JP3592616B2 - Group III nitride semiconductor light emitting device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to gallium phosphide (GaN) provided on a substrate surface such as silicon (Si) via a boron phosphide (BP) buffer layer._{1 ー X}P_X: 0 <X <1) A group III nitride semiconductor light emitting device having a light emitting portion structure including a single crystal layer.
[0002]
[Prior art]
A group III nitride semiconductor light emitting device that emits light in a blue band or a green band is, for example, sapphire (α-Al₂O₃A) a multilayer structure having a gallium nitride (GaN) crystal layer as a component, which is deposited on a single crystal substrate by using a growth means such as a metal organic chemical vapor deposition (MOCVD) method. . The laminated structure is provided with a light emitting unit structure having a light emitting function. Conventionally, the light emitting unit structure has been indium gallium nitride (Ga)._YIn_1-YN: 0 <Y ≦ 1) and a pn junction type hetero (hetero) structure composed of a p-type or n-type cladding layer made of an aluminum gallium indium (AlGaInN) -based crystal layer. It is common.
[0003]
FIG. 5 is a schematic cross-sectional view illustrating the configuration of a stacked structure of a light emitting element (LED) 100 having a conventional pn junction type double hetero (DH) light emitting unit structure 42 made of an AlGaInN-based crystal layer. is there. In the conventional lamination structure, the light emitting portion structure 42 is made of, for example, n-type aluminum gallium nitride (Al_ZGa_{1 ー Z}N: 0 ≦ Z ≦ 1) a lower cladding layer 103 made of a crystal layer, and an n-type indium-gallium nitride (Ga)_YIn_1-YN) and a p-type aluminum gallium nitride (Al)_ZGa_1-ZN: 0 ≦ Z ≦ 1) and an upper cladding layer 105 (refer to JP-A-6-260682). Each of the functional layers 103 to 105 constituting the light emitting unit structure 42 is deposited with a buffer layer formed at a lower temperature than the film forming temperature of these functional layers, that is, a so-called low-temperature buffer layer 102 interposed therebetween. Is customary (see Japanese Patent Application Laid-Open No. H4-297023). In a laminated structure of a group III nitride semiconductor crystal layer provided on a sapphire substrate 101, a low-temperature buffer layer 102 is made of aluminum gallium nitride (Al)._ZGa_1-Z(N: 0 ≦ Z ≦ 1) (see Japanese Patent Application Laid-Open No. 6-151962).
[0004]
The low-temperature buffer layer 102 is made of a sapphire substrate 101 and Al._ZGa_{1 ー Z}It is provided mainly for the purpose of reducing the mismatch (mis-match) of the lattice of the N crystal with the lower cladding layer 103 to obtain a good quality group III nitride single crystal layer having a low density of crystal defects such as dislocations. I have. In particular, the low-temperature buffer layer 102 is composed of gallium nitride (GaN), the lower cladding layer 103 is composed of a GaN layer formed at a temperature higher than the deposition temperature of the low-temperature buffer layer 102, and the light-emitting layer 104 is composed of gallium-indium nitride. A conventional example composed of a crystal phase is known (see JP-A-6-216409).
Further, in the conventional light emitting device shown in FIG. 5, since the substrate 101 is an insulating sapphire, a part of the lower cladding layer 103 must be cut off to provide the n-type ohmic electrode 107. The p-type ohmic electrode 106 is provided on the conductive upper cladding layer 105.
[0005]
[Problems to be solved by the invention]
However, due to the mismatch between the sapphire substrate and the GaN layer forming the low-temperature buffer layer, the size of which is about 13.8% ("Journal of the Japanese Association for Crystal Growth", Vol. 15, No. 3 & 4 (issued January 25, 1989)) At present, it is difficult to stably obtain a low-temperature buffer layer having continuity. In the discontinuous portion partially existing in the low-temperature buffer layer due to lack of film continuity, that is, in the region where the surface of the sapphire substrate is exposed, the growth of hexagonal GaN in the c-axis direction becomes dominant. . Dislocations generated from the coalescence of the columnar crystals of GaN generated as a result propagate to the GaInN light emitting layer via the upper GaN layer, and the crystal quality of the light emitting layer is degraded. That is, in the above-described conventional lamination structure in which the GaInN light emitting layer is stacked with the GaN low-temperature buffer layer and the GaN layer interposed therebetween, the propagation of crystal defects such as dislocations caused by the discontinuity of the low-temperature buffer layer causes A high-quality GaInN-based light-emitting layer cannot be formed, and therefore, a light-emitting portion structure composed of a group III nitride single crystal layer having excellent operation reliability and device life cannot be stably formed, particularly in a laser diode (LD). Is a problem.
[0006]
The present invention has been made in view of the above-described drawbacks of the related art, and provides a buffer layer having continuity capable of uniformly covering a substrate surface and suppressing generation of dislocations, regardless of a large mismatch with a substrate crystal. . Another object of the present invention is to provide a structure of a group III nitride single crystal layer having a low crystal defect density such as dislocations to be deposited on the buffer layer and excellent in crystallinity.
[0007]
[Means for Solving the Problems]
That is, the group III nitride semiconductor light emitting device of the present invention provides gallium phosphide (GaN) provided on a single crystal substrate with a boron phosphide (BP) -based buffer layer interposed therebetween._{1 ー X}P_X: 0 <X <1) A group III nitride semiconductor light-emitting device having a light-emitting portion structure including a single crystal layer was provided.
The use of the boron phosphide-based buffer layer eliminates the lattice mismatch between the substrate and the gallium phosphide-based light-emitting portion structure to form a gallium phosphide-based light-emitting portion structure with excellent crystallinity. Is obtained, so that there is an advantage that a light emitting element with high luminance can be obtained.
[0008]
Further, in the group III nitride semiconductor light emitting device of the present invention, the BP-based buffer layer is amorphous.
By growing the BP-based buffer layer at a low temperature and making it amorphous, there is an effect that it can be applied to a substrate having a wide range of lattice constants.
[0009]
Further, in the group III nitride semiconductor light emitting device of the present invention, the BP-based buffer layer may be composed of an amorphous and crystalline laminate.
By forming an amorphous BP-based buffer layer near the interface with the substrate and providing a crystalline BP-based buffer layer near the light-emitting portion structure thereon, a gallium phosphide-based light-emitting portion structure with better crystallinity can be obtained. There is an advantage that it can be easily obtained.
[0010]
Further, as the group III nitride semiconductor light emitting device of the present invention, a light emitting unit having a single hetero junction structure including a gallium nitride phosphide single crystal layer can be used.
Since the crystallinity of the light emitting portion is improved, there is an advantage that a light emitting element with high luminance can be obtained even with a simple light emitting portion structure.
[0011]
Further, in the group III nitride semiconductor light emitting device of the present invention, the light emitting unit structure may have a double hetero junction structure including a gallium nitride phosphide single crystal layer.
The use of the double hetero junction structure has an advantage that a light-emitting element with higher luminance can be obtained.
[0012]
In the group III nitride semiconductor light emitting device of the present invention, the degree of lattice mismatch between the BP-based buffer layer and the gallium phosphide single crystal layer is preferably ± 1% or less.
In particular, the degree of lattice mismatch between the BP-based buffer layer and the gallium phosphide single crystal layer is preferably set to ± 0.4% or less.
[0013]
By controlling the phosphorus composition, the boron phosphide-based buffer layer and the gallium phosphide-based light-emitting layer can make the lattice constants of each other as close to each other as possible. This is because a simple epitaxial crystal layer can be easily obtained, which contributes to increasing the luminance of the light emitting element.
[0014]
In the group III nitride semiconductor light emitting device of the present invention, the boron phosphide-based buffer layer is composed of boron phosphide (BP), and the phosphorus (P) composition ratio of the gallium nitride phosphide single crystal layer in the light emitting portion structure. Is preferably 1% or more and 5% or less.
This is because the degree of lattice mismatch between the buffer layer and the light-emitting portion is 1% or less, and a high-luminance light-emitting element can be obtained.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
The light emitting part structure of the group III nitride semiconductor light emitting device of the present invention is formed on the surface of a substrate made of a single crystal material.
