiO ₂ film doped with s), As
The doped Si ₃ N ₄ film or the like has an excellent effect when it is desired to suppress the volatilization of As from the surface due to the heat treatment of the present invention. Therefore, for example, As-containing III such as GaAs
It is suitably used as a film of a group III compound semiconductor crystal layer.
Further, the coating is made of aluminum gallium nitride (A
_{l L Ga M N: 0 ≦} L ≦ 1, L + M = 1) may be constituted by a high melting point of the Group III-V nitride semiconductor formed of such.

The shape of the opening of the coating is determined in consideration of the target quantum structure. For example, when forming a quantum wire, a linear (or band-shaped) opening is provided in the coating. In a typical lattice-matched heterojunction structure, a quantum (wire) structure is formed by surrounding a line (band) layer as a well layer with a barrier layer wider than the well layer. Is common. Therefore, in order to form a quantum wire structure from a lattice-matched heterojunction structure, a region to be subjected to the nitrogen substitution treatment is used as a barrier layer or a well layer corresponding to either a line (band). It is necessary to change the width of the opening.

When a quantum wire structure is formed from a lattice-matched heterojunction structure, the width of the well layer is several nm to several tens nm.
It is necessary to precisely process a predetermined width in the range with an error of at least several mm. The barrier layer has a thickness of about several tens of nm, at most about 60 to 70 nm. Therefore, it is difficult to form such an opening having such a small width in a coating film by a general photolithography technique, and a precision microfabrication technique which requires scanning in a high vacuum environment such as a focused ion beam technique is required. Becomes possible.

The above-mentioned III-V compound semiconductor crystal and the nitrogen-containing III-V compound semiconductor crystal of the present invention do not have a lattice matching relationship. That is, the heterojunction structure provided by the present invention has a lattice mismatched structure.
Therefore, according to the present invention, it is possible to form a strained quantum well structure having lattice strain based on a difference in lattice constant at the junction interface. In such a strained quantum well structure, rather than precisely controlling the width of a well layer or a barrier layer,
Rather, it is important to control the steepness of the heterojunction interface between them. Therefore, it is more important to clarify the boundary between the opening and the non-opening than to precisely control the opening width corresponding to the width of the well layer and the barrier layer.

Of course, if the patterning of the coating film at the boundary between the opening and the non-opening portion can be surely performed without so-called "sagging", an opening portion and a non-opening portion having a clear boundary can be obtained. For example, patterning that can form a clear boundary can be sufficiently performed by using a general photolithography technique, but this technique is complicated and requires precision. On the other hand, in the present invention, I
By performing the nitrogen substitution process only on a specific region of the II-V compound semiconductor crystal layer, a strained quantum well structure in which the steepness of the heterojunction interface is controlled can be formed. It has the convenience of not requiring advanced technology.

To form a quantum box, for example,
An opening having a square planar shape such as a square or a rectangle is formed. Further, a film in which an opening having a planar shape such as a circle or a polygon is formed in a film is suitable for forming a quantum dot. Since the quantum box or quantum dot formed by the present invention is a lattice-mismatched system, in these quantum well structures, rather than their size, the structure forming the quantum well and the surrounding body Lattice strain between and plays a large role in the development of quantum levels. Therefore, an opening for forming a quantum box or a quantum dot having such a strained quantum well structure (also referred to as a strained superlattice structure) is formed by ordinary photolithography with respect to the coating film, as in the case of the quantum wire described above. It can be easily formed using a combination of techniques, patterning techniques, etching techniques and the like.

For example, As-doped S on a GaAs crystal layer
After a general resist material is applied to the surface of the iO ₂ film, exposure is performed through a glass mask or the like on which a pattern is drawn, and the resist material is subjected to patterning. After this patterning process, a resist process is performed to remove unnecessary resist material. The region where the resist material has been stripped is in a state where the SiO ₂ coating is exposed. Then, the exposed region of SiO
_{(2) If the} coating is removed substantially vertically so that the side walls of the coating remain clearly, a coating having an opening formed only in a selected region can be obtained.

In the present invention, in the atmosphere containing a nitrogen-containing substance, a nitrogen substitution treatment involving heating is applied only to the group III-V compound semiconductor crystal layer exposed at the opening of the film.
The nitrogen substitution treatment means that a group V element such as arsenic (As) constituting a group III-V compound semiconductor crystal layer is replaced with a nitrogen atom (N).
Is a process of replacing with. That is, I
This is a process for increasing the nitrogen composition ratio in the II-V compound semiconductor crystal.

For example, Al _L Ga _M As (0 ≦ L ≦ 1, L
+ M = 1 In _{the), Al L Ga M As 1} -U N U (0 ≦ L ≦ 1 by performing nitrogen substitution process, L + M = 1,0 <
U ≦ 1). In addition, Ga _M In _N As (0 ≦ M
≦ 1, M + N = 1 In the), Ga _M by performing nitrogen substitution process _{In N As 1-U N U} (0 ≦ M ≦ 1, M + N =
1, 0 <U ≦ 1). Note that the nitrogen substitution treatment of the present invention also corresponds to a case where a nitrogen composition ratio (U) is 100%, that is, a group V element other than nitrogen is converted to a group III-V compound semiconductor crystal layer of 0%. The purpose of heating is II
Vacancy of the group V element (V), which promotes the elimination of the group V element such as arsenic (As) constituting the group IV compound semiconductor crystal layer and effectively works to improve the efficiency of substitution by the nitrogen atom ( This is for increasing the density of the holes.

The following methods are mainly used as the nitrogen replacement treatment involving heating in the present invention. (1) Simple heat treatment method In this method, a material is heated in an atmosphere containing a nitrogen-containing substance to volatilize a group V element such as As or P, whereby the group V element is stoichiometrically In a state in which the material is in an insufficient state and nitrogen is infiltrated into the material in this state to increase the nitrogen composition ratio, in the same group III-V compound semiconductor crystal layer, generally, the higher the processing temperature, the more the processing temperature becomes higher. A high nitrogen composition ratio is obtained. In the case of using the heat treatment method, if a heat treatment is performed after a pre-process for promoting desorption of As or P from the growth surface by exposing the growth layer to a vacuum environment in advance or the like, nitrogen This is advantageous because the replacement efficiency can be further improved.

(2) Vacuum Plasma Method In this method, a material is heated and left standing in a vacuum to promote the volatilization of a group V element such as As or P, and a plasma comprising a nitrogen-containing ionized gas generated in a vacuum. (Plasma) to allow nitrogen in the plasma to penetrate into the material, resulting in a crystal having a large nitrogen composition ratio in a specific region in the material.

In the above methods (1) and (2), A
Substantially all of the Group V elements such as s atoms can be replaced with nitrogen atoms. Therefore, it is difficult to obtain a stable gas by the conventional vapor deposition method.
The group IV nitride semiconductor crystal layer can also be easily formed. The method for increasing the nitrogen composition ratio as described above can be carried out in combination with another process technology. For example, in the ion implantation technique, any of the above methods can be performed as an annealing after the ion implantation.

