JP3895266B2 - BORON PHOSPHIDE COMPOUND SEMICONDUCTOR DEVICE, ITS MANUFACTURING METHOD, AND LIGHT EMITTING DIODE - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a boron phosphide compound semiconductor device including a boron phosphide compound semiconductor layer having a wide band gap at room temperature, a method for manufacturing the same, and a light emitting diode.
[0002]
[Prior art]
Hitherto, group III nitride semiconductors such as gallium nitride (GaN) have been used to construct nitride semiconductor elements such as light emitting diodes (LEDs) or laser diodes (LDs) (Non-patent Document 1, etc.) . Group III nitride semiconductors are known to have a relatively wide band gap at room temperature. For example, the band gaps of hexagonal wurtzite crystal type gallium nitride and aluminum nitride (AlN) at room temperature are respectively It is as large as 3.4 eV and 5.9 eV (Non-Patent Document 2, etc.). For this reason, the group III nitride semiconductor layer is used as a functional layer such as a clad layer or a light emitting layer of the light emitting element. A group III nitride semiconductor layer having such a large band gap is suitable for forming a junction structure with a high barrier. For example, an aluminum nitride / gallium mixed crystal (Al _X Ga _1-X A high mobility transistor in which a hetero (heterogeneous) junction of an electron supply layer and an electron transit layer is configured using an N: 0 <X ≦ 1) layer is disclosed (Non-patent Document 3, etc.).
[0003]
By the way, boron phosphide-based compound semiconductors such as monomeric boron phosphide (BP) are known as indirect transition group III-V compound semiconductors.
Unlike a group III nitride semiconductor such as gallium nitride (GaN), in a boron phosphide-based compound semiconductor, a p-type conductive layer can be obtained relatively easily if an impurity is intentionally added (doping). For example, a technique for obtaining a p-type conductive layer by doping magnesium (Mg) as a p-type impurity is disclosed (Patent Document 1, etc.). Therefore, it is conceivable that a pn junction having a barrier difference can be easily obtained by joining the boron phosphide-based compound semiconductor layer having a wide forbidden band and the group III nitride semiconductor layer.
Here, for example, the forbidden band width of boron phosphide at room temperature has been conventionally 2.0 eV (Non-patent Document 2, etc.). A technique for widening the band width to 2.8 to 3.4 eV has been developed. However, this is not sufficient to form a heterojunction with a barrier between a boron phosphide-based compound semiconductor layer and a group III nitride semiconductor layer such as a gallium nitride layer. A boron phosphide-based compound semiconductor layer is required. Conventionally, no boron phosphide compound semiconductor layer having a wide forbidden band suitable for forming a heterojunction with a wide band gap semiconductor such as a group III nitride semiconductor has been reported.
[0004]
[Patent Document 1]
JP-A-2-288388
[Non-Patent Document 1]
Takeaki Akasaki, “Group III Nitride Semiconductor”, first edition, Bafukan Co., Ltd., December 8, 1999, Chapters 13 and 14
[Non-Patent Document 2]
Akazaki Isao, “III-V compound semiconductor”, first edition, Baifukan Co., Ltd., May 20, 1994, p. 150
[Non-Patent Document 3]
Akazaki Isao, “Group III Nitride Semiconductor”, First Edition, Bafukan Co., Ltd., December 8, 1999, Chapters 6-8
[0005]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and a boron phosphide system having a forbidden bandwidth suitable for forming a heterojunction having a moderate barrier difference with a group III nitride semiconductor such as gallium nitride (GaN). An object of the present invention is to provide a boron phosphide-based compound semiconductor element having a boron phosphide-based compound semiconductor layer having a wide forbidden band and having excellent device characteristics.
[0006]
[Means for Solving the Problems]
As a result of investigations to solve the above problems, the present inventors have invented the following boron phosphide-based compound semiconductor element, a method for manufacturing the same, and a light emitting diode.