As long as the substrate is a single crystal material, the conductivity type may be either n-type or p-type. This is because an ohmic electrode of either a positive electrode or a negative electrode can be formed on one surface of the substrate by utilizing the conductivity of the substrate, and an LED can be easily manufactured. For example, a cubic single crystal such as silicon (Si) and gallium phosphide (GaP), a silicon carbide (SiC), a perovskite-type oxide single crystal, or the like is more preferably used as a substrate than an insulating single crystal material such as sapphire. it can. In particular, an n-type or p-type silicon single crystal of a diamond crystal structure type exhibiting clear cleavage can be suitably used as a substrate. The use of {100} -silicon single crystal as a substrate is advantageous because it can be easily divided into individual elements using cleavage.
[0016]
The buffer layer provided on the single crystal substrate surface is made of boron phosphide (BP) -based material. The BP-based material refers to a material containing at least boron (B) and phosphorus (P) as constituent elements. BP-based materials include boron nitride phosphide (BP) in addition to boron phosphide (BP)._MN_1-M: 0 <M <1). The buffer layer made of these BP-based materials can be formed by, for example, boron trichloride (BCl₃  ) As a boron (B) source, eg, phosphine (PH)₃  ) Can be formed by a hydride vapor phase epitaxy method using a phosphorus (P) source.
[0017]
In the present invention, gallium nitride phosphide (GaN) which is a mixed crystal of gallium nitride (GaN) and gallium phosphide (GaP) is interposed via a buffer layer made of a BP-based material._{1 ー X}P_X: 0 <X <1) Single crystal layers are stacked. Gallium phosphide nitride (GaN_{1 ー X}P_X: 0 <X <1), by adjusting the phosphorus composition ratio (X), lattice matching with the boron phosphide-based material constituting the buffer layer is achieved, and in particular, a single crystal layer excellent in crystallinity is obtained. It depends on what you get. Here, the lattice constant of zinc-blende gallium phosphide (GaP) is 5.450 angstroms (Å) (Yasuharu Suematsu, “Optical Device”, May 15, 1997, Corona Co., Ltd.) Published, first edition, 8th edition, page 28). On the other hand, the lattice constant of cubic gallium nitride (GaN) is 4.510 ° (Edited by Isamu Akasaki, “Group III Nitride Semiconductor”, December 8, 1999, published by Baifukan Co., Ltd., first edition, page 169, table). 9.1). Therefore, it is derived according to the Vegard rule (co-authored by Haruo Nagai et al., "III-V Group Semiconductor Mixed Crystal", Oct. 25, 1988, first edition, first edition, pp. 27-31, published by Corona Co., Ltd.). GaN with a phosphorus composition ratio of about 3% (X ≒ 0.03)_0.97P_0.03Has a lattice constant of 4.538 °, and is lattice-matched with boron phosphide (lattice constant: 4.538 °) forming the buffer layer. That is, GaN stacked on the BP buffer layer_0.97P_0.03Since the layer maintains lattice matching with the buffer layer, there is an advantage that the layer becomes a single crystal layer having good crystallinity.
Also, for example, boron phosphide nitride (BP) having a nitrogen composition ratio of 2% (M = 0.02)_0.98N_0.02High quality gallium phosphide (GaN) on the buffer layer made of_0.99P_0.01, Lattice constant: 4.519Å) Single crystal layers can be stacked.
[0018]
The gallium nitride phosphide single crystal layer can be formed by MOCVD, halogen, hydride vapor phase epitaxy, or the like, as in the case of the BP-based buffer layer. At this time, the BP-based buffer layer and GaN_{1 ー X}P_XIt is preferable that the conductivity type of the single crystal layer be the same as that of the single crystal layer. GaN with excellent crystallinity_{1 ー X}P_XThe layer can be conveniently used as a constituent layer for forming a light-emitting portion having a single hetero junction structure or a double hetero junction structure that improves emission intensity. For example, it can be effectively used as a cladding layer forming a light emitting portion having a pn junction type double hetero junction structure.
[0019]
GaN_{1 ー X}P_XWhen the light emitting section is configured with the (0 <X <1) layer as the cladding layer, it is necessary to set the phosphorus composition ratio to a composition ratio that gives a forbidden band width larger than the transition energy corresponding to the emission wavelength. For example, the transition energy corresponding to blue light emission at a wavelength of 450 nm is about 2.75 eV. The transition energy corresponding to green light emission at a wavelength of 520 nm is about 2.38 eV. Therefore, the phosphor composition ratio (X) giving a band gap of about 2.8 eV or more for the light emitting layer emitting blue light, and the band gap of about 2.4 eV or more for the light emitting layer giving green light emission. Having a phosphorus composition ratio (X) that gives_{1 ー X}  P_X  It is necessary to form the cladding layer from (0 <X <1). GaN_{1 ー X}P_X  Non-linearformTargetForbidden widthFrom the changes (see Appl. Phys. Lett., Vol. 60, No. 20 1992, pp. 2540-2542), the cladding layer is suitable, for example, for a light emitting layer that emits blue or green light, the phosphorus composition ratio ( GaN with X) of about 5% or less (X ≒ 0.05) or less_{1 ー X}  P_X  It is. In particular, GaN having a phosphorus composition ratio (X) of 3% or less can be suitably used as a cladding layer for a light emitting layer that emits blue and green light._{1 ー X}P_XIt is.
[0020]
The BP-based buffer layer is optimally composed mainly of amorphous in an as-grown state. The buffer layer mainly composed of amorphous is composed of GaN on the substrate and the buffer layer._{1 ー X}P_X(0 <X <1) This is effective in efficiently relieving the lattice mismatch with the crystal layer or the like. When a BP-based material is formed at a low temperature as described later, it can be formed as an amorphous film without being significantly affected by the lattice constant of the substrate.
The degree of lattice mismatch (△: unit%) is represented by the following relational expression (1).
Δ (%) = {(A−As) / As} × 100 (1)
In the relational expression (1), the symbol As is the lattice constant of the layer to be deposited (underlying layer), and the symbol A is the lattice constant of the layer deposited on the underlying layer.
For example, the degree of lattice mismatch between a silicon single crystal (As: 5.431 °) serving as a substrate and a crystalline BP (A: 4.538 °) layer grown using the same as a layer to be deposited is based on the silicon single crystal. (△) reaches a size of −16.4%. When the substrate is a GaP single crystal (As: 5.450 °), the degree of lattice mismatch (△) between the GaP substrate and the BP buffer layer is −16.7%. However, if the buffer layer is composed of amorphous BP, even if a large lattice mismatch of about 16% to about 17% exists, the mismatch is alleviated and the surface is excellent in flatness. A deposition layer is obtained. Moreover, even if the thickness of the deposited layer is relatively thin, for example, about 0.2 μm, a continuous deposited layer can be formed. According to the inventor's insight, even when the lattice mismatch between the BP-based material constituting the buffer layer and the substrate is large, the BP-based material is excellent in covering the substrate surface without interruption. It depends on the material. Therefore, in the present invention, it is particularly preferable that the buffer layer is made of an amorphous BP-based material.
[0021]
The buffer layer made of an amorphous BP-based material in an as-grown state is formed at a low temperature of about 250 ° C. to about 550 ° C. by the MOCVD method or the halogen or hydride vapor phase epitaxy method. It can be obtained by: In particular, temperatures from about 300 ° C to about 400 ° C are suitable. Whether or not the buffer layer is made of an amorphous material can be known by, for example, a normal X-ray diffraction analysis method or an electron diffraction method. When the buffer layer is mainly composed of amorphous, almost no diffraction peak appears in the X-ray diffraction pattern. Even if the amorphous layer is in the as-grown state, if it is exposed to a high temperature environment exceeding the growth temperature of the buffer layer, for example, when another layer is formed at a higher temperature on the buffer layer, it is simply used. The amorphous buffer layer near the bonding interface with the crystal substrate is monocrystallized while inheriting the lattice arrangement of the single crystal material of the substrate (see JP-A-10-22224). The lattice constant of the single crystallized layer is close to that of the single crystal constituting the substrate. Even in the internal region of the buffer layer near the junction interface, the single crystallized layer is used as a “seed crystal” to change the amorphous layer into a single crystal layer. As the layer thickness increases, the lattice constant gradually approaches the lattice constant of the original crystal of the material constituting the buffer layer.