The heating temperature at which the effect of increasing the nitrogen composition ratio of the group III-V compound semiconductor crystal is recognized depends on the type of the group III-V compound semiconductor to be treated. In other words, the optimum heating temperature for each group III-V compound semiconductor can be roughly determined based on the melting point of the group III-V compound semiconductor crystal used. For example, the melting point of aluminum arsenide (AlAs) is 1
760 ° C. and the melting point of GaAs is 1238 ° C. (These melting points are described in Iwao Teramoto: Introduction to Semiconductor Devices, p.
28, (March 30, 1995, first edition, published by Baifukan Co., Ltd.).

Therefore, Al _L Ga _M As (0 ≦ L ≦ 1, L + M = 1) which is the main object of the nitrogen substitution treatment of the present invention.
In the above, good results can be obtained by setting the heating temperature higher as the Al composition ratio (L) increases. This Al _LG
The temperature at which impregnation of nitrogen atoms into a _M As (0 ≦ L ≦ 1, L + M = 1) is, for example, Al _0.20 Ga _0.80 As
In this case, the temperature is about 700 ° C. For the Al _L Ga _M As, the temperature at which the effect of the nitrogen replacement process is remarkably observed is due to the increase in the Al composition ratio (L), more shifts to a high temperature. In the case of GaAs, the temperature at which the region near the surface has begun to be converted to gallium arsenide nitride mixed crystal (GaAs _1-R N _R : 0 <R ≦ 1) is, for example, ammonia (NH) at approximately atmospheric pressure. ₃ ) It is around 600 ° C under the atmosphere.

As described above, in the nitrogen replacement treatment of the present invention, the nitrogen composition ratio can be increased as the heat treatment is performed at a higher temperature. On the other hand, for example, in the case of Al _L Ga _M As, if the heating temperature is set to a temperature near the melting point of GaAs (1238 ° C.), there arises a problem that the surface state of the Al _L Ga _M As crystal deteriorates. This surface morphology (morpho
is mainly caused by the generation of Ga droplets, which are group III constituent elements, due to the volatilization of As. When the heat treatment is performed in a state where Ga droplets are generated, Al _L
The surface layer of the Ga _M As crystal, there is a case where polycrystalline layer is formed alignment direction consists irregular plate-like nitrogen-containing group III-V compound semiconductor single crystal is superimposed. In this polycrystalline layer, there occur problems such as non-uniformity in electrical characteristics, such as a difference in resistance due to a difference in the direction of current flow. Therefore, Al _L aimed at increasing the nitrogen composition ratio
In the heat treatment of Ga _M As is the processing temperature, desirably equal to or less than about 1000 ° C.. More preferably, the temperature is set to 900 ° C. or lower.

The melting point of indium arsenide (InAs) is 943 ° C. (Iwao Teramoto: Introduction to Semiconductor Devices, p.
28, (March 30, 1995, first edition, published by Baifukan Co., Ltd.). Therefore, in the Ga _M In _N As for the main target of the nitrogen replacement process of the present invention (0 ≦ M ≦ 1, M + N = 1) is generally the temperature in the heat treatment than the case of the Al _L Ga _M As Set lower. Further, the heating temperature for the nitrogen replacement treatment is set lower as the indium composition ratio (N) is higher. The range of the heating temperature suitable for this Ga _M In _N As is generally 650 ° C. or lower and 350 ° C. or higher.

The reason for this is that if the heating temperature exceeds about 700 ° C., there arises a problem that the surface state of the crystal layer deteriorates due to the generation of In and Ga droplets. Further, in the Ga _M In _N As, but the impregnation of nitrogen is observed even at a low temperature of about about 350 ° C., at low temperatures, can not be sufficiently performed thermal decomposition of nitrogen-containing substances in the atmosphere during the heat treatment. That is, it is not possible to sufficiently release nitrogen atoms for substituting the group V element into the atmosphere during the heat treatment, resulting in inefficiency of the nitrogen substitution treatment. Therefore, regardless of the Ga _M In _N As or Al _L Ga _M As, the heating temperature is preferably set to at least 400 ° C. at a minimum.

The nitrogen replacement treatment with heating is carried out by using the raw material I
II-V compound semiconductor crystal with N atom
In order to perform the substitution of the group element, it is performed in an atmosphere composed of a gaseous substance containing N atoms. Examples of the gaseous substance containing N atoms include nitrogen gas (N ₂ ) and ammonia (NH ₃ ). However, for example, a nitro group (-N
Compounds having a functional group containing an oxygen (O) atom, such as O ₂ ) or an acetamido group (—NH—CO—CH ₃ ), even if they contain a N atom, are included in the atmosphere constituting the heat treatment atmosphere of the present invention. It is not preferable as a nitrogen substance. The reason is that oxygen (O) generated by thermal decomposition may act as a trap (deep trap) that forms a deep level with respect to the group III-V compound semiconductor.
Further, a compound containing a cyano group (—CN) is also unsuitable as a nitrogen-containing substance constituting an atmosphere during heat treatment from the viewpoint of toxicity.

In the present invention, as the nitrogen-containing substance constituting the atmosphere during the heat treatment, a nitrogen-containing substance containing a bond (N—H) between an N atom and a H atom is particularly preferably used. The reason is that the H atom released by the dissociation of the NH bond is Ga
Combined with _M an In _N As or Al _L Ga _M As crystal layer As the exposed and on the surface of, because generating a more volatile arsenic compounds. Thereby, on the surface layer of the crystal layer,
As vacancies in which As atoms have escaped can be made to exist at a high concentration, and nitrogen can be efficiently impregnated.

Including a bond (N—H) between an N atom and an H atom
As the nitrogen-containing substance, the above-mentioned NH _ThreePlus hydrazi
And compounds such as methylhydrazine can be used.
You. Also, amines such as methylamine and dimethylamine
Can also be used. Also, pyrrole, etc.
Can also be used. In particular, NH
Thermal decomposition even at temperatures below 400 ° C
Starting with asymmetric molecular structure type dimethylhydrazine, etc.
It is particularly suitable as a substance constituting an atmosphere.

The atmosphere for the heat treatment can be constituted by using a mixed gas of a nitrogen-containing substance and an inert gas such as hydrogen (H ₂ ) gas or N ₂ gas or argon (Ar). As this mixed gas, H ₂ —NH ₃ system, Ar—NH
₃ system, N ₂ -NH ₃ system, H ₂ -N ₂ -NH ₃ system, N ₂ -Ar-
A mixed gas such as hydrazine is preferably used. When the atmosphere for heat treatment is formed from these mixed gases, the volume occupancy of the gas composed of the nitrogen-containing substance is desirably approximately 50% or more. Here, as the processing temperature is set lower and the decomposability of the substance is lower, the partial pressure of the nitrogen-containing substance constituting the atmosphere is set higher.