[0007]
That is, the present invention
(1) A boron phosphide-based compound semiconductor layer comprising an amorphous layer and a polycrystalline layer bonded to the layer is provided, and the forbidden band width of the boron phosphide-based compound semiconductor layer at room temperature Is a boron phosphide-based compound semiconductor device, characterized by being 3.0 eV or more and less than 4.2 eV,
(2) The boron phosphide-based compound semiconductor device according to (1), wherein a forbidden band width at room temperature of the polycrystalline layer is smaller than a forbidden band width at room temperature of the amorphous layer,
(3) The boron phosphide-based compound semiconductor device according to (1) or (2), wherein the polycrystalline layer is disposed above the amorphous layer,
(4) The amorphous layer and the polycrystalline layer are both undoped layers in which no impurity is intentionally added, (1) to (3), Boron phosphide compound semiconductor element,
(5) The phosphation according to any one of (1) to (4), wherein a group III nitride semiconductor layer is provided in contact with the boron phosphide compound semiconductor layer. Boron compound semiconductor devices,
(6) The group III nitride semiconductor layer has a composition formula Al _α Ga _β In _γ N (where 0 ≦ α, β, γ ≦ 1, α + β + γ = 1), or compositional Al _α Ga _β In _γ N _δ M _1-δ (5) characterized in that it is made of a compound represented by (0 ≦ α, β, γ ≦ 1, α + β + γ = 1, 0 <δ ≦ 1, M is a Group V element different from nitrogen). The boron phosphide-based compound semiconductor device described,
(7) The boron phosphide-based compound semiconductor element according to (6), wherein the boron phosphide-based compound semiconductor layer is made of boron phosphide, and the group III nitride semiconductor layer is made of gallium nitride.
(8) The boron phosphide-based compound semiconductor layer is a p-type conductive layer, the group III nitride semiconductor layer is an n-type conductive layer, the boron phosphide-based compound semiconductor layer and the group III nitride semiconductor layer A boron phosphide-based compound semiconductor device according to any one of (5) to (7), comprising a pn junction structure formed by bonding with
(9) The phosphorus according to any one of (1) to (8), characterized in that an ohmic contact or rectifying electrode is provided bonded to the boron phosphide compound semiconductor layer. Boron compound semiconductor device.
[0008]
In this specification, the term “polycrystalline layer” refers to a layer in which portions of amorphous and single crystals are mixed, or a layer composed of an assembly of a plurality of columnar single crystals having different orientation crystal directions. Means.
The forbidden bandwidth of the boron phosphide-based compound semiconductor layer is, for example, the photon energy of the imaginary part of the complex dielectric constant represented by 2 · n · k, where n is the refractive index and k is the extinction coefficient at the same wavelength. Required from dependency. The refractive index n and extinction coefficient k of the thin film are determined by, for example, ellipsometry.
Further, “the polycrystalline layer is disposed above the amorphous layer” means that after the amorphous layer is formed, the polycrystalline layer is formed using this as a base.
[0009]
The present invention also provides:
(10) The method for producing a boron phosphide-based compound semiconductor device according to any one of (1) to (4), wherein the amorphous layer is gasified at a temperature of 250 ° C. or higher and 1200 ° C. or lower. A method for producing a boron phosphide-based compound semiconductor device, comprising: a step of phase growth; and a step of vapor-phase-growing the polycrystalline layer at a temperature of 750 ° C. to 1200 ° C.
(11) The amorphous layer and the polycrystalline layer are vapor-phase grown at the same temperature, and the V / III ratio during the vapor-phase growth of the amorphous layer is set to 0.2 to 50, The method for producing a boron phosphide-based compound semiconductor device according to (10), wherein the V / III ratio during vapor phase growth of the crystal layer is 100 or more and 500 or less,
(12) The vapor phase growth rate of the amorphous layer is 50 to 80 nm / min, and the vapor phase growth rate of the polycrystalline layer is 20 to 40 nm / min. (10) or (11) A method for producing a boron phosphide-based compound semiconductor device described in 1.
In this specification, “V / III ratio” means the ratio of the concentration of a group V atom such as phosphorus to the concentration of a group III atom such as boron supplied to the vapor phase growth region. And
[0010]
The present invention also provides:
(13) In a light emitting diode having a stacked structure in which a lower cladding layer, a light emitting layer, and an upper cladding layer are sequentially stacked, the light emitting layer is a group III nitride semiconductor layer, and the upper cladding layer is A boron phosphide-based compound semiconductor layer having a forbidden band width at room temperature of 3.0 eV or more and less than 4.2 eV comprising an amorphous layer and a polycrystalline layer bonded to the layer. A light emitting diode.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[Boron phosphide compound semiconductor element]
The boron phosphide-based compound semiconductor element of the present invention includes a boron phosphide-based compound semiconductor layer, and the boron phosphide-based compound semiconductor layer is provided so as to be bonded to the amorphous layer and the layer. And a polycrystalline layer. By adopting such a configuration, it is possible to provide a boron phosphide-based compound semiconductor element having a boron phosphide-based compound semiconductor layer having a wide forbidden band width of 3.0 eV or more and less than 4.2 eV at room temperature. it can.