[0022]
When it is necessary to stack a single crystal layer having excellent crystallinity on the amorphous buffer layer, the buffer layer is formed at least in the vicinity of the buffer layer surface opposite to the bonding surface of the amorphous buffer layer with the substrate. Is preferably changed to a crystal layer having the lattice constant of the original crystal of the material constituting Thereafter, if a film is formed at a high temperature, a single crystal layer having excellent crystallinity can be obtained. Whether or not it is conveniently converted to a single crystal layer in a high temperature environment depends on the thickness of the amorphous buffer layer. In the case of an extremely thin film having an amorphous buffer layer having a thickness of less than about 1 to 2 nm, when the buffer layer is exposed to a high temperature environment, the interior of the buffer layer is almost single crystal due to the influence of the single crystal substrate. Convert to layers. In addition, the lattice constant of the single crystal layer is close to that of the substrate crystal. Even if an epitaxial layer is further laminated on a buffer layer having the same lattice constant as that of such a substrate crystal, the lattice mismatch between the substrate and the substrate is increased. Is not sufficiently mitigated. As a result, only a result similar to that of directly depositing on the substrate is brought about, and a coarse crystal layer having a high density of crystal defects such as misfit dislocations due to the influence of the mismatch is obtained.
Further, when the thickness of the amorphous buffer layer exceeds about 50 nm, the polycrystalline body develops remarkably in the amorphous layer even in the as-grown state. If the polycrystals are mixed in the amorphous layer, the crystal structure in the amorphous layer becomes non-uniform, and the action of relaxing the lattice mismatch becomes non-uniform, which is not preferable. In addition, the polycrystal already existing in the as-grown state inhibits the single crystallization of the buffer layer, and the polycrystal sometimes exposed on the surface of the buffer layer is a single crystal layer having a uniform orientation. There is an inconvenience that hinders growth. The layer thickness of the buffer layer is preferably about 5 nm to about 50 nm in which a single crystal layer having a lattice constant peculiar to the material constituting the buffer layer is formed in an as-grown state with extremely few polycrystals.
[0023]
In the present invention, a BP-based amorphous layer grown at a low temperature is further overlaid with a single-crystal layer made of a BP-based material to form a buffer layer from the amorphous layer and the single-crystal layer thereon. You may. The BP-based low-temperature buffer layer mainly composed of an amorphous material in an as-grown state is effective in alleviating lattice mismatch between the substrate crystal such as GaP and the like and providing an epitaxial layer having excellent crystallinity. . In other words, the amorphous buffer layer made of a BP-based material can reduce the lattice mismatch with the single crystal substrate to form a BP single crystal layer having a low density of crystal defects such as misfit dislocations and excellent crystallinity. Acts as a suitable underlayer. A BP-based single crystal layer having excellent crystallinity can be used as a base layer, and a gallium phosphide single crystal layer having excellent crystallinity inheriting good crystallinity of the base layer can be stacked thereon. For example, a buffer layer having a double-layered structure including an amorphous buffer layer made of boron phosphide (BP) and a single crystal layer also made of boron phosphide is formed thereon. The boron phosphide-based single crystal layer deposited on this double-layered buffer layer is made of trimethylboron ((C₂H₅)₃B) / Phosphine (PH)₃) / Hydrogen (H₂) Can be formed by MOCVD or the like using a source gas as the source gas. When forming an amorphous layer or a single crystal layer of boron phosphide, an n-type or p-type impurity may be doped to form an n-type or p-type conductive buffer layer. When the buffer layer is composed of a plurality of layers, it is preferable that the conductivity types of the layers constituting the buffer layer match.
[0024]
In the present invention, gallium phosphide nitride (GaN) laminated via a buffer layer made of a BP-based material as described above is used._{1 ー X}P_X: 0 <X <1) A single-heteros (SH) junction type light emitting portion structure can be formed using the single crystal layer as the lower cladding layer. For example, p-type GaN laminated on a buffer layer made of p-type boron phosphide_0.97P_0.03A cladding layer composed of a single crystal layer and an n-type gallium indium nitride (Ga_YIn_1-YThe light emitting layer structure of the pn junction type single hetero structure is constituted by the N) light emitting layer. Since the boron phosphide (BP) forming the buffer layer is a zinc blende type cubic crystal, cubic GaN is formed thereon._{1 ー X}P_XCan be formed neatly. In sphalerite-type boron phosphide (BP) -based crystals, a p-type crystal layer can be easily obtained in terms of the band structure as compared with hexagonal (GaN) -based GaN (see JP-A-2-275682). ). Therefore, if the buffer layer is composed of a BP-based material, the p-type GaN_{1 ー X}P_XIt is convenient to form a single crystal layer and obtain a pn junction type single hetero junction light emitting portion structure. In addition, GaN on the BP-based buffer layer_{1 ー X}P_XCladding layer and GaN of opposite conductivity type_{1 ー X}P_XAn example of a light emitting portion structure of a single hetero junction composed of a light emitting layer is given.
[0025]
Also, in the present invention, gallium phosphide nitride (GaN) laminated via a BP-based buffer layer is used._{1 ー X}P_X: 0 <X <1) A light emitting portion structure of a double hetero (DH) junction structure can be formed by using a single crystal layer as a lower cladding layer. GaN_{1 ー X}P_X(0 <X <1) The double-heterojunction type light emitting unit structure including the single crystal layer is formed of n-type or p-type GaN._{1 ー X}P_XLayer as a lower cladding layer, and a gallium indium nitride layer (Ga_YIn_{1 ー Y}N: 0 ≦ Y ≦ 1) as the light emitting layer, and aluminum gallium nitride (Al) having a conductivity type opposite to that of the lower cladding layer._ZGa_1-ZN: 0 ≦ Z ≦ 1) The layer can be configured as an upper cladding layer. In this example, the light emitting layer was formed of GaN which is a lower cladding layer._{1 ー X}P_XGa that achieves good lattice matching with the layer_YIn_{1 ー Y}If N (0 ≦ Y ≦ 1), it can be effectively used as a hetero-junction light-emitting portion structure that provides high-intensity light emission. For example, GaN_0.95P_0.05(A = 4.557 °) and a cubic Ga with a gallium composition ratio (= Q) of 0.1% (Q = 0.10) for achieving lattice matching with this layer._0.10In_0.90And a light-emitting portion structure including a light-emitting layer made of N. Also, GaN_0.99P_0.01Layer and Ga_0.96In_0.04An example is a heterojunction light emitting portion structure having a heterojunction composed of an N layer. In any of the exemplified configurations of the light-emitting portion structures, the light-emitting layer having good lattice matching is a light-emitting layer having excellent crystallinity, and therefore, a group III nitride semiconductor light-emitting device that emits light of high intensity. Become.
[0026]
In case of SH jointGaN_1-XP_X(0 <X <1) As the single crystal layer has a smaller degree of lattice mismatch (△) with the BP-based material constituting the buffer layer, a higher quality crystal layer can be obtained. By the way, the buffer layer and GaN_1-XP_XWhen there is no lattice mismatch with the single crystal layer and both have a lattice matching relationship, the degree of lattice mismatch is 0 (zero) (that is, △ = 0). When the degree of lattice mismatch (△) is set to about ± 1% or less, more preferably ± 0.4% or less, GaN having particularly excellent crystallinity can be obtained._1-XP_X(0 <X <1) A single crystal layer is obtained. Buffer layer and GaN_1-XP_XThe degree of lattice mismatch with the single crystal layer is determined based on the lattice constant of the buffer layer. In this case, the GaN_1-XP_XWhen the lattice constant of the single crystal layer is large, the degree of lattice mismatch becomes a positive value. When the lattice constants have the opposite magnitude relation, the degree of lattice mismatch is given as a negative value.