Further, the atmosphere can be constituted by only the nitrogen-containing substance alone. That is, for example, the heat treatment can be performed in an atmosphere consisting only of NH ₃ . The nitrogen substitution efficiency (the ratio (ratio) at which Group V elements such as As and P are substituted by N atoms) is determined, for example, by secondary ion mass spectroscopy (SIMS) or Auger electron spectroscopy (AES). : Auger Electron Spe
ctroscopy). In these, the analysis can be performed quantitatively based on the detection signal intensity ratio between the group V element such as As and P and the N atom.

In the present invention, in order to mainly form a quantum well structure in one crystal layer, a region having a different nitrogen composition ratio from a surrounding region is selectively formed in the crystal layer. .
In order to form a heterojunction structure exhibiting the quantum effect, a difference in the band gap sufficient to provide a quantum level is provided between the region subjected to the nitrogen substitution treatment and the surrounding region surrounding the region. There is a need to. In order for a region that has been selectively subjected to nitrogen replacement to be a region that has a barrier effect on the surrounding region, the band gap of the region that has been subjected to nitrogen replacement is larger than the band gap of the surrounding region. It consists of the following substances.
That is, the nitrogen replacement processing is performed so as to increase the forbidden band width.

On the other hand, in order to make a region selectively subjected to the nitrogen substitution treatment a well layer or a carrier confinement region with respect to the surrounding region, the band gap of the region is smaller than the band gap of the surrounding region. Is performed. Regardless of whether the nitrogen-substituted region is a region providing a barrier effect, a well layer, or a carrier confinement region, a forbidden band between two regions in a heterojunction structure necessary for creation of a quantum level. It is desirable that the difference between the widths is about 0.1 eV or more. This is because the difference in the forbidden bandwidth is 0.1
If it is less than eV, it is difficult to obtain a barrier sufficient to confine carriers. In particular, a heterojunction structure provided with a difference in band gap of 0.3 eV or more is suitably used for a quantum well structure.

Here, the band gap at room temperature is about 1.4.
GaAs of 3 eV is selectively subjected to nitrogen substitution treatment,
GaAs with bandgap suitable for providing a barrier effect
_1-U N will be described taking as an example a case of converting the _U mixed crystal. This G
In aAs _1-U N _U mixed crystal, considering its bowing (bowing), it is possible to obtain the GaAs equivalent band gap at a concentration of from about 0.66 nitrogen composition ratio (U). Therefore, GaAs _1-U having a barrier effect on GaAs
In order to obtain N _U , it is basically necessary to perform a nitrogen substitution treatment so that the nitrogen composition ratio (U) exceeds 0.66.

Further, the band gap is about 0.3 than GaAs.
nitrogen composition ratio of eV than GaAs _1-U N U mixed crystal, larger, is about 0.73. Therefore, for example, GaA
In the s crystal, the band gap is about 0.3 e than that of GaAs.
To form a region consisting GaAs _1-U N _U mixed crystal is a V large, it is necessary to perform nitrogen substitution process with a nitrogen substitution efficiency of more than 73%. Further, in the _{Al L Ga M As 1-U} N heterojunction structure consisting of _U mixed crystal, the material thereof Al
_L Ga _M As 0.3 regardless almost Al composition ratio (L) of
In order to give a difference in the band gap of eV, it is necessary to make the nitrogen composition ratio differ by at least 3% or more.

Conversely, GaAs having a band gap smaller than that of GaAs by about 0.3 eV is formed inside the GaAs crystal.
s _1-U N to selectively form a heterojunction structure with _U mixed crystal, to the selected area, nitrogen substituted so that nitrogen composition ratio in the range of from about 0.08 to about 0.59 It is desirable to apply a treatment. In particular, in the GaAs _1-U N _U mixed crystal, as long as it is within the range nitrogen composition ratio is about 0.3 to about 0.4, the band gap is extremely small (Mat. Res. Soc . Symp. Proc.
vol.449. pp.203-208 (1997)). As described above, in a heterojunction structure in which a region subjected to a nitrogen substitution process exhibiting metallic conduction is distributed and arranged in a single crystal layer, the region subjected to the nitrogen substitution process is, for example, a device. It can also be used as an electrode.

In the present invention, for example, a group III-V compound semiconductor crystal layer containing microcrystals in the form of quantum dots is formed by selectively subjecting one crystal layer to a nitrogen substitution treatment. Is used as the light emitting layer, the quantum dot L
D is obtained. A crystal layer in which GaAs _0.10 N _0.90 crystal is embedded in a selected region of the GaAs _0.15 N _0.85 crystal layer is used as a light emitting layer of a light emitting element including a quantum wire structure having a band gap different by about 0.3 eV. be able to.
Further, the use of GaAs _0.15 N _0.85 crystal layer was formed a box-like GaAs _0.10 N _{0. 90} crystals therein, it is possible to obtain a light emitting device having a quantum box structure.

This GaAs_0.10N_0.90Crystal embedded
GaAs_0.15N_0.85In order to obtain a crystal layer, nitrogen replacement
The entire surface of a crystal layer to be applied, for example, a GaAs crystal layer
First, a nitrogen replacement treatment with a nitrogen replacement efficiency of 85%
And GaAs_0.15N_0.85It is a crystal layer. Then,
GaAs_0.15N_0.85In the band-shaped (box-shaped) region of the crystal layer,
Selective nitrogen replacement with 90% nitrogen replacement efficiency
Alms, GaAs_0.10N _0.90Crystal.

According to the present invention, the crystal layer, which is selectively subjected to the nitrogen substitution treatment and has a region having a band gap different from the surrounding region, has a fine structure such as a quantum well structure. Even if not, it is useful as a constituent layer of a semiconductor device. For example, a region corresponding to a recessed portion of a gate electrode, for example, a region having a width of several μm and a depth of less than about 0.1 μm is subjected to a nitrogen substitution process so that the band gap is larger than other regions. The crystal that has been
e) A field effect transistor (FE) that improves withstand voltage
T: Field Effect Transistor channel
Available as layers.

[0065]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a III-V compound semiconductor device of the present invention and a method for manufacturing the same will be described with reference to the drawings. FIG. 1 shows a modulation doping type field effect transistor (MODFET: Modula) according to an embodiment of the present invention.
FIG. 1 is a schematic diagram showing a cross-sectional structure of a semiconductor device (III-V compound semiconductor element) of a MODFET. In this MODFET, a region for forming a gate electrode in a single crystal layer is selectively subjected to a nitrogen substitution process. The forbidden band width of this region is partially larger than the forbidden band width of the surrounding region to form a channel layer.

The MODFET will be described in more detail. A high resistance GaAs buffer layer 2 is formed on a GaAs substrate 21.
2. An n-type channel layer 23 made of GaAs and an electron supply layer (first crystal region) 24 made of n-type Al _0.30 Ga _0.70 As doped with δ are sequentially laminated. Then, a surface region (second crystal region) 24a, which will be a recess structure portion described later, in a substantially central portion of the electron supply layer 24 is subjected to a nitrogen substitution treatment so that a part or all of the group V atoms are N atoms.
Al _0.30 Ga _0.70 As _1-U N _U substituted with atoms (0 <U
.Ltoreq.1), and the forbidden band width of the surface region 24a is larger than the forbidden band width of the surrounding region 24b surrounding the surface region 24a.