[0012]
In the present invention, the “boron phosphide-based compound semiconductor” is a cubic zinc blende crystal type III-V compound semiconductor containing boron (B) and phosphorus (P). _α Al _β Ga _γ In _1-α-β-γ P _1-δ As _δ (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 ≦ δ <1), composition formula B _α Al _β Ga _γ In _1-α-β-γ P _1-δ N _δ And compounds represented by (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 ≦ δ <1). Specifically, monomeric boron phosphide (BP), boron phosphide / gallium / indium (composition formula B _α Ga _γ In _1-α-γ P: 0 <α ≦ 1, 0 ≦ γ <1), boron nitride phosphide (composition formula BP _1-δ N _δ : 0 ≦ δ <1), boron arsenide phosphide (composition formula B _α P _1-δ As _δ : Mixed crystals containing a plurality of group V elements such as 0 <α ≦ 1, 0 ≦ δ <1). In particular, monomeric boron phosphide is preferably used because it is a basic component of a boron phosphide-based compound semiconductor. If boron phosphide having a wide forbidden band is used as a base material, a boron phosphide mixed crystal having a wide forbidden band can be obtained.
[0013]
The boron phosphide-based compound semiconductor layer is made of silicon (Si) crystal, sapphire (α-Al ₂ O ₃ Single crystal), hexagonal or cubic silicon carbide (SiC), gallium nitride (GaN) crystal substrate, or a group III nitride semiconductor layer formed on these crystal substrates can be formed as a base. .
As the formation method, for example, a halogen method (see “Journal of Japanese Society for Crystal Growth”, Vol. 24, No. 2 (1997), p. 150), a hydride method (J. Crystal Growth, 24/25 (1974), p.193-196), molecular beam epitaxy (see J. Solid State Chem., 133 (1997), p.269-272), metal organic chemical vapor deposition (MOCVD) (Inst) Phys. Conf. Ser., No. 129 (see IOP Publishing Ltd. (UK, 1993), p. 157-162), etc. Vapor phase epitaxy is preferred, among which MOCVD is triethyl boron (( C ₂ H ₅ ) ₃ Since an easily decomposable substance such as B) is used as a boron source, the amorphous layer can be vapor-grown at a relatively low temperature, which is preferable.
[0014]
In the present invention, the order of forming the amorphous layer and the polycrystalline layer constituting the boron phosphide-based compound semiconductor layer is not limited. However, when the lattice mismatch between the underlying constituent material such as a crystal substrate and the boron phosphide compound semiconductor is large, an amorphous layer is formed, and then a polycrystalline layer is bonded to the upper layer. A polycrystalline layer free of cracks is obtained and is preferred. This is because the boron phosphide-based compound semiconductor amorphous layer has an action of relaxing lattice mismatch.
When a polycrystalline layer is disposed on an amorphous layer, the thickness of the amorphous layer is preferably 2 nm or more. If the thickness of the amorphous layer is less than 2 nm, the amorphous layer cannot be uniformly grown over the entire surface of the base so as to uniformly cover the surface of the base to be deposited. is there. Further, in the boron phosphide-based compound semiconductor element of the present invention, the larger the thickness of the amorphous layer, the wider the forbidden band width of the entire boron phosphide-based compound semiconductor layer, which is preferable. For example, the forbidden band width at room temperature of a boron phosphide-based compound semiconductor layer having an amorphous layer with a thickness of 50 nm is about 4.2 eV.
The thickness of the amorphous layer or the polycrystalline layer can be measured using, for example, a high-resolution scanning electron microscope (SEM) or a transmission electron microscope (TEM) for length measurement.
[0015]
In the boron phosphide-based compound semiconductor of the present invention, a group III nitride semiconductor layer is preferably provided so as to be bonded to the boron phosphide-based compound semiconductor layer. Here, as a group III nitride semiconductor, composition formula Al such as gallium nitride is used. _α Ga _β In _γ A compound represented by N (0 ≦ α, β, γ ≦ 1, α + β + γ = 1) or a compositional formula Al _α Ga _β In _γ N _δ M _1-δ (0 ≦ α, β, γ ≦ 1, α + β + γ = 1, 0 <δ ≦ 1, M is a Group V element different from nitrogen), and the like.
Unlike boron phosphide-based compound semiconductors such as monomeric boron phosphide (BP), unlike a group III nitride semiconductor, a low-resistance p-type conductive layer can be easily obtained in an as-grown state. On the other hand, in the group III nitride semiconductor, the n-type conductive layer can be easily vapor-phase grown. Therefore, by providing an n-type group III nitride semiconductor layer bonded to the p-type boron phosphide compound semiconductor layer, a pn-junction heterostructure having an appropriate barrier difference can be easily configured. For example, n-type gallium nitride indium (Ga) having a forbidden band width of about 2.7 eV at room temperature. _β In _γ N: 0 ≦ β, γ ≦ 1) and a p-type boron phosphide layer having a forbidden band width of about 3.0 eV, and a light emitting portion of a pn junction type heterostructure having a barrier difference of about 0.3 eV Can be configured. Further, such a pn junction structure provided with a boron phosphide layer having a wide forbidden band width can be suitably used to construct a high breakdown voltage pn junction diode.