[0027]
Since the lattice constant of cubic boron nitride (BN) is 3.615 ° (see Yasuharu Suematsu, “Optical Device”, page 28), BP_XN_1-X  The lattice constant of a single crystal (a₁) Is represented by the following equation (2).
a₁(Å) = 3.615 + 0.923 · X (2)
On the other hand, cubic gallium nitride phosphide (GaN_{1 ー X}P_X: 0 <X <1) lattice constant (a₂) Is calculated from the following equation (3) based on the Vegard rule.
a₂(Å) = 4.510 + 0.940 · X (3)
For example, BP with a phosphorus composition ratio (X) of 0.99_0.99N_0.01Lattice constant (a₁) Is 4.530 ° from equation (2). The lattice mismatch degree (△) within ± 0.4% with respect to the lattice constant of 4.530 ° is obtained from the lattice constant (a₂) With ≧ 4.512 ° and ≦ 4.548 °_{1 ー X}P_XIt is. From equation (3), the lattice constant (a₂) Is given by GaN having a phosphorus composition ratio (X) of 0.2% or more and 4.0% or less._{1 ー X}P_XIt is. That is, BP_0.99N_0.01GaN having a phosphorus composition ratio (X) of 0.2% or more and 4% or less on the buffer layer_{1 ー X}P_XWith a structure in which single crystal layers are stacked, a light-emitting portion structure having an SH structure or a DH structure composed of a high-quality crystal layer can be formed.
[0028]
BP above_XN_1-XCompared to a ternary mixed crystal, boron phosphide is a binary compound and can be easily formed into a film by a vapor phase growth means such as MOCVD. That is, there is a convenience that the buffer layer of the present invention can be more easily formed. According to equation (3), GaN_{1 ー X}P_XLattice constant (a₂) Has the same lattice constant as the monomeric boron phosphide (BP) (a = 4.538 °) when the phosphorus composition ratio (X) is 3% (X = 0.03). Gallium phosphide (GaN) with a phosphorus composition ratio (X) of 1% (X = 0.01) or more and 5% (X = 0.05) or less_1-XP_X: 0.01 ≦ X ≦ 0.05) is within a range from 4.519 ° (when X = 0.01) to 4.557 ° (when X = 0.05). If the phosphorus composition ratio (X) is regulated within this range, the degree of lattice mismatch with the BP constituting the buffer layer is suppressed to within about 0.4%, so that the density of crystal defects such as dislocation caused by the lattice mismatch. GaN with small size and excellent crystallinity_1-XP_XA single crystal layer can be obtained.
[0029]
[Action]
The buffer layer made of the boron phosphide material of the present invention comprises a single crystal material as a substrate and gallium phosphide nitride (GaN) provided on the buffer layer._{1 ー X}P_X: GaN that relaxes the degree of lattice mismatch with 0 <X <1) and has excellent crystallinity with small crystal defect density_{1 ー X}P_XIt exerts an effect of providing a system lower cladding layer. In addition, GaN with excellent crystallinity formed by interposing a buffer layer made of a BP-based material is used._{1 ー X}P_XOn the lower cladding layer, a light emitting layer or the like having good crystallinity can be laminated by inheriting the good crystallinity, and thus has an effect of providing a light emitting portion structure capable of emitting light of high intensity.
[0030]
In particular, the BP-based buffer layer composed of amorphous according to the present invention works particularly effectively to reduce the degree of lattice mismatch with the single crystal substrate material.
[0031]
In addition, if a BP-based buffer layer composed of a laminate of an amorphous layer and a crystal layer is used, the degree of lattice mismatch with the substrate can be reduced, and the crystallinity with a low crystal defect density that is lattice-matched with the buffer layer can be reduced. Excellent quality gallium phosphide (GaN)_{1 ー X}P_X) It has an effect of providing a single crystal layer.
[0032]
The group III nitride semiconductor light-emitting device of the present invention has a single-heterojunction structure or a double-heterojunction structure that exhibits high-intensity light emission, reflecting good crystallinity of the light-emitting portion. Exerts a similar effect.
[0033]
In the group III nitride semiconductor light emitting device of the present invention, the gallium nitride phosphide single crystal layer whose lattice mismatch with the BP-based buffer layer is within ± 1% is a single hetero or double hetero layer composed of a crystal layer having excellent crystallinity. It contributes to providing the light emitting portion of the junction structure.
[0034]
In particular, by setting the degree of lattice mismatch with the BP buffer layer to ± 0.4% or less, it is possible to obtain more excellent crystallinity, and to exhibit stronger emission intensity.
[0035]
【Example】
Hereinafter, the group III nitride semiconductor light emitting device according to the present invention will be described in detail based on examples.
(Example 1)
FIG. 1 is a schematic plan view of a gallium nitride (GaN) -based blue LED having a single-hetero (SH) structure light-emitting portion structure provided with a gallium nitride phosphide crystal layer. FIG. 2 is a diagram for illustrating a stacked structure of the gallium nitride (GaN) -based blue LED illustrated in FIG. 1, and is a schematic cross-sectional view taken along line A-A ′ in FIG. 1.
[0036]
The epitaxial laminated structure including the single heterojunction light-emitting portion structure 12 having the SH structure has the following ( It was composed of layers laminated by the respective vapor phase growth methods described in 1) to (3). That is,
(1) First, triethylborane ((C₂H₅)₃B) / phosphine (PH₃) / (H₂  ) Was used as a source gas to deposit a low-temperature buffer layer 2 made of Zn-doped p-type boron phosphide (BP). The film is formed by atmospheric pressure (substantially atmospheric pressure) MOCVD at a temperature of 350 ° C.₃/ (C₂H₅)₃The growth was performed with the supply ratio of B (V / III ratio) set to about 300. The obtained low-temperature buffer layer 2 made of boron phosphide was amorphous in an as-grown state and had a thickness of about 45 nm.
(2) Next, on the p-type BP low-temperature buffer layer 2, trimethylgallium ((CH₃)₃Ga) / ammonia (NH₃) / Phosphine (PH₃) / Hydrogen (H₂) As a source gas, dimethyl zinc ((CH₃)₂Zn-doped p-type GaN of zinc blende type having a phosphorus composition ratio of 3% (x = 0.03) by MOCVD using Zn) as a Zn doping source._0.97P_0.03A lower clad layer 3 composed of a single crystal layer was formed. The film formation temperature is about 950 ° C., the film thickness is about 2.0 μm, and the carrier concentration is about 2 × 10¹⁸cm^-3And
(3) Finally, trimethyl gallium ((CH₃)₃Ga) / cyclopentadienyl indium (I) ((C₅H₅In (I)) / ammonia (NH₃) / Hydrogen (H₂) As a source gas, an n-type gallium nitride-indium mixed crystal (Ga) having an indium (In) composition ratio of about 3% (x = 0.03)_0.97In_0.03The light emitting layer 4 composed of the N) layer was formed by a normal pressure MOCVD method. The film formation temperature was 880 ° C., and the film thickness was about 0.5 μm.
The light emitting part structure 12 of the pn junction type SH junction is composed of the p-type GaN._0.97P_0.03A lower cladding layer 3 composed of a single crystal layer;_0.97In_0.03The light emitting layer 4 was composed of N layers.
[0037]
In the vicinity of the junction interface between the low-temperature buffer layer 2 which was amorphous in the as-grown state and the single crystal substrate 1, during the vapor phase growth of the epitaxial growth layer described in the above (2) and (3), A single crystal layer having a lattice constant close to that of the single crystal develops. Crystal grains are generated at a position slightly away from the bonding interface with the single crystal substrate 1. In the layer near the surface of the low-temperature buffer layer 2 opposite to the bonding surface with the single crystal substrate 1, the amorphous layer changes to a single crystal layer using the crystal grains as “seed” (growth nuclei). Therefore, the lattice constant (a) of the surface of the low-temperature buffer layer 2 on the side opposite to the junction interface with the single crystal substrate 1 is a = 4.538 ° in consideration of this growth mode. Also, GaN_0.97P_0.03The lattice constant of the lower cladding layer 3 made of a single crystal layer is 4.538 ° from the above relational expression (3). Based on these lattice constants, the degree of lattice mismatch (△) between the layers is calculated as follows.