On the other hand, the source (so
The low-resistance n-type GaAs contact layer 2 is located at the position where both ohmic electrodes for the urce and the drain are arranged.
5 and 26 are stacked, and a source electrode 27 is formed on the contact layer 25, and a drain electrode 28 is formed on the contact layer 26, respectively. And this contact layer 2
Substantially central portions of the electron supply layers 5, 26 and the electron supply layer 24 are removed by etching to form a recessed portion 31, and a gate having a multilayer structure in which a Ti layer, an Al layer, and the like are laminated on the surface region 24a of the recessed portion 31. An electrode 32 is formed. This M
In the ODFET, a heterojunction structure is formed by the surface region 24a and the surrounding region 24b surrounding the surface region 24a.

Next, a method of manufacturing the MODFET will be described. First, a high-resistance G is formed on a GaAs substrate 21.
aAs buffer layer 22, n-type channel layer 2 made of GaAs
3. An electron supply layer 24 made of n-type Al _0.30 Ga _0.70 As doped with δ is sequentially laminated. Next, a nitrogen replacement process is performed only on the surface region 24a where the recess structure 31 at the substantially central portion of the electron supply layer 24 is to be formed. By this processing operation, the forbidden band width of the surface region 24a becomes larger than the forbidden band width of the surrounding region 24b.

Here, the Al constituting the electron supply layer 24 is
_0.30Ga_0.70Is the band gap of As about 1.65 eV?
Al that constitutes the surface region 24a_0.30Ga_0.70As
_1-UN_UForbidden band width of (0 <U ≦ 1) from about 1.65 eV
In order to obtain a wide bandgap, the nitrogen composition ratio (U) is about
It is necessary to perform a nitrogen substitution process so that it becomes 0.66 or more.
You. That is, in this case, Al_0.30Ga_0.70As / Al
_0.30Ga_0.70As_0.34N _0.66Heterojunction structure of both substances
The difference in the nitrogen composition ratio is 66%.

The depth of Al _0.30 Ga _0.70 As _{1 -U} N _U (0 <U ≦ 1) formed in the surface region 24 a by the nitrogen substitution treatment is set to be several hundred degrees thick just below the gate electrode 32. It is preferable to set so as to leave the layer. Next, low resistance n-type GaAs contact layers 25 and 26 for arranging both source and drain ohmic electrodes are stacked on the electron supply layer 24. Next, the gate electrode 3
In order to form 2, a substantially central portion of the contact layers 25 and 26 and the electron supply layer 24 is removed by etching to form a recess 31. Next, a gate electrode 32 having a multilayer structure such as a Ti layer and an Al layer is formed on the surface region 24a of the recess portion 31 which has been subjected to the nitrogen replacement treatment.
And

The complexity involved in forming a conventional group III-V nitride semiconductor quantum structure results from frequent changes in the film formation temperature. In turn, a general III-V compound semiconductor layer such as GaAs or AlGaAs can be generally formed at a temperature of less than about 800C. Since the film can be formed at a relatively low temperature, a group III-V compound semiconductor single crystal can be used as the substrate. In addition, GaAs / AlGaAs
The s heterojunction structure also has an advantage that a film can be formed without changing or hardly changing the film forming temperature.

That is, in the present embodiment, a III-V compound semiconductor which can be easily formed into a film is used as a base material.
Since it is possible to manufacture a quantum well structure made of a -V nitride semiconductor, it is possible to overcome at least the problems associated with the conventional manufacturing method described above.

FIG. 2 is a diagram showing the atomic concentration distribution in the depth direction of GaAs subjected to the nitrogen substitution treatment.
The type (001) -GaAs single crystal was formed at 700 ° C. for 15 minutes.
After heat treatment in an H ₂ gas stream, and subsequently, heat treatment (nitrogen replacement treatment) in the NH ₃ gas stream at the same temperature for 15 minutes, secondary ion mass spectrometry (Secondary IonMass) was performed.
Spectrometry) to measure the atomic concentration distribution in the depth direction from the surface. Here, As, N, H, O
The atomic concentration distribution was measured for each of the four elements.

According to FIG. 2, the concentration distribution of N atoms shows a normal distribution having a local maximum near the surface, and the normal film formation method shows any one of monotonically increasing, monotonically decreasing, and substantially constant concentration distributions. Is significantly different from that shown. Further, since the As atoms are replaced with N atoms, the concentration distribution of the N atoms exhibits a distribution corresponding to the decrease in the concentration of the As atoms. Is very different. The concentration distribution of H atoms and O atoms also shows a distribution similar to the concentration distribution of N atoms.

As described above, according to the present embodiment, the surface region 24a of the electron supply layer 24 is subjected to a nitrogen substitution treatment, and a part or all of the group V atoms are substituted with N atoms. Al _0.30 Ga _0.70 As _1-U N _U (0 <U ≦ 1)
Since the forbidden band width of the surface region 24a is larger than the forbidden band width of the surrounding region 24b surrounding the surface region 24a, the gate withstand voltage is reduced by forming the gate electrode 32 on the surface region 24a. Improvement can be achieved, and leakage current can be reduced. Further, according to the nitrogen replacement treatment of the present embodiment, a crystal region having a high gate withstand voltage can be included in a single crystal layer in a plane, so that a high resistance layer is intentionally formed as seen in a conventional FET. Since it is not necessary to form a film in a laminated structure of a base material, the device is excellent in terms of device fabrication.

Further, according to the nitrogen replacement treatment of this embodiment, the nitrogen replacement treatment is performed only on the surface region 24a of the electron supply layer 24, and the band gap of the surface region 24a is reduced to the band gap of the surrounding region 24b. Since the width is larger than the width, the surface area 24
The nitrogen composition ratio of a can be easily increased, and a heterojunction structure can be formed by the surface region 24a and the surrounding region 24b. Therefore, a MODFET with improved gate breakdown voltage and reduced leakage current can be easily manufactured.

Here, examples of the present embodiment will be described. [Embodiment 1] In this embodiment, a nitrogen replacement process (also referred to as a nitrogen replacement process) is performed in advance only on a specific region of a GaInAs crystal layer grown by a metal organic chemical vapor deposition (MOCVD) method. on the GaInAs crystal layer band (stripe-shaped) _{Ga X in Y As 1-U} N U (0 <Y ≦ 1, X
+ Y = 1, 0 <U ≦ 1), thereby forming a strained-lattice heterojunction structure by both junctions.