[0016]
In particular, when the boron phosphide compound semiconductor layer is made of boron phosphide and the group III nitride semiconductor layer is made of gallium nitride (GaN), a high-quality boron phosphide compound semiconductor layer can be formed, Is preferred.
Since the a-axis lattice constant of cubic zinc blende crystal type boron phosphide (BP) is 0.454 nm, the lattice spacing of {111} -crystal planes of boron phosphide is 0.319 nm. On the other hand, the a-axis lattice constant of wurtzite crystal type gallium nitride (GaN) is 0.318 nm, and the a-axis lattice constant of cubic gallium nitride is 0.451 nm. As described above, the lattice spacing of {111} -crystal planes of boron phosphide substantially coincides with the a-axis lattice constant of wurtzite crystal type or cubic gallium nitride. Accordingly, since there is almost no lattice mismatch on the hexagonal or cubic gallium nitride single crystal layer, a high-quality boron phosphide layer having a small crystal defect density such as misfit dislocation can be grown. . For this reason, the boron phosphide layer and the hexagonal or cubic gallium nitride layer can form a heterojunction structure that can suppress the occurrence of local breakdown (local breakdown), and can be used for applications such as LEDs or LDs. It can be suitably used.
[0017]
When a boron phosphide-based compound semiconductor layer to which impurities are intentionally added (doped) is bonded to a base such as a group III nitride semiconductor layer, the impurities in the boron phosphide-based compound semiconductor layer diffuse and penetrate into the base. In some cases, the electrical characteristics of the substrate are deteriorated. For example, when a boron phosphide layer is formed as a p-type conductive layer by adding magnesium (Mg) on a group III nitride semiconductor layer made of an n-type gallium nitride single crystal, the added magnesium is converted into a single n-type gallium nitride single layer. It diffuses into the crystal layer, electrically compensates for n-type carriers, and increases the resistance of the gallium nitride layer.
Therefore, in the present invention, it is preferable that both the amorphous layer and the polycrystalline layer constituting the boron phosphide-based compound semiconductor layer are constituted by so-called undoped layers to which impurities are not intentionally added. When the boron phosphide-based compound semiconductor layer is formed of an undoped layer, a pn junction structure can be formed without adversely changing the underlying layer such as a group III nitride semiconductor layer that forms a junction with the boron phosphide compound semiconductor layer.
In order to form an undoped p-type boron phosphide-based compound semiconductor layer, the vapor phase growth temperature or the like may be controlled. For example, when vapor-phase-growing undoped (111) -boron phosphide on the surface of (0.0.0.1.)-Gallium nitride single crystal, if the vapor-phase growth temperature is higher than about 1000 ° C., p An n-type conductive layer is easily obtained, and if it is about 1000 ° C. or less, an n-type conductive layer is easily obtained.
[0018]
Even in the undoped state, the carrier concentration of boron phosphide-based compound semiconductor is 1 × 10 ¹⁹ cm ^-3 A p-type or n-type conductive layer having a low resistance as described above can be obtained. For example, the carrier concentration at room temperature is about 2 × 10 ¹⁹ cm ^-3 The resistivity (specific resistance) is about 5 × 10 ^-2 A p-type conductive layer having a low resistance of Ω · cm can be obtained. In particular, when the amorphous layer is vapor-phase grown at a high temperature exceeding 1000 ° C., a boron phosphide compound semiconductor layer having a low resistance as a whole can be effectively obtained. And, on such a low resistance p-type or n-type boron phosphide compound semiconductor layer, an ohmic electrode (ohmic contact electrode) or a rectifying electrode with good contact can be formed, Is preferred. As the ohmic electrode material, a material generally used for an ohmic electrode formed on a group III-V compound semiconductor layer such as gallium arsenide (GaAs) can be used. For example, a p-type ohmic electrode made of a gold alloy such as gold / zinc (Zn) or gold / beryllium (Be) can be formed on the p-type boron phosphide layer, and on the n-type boron phosphide layer. An n-type ohmic electrode made of gold alloy such as gold (Au) / germanium (Ge), gold / tin (Sn), gold / indium (In) or the like can be formed. If an ohmic electrode having excellent contact properties is formed on the boron phosphide compound semiconductor layer, for example, a forward voltage (V _f ) Or threshold voltage (V _th LED) or LD with low) can be obtained, which is preferable. The ohmic electrode can be particularly well formed on a boron phosphide compound semiconductor layer having a structure in which an amorphous layer is disposed below and a polycrystalline layer is disposed above. This is because the forbidden band width of the polycrystalline layer at room temperature is smaller than that of the amorphous layer, and an ohmic electrode with good contactability is easily obtained. For example, a configuration in which a source or drain ohmic electrode is placed in contact with a polycrystalline layer having a smaller forbidden band width can be suitably used to construct a high electron mobility MESFET.