(A) BP low temperature buffer layer 2 and GaN_0.97P_0.03The degree of lattice mismatch (△) with respect to the surface of the lower cladding layer 3 based on the BP crystal becomes 0 (ie, a lattice matching relationship).
If the Vegard rule is applied, the cubic Ga_0.97In_0.03The lattice constant of N is calculated to be 4.524 °.
(B) Therefore, GaN_0.97P_0.03Lower cladding layer 3 made of single crystal (a = 4.538 °) and cubic Ga_0.97In_0.03With N (a = 4.524 °) light emitting layer 4, GaN_0.97P_0.03The lattice mismatch degree (△) is -0.3% based on the lattice constant of.
[0038]
In general, the dislocation density of a conventional cladding layer composed of a GaN-based crystal layer provided on a sapphire substrate via a gallium nitride (GaN) -based low-temperature buffer layer is approximately 5 × 10⁸  ~ 2 × 10⁹cm^-2(See Mater. Res. Soc. Symp. Proc., Volume 395 Mater. Res. Soc. 1996 pp. 889-895).
On the other hand, according to general cross-sectional TEM observation using a transmission electron microscope (TEM), p-type GaN forming the lower cladding layer 3 described in the present embodiment is_0.97P_0.03The dislocation density of the single crystal layer is about 10⁵cm^-2  ~ About 10⁶  cm^-2It was recognized that. From the viewpoint of the degree of lattice mismatch, the degree of lattice mismatch between the silicon single crystal substrate 1 and the BP low-temperature buffer layer 2 is the largest. However, as described in the present embodiment, if the buffer layer is composed of BP mainly composed of amorphous in an as-grown state grown at a low temperature, the degree of lattice mismatch is reduced by the lattice mismatch reducing action of the amorphous body. Thus, a surface state suitable for forming a light emitting portion such as a cladding layer can be obtained. If a cladding layer is formed on this buffer layer, a single crystal layer having a low dislocation density and excellent crystallinity can be obtained. When the light emitting layer 4 is formed on the lower clad layer 3 obtained in this manner, the dislocation density of the light emitting layer is reduced to the same extent. This shows that the light emitting unit structure 12 of the SH junction is formed from the crystal layer.
[0039]
Using a well-known photolithography (photolithography) technique, a circular n-type ohmic electrode 6 made of gold (Au) and having a diameter of about 130 μm is formed on the light emitting layer 4 as the outermost layer of the light emitting part structure 12 of the SH junction. Was formed. A p-type ohmic electrode 7 made of aluminum (Al) was formed on almost the entire back surface of the silicon single crystal substrate 1 to obtain a group III nitride semiconductor light emitting device 20. After that, by utilizing the clear cleavage of the silicon single crystal substrate 1 in the [110] direction, the stacked structure on which the n-type and p-type ohmic electrodes 6 and 7 are formed is separated into individual elements by a general scribe means. (Chip). The planar shape of the chip was a square with a side of about 350 μm.
[0040]
A forward operating current was passed through the n-type and p-type ohmic electrodes 6 and 7, and the following emission characteristics were obtained.
(A) Emission wavelength = 410 nm
(B) Light emission luminance = 0.4 cd (forward current = 20 mA)
(C) Forward voltage = 3.6 V (forward current = 20 mA)
(D) Reverse voltage = 20 V or more (reverse current = 10 μA)
As in the present embodiment, a pn junction type single heterojunction light emitting portion structure can be formed using a gallium phosphide layer having excellent crystallinity. Can be provided.
[0041]
(Example 2)
In the present embodiment, the content of the present invention will be described by taking as an example a group III nitride semiconductor light emitting device having a double hetero (DH) light emitting portion structure having a gallium phosphide single crystal layer.
FIG. 3 is a schematic cross-sectional view of a gallium nitride (GaN) -based blue LED based on a laminated structure having a DH structure light emitting unit structure according to the present invention.
In FIG. 3, the same components as those described in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.
[0042]
On the same silicon single crystal substrate 1 used in Example 1, a BP low-temperature buffer layer 2 and GaN_0.97P_0.03The lower cladding layer 3 made of a single crystal was laminated. Each of the crystal layers described in the following items (1) and (2) was laminated thereon to form a laminated structure.
(1) Trimethylgallium ((CH₃)₃Ga) / cyclopentadienyl indium (I) (C₅H₅In (I)) / ammonia (NH₃) / Hydrogen (H₂) Is used as a source gas, and n-type gallium indium nitride (Ga) having an average indium (In) composition ratio of about 6% (Y ≒ 0.06) is obtained by atmospheric pressure MOCVD._0.94In_0.06N) Light-emitting layer 4 composed of a mixed crystal layer was formed. The growth temperature was 880 ° C. The light-emitting layer 4 had a multi-phase structure including a plurality of phases having different In compositions, and had a layer thickness of about 10 nm.
A GaInN layer having a multi-phase structure is composed of a main phase composed of a GaInN layer and a subphase mainly composed of microcrystals, which has a different indium concentration from the main layer and is scattered in the main phase. Is a crystal layer to be formed.
(2) Trimethylgallium ((CH₃)₃Ga) / ammonia (NH₃  ) / Hydrogen (H₂  The upper cladding layer 5 composed of a Si-doped n-type gallium nitride (GaN) layer was grown by a reduced pressure MOCVD method using ()) as a source gas. The growth temperature is 1,080 ° C., the layer thickness is about 0.1 μm, and the carrier concentration is about 2 × 10¹⁷cm^-3And
The light emitting part structure 62 of the DH junction is formed by the p-type GaN._0.97P_0.03The single crystal is used as the lower cladding layer 3 and has a multiphase structure of Ga._0.94In_0.06The N layer was configured as the light emitting layer 4 and the n-type GaN layer was configured as the upper cladding layer 5.
[0043]
The lattice mismatch (△) between the constituent layers configured as described above was as follows.
(A) As in the case of the first embodiment, the BP low-temperature buffer layer 2 and the GaN_0.97P_0.03The degree of lattice mismatch (△) with respect to the BP crystal between the single crystal and the lower cladding layer 3 is 0 (zero) (that is, there is a lattice matching relationship).
(B) GaN_0.97P_0.03Lower cladding layer 3 made of single crystal (a = 4.538 °) and cubic Ga_0.94In_0.06N (a = 4.538 °) between the light emitting layer 4 and GaN_0.97P_0.03The lattice mismatch degree (△) becomes 0 (zero) based on the lattice constant of (i.e., a lattice matching relationship).
(C) Ga_0.94In_0.06Ga is present between the N (a = 4.538 °) light emitting layer 4 and the upper cladding layer 5 (a = 4.510 °) made of cubic GaN._0.94In_0.06Based on the lattice constant of N, the degree of lattice mismatch (△) is -0.6%.
As in the first embodiment, the low-temperature buffer layer 2 made of BP and GaN_0.97P_0.03The degree of lattice mismatch with the lower cladding layer 3 made of a single crystal layer is 0 (zero), that is, a lattice matching relationship. In addition, in this embodiment, GaN_0.97P_0.03Lower clad layer 3 made of a single crystal layer and Ga_0.94In_0.06The lattice mismatch with the light emitting layer 4 made of N is also zero, and the light emitting layer 4 with few crystal defects caused by the lattice mismatch can be formed.
[0044]
According to a general cross-sectional TEM observation using a transmission electron microscope, the p-type GaN forming the lower cladding layer 3 of the present embodiment is_0.97P_0.03The dislocation density of the single crystal layer is about 10 since the lattice matching with the BP buffer layer 2 is maintained.⁵cm^-2~ About 10⁶cm^-2It was recognized that. In particular, Ga forming the light emitting layer 4_0.94In_0.06The dislocation density of the N layer is 5 × 10⁵cm^-2  According to this example, the light emitting portion can be constituted by a high quality light emitting layer having a smaller crystal defect density.