First, as shown in FIG.
An S-doped n-type InP vapor growth layer 42 and an S-doped n-type Ga _0.47 In _0.53 As mixed crystal layer 43 are sequentially deposited on a substrate 41 made of n-type InP single crystal doped with sulfur (S) by CVD. Thus, a laminated structure 44 was obtained. here,
The plane orientation of the substrate 41 was (001), and an S-doped n-type InP vapor deposition layer 42 was first deposited on the substrate 41. Next, on this InP vapor deposition layer 42, In
An S-doped n-type Ga _0.47 In _0.53 As mixed crystal layer 43 having lattice matching with P and an In composition ratio of 0.53 was deposited.

The InP vapor deposition layer 42 and Ga _0.47 I
Both the n _0.53 As mixed crystal layer 43 were formed at 610 ° C. Trimethylgallium ((CH ₃ ) ₃ Ga) was used as a Ga source. As the In source, cyclopentadienyl indium (C ₅ H ₅ In) having a monovalent valence was used (J. Cry).
stal Growth, 107, pp. 360-364 (1991)). Further, as the As supply source, high-purity hydrogen mixed with arsine (AsH ₃ ) at a volume concentration of 10% was used. Here, the thickness of the InP vapor deposition layer 42 is about 0.5 μm,
The carrier concentration was about 1 × 10 ¹⁸ cm ⁻³ . Also, Ga
_The thickness of the _0.47 In _0.53 As mixed crystal layer 43 was set to about 0.5 μm, and the carrier concentration was set to about 2 × 10 ¹⁸ cm ⁻³ .

Next, as shown in FIG.
The entire surface of the Ga _0.47 In _0.53 As mixed crystal layer 43, which is the outermost layer of No. 4, was undope with a thickness of about 0.1 μm.
With a silicon nitride (Si ₃ N ₄ ) film 45. This Si ₃
The N ₄ film 45 is used as a selective mask material for selectively performing a nitrogen substitution process in a later step. Next, the Si ₃ N ₄ film 45 is processed by electron beam lithography to form a plurality of strip-shaped openings 46 having a line width (opening width) of 2500 °.
Substrate <0. -1. -1. > Perpendicular to the direction and at equal intervals. Thus, as long as the opening 46, Ga _0.47 In _{0. 53} As mixed crystal layer 43 is a structure to be exposed. Here, the distance t between the center lines of the openings 46, so-called pitch, was set to 20 μm.

Next, the laminated structure 44 covered with the Si ₃ N ₄ film 45 was placed in a heat treatment furnace (heating furnace) 51 shown in FIG. 5 and subjected to a nitrogen substitution treatment. Heat treatment furnace 51 used here
A high-frequency induction coil 53 is spirally wound around the outer periphery of a cylindrical furnace body 52, and a support 54 made of high-purity graphite for supporting an object to be processed such as a laminated structure 44 is provided inside the furnace. Is mounted, and a bag closing hole 56 for inserting a thermocouple 55 is formed in the middle part of the support table 54. Ar gas and H ₂ gas are supplied to a gas inlet 57 formed at the end of the furnace body 52. Gas introduction pipe 58 and NH ₃ gas introduction pipe 5
The pipes 58 and 59 are provided with open / close valves 60 and 61, respectively. The thermocouple 55 is a platinum-platinum-rhodium alloy (Pt-
A thermocouple (Pt.Rh (13%)) (Japanese Industrial Standard JIS-R) was used.

In this nitrogen replacement treatment, first, the laminated structure 44 covered with the Si ₃ N ₄ film 45 is placed on the support base 5 in the furnace body 52.
4. After the mounting, the inside of the furnace body 52 was swept using a general vane vacuum pump or the like so that the degree of vacuum was about 2.6 × 10 ⁻² hPa. Next, the gas introduction pipe 5
After approximately is returned to atmospheric pressure with Ar gas from 8 is introduced into the furnace body 52 through the gas introducing hole 57, the Ar gas H ₂
Instead of gas, the gas was introduced into the furnace body 52 from the gas introduction hole 57 at a flow rate of 1 liter per minute.

In this state, a high frequency having a frequency of about 30 KHz is applied to the high frequency induction coil 53, and the laminated structure 44 is placed in an H ₂ atmosphere (in a reducing atmosphere) for about 30 minutes.
Was raised from room temperature to 675 ° C. The temperature of the laminated structure 44 was measured using a thermocouple 55 inserted into a bag closing hole 56 of the support base 54.

The laminated structure 44 was left on the support 54 until the fluctuation of the temperature became small, and then kept at 675 ° C. for exactly 15 minutes in an H ₂ atmosphere. Next, the open / close state of the open / close valves 60 and 61 attached to the gas introduction hole 57 was instantaneously reversed. That is, the H ₂ gas is supplied to the furnace body 52.
The on-off valve 60 is closed to supply the water into the inside, and conversely,
The on-off valve 61 for introducing NH ₃ gas was opened. Thereby, the gas introduced into the furnace body 52 is changed from H ₂ gas to N
After switching to H ₃ gas, the laminated structure 44 was kept at the same temperature for 15 minutes. Furnace body 5 via opening / closing valve 61
The flow rate of NH ₃ gas introduced into 2 was set to 1 liter per minute.

Here, the laminated structure 44 is previously exposed to the H ₂ gas atmosphere because the Ga _0.47 In _0.53 As mixed crystal exposed in the strip-shaped opening 46 of the Si ₃ N ₄ film 45 shown in FIG. This is for promoting the volatilization of As which is a Group V element constituting the mixed crystal layer 43 from the surface of the layer 43. Also, NH
_The heat treatment is performed in a _three- gas atmosphere in order to replace As atoms with N atoms.

By the heat treatment in the NH ₃ gas stream,
As shown in FIG. 4, Ga _0.47 In _{0.5 3} As mixed crystal layer 43
With Ga _0.47 In _0.53 As with a nitrogen composition ratio of 82%
It was changed to _0.18 N _{0.8 2} crystal layer 71. That is, in this embodiment, the linear Ga _0.47 In _0.53 As _0.18 N _0.82 crystal layer 71 and the Ga _0.47 In _0.53 As
A heterojunction structure having a nitrogen composition ratio different from the mixed crystal layer 43 by 82% was formed.

This NH_Three15 minutes heat treatment in gas stream
After the processing is completed, the laminated structure 44 is cooled at 30 ° C. per minute.
The temperature was lowered at a rate from 675 ° C to 500 ° C. During this time,
NH _ThreeThe gas was continuously supplied. After that, 500 ° C
From room temperature to room temperature_ThreeSwitch from gas to Ar
Allowed to cool naturally. After cooling, select the surface of the laminated structure 44
Ammonium fluoride (NH_FourF) The aqueous solution
Using Si_ThreeN_FourThe film 45 was removed.

Thereafter, the laminated structure 44 is cleaved, and the InP
<0. A section having a main side surface parallel to the -1.1> direction was prepared. This section was further sputtered with Ar, and was observed with a transmission electron microscope (TEM: transmis
A thin layer piece suitable for observation with a sion electron microscope). FIG. 6 is a schematic view showing an example of a TEM image of this thin layer piece. The region composed of the Ga _0.47 In _0.53 As mixed crystal layer 43 and the Ga _0.47 In _0.
Junction 7 with the region composed of ₅₃ As _0.18 N _0.82 crystal layer 71
2 is shown.