[0019]
Although it has been described that it is preferable to configure the boron phosphide-based compound semiconductor layer by disposing the amorphous layer below and the polycrystalline layer above, it may be reversed. A boron phosphide-based compound semiconductor layer in which an amorphous layer having a larger forbidden band is provided on a polycrystalline layer forms a non-rectifying electrode (for example, a Schottky contact type electrode). It is suitable for. Schottky contact electrode materials include materials generally used for Schottky contact electrodes formed on III-V compound semiconductor layers, such as aluminum (Al), gold (Au), titanium (Ti), and tantalum. (Ta), niobium (Nb), or the like can be used.
A structure in which a Schottky contact electrode is provided on a high-resistance amorphous layer and a polycrystalline layer disposed below the amorphous layer is used as an electron supply layer is, for example, a field effect transistor (MESFET). It can be suitably used.
[0020]
[Method of forming boron phosphide-based compound semiconductor layer]
Hereinafter, a method for forming a boron phosphide-based compound semiconductor layer constituting the boron phosphide-based compound semiconductor device of the present invention will be described in detail.
The amorphous layer and the polycrystalline layer constituting the boron phosphide-based compound semiconductor layer can be formed using different vapor phase growth apparatuses, or can be formed using the same vapor phase growth apparatus. However, it is preferable from the viewpoint of productivity that these layers are continuously vapor-grown using the same vapor-phase growth apparatus.
For example, after forming an amorphous layer at a constant temperature within the range of 250 ° C. or higher and 1200 ° C. or lower using the same vapor phase growth apparatus, the polycrystalline layer is subsequently removed at a temperature of 750 ° C. or higher and 1200 ° C. or lower. Phase growth is possible. Note that the order of forming the amorphous layer and the polycrystalline layer may be reversed. In the formation of the amorphous layer, the vapor phase growth temperature is set to 250 ° C. or higher so that the raw material of the element constituting the amorphous layer can be sufficiently thermally decomposed in the vapor phase growth region and the film formation can proceed. Is suitable. On the other hand, in forming the polycrystalline layer, it is suitable that the vapor phase growth temperature is 750 ° C. or higher in order to promote crystallization. In any film formation, B ₁₃ P ₂ Generation of boron multimers such as boron phosphide (BP) and the growth of boron phosphide compound semiconductor layers composed of boron phosphide compound semiconductors based on this are avoided Therefore, the vapor phase growth temperature is preferably 1200 ° C. or lower.
[0021]
Using the same vapor phase growth apparatus, the amorphous layer and the polycrystalline layer can be continuously vapor grown at the same temperature. In this case, the supply ratio (V / III ratio) of the constituent elements of the boron phosphide-based compound semiconductor may be changed continuously or stepwise. By changing the V / III ratio, the amorphous layer and the polycrystalline layer can be distinguished from each other. For example, boron trichloride (BCl ₃ ) And phosphorus trichloride (PCl) ₃ ) As a raw material, the V / III ratio is BCl supplied to the vapor phase growth region. ₃ PCl against ₃ It can be adjusted by controlling the flow rate.
When an amorphous layer is formed and then a polycrystalline layer is formed thereon, after the amorphous layer is grown at a relatively low V / III ratio, the polycrystalline layer is grown at a higher V / III ratio. May be vapor-phase grown. Conversely, when the amorphous layer is formed above the polycrystalline layer, the V / III ratio may be changed from a high ratio to a low ratio. Furthermore, if the V / III ratio is periodically changed, it is also possible to periodically form amorphous layers and polycrystalline layers alternately. A V / III ratio suitable for vapor phase growth of the amorphous layer is 0.2 or more and 50 or less, and a V / III ratio suitable for forming a polycrystalline layer is 100 or more and 500 or less.
Whether the formed layer is an amorphous layer or a polycrystalline layer can be determined from, for example, a diffraction pattern by an X-ray diffraction method or an electron beam diffraction method.
[0022]
The vapor growth rate of the amorphous layer and the polycrystalline layer is not particularly limited. However, when the growth rate of the amorphous layer is set to be equal to or higher than the growth rate of the polycrystalline layer, the boron phosphide compound having a wide band gap as a whole. A semiconductor layer can be formed, which is preferable. Specifically, the growth rate of the amorphous layer is preferably 50 to 80 nm / min, and the growth rate of the polycrystalline layer is preferably 20 to 40 nm / min, which is smaller than that in the case of vapor phase growth of the amorphous layer. .