[0045]
Similarly to the first embodiment, a well-known photolithography (photolithography) technique is used to form a circular n having a diameter of about 130 μm made of gold (Au) on the upper clad layer 5 as the outermost layer of the laminated structure. An ohmic electrode 6 was formed. A p-type ohmic electrode 7 made of aluminum (Al) was formed on almost the entire back surface of the silicon single crystal substrate 1 to obtain a group III nitride semiconductor light emitting device 30. Next, utilizing the cleavage property of the silicon single crystal substrate 1 in the [110] direction, the laminated structure on which the n-type and p-type ohmic electrodes 6 and 7 are formed is separated into individual elements (chips) by a general scribe means. ). The planar shape of the chip was a square with a side of about 350 μm.
[0046]
An operating current was applied to the n-type and p-type ohmic electrodes 6 and 7 in the forward direction, and the following emission characteristics were obtained.
(A) Emission wavelength = 430 nm
(B) Emission luminance = 0.8 cd (forward current = 20 mA)
(C) Forward voltage = 3.8 V (forward current = 20 mA)
(D) Reverse voltage = 20 V or more (reverse current = 10 μA)
According to the laminated structure as in this embodiment, a gallium phosphide layer having excellent crystallinity can be used as a cladding layer because of good lattice matching with the BP low-temperature buffer layer. A pn-junction DH junction light-emitting portion structure can be formed by using a matched gallium-indium nitride layer having excellent crystallinity as a light-emitting layer. For this reason, it is possible to provide a group III compound semiconductor light emitting device that emits light of particularly high intensity.
[0047]
(Example 3)
In this embodiment, a blue group III nitride semiconductor light emitting device having a DH junction light emitting portion structure including a gallium phosphide single crystal layer laminated on a buffer layer having a double laminated structure is taken as an example. The content of the invention will be described.
[0048]
FIG. 4 is a schematic cross-sectional view of a gallium nitride-based LED configured based on a laminated structure having a DH structure light emitting unit structure according to the present invention. 4, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.
[0049]
First, a low-temperature buffer layer 2 made of boron phosphide (BP) was formed on a silicon single crystal substrate 1 under the growth conditions described in Example 1. Thereafter, a crystalline buffer layer 8 composed of a zinc (Zn) -doped p-type boron phosphide (BP) crystal layer was laminated on the low-temperature buffer layer 2. The crystalline buffer layer 8 made of BP was grown at 980 ° C. using the MOCVD vapor phase growth means described in Example 1. The carrier concentration of the crystalline buffer layer 8 is about 2 × 10¹⁸cm^-3And the layer thickness was about 0.8 μm. The present embodiment is characterized in that the buffer layer 9 has a multilayer structure of the low-temperature buffer layer 2 and the crystalline buffer layer 8 grown at a higher temperature as described above. On the buffer layer 9 having the multilayer structure, a pn junction type double hetero junction light emitting portion structure 32 having the crystal layer configuration described in Example 2 is laminated, and a group III nitride semiconductor light emitting device having a pn junction type DH structure is formed. An element 40 was formed.
[0050]
Unlike the first and second embodiments, the stacked structure of this embodiment is different from the p-type GaN_0.97P_0.03A lower cladding layer 3 made of a single crystal layer is deposited on a crystalline buffer layer 8 made of BP, which is the same constituent material as the low-temperature buffer layer 2. Here, the crystalline buffer layer 8 composed of BP single crystal and GaN_0.97P_0.03The lower cladding layer 3 made of a single crystal layer has the same lattice constant. Therefore, a high-quality GaN having a low density of crystal defects such as misfit dislocations is formed on the crystalline buffer layer 8 composed of the BP single crystal layer constituting the laminated buffer layer 9._0.97P_0.03A single crystal layer will result.
[0051]
A n-type ohmic electrode 6 of Au is formed on the front and back surfaces of the laminated structure, and a p-type ohmic electrode 7 of Al is formed on the front and back surfaces of the laminated structure by using a well-known photolithography (photolithography) technique as in the second embodiment. Thus, a group III nitride semiconductor light emitting device 40 was formed. When an operating current was applied to the n-type and p-type ohmic electrodes 6 and 7 in the forward direction, the following emission characteristics were obtained.
(A) Emission wavelength = 430 nm
(B) Emission luminance = 1.0 cd (forward current = 20 mA)
(C) Forward voltage = 3.7 V (forward current = 20 mA)
(D) Reverse voltage = 20 V or more (reverse current = 10 μA)
Since the buffer layer is composed of a multilayer structure in which an amorphous low-temperature buffer layer composed of BP and a crystalline buffer layer composed of BP single crystal are laminated, a gallium phosphide layer having particularly excellent crystallinity can be obtained. By using this as a cladding layer to form a pn junction DH junction light emitting portion structure, a group III nitride semiconductor light emitting device having high emission luminance as described above was obtained.
[0052]
(Example 4)
In this embodiment, a green group III nitride semiconductor light emitting device having a DH junction light emitting portion structure including a gallium phosphide single crystal layer laminated on a silicon single crystal substrate with a BP buffer layer interposed therebetween is exemplified. Then, the contents of the present invention will be described. The configuration of the laminated structure is the same as that of the third embodiment shown in FIG.
[0053]
As in the third embodiment, a double-layered buffer layer 9 composed of a BP amorphous low-temperature buffer layer 2 and a BP crystalline buffer layer 8 is provided on a silicon single crystal substrate 1, and a lower cladding layer is formed thereon. GaN having a phosphorus composition ratio of 5% (X = 0.05) as the layer 3_0.95P_0.05Single crystal layers were stacked. Next, GaN_0.95P_0.05On the lower cladding layer 3 made of a single crystal layer, as the light emitting layer 4, a Si-doped n-type Ga having an average indium composition ratio of 10% (Y = 0.10) is used._0.90In_0.10An N crystal layer was laminated. This Ga_0.90In_0.10The carrier concentration of the N light emitting layer 4 is about 8 × 10¹⁷cm^-3And the layer thickness was about 20 nm. An upper clad layer 5 made of an n-type gallium nitride (GaN) layer was laminated on the light emitting layer 4 as in the third embodiment. The carrier concentration of the upper cladding layer 5 is about 2 × 10¹⁷cm^-3And the layer thickness was about 0.1 μm. Therefore, the light emitting part structure 42 of this pn junction type DH junction is formed of n-type GaN._0.95P_0.05Layer / n-type Ga_0.90In_0.10It will be composed of an N layer / p-type GaN layer.
[0054]
The following describes the stacked system of this embodiment from the viewpoint of the degree of lattice mismatch.
(A) The degree of lattice mismatch (△) between the BP low-temperature buffer layer 2 and the BP crystalline buffer layer 8 is 0 (ie, a lattice matching relationship).
(B) BP crystalline buffer layer 8 and GaN_0.95P_0.05The degree of lattice mismatch with the single crystal lower cladding layer 3 is 0.4% based on the BP crystalline buffer layer 8.
(C) GaN_0.95P_0.05Lower cladding layer 3 made of single crystal (a = 4.557 °) and cubic Ga_0.90In_0.10The degree of lattice mismatch (△) between the light-emitting layer 4 and N (a = 4.557Å) is GaN_0.95P_0.05Is 0 (zero) based on the lattice constant of (i.e., has a lattice matching relationship).
(D) Ga_0.90In_0.10The degree of lattice mismatch between the light emitting layer 4 made of N (a = 4.557 °) and the upper cladding layer 5 made of cubic GaN (a = 4.510 °) is Ga_0.90In_0.101.0% based on the lattice constant of N.
In the present embodiment, the GaN_0.95P_0.05Single crystal layer and Ga of light emitting layer 4_0.90In_0.10By setting the degree of lattice mismatch with the N single crystal layer to 0 (zero), a laminated structure was formed in which the light emitting layer 4 with few crystal defects due to lattice mismatch could be formed. Therefore, according to the cross-sectional TEM observation, Ga_0.90In_0.10The dislocation density of the N light emitting layer 4 is about 2 × 10⁵cm^-2It was observed that the degree had decreased.
[0055]
As shown in FIG. 4, an n-type ohmic electrode 6 made of Au and a p-type ohmic electrode 7 made of Al are formed on the front and back surfaces of the laminated structure by using a well-known photolithography (photolithography) technique as in the second embodiment. The green LED was formed. When an operating current was applied to the n-type and p-type ohmic electrodes 6 and 7 in the forward direction, the following emission characteristics were obtained.