Also, an electron beam diffraction image obtained by the selected area diffraction method
According to (electron diffraction pattern), Ga_0.47
In_0.53The region composed of the As mixed crystal layer 43 is composed of a single crystal.
And Ga_0.47In_0.53As_0.18N_0.82
The region composed of the crystal layer 71 is mainly composed of an amorphous
s). Also,
Observation of lattice image under high magnification of about 2 million times
For example, a region composed of the mixed crystal layer 43 and a region composed of the crystal layer 71
Exists at the junction 72 with distortion due to lattice mismatch.
It was recognized that it was. That is, according to this embodiment,
If Ga_0.47In _0.53In the region composed of the As mixed crystal layer 43
Linear Ga_0.47In_0.53As_0.18N_0.82From the crystal layer 71
Thus, a strained-grating heterojunction structure including the following region was obtained.

[Embodiment 2] In this embodiment, the GaAs
Approximate sphere made of GaAsN mixed crystal inside the axial growth layer
To form a strained-lattice heterojunction structure containing fine crystal grains
Was. First, as shown in FIG.
A trimethylgallium ((CH_Three)_Three
Ga) / trimethylaluminum ((CH_Three)_ThreeAl) /
Arsine (AsH_Three: 10% AsH_Three-90% H_TwoMixed gas
S) / H_TwoGeneral atmospheric pressure (atmospheric pressure) MO using reaction system
Doping Zn at a film forming temperature of 700 ° C. by a CVD method
The grown p-type GaAs growth layer 81 is epitaxially grown.
Was. As a dopant source for Zn, a volume concentration of about 1
00 ppm of diethyl zinc ((C_TwoH_Five)_TwoZn)
Was. The carrier concentration of the p-type GaAs growth layer 81
Is 6 × 10 ¹⁸cm^-3And the layer thickness was set to about 2 μm.

Next, a Zn-doped p-type GaAs growth layer 8
1 was covered with an As-doped SiO ₂ film having a thickness of about 80 nm. Thereafter, a focused ion beam (FIB) using Ga ions for the SiO ₂ film.
Pore processing was performed by the method. Here, the diameter is 1.5μ
m and a circular opening of <0. -1. -1. >
It was formed at a pitch (interval) of 10 μm in a direction parallel to the direction and in a direction perpendicular to the direction. Areas other than these openings are A
The s-doped SiO ₂ film was kept in a crowned state. Here, the reason why the coating material was composed of As-doped SiO ₂ is that the Zn existing in the region other than the opening during the heat treatment was used.
This is to reduce the loss of As in the surface layer portion of the doped GaAs growth layer 81.

Thereafter, using the horizontal heat treatment furnace shown in FIG. 5, the Zn-doped GaAs growth layer 81 exposed to the region selectively opened in a circular shape was subjected to nitrogen substitution by the above-described FIB method. This nitrogen replacement treatment was performed according to the same procedure as in Example 1. However, the temperature for exposing in the H ₂ atmosphere and the temperature for the nitrogen replacement treatment were both changed to 700 ° C. After this nitrogen replacement treatment, at a temperature decreasing rate of about 30 ° C./min,
It was slowly cooled from 700 ° C. to about 400 ° C. in an NH ₃ gas stream. The reason for the slow cooling here is that no thermal strain is applied to the Zn-doped GaAs growth layer 81 during cooling. Thereafter, the temperature was naturally cooled from about 400 ° C. to room temperature in an Ar gas flow.

After cooling, a thin piece suitable for observation by a transmission electron microscope (TEM) is prepared by utilizing the cleavage property of the Zn-doped GaAs substrate, and a Zn-doped GaAs growth layer 81 is formed.
The morphology of the GaAsN fine crystal grains 82 selectively formed therein was observed microscopically. FIG. 7 shows Zn-doped GaAs including GaAsN fine crystal grains 82 selectively subjected to nitrogen substitution.
It is a TEM image of the growth layer 81. In the GaAs growth layer 81, the existence of substantially spherical microcrystal grains 82 having a diameter of about 2 μm was recognized. Fine crystal grains 8 existing in GaAs growth layer 81
2 was substantially spherical and the diameter was found to be approximately 2 μm.

The TEM is provided with an energy dispersive X-ray analyzer (EDX), and according to the composition analysis performed by the EDX, the fine crystal grains 82 are GaAs _0.14 N _0.86
Was identified. That is, the difference in the nitrogen composition ratio between the microcrystal grains 82 and the GaAs growth layer 81 surrounding the microcrystal grains 82 which had not been subjected to the nitrogen replacement treatment was 86%. GaA
In a junction region 83 between the s growth layer 81 and the GaAs _0.14 N _0.86 fine crystal grains 82, a strain field 84 due to the junction of crystal lattices having different sizes was formed.

Electron energy loss spectroscopy (EELS: el
As a result of analyzing the change of the forbidden band energy in the minute region by ectron energy loss spectroscopy), the strain field 84 having a region width of about 20 nm shows that the GaAs growth layer 8
1 and GaAs _0.14 N _0.86 fine crystal grains 82 were found to be in different energy states. To summarize, in this embodiment,
III- containing substantially spherical (dot-shaped) microcrystal grains 82
A method for forming a group V compound semiconductor crystal layer has been described.

[Embodiment 3] In this embodiment, a nitrogen-substituted treatment is further performed on a selected region of a group III-V compound semiconductor crystal layer that has been entirely subjected to nitrogen treatment to include a heterojunction structure. A crystal layer was formed. First, as shown in FIG. 8, a Si-doped n-type GaAs single crystal substrate 91 is
Doped n-type GaAs buffer layer 92 (layer thickness = 0.5 μm, carrier concentration = 2 × 10 ¹⁸ cm ⁻³ ), Si-doped n-type Al
_0.30 Ga _0.70 As crystal layer 93 (layer thickness = 2 μm, carrier concentration = 1 × 10 ¹⁸ cm ⁻³ ), and Si-doped n-type Al
_{A 0.10} Ga _0.90 As crystal layer 94 (layer thickness = 0.1 μm, carrier concentration = 1 × 10 ¹⁷ cm ⁻³ ) was sequentially deposited.

The three crystal layers 92 to 94 were formed by a general MOCVD method under a reduced pressure of 260 hPa. The aluminum source is trimethyl aluminum ((CH ₃ ) ₃
Al) was used. The Al composition ratio is determined by using trimethylgallium ((CH ₃ ) ₃ as a Ga source supplied to the MOCVD reaction system.
The supply amount of the Al source to the total amount of Ga) and the Al source was adjusted and controlled. The layer thickness was controlled by adjusting the growth time. As a Si doping gas, a volume concentration of 5 pp
High-purity hydrogen gas containing m disilane (Si ₂ H ₆ ) was used. The carrier concentration was adjusted by increasing or decreasing the supply amount of the Si-doped gas to the MOCVD reaction system.