The growth rate when vapor-phase-growing the amorphous layer and the polycrystalline layer can be adjusted mainly by the supply amount per unit time of a Group III constituent element such as boron supplied to the vapor-phase growth region. However, in vapor phase growth at temperatures exceeding 1000 ° C, the growth rate may vary depending on the concentration of the phosphorus raw material in the vapor phase growth region, so the growth rate is finely adjusted in vapor phase growth at high temperatures. For this purpose, it is preferable to precisely adjust the supply amounts of both the Group III constituent element and the Group V constituent element to the vapor phase growth region.
For example, triethyl boron ((C ₂ H ₅ ) ₃ B) / phosphine (PH ₃ ) / H ₂ In vapor phase growth of an amorphous layer of boron phosphide by the reactive MOCVD method, the supply amount of the boron source is about 2.5 × 10 ^-4 Mol / min, and the supply amount of the phosphorus source is about 5.1 × 10 ^-3 By setting it as mol / min, a growth rate of about 60 nm / min at 1025 ° C. can be obtained.
[0023]
In the present invention, the boron phosphide-based compound semiconductor layer is composed of an amorphous layer and a polycrystalline layer provided bonded to the layer, so that the forbidden band width at room temperature is 3. A boron phosphide-based compound semiconductor element having a boron phosphide-based compound semiconductor layer with a wide forbidden band of 0 eV or more and less than 4.2 eV can be provided. In the present invention, the amorphous layer constituting the boron phosphide-based compound semiconductor layer has an effect of providing a boron phosphide-based compound semiconductor layer having a large forbidden band width.
The boron phosphide compound semiconductor element of the present invention having such a boron phosphide compound semiconductor layer having a wide forbidden band is an LED having a heterojunction structure with a large barrier difference and excellent device characteristics. It can be suitably used as an LD or the like. For example, a boron phosphide-based compound semiconductor layer having a wide forbidden band width of 3.0 eV or more and less than 4.2 eV at room temperature has 0.3 eV sufficient to confine carriers in the light emitting layer in an LED or LD. It can be suitably used as a clad layer having a barrier difference exceeding. Further, in an LED, it can be suitably used as a window layer that sufficiently transmits near-ultraviolet light or short-wavelength visible light to the outside.
[0024]
【Example】
Next, examples according to the present invention will be described.
(Example)
As a boron phosphide-based compound semiconductor element of the present invention, a pn-junction type double hetero provided with a boron phosphide-based compound semiconductor layer composed of an amorphous layer and a polycrystalline layer grown on a Si single crystal substrate. A light emitting diode (LED) having a (DH) junction structure was manufactured. A cross-sectional structure of the manufactured LED is schematically shown in FIG.
[0025]
As the substrate 101, a phosphorus (P) -doped n-type (111) -Si single crystal substrate was used.
First, an undoped boron phosphide (BP) amorphous layer 102 was deposited on the (111) -surface of the substrate 101 by an atmospheric pressure (substantially atmospheric pressure) metal organic vapor phase epitaxy (MOVPE) method. The boron phosphide amorphous layer 102 is formed of triethyl boron ((C ₂ H ₅ ) ₃ B) as a boron source and phosphine (PH ₃ ) As a phosphorus source. Ratio of supply concentration per unit time to the MOVPE reaction system of phosphorus source to boron source (PH ₃ / (C ₂ H ₅ ) ₃ B; V / III ratio) was 16. The layer thickness of the boron phosphide amorphous layer 102 was 10 nm.
[0026]
After the supply of the boron source is stopped and the vapor phase growth of the boron phosphide amorphous layer 102 is completed, the phosphorus source (PH ₃ ) And hydrogen (H ₂ ) In the mixed atmosphere, the temperature of the substrate 101 was raised to 925 ° C. Thereafter, the boron source was again passed, and an undoped n-type {111} -boron phosphide single crystal layer 103 was deposited at 925 ° C. on the boron phosphide amorphous layer 102. The V / III ratio during vapor phase growth was 1300. The layer thickness of the boron phosphide single crystal layer 103 was 120 nm.
[0027]
Next, on the boron phosphide single crystal layer 103, gallium (Ga) / ammonia (NH ₃ ) / Hydrogen (H ₂ ) A lower cladding layer 104 made of gallium nitride (GaN) single crystal was deposited at 1050 ° C. by a reactive hydride VPE method. The thickness of the lower cladding layer 104 was 3 μm.