(A) Emission wavelength = 512 nm
(B) Emission luminance = 1.6 cd (forward current = 20 mA)
(C) Forward voltage = 3.7 V (forward current = 20 mA)
(D) Reverse voltage = 20 V or more (reverse current = 10 μA)
A gallium phosphide lower cladding layer having excellent crystallinity, and a light emitting layer lattice-matched to the lower cladding layer, on a structure in which a low-temperature growth buffer layer of BP and a high-temperature growth crystalline buffer layer of BP are laminated. And a pn-junction DH junction light-emitting portion structure is formed by depositing an upper cladding layer made of GaN having a small lattice mismatch degree. Obtained.
[0056]
(Example 5)
In this embodiment, a blue group III nitride semiconductor light emitting device having an SH junction light emitting portion structure including a gallium phosphide light emitting layer laminated on a conductive GaP substrate via a BP buffer layer The contents of the present invention will be described with reference to an example. Note that the order of the stacked structure of the light emitting element is the same as that of the first embodiment shown in FIG.
[0057]
In this embodiment, unlike the first to fourth embodiments, an n-type gallium phosphide (GaP) single crystal to which sulfur (S) is added is used as the single crystal substrate 21. On the n-type GaP single crystal substrate 21 having a plane orientation of (100), the respective vapor-phase growth layers described in the following items (1) to (3) are stacked to form a pn junction type SH junction light emitting part structure. 52 (see FIG. 2).
(1) First, triethylborane ((C₂H₅)₃B) / phosphine (PH₃) / Hydrogen (H₂  ) As a source gas, a low-temperature buffer layer 22 made of Si-doped n-type boron phosphide (BP) was grown by normal pressure (substantially atmospheric pressure) MOCVD. The growth temperature is 350 ° C, PH₃/ (C₂H₅)₃The growth was performed with the supply ratio of B (V / III ratio) set to about 300. The obtained boron phosphide layer was mainly composed of an amorphous material in an as-grown state, and had a thickness of about 20 nm.
(2) On the n-type BP low-temperature buffer layer 22, trimethylgallium ((CH₃)₃Ga) / ammonia (NH₃) / Phosphine (PH₃) / Hydrogen (H₂  ) As a source gas, disilane (Si₂H₆) Of Si-doped n-type GaN having a phosphorus composition ratio of 3% (X = 0.03) by MOCVD using Si as a doping source_0.97P_0.03The single crystal layer was formed as the lower cladding layer 23. The growth temperature is about 910 ° C., the layer thickness is about 1.0 μm, and the carrier concentration is about 1 × 10¹⁸cm^-3And
(3) Next, on the lower cladding layer 23, trimethylgallium (CH₃)₃Ga / trimethylindium ((CH₃)₃In) / Ammonia (NH)₃) / Hydrogen (H₂  ) As a source gas, Mg-doped p-type gallium indium nitride (Ga) having an indium (In) composition ratio of about 3% (Y = 0.03) by atmospheric pressure MOCVD._0.97In_0.03N) layer was formed. The growth temperature was 880 ° C., and the layer thickness was about 0.2 μm.
Therefore, the light emitting part structure 52 of the pn junction type SH junction is formed by_0.97P_0.03The single crystal layer is used as the lower cladding layer 23, and the p-type Ga_0.97In_0.03This means that the N layer is configured as the light emitting layer 24.
[0058]
The lattice constant a of GaP used as the single-crystal substrate 21 is 5.450 ° (see the aforementioned “III-V compound semiconductor”, published by Baifukan Co., Ltd., p. 148). The lattice mismatch degree (△) of the laminated structure of the present embodiment calculated based on this is as follows.
(A) BP low temperature buffer layer 22 and GaN_0.97P_0.03The degree of lattice mismatch (△) with the lower cladding layer 23 made of a single crystal is 0 (zero) with respect to the BP low-temperature buffer layer (that is, there is a lattice matching relationship).
(B) GaN of lower cladding layer 23_0.97P_0.03(A = 4.538 °) and cubic Ga of the light emitting layer 24_0.97In_0.03With N (a = 4.524 °), GaN_0.97P_0.03The lattice mismatch degree (△) is -0.3% based on the lattice constant of.
[0059]
Using a well-known photolithography (photolithography) technique, as shown in FIG. 2, the p-type ohmic electrode 7 of Al and the n-type ohmic electrode of Au 6 to form a so-called p-side-up blue LED. When an operating current was applied to the n-type and p-type ohmic electrodes 6 and 7 in the forward direction, the following emission characteristics were obtained.
(A) Emission wavelength = 408 nm
(B) Light emission luminance = 0.4 cd (forward current = 20 mA)
(C) Forward voltage = 3.7 V (forward current = 20 mA)
(D) Reverse voltage = 20 V or more (reverse current = 10 μA)
A gallium phosphide single crystal layer having excellent crystallinity obtained through a BP low-temperature buffer layer is used as a lower cladding layer, and a lattice mismatch with the lower cladding layer is suppressed to within ± 0.4%. Thus, the light emitting portion structure of the SH junction was formed, and thus a group III nitride semiconductor light emitting device having excellent light emitting characteristics as described above was obtained.
[0060]
(Comparative example)
A conventional blue group III nitride semiconductor device having the configuration shown in FIG. 5 was manufactured, and the light emission characteristics were compared with the group III nitride semiconductor device according to the present invention.
[0061]
In this comparative example, unlike the above-described Examples 1 to 5, insulating (0001) (C plane) -sapphire (alumina single crystal) was used as the substrate 101. On the sapphire substrate 101, the respective vapor-phase growth layers described in the following items (1) to (3) were sequentially laminated to form a pn junction type DH junction light emitting portion structure 42 (see FIG. 5).
(1) Trimethylgallium ((CH₃)₃Ga) / ammonia (NH₃) / Hydrogen (H₂  ) Was used as a source gas to grow a low-temperature buffer layer 102 made of undoped gallium nitride (GaN) by a reduced pressure MOCVD method. The growth temperature was 420 ° C., and the layer thickness was about 17 nm.
(2) On the low-temperature buffer layer 102, disilane (Si₂H₆) Was used as a Si doping source to grow a lower cladding layer 103 made of a wurtzite-type hexagonal Si-doped n-type GaN single crystal layer by MOCVD. The growth temperature is about 1050 ° C., the layer thickness is about 3.0 μm, and the carrier concentration is about 3 × 10¹⁸cm^-3And
(3) Trimethyl gallium ((CH₃)₃Ga) / trimethylindium ((CH₃)₃In) / Ammonia (NH)₃) / Hydrogen (H₂  ) Is used as a source gas, and n-type gallium nitride-indium mixed crystal (Ga) having an indium (In) composition ratio of about 3% (Y ≒ 0.03) is obtained by atmospheric pressure MOCVD._0.97In_0.03The N) layer was grown as the light emitting layer 104. The growth temperature was 880 ° C., and the layer thickness was about 0.1 μm.
(4) Next, a wurtzite-type hexagonal Mg-doped p-type GaN single crystal layer was grown as the upper cladding layer 105 on the light emitting layer 104. The growth temperature is about 1020 ° C., the layer thickness is about 0.1 μm, and the carrier concentration is about 2 × 10¹⁷cm^-3And
The light emitting part structure 42 of the pn junction type DH junction has an n-type Ga_0.97In_0.03The N layer was configured as the light emitting layer 104, and the p-type GaN layer was configured as the upper cladding layer 105.
[0062]
The conventional laminated system described in this comparative example is described as follows from the viewpoint of the degree of lattice mismatch.
(A) The degree of lattice mismatch (△) between the GaN low-temperature buffer layer 102 and the GaN lower cladding layer 103 is 0 (zero) (that is, they are in a lattice matching relationship).
(B) Hexagonal Ga single crystal lower cladding layer 103 and hexagonal Ga_0.90In_0.10The degree of lattice mismatch (△) between the light-emitting layer 104 and N (a-axis lattice constant: 3.222 °) was 1.1% based on the lattice constant of GaN.