Next, as shown in FIG.
A Si ₃ N ₄ film 45 was deposited on the surface of the type Al _0.10 Ga _0.90 As crystal layer 94 by a general plasma CVD method. Then, using a known near-ultraviolet exposure patterning technique, a process was performed in which the Si ₃ N ₄ film 45 was left limited to a rectangular region 95 having a width (w) of 3 μm and a length (l) of 5 μm. . The region 95 where the Si ₃ N ₄ film 45 is left is G
a <0. -1. -1. > In each of a direction parallel to the direction and a direction perpendicular to the direction, a pitch (t) of 10 μm was provided.

Then, with the Si ₃ N ₄ film 45 remaining, using the heat treatment furnace shown in FIG. 5, at 720 ° C. for 15 minutes in an H ₂ atmosphere, Si-doped n-type Al _0.10 Ga
The surface of the _0.90 As crystal layer 94 was heat-treated. Continued
Nitrogen replacement treatment was performed at 720 ° C. for 15 minutes in an NH ₃ stream. As a result, the Al _0.10 Ga _0.90 As crystal layer 94 a in a region other than the region covered with the Si ₃ N ₄ film 45 was made into an Al _0.10 Ga _0.90 As _0.11 N _0.89 crystal having a nitrogen composition ratio of 89%.

By this heat treatment, Si-doped n-type Al
_The thickness of the layer below the _0.10 Ga _0.90 As crystal layer 94 is 2 μm.
Also in Si-doped n-type Al _0.30 Ga _0.70 As layer 93 m, and the _{Al 0.30 Ga 0.70 As 0. 11 N} 0.89 crystals also to the surface portion extending to a depth of approximately 0.8μm from the surface thereof. Thereafter, cooling was performed while the supply of NH ₃ was continued from 720 ° C. to room temperature.

After cooling, the surface of the Al _0.10 Ga _0.90 As crystal layer 94 is again covered with a Si ₃ N ₄ film, and the Al _0.10 Ga
_0.90 As _0.11 N _0.89 Only in the region other than the crystal region,
Punching was performed to selectively open the Si ₃ N ₄ film. That is, contrary to the pattern shown in FIG.
m, a rectangular area having a length (l) of 5 μm is opened, and Al
The surface of a specific region of the _0.10 Ga _0.90 As crystal layer 94 was exposed.

Next, with the Si ₃ N ₄ film covered, A
At 700 ° C., a portion of the l _0.10 Ga _0.90 As crystal layer 94 exposed to the inside of the opening is subjected to nitrogen purging.
After being exposed to the H ₂ atmosphere for 10 minutes, the substrate was subjected to a nitrogen substitution treatment in an NH ₃ stream for 10 minutes. This allows
The portion exposed in the opening of the Al _0.10 Ga _0.90 As crystal layer 94 is formed by Al _0.10 Ga _0.90 As with a nitrogen composition ratio of 86%.
_The crystals were converted into 96 crystals of _0.14 N _0.86 .

As shown in FIG. 8, by performing the above-described nitrogen substitution treatment twice, a box-shaped Al _0.10 Ga is formed inside the base material composed of the Al _0.10 Ga _0.90 As _0.11 N _0.89 crystal layer 94.
A heterojunction structure containing the _0.90 As _0.14 N _0.86 crystal 96 could be formed. That is, III-V
Which is a group V element constituting a group III compound semiconductor crystal layer
Was substituted with an N atom, and a heterojunction structure comprising a nitrogen-containing group III-V compound semiconductor crystal having a nitrogen composition ratio different by 3% was able to be formed.

[Embodiment 4] In this embodiment, a light emitting device (LED; comprising a crystal layer containing a heterojunction made of a group III-V compound semiconductor crystal having a nitrogen composition ratio different by 3%);
Semiconductor element). First, as shown in FIG.
In Example 3, the Al _0.10 Ga _0.90 As _0.11 obtained by subjecting the Al _0.10 Ga _0.90 As crystal layer 94 to a nitrogen substitution treatment.
On the N _0.89 crystal layer 94a, M
g-doped p-type gallium nitride (GaN) crystal layer 97
(Layer thickness: 0.1 μm, carrier concentration: 4 × 10 ¹⁷ c
m ⁻³ ) was deposited.

The p-type GaN crystal layer 97 was used as the p-type upper cladding layer 5 hereinafter. In addition, box-shaped Al _0.10
Al _0.10 Ga _0.90 As _0.11 N _0.89 crystal layer 94 containing a heterojunction structure with Ga _0.90 As _0.14 N _0.86 microcrystal
a is the light emitting layer 13 and the surface layer portion is Al _0.30 Ga _0.70
The Al _0.30 Ga _0.70 As crystal layer 93 converted to the As _0.11 N _0.89 layer was used as the lower cladding layer 1. The diameter of the central part on the upper clad layer 5 is about 120.
A circular electrode made of μm of Au was formed to form a p-type ohmic electrode 98.

The n-type ohmic electrode 99 is formed on the entire back surface of the GaAs substrate 91, taking advantage of the advantage of using a conductive n-type GaAs single crystal as the substrate 91. The n-type ohmic electrode 99 is made of Au.G consisting of 97% Au-3% Ge containing 3% Ge by weight.
It was composed of an e-alloy. Thereafter, the substrate 9 is cut along the cleavage direction of the GaAs constituting the substrate 91 by a scribe method.
1 was cut into individual LED chips. The size of this LED chip was a square with one side of 350 μm. In addition, the light emission plane area of this LED (about 0.12 m
The number of box-like microcrystals 96 having a width of 3 μm and a length of 5 μm existing in m ² ) was calculated to be 1,225.

A DC current was applied between the n-type and p-type ohmic electrodes 98 and 99 of the LED thus obtained.
As an example, when a forward current of 20 mA was applied, blue-green light having a wavelength of about 510 nm was obtained. The half width of this emission spectrum was about 8 nm. This half-value width is less than about 2/3 of that of an LED which emits short-wavelength visible light having substantially the same wavelength and has a laminated structure in which conventional group III-V nitride semiconductor growth layers are laminated one by one. It was very good. In this case, the forward voltage was about 4V. Further, when a reverse current of 10 μA is applied between the n-type and p-type ohmic electrodes 98 and 99, the reverse voltage exceeds 10 V, and the pn junction characteristics (rectifying property) are reduced. It was shown that an excellent light emitting element was obtained.

Although the embodiments of the present invention have been described with reference to the drawings, the specific configuration is not limited to the embodiments, and a design change or the like can be made without departing from the gist of the present invention. It is. For example, the shape of the opening 46, such as the area and shape of the surface region 24a in the electron supply layer 24,
The number, arrangement, and the like can be changed according to the desired characteristics of each semiconductor element.

[0109]

As described above, according to the present invention, III-V
According to the group III compound semiconductor element, the second crystal is obtained by substituting a selected region in the first crystal region made of a group III-V compound semiconductor with a nitrogen atom for part or all of the group V atom. A heterojunction structure is formed by the second crystal region and the first crystal region surrounding the second crystal region, so that the group III-V compound semiconductor crystal is replaced with a nitrogen atom. And a nitrogen-containing group III-V compound semiconductor crystal.