Furthermore, trimethylgallium ((CH ₃ ) ₃ Ga) / trimethylindium ((CH ₃ ) ₃ In) / H ₂ N-type gallium nitride indium (Ga _0.90 In _0.10 The n-type light emitting layer 105 made of N) was vapor grown at 850 ° C. The carrier concentration of the n-type light emitting layer 105 is 7 × 10. ¹⁷ cm ^-3 The layer thickness was 50 nm.
[0028]
Next, on the n-type light emitting layer 105, (C ₂ H ₅ ) ₃ B / PH ₃ / H ₂ Vapor phase growth of the boron phosphide amorphous layer 106a was started at 1025 ° C. by the reaction atmospheric pressure MOCVD method. V / III ratio (= PH) in vapor phase growth of boron phosphide amorphous layer 106a ₃ / (C ₂ H ₅ ) ₃ B) was 16. The boron phosphide amorphous layer 106a was grown at a growth rate of 50 nm / min. After the vapor phase growth is continued for exactly 30 seconds to form the boron phosphide amorphous layer 106a having a layer thickness of 25 nm, the PH supplied immediately to the vapor phase growth region is formed. ₃ The V / III ratio was 120. As a result, a boron phosphide polycrystalline layer 106b was subsequently deposited on the boron phosphide amorphous layer 106a. The boron phosphide polycrystalline layer 106b was vapor-phase grown at a growth rate of 30 nm / min. The layer thickness of the boron phosphide polycrystalline layer 106b was 380 nm. In this manner, a p-type boron phosphide layer 106 having a layer thickness of 405 nm composed of a two-layer structure of an undoped boron phosphide amorphous layer 106a and an undoped boron phosphide polycrystalline layer 106b was formed.
[0029]
The carrier concentration of the obtained p-type boron phosphide layer 106 is about 1 × 10 4 by a general Hall effect measurement method. ¹⁹ cm ^-3 It was measured.
Further, the p-type boron phosphide layer obtained from the photon energy dependence of the product value (= 2 · n · k) of the refractive index (n) and the extinction coefficient (k) measured using a general ellipsometer The forbidden band width at room temperature of 106 is determined to be about 3.6 eV, and the p-type boron phosphide layer 106 is a window layer sufficient to transmit light emitted from the upper cladding layer and the light emitting layer 105 to the light emitting layer 105 to the outside. It was found that it can be suitably used as. The p-type boron phosphide layer 106 obtained has an average dislocation density of 1 × 10 4 measured by a general cross-sectional TEM technique. ³ / Cm ² Less than, dislocation density 1 × 10 ² / Cm ² The following areas also existed partially.
[0030]
A p-type ohmic electrode 107 having a multilayer structure in which the p-type boron phosphide layer 106 is an upper clad layer and the lower layer is an Au / Be alloy (Au 99 mass% / Be 1 mass%) and the upper layer is Au is provided at the center. . The p-type ohmic electrode 107 that also serves as a pedestal (pad) electrode for connection has a circular shape with a diameter of about 120 μm. On the other hand, an n-type ohmic electrode 108 made of an aluminum (Al) / antimony (Sb) alloy was disposed on substantially the entire back surface of the substrate 101.
[0031]
As described above, an LED having a pn junction type DH structure in which the n-type light emitting layer 105 is sandwiched between the lower clad layer 104 made of the n-type gallium nitride layer and the upper clad layer made of the p-type boron phosphide layer 106 is manufactured. did.
[0032]
When an operating current of 20 mA was passed in the forward direction between the p-type and n-type ohmic electrodes 107 and 108 of the obtained LED, blue band light having a wavelength of about 430 nm was emitted, and a general integrating sphere was used. The luminance in the measured chip state was 7 mcd. Further, from the near-field light emission pattern, it was found that the light emission intensity was uniform over substantially the entire surface of the light emitting layer 105. This is because the ohmic electrode 107 is provided in contact with the p-type boron phosphide layer 106 having a low dislocation density, so that the element driving current via the dislocation as seen in the prior art is short-circuited to the light-emitting layer 105. This is because the generation of minute emission luminescent spots due to distribution is suppressed.
From the emission wavelength, the forbidden band width of the light emitting layer 105 is calculated to be about 2.9 eV, and the difference in the forbidden band width from the p-type boron phosphide layer 106 forming the upper cladding layer reaches about 0.7 eV. found. In addition, since the ohmic electrode 107 was provided in contact with the p-type boron phosphide layer 106 having a low dislocation density, no local breakdown was observed. For this reason, the forward voltage when the forward current is 20 mA (V _f ) Is about 3 V, and the reverse voltage (V) when the reverse current is 10 μA. _r LED with good rectification characteristics of 8V or more was provided.
As described above, in this example, an LED having excellent rectification characteristics and excellent uniformity of light emission intensity was provided.