(C) Ga_0.90In_0.10The degree of lattice mismatch (△) between the light emitting layer 104 made of N (a-axis lattice constant: 3.222 °) and the upper cladding layer 105 made of hexagonal GaN (a = 3.186 °) is determined by the lattice constant of GaN. On the basis of 1.1%.
[0063]
In the conventional laminated structure, the degree of lattice mismatch between the GaN low-temperature buffer layer 102 and the GaN single crystal layer forming the lower cladding layer 103 is 0, but according to cross-sectional TEM observation, the GaN lower cladding layer 103 Internal dislocation density is about 2 × 10⁹cm^-2Was reached. This is because gallium nitride phosphide having an extremely low crystal defect density using a buffer layer made of BP is extremely high even though the degree of lattice mismatch with the substrate crystal is large as in the case of Example 1. It is symmetric that a crystal layer is obtained. Most of the dislocations in the GaN lower cladding layer 103 are hexagonal Ga_0.90In_0.10It was clear that the film penetrated the N light emitting layer 104 and the hexagonal GaN upper cladding layer 105 and reached the surface of the upper cladding layer 105.
[0064]
The lamination structure provided with the light emitting part structure 42 of the pn junction type DH junction was subjected to a cutting process for installing an ohmic electrode by plasma etching means. Thereafter, a p-type ohmic electrode 106 was provided on the p-type GaN upper cladding layer 105. Further, an n-type ohmic electrode 107 was provided on the surface of the n-type GaN lower cladding layer 103 exposed by the above-described plasma etching, thereby forming a conventional LED.
[0065]
An operating current was applied to the p-type and n-type ohmic electrodes 106 and 107 in the forward direction, and the following emission characteristics were obtained.
(A) Emission wavelength = 418 nm
(B) Light emission luminance = 0.2 cd (forward current = 20 mA)
(C) Forward voltage = 4.0 V (forward current = 20 mA)
(D) Reverse voltage = 15 V or more (reverse current = 10 μA)
As compared with the LED according to the present invention, particularly the blue group III nitride semiconductor light emitting device 20 having the pn junction type SH junction structure described in the first embodiment, the light emission luminance is as low as １ ／ and the forward direction is small. The voltage was also high. Further, in the conventional LED, a spot-like light emitting spot (spot) having a higher intensity than the surroundings is present corresponding to the region where the threading dislocations are dense in the upper cladding layer 105, and the light emitting region has The emission intensity distribution was non-uniform. The emission spot is hexagonal Ga_0.90In_0.10It is presumed that the cause is that indium (In) is generated by agglomeration in the region having a high dislocation density in the N light emitting layer 104.
[0066]
【The invention's effect】
The group III nitride semiconductor light-emitting device of the present invention provides gallium phosphide (GaN) having excellent crystallinity while maintaining good lattice matching with a boron phosphide-based buffer layer._{1 ー X}P_X(3) Since the light emitting portion can be formed using the crystal layer, a group III nitride semiconductor light emitting device having high light emission intensity can be obtained.
[0067]
In particular, if the boron phosphide-based buffer layer is composed of an amorphous material, the lattice mismatch with the single crystal substrate can be greatly reduced, and a gallium nitride phosphide single crystal layer having good crystallinity can be grown. A group III nitride semiconductor light emitting device having excellent emission intensity can be obtained.
[0068]
In addition, the boron phosphide-based buffer layer is composed of an amorphous and crystalline multilayered laminated structure.OrWith this configuration, a gallium phosphide single crystal layer having good crystallinity can be mounted on the boron phosphide-based single crystal layer having already improved crystallinity to form a light-emitting portion. There is an effect that an excellent group III nitride semiconductor light emitting device is provided.
[0069]
Further, if the light emitting structure is constituted by a single hetero junction structure, a group III nitride semiconductor light emitting device having a simple structure and high light emission intensity can be obtained.
[0070]
Further, when the light emitting structure is constituted by a double hetero junction structure, the effect of obtaining a group III nitride semiconductor light emitting device having higher light emission intensity can be obtained.
[0071]
In the present invention, the light emitting portion having the SH or DH junction structure is formed through the cladding layer by setting the degree of lattice mismatch between the cladding layer composed of the BP-based buffer layer and the gallium phosphide single crystal layer to ± 1% or less. That is, since the light emitting portion is formed using a gallium nitride phosphide single crystal layer having low crystal defect density due to lattice misfit and excellent crystallinity, a group III nitride having high light emission intensity is used. This is effective in obtaining a semiconductor light emitting device.
[0072]
In the group III nitride semiconductor light emitting device of the present invention, the degree of lattice mismatch between the BP-based buffer layer and the lower cladding layer is set to ± 1% or less, particularly ± 0.4% or less, so that the crystal defect density is low. Since the light-emitting portion can be formed by using a gallium phosphide single crystal layer having excellent light-emitting properties, an effect of obtaining a group III nitride semiconductor light-emitting device having high light emission intensity can be obtained.
[0073]
For example, if the BP-based buffer layer is composed of boron phosphide (BP) and the phosphorus (P) composition ratio of the gallium nitride phosphide single crystal layer grown through the BP buffer layer is 1% or more and 5% or less, Since the light-emitting portion can be constituted by a gallium phosphide single crystal layer having good lattice matching and excellent crystallinity, it is possible to easily obtain a group III nitride semiconductor light-emitting device having high light emission intensity. It becomes.
[Brief description of the drawings]
FIG. 1 is a schematic plan view of a group III nitride semiconductor light-emitting device described in Example 1.
FIG. 2 is a schematic sectional view taken along a line A-A 'in FIG.
FIG. 3 is a schematic cross-sectional view of a group III nitride semiconductor light-emitting device described in Example 2.
FIG. 4 is a schematic cross-sectional view of a group III nitride semiconductor light-emitting device described in Example 3.
FIG. 5 is a schematic cross-sectional view of a conventional light emitting device having an AlGaInN-based double heterojunction structure.
[Explanation of symbols]
1,21 ... Single crystal substrate
2,22 ... Low-temperature buffer layer
3,23 .... Lower cladding layer
4,24 ... light-emitting layer
5 ... Upper cladding layer
6 ... n-type ohmic electrode
7 ... p-type ohmic electrode
8 ... Crystalline buffer layer
9 ... Buffer layer
12,52 ····· Single heterojunction light emitting unit
20, 30, 40... III-nitride semiconductor light emitting device
32, 42, 62 ... Light emitting unit structure of double hetero junction
100 light-emitting elements
..... substrate
····· Low-temperature buffer layer
103 Lower cladding layer
104 Light-emitting layer
105 ... Top cladding layer
106 p-type ohmic electrode
107 ····· n-type ohmic electrode

Claims (8)

Light-emitting portion structure including a gallium phosphide (GaN _1-X P _X : 0 <X <1) single crystal layer provided as a lower cladding layer provided on a single crystal substrate with a boron phosphide (BP) -based buffer layer interposed therebetween A group III nitride semiconductor light-emitting device, comprising: The group III nitride semiconductor light emitting device according to claim 1, wherein the boron phosphide-based buffer layer is amorphous. 2. The group III nitride semiconductor light emitting device according to claim 1, wherein the boron phosphide-based buffer layer has a laminated structure of amorphous and crystalline. The III-nitride semiconductor light-emitting device according to claim 1, wherein the light-emitting portion structure is a single heterojunction structure including a gallium nitride phosphide single crystal layer. The III-nitride semiconductor light-emitting device according to claim 1, wherein the light-emitting portion structure is a double hetero junction structure including a gallium nitride phosphide single crystal layer. 2. The group III nitride semiconductor light emitting device according to claim 1, wherein the degree of lattice mismatch between the boron phosphide-based buffer layer and the gallium nitride phosphide single crystal layer is ± 1% or less. 6. The group III nitride according to claim 6, wherein the degree of lattice mismatch between the boron phosphide-based buffer layer and the gallium nitride phosphide single crystal layer is ± 0.4% or less. Object semiconductor light emitting device. The boron phosphide-based buffer layer is made of boron phosphide (BP), and the gallium nitride phosphide single crystal layer in the light emitting portion structure has a phosphorus (P) composition ratio of 1% or more and 5% or less. The group III nitride semiconductor light-emitting device according to claim 1 or claim 4.

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