Further, by using a heterojunction of a group III-V compound semiconductor crystal and a nitrogen-containing group III nitride semiconductor microcrystal, for example, it is possible to achieve narrowing of the half width of the emission spectrum. , III-V nitride semiconductor device can be improved in monochromaticity.

Further, according to the method for manufacturing a group III-V compound semiconductor device of the present invention, a part of the group V atoms is added to the selected region in the first crystal region made of the group III-V compound semiconductor. Alternatively, a second crystal region is formed by performing a nitrogen substitution process of entirely replacing the second crystal region with a nitrogen atom, and the second crystal region and the first crystal region surrounding the second crystal region are hetero-structured. Since a junction structure is formed, a low-dimensional quantum structure having a region having a selectively different band gap within a III-V compound semiconductor layer can be easily formed without using a complicated method as in the related art. can do.

Therefore, for example, the half width of the emission spectrum is narrowed, and the monochromaticity is improved II.
A semiconductor element having excellent characteristics can be manufactured, for example, an IV nitride semiconductor light emitting element can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a cross-sectional structure of a modulation doping type field effect transistor according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating an atomic concentration distribution in a depth direction of GaAs subjected to a nitrogen substitution process according to an embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a cross-sectional structure of a laminated structure according to Example 1 of the present invention.

FIG. 4 is a diagram illustrating Si as a selective mask material according to the first embodiment of the present invention.
In ₃ N ₄ film is a schematic view showing a state subjected to Shiboana processing.

FIG. 5 is a configuration diagram schematically illustrating a heat treatment apparatus according to a first embodiment of the present invention.

FIG. 6 shows Ga _0.47 In _0.53 As of Example 1 of the present invention.
FIG. 3 is a schematic diagram showing a transmission electron microscope image of a peripheral region of a _0.18 N _0.82 crystal.

FIG. 7 is a schematic diagram showing a transmission electron microscope image of GaAsN fine crystal grains selectively formed inside a GaAs crystal layer of Example 2 of the present invention.

FIG. 8 is a schematic diagram showing a cross-sectional structure of a fine hetero-junction structure of a base material and fine crystal grains of Example 3 of the present invention.

FIG. 9 shows a Si-doped n-type Al _{0.10 of} Example 3 of the present invention.
Rectangular Si remaining on the surface of the Ga _0.90 As crystal layer
Is a schematic view showing an arrangement of ₃ N ₄ film.

FIG. 10 is a schematic diagram illustrating a cross-sectional structure of a light emitting device according to Example 4 of the present invention.

FIG. 11 is a schematic diagram showing a cross-sectional structure of a light emitting unit having a DH (double hetero) structure having a conventional multiple quantum well (MQW) structure.

FIG. 12 is a schematic view showing a cross-sectional structure of a conventional quantum dot structure using a group III-V nitride semiconductor crystal.

[Explanation of symbols]

4 MQW structure 1 a lower cladding layer 2 barrier layer 3 well layers 5 the upper cladding layer 11 crystal substrate 12 the buffer layer 13 emitting layer 14 Ga _B In _C N crystal 15 barrier layer 16 emitting portion 21 GaAs substrate 22 GaAs buffer layer 23 n-type channel Layer 24 Electron supply layer (first crystal region) 24a Surface region (second crystal region) 24b Peripheral region 25, 26 n-type GaAs contact layer 27 Source electrode 28 Drain electrode 31 Recessed part 32 Gate electrode 41 Substrate 42 S Doped n-type InP vapor phase growth layer 43 S-doped n-type Ga _0.47 In _0.53 As mixed crystal layer 44 laminated structure 45 undoped Si ₃ N ₄ film 46 opening 51 heat treatment furnace (heating furnace) 52 furnace body 53 high frequency induction coil 54 Supporting stand 55 Thermocouple 56 Bag closing hole 57 Gas inlet 58 Ar gas and H ₂ gas introduction piping 5 9 NH ₃ gas introduction piping 60, 61 opening / closing valve 71 Ga _0.47 In _0.53 As _0.18 N _0.82 crystal layer 72 junction 81 p-type GaAs growth layer 82 GaAsN fine crystal grains 83 junction region 84 strain field 91 Si-doped n-type GaAs single Crystal substrate 92 Si-doped n-type GaAs buffer layer 93 Si-doped n-type Al _0.30 Ga _0.70 As crystal layer 94 Si-doped n-type Al _0.10 Ga _0.90 As crystal layer 94 a Al _0.10 Ga _0.90 As crystal layer 95 rectangular region 96 Al _0.10 Ga _0.90 As _0.14 N _0.86 crystal 97 p-type GaN crystal layer 98 p-type ohmic electrode 99 n-type ohmic electrode

Claims (6)

[Claims] 1. A semiconductor device having a heterojunction structure made of a group III-V compound semiconductor, wherein a selected region in a first crystal region made of a group III-V compound semiconductor is replaced with a group V atom. And a second crystal region formed by substituting a part or the whole of the region with a nitrogen atom. The second crystal region and the first crystal region surrounding the second crystal region form a hetero junction structure. A group III-V compound semiconductor device characterized by being formed. 2. The first crystal surrounding the second crystal region.
Is replaced with a nitrogen atom in part or all of the group V atom, and the band gap of the first crystal region replaced with the nitrogen atom is different from the band gap of the second crystal region. 3. The group III-V compound semiconductor device according to claim 1, wherein: 3. The semiconductor device according to claim 1, wherein a nitrogen composition ratio of the first crystal region has a difference of 3% or more as compared with a nitrogen composition ratio of the second crystal region.
Group IV compound semiconductor device. 4. The group III-V compound semiconductor includes gallium arsenide (GaAs) and gallium indium arsenide (G).
a _X In _Y As: 0 <Y ≦ 1, X + Y = 1), aluminum gallium arsenide (Al _W Ga _X As: 0 <W ≦ 1, W +
4. The group III-V compound semiconductor device according to claim 1, wherein the compound is one selected from the group consisting of X = 1). 5. A method of manufacturing a semiconductor device having a heterojunction structure made of a group III-V compound semiconductor, wherein a selected region in a first crystal region made of a group III-V compound semiconductor has a first A second crystal region is formed by performing a nitrogen substitution process for substituting a part or all of the group V atoms with nitrogen atoms, and forming the second crystal region and the first crystal region surrounding the second crystal region. A method for manufacturing a group III-V compound semiconductor device, comprising forming a heterojunction structure with a crystal region. 6. After forming the second crystal region, the first crystal region surrounding the second crystal region is provided with nitrogen for replacing a part or all of the group V atoms with nitrogen atoms. 6. The method for manufacturing a group III-V compound semiconductor device according to claim 5, wherein a substitution process is performed to make a nitrogen composition ratio of said first crystal region different from a nitrogen composition ratio of said second crystal region.