[0033]
【The invention's effect】
According to the present invention, the boron phosphide-based compound semiconductor layer including the amorphous layer and the polycrystalline layer bonded to the layer is provided, so that the forbidden band width at room temperature is 3.0 eV. As described above, a boron phosphide-based compound semiconductor element having a boron phosphide-based compound semiconductor layer having a wide forbidden band of less than 4.2 eV and excellent in device characteristics can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a cross-sectional structure of a pn junction type LED manufactured in an example according to the present invention.
[Explanation of symbols]
101 substrate
102 Boron phosphide amorphous layer
103 Boron phosphide single crystal layer
104 Lower cladding layer (gallium nitride crystal layer)
105 n-type light emitting layer (gallium nitride / indium layer)
106 Boron phosphide layer (upper cladding layer)
106a Amorphous layer of boron phosphide
106b Boron phosphide polycrystalline layer
107 p-type ohmic electrode
108 n-type ohmic electrode

Claims (13)

2. A boron phosphide-based compound semiconductor layer comprising an amorphous layer and a polycrystalline layer bonded to the layer is provided, and the boron phosphide-based compound semiconductor layer has a forbidden band width at room temperature of 3. A boron phosphide-based compound semiconductor device characterized by being 0 eV or more and less than 4.2 eV. 2. The boron phosphide-based compound semiconductor device according to claim 1, wherein a forbidden band width at room temperature of the polycrystalline layer is smaller than a forbidden band width at room temperature of the amorphous layer. The boron phosphide-based compound semiconductor device according to claim 1, wherein the polycrystalline layer is disposed above the amorphous layer. 4. The boron phosphide according to claim 1, wherein each of the amorphous layer and the polycrystalline layer is an undoped layer to which no impurity is intentionally added. 5. Compound semiconductor device. 5. The boron phosphide-based compound according to claim 1, wherein a group III nitride semiconductor layer is provided so as to be bonded to the boron phosphide-based compound semiconductor layer. Semiconductor element. The group III nitride semiconductor layer has a composition formula Al _α Ga _β In _γ N (where 0 ≦ α, β, γ ≦ 1, α + β + γ = 1), or a composition formula Al _α Ga _β In _γ N _δ M _{1− 6.} A compound represented by _δ (where 0 ≦ α, β, γ ≦ 1, α + β + γ = 1, 0 <δ ≦ 1, M is a Group V element different from nitrogen). A boron phosphide-based compound semiconductor device described in 1. 7. The boron phosphide-based compound semiconductor element according to claim 6, wherein the boron phosphide-based compound semiconductor layer is made of boron phosphide, and the group III nitride semiconductor layer is made of gallium nitride. The boron phosphide-based compound semiconductor layer is a p-type conductive layer, the group III nitride semiconductor layer is an n-type conductive layer, and the bond between the boron phosphide-based compound semiconductor layer and the group III nitride semiconductor layer 8. The boron phosphide-based compound semiconductor device according to claim 5, further comprising a pn junction structure according to claim 5. 9. The boron phosphide-based material according to claim 1, wherein an ohmic contact or rectifying electrode is provided in contact with the boron phosphide-based compound semiconductor layer. 10. Compound semiconductor device. A method for manufacturing a boron phosphide-based compound semiconductor device according to any one of claims 1 to 4,
A step of vapor-phase-growing the amorphous layer at a temperature of 250 ° C. or higher and 1200 ° C. or lower; and a step of vapor-phase-growing the polycrystalline layer at a temperature of 750 ° C. or higher and 1200 ° C. or lower. A method for manufacturing a boron phosphide-based compound semiconductor device. The amorphous layer and the polycrystalline layer are vapor-phase grown at the same temperature, and the V / III ratio during the vapor-phase growth of the amorphous layer is 0.2 to 50, The method for producing a boron phosphide-based compound semiconductor element according to claim 10, wherein a V / III ratio during vapor phase growth is 100 or more and 500 or less. The vapor phase growth rate of the amorphous layer is set to 50 to 80 nm / min, and the vapor phase growth rate of the polycrystalline layer is set to 20 to 40 nm / min. A method for producing a boron phosphide-based compound semiconductor element. In a light emitting diode having a laminated structure in which a lower cladding layer, a light emitting layer, and an upper cladding layer are sequentially laminated,
The light emitting layer is a group III nitride semiconductor layer;
The boron phosphide-based compound semiconductor layer having a forbidden band width of 3.0 eV or more and less than 4.2 eV at room temperature, wherein the upper cladding layer is composed of an amorphous layer and a polycrystalline layer bonded to the layer. A light emitting diode characterized by the above.

Images