JP4282976B2 - 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-based compound semiconductor device having a heterogeneous (hetero) junction structure composed of a group III nitride semiconductor layer and a boron phosphide layer excellent in orientation, a method for manufacturing the same, and a light emitting diode It is about.
[0002]
[Prior art]
Conventionally, aluminum nitride, gallium, indium (Al _X Ga _Y In _Z Group III nitride semiconductors such as N: 0 ≦ X, Y, Z ≦ 1, X + Y + Z = 1) are light emitting diode (LED) light emitting layers or clad layers, high mobility field effect transistors (TEGFETs) ) As an electron channel layer or an electron supply layer (Patent Document 1, Non-Patent Document 1, etc.).
In a device using a group III nitride semiconductor (group III nitride semiconductor device), a device having a heterogeneous (hetero) junction structure between group III nitride semiconductor layers is generally used in order to develop a device function. Is. For example, Patent Document 1 discloses gallium nitride (GaN) and gallium nitride indium (Ga). _Y In _Z An example is disclosed in which a light emitting portion of an LED or a laser diode (LD) is formed by heterogeneous junctions with N: 0 ≦ Y, Z ≦ 1, Y + Z = 1).
[0003]
A heterojunction structure composed of a group III nitride semiconductor layer or a group III nitride semiconductor layer constituting a compound semiconductor element has conventionally been mainly sapphire (α-Al ₂ O ₃ (Single crystal) produced on a substrate by vapor phase growth (Patent Document 2, etc.).
However, for example, the lattice mismatch between the sapphire substrate and gallium nitride (GaN) is as large as about 16% (Non-Patent Document 2, etc.), and the gallium nitride layer formed on the sapphire substrate has 1 × 10 ⁸ / Cm ² It is known that a large amount of misfit rearrangement exceeding 1 is included (Non-patent Document 3, etc.). In a heterogeneous junction made of a group III nitride semiconductor such as gallium nitride, misfit dislocations propagate beyond the heterogeneous junction to the upper layer. For this reason, it has been difficult for the prior art to stably obtain a heterogeneous junction structure having a low dislocation density.
[0004]
On the other hand, the present inventor has found that the boron phosphide (BP) layer is effective in preventing the propagation of misfit dislocations from the group III nitride semiconductor layer.
Patent Documents 2 to 7 disclose a technique for forming a light-emitting element by bonding a boron phosphide layer on a group III nitride semiconductor layer made of hexagonal wurtzite crystal type (Wurtzite) gallium nitride or the like. Has been. However, this conventional technique is not intended to prevent the propagation of misfit dislocations from the group III nitride semiconductor layer (see Patent Documents 8 and 9). The crystallographic structure to be provided in the boron phosphide layer effective to sufficiently and stably prevent propagation is not yet known. Therefore, conventionally, it has been difficult to stably obtain a pn junction structure of a group III nitride semiconductor layer and a boron phosphide layer that has a small leakage current and can exhibit good rectification characteristics.
[0005]
[Patent Document 1]
Japanese Patent Publication No.55-3834
[Patent Document 2]
JP-A-10-242514
[Patent Document 3]
Japanese Patent Laid-Open No. 10-242515
[Patent Document 4]
Japanese Patent Laid-Open No. 10-242567
[Patent Document 5]
JP-A-10-242568
[Patent Document 6]
Japanese Patent Laid-Open No. 10-242569
[Patent Document 7]
Japanese Patent Laid-Open No. 10-247745
[Patent Document 8]
JP 10-247760 A
[Patent Document 9]
JP 10-247671 A
[Non-Patent Document 1]
Akazaki Isao, “Group III Nitride Semiconductor (Advanced Electronics I-21)”, first edition, Baifukan Co., Ltd., December 8, 1999, p. 285-293
[Non-Patent Document 2]
Isamu Akasaki et al., “EFFECTS OF AlN BUFFER LAYER ON CRYSTALLOGRAPHIC STRUCTURE AND ON ELECTRICAL AND OPTICAL PROPERTIES OF GaN AND Ga1-xAlxN (0 <X ≦ 0.4) FILMS GROWN ON SAPPHIRE SUBSTARTE BY MOVPE” (Netherlands) , Journal of Crystal Growth, 1989, Vol. 98, p. 209-219
[Non-Patent Document 3]
LTRomana et al., “STRUCTUAL CHARACTERIZATION OF THICK GaN FILMS GROWN BY HYDRIDE VAPOR PHASE EPITAXY” (USA), Material Research Society Symposium Proc. (Mat. Res. Soc. Symp. Proc.), 1996 423, p. 245-250
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and the crystal structure of the boron phosphide layer capable of sufficiently and stably suppressing the propagation of misfit dislocations from the group III nitride semiconductor layer is clarified. Thus, an object of the present invention is to provide a boron phosphide-based compound semiconductor device having a junction structure of a group III nitride semiconductor layer and a boron phosphide layer and having excellent device characteristics. Moreover, it aims at providing the manufacturing method.
[0007]
[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.
[0008]
That is, the present invention
(1) In a boron phosphide-based compound semiconductor element having a heterogeneous junction structure composed of a group III nitride semiconductor layer and a boron phosphide layer, The group III nitride semiconductor layer is a wurtzite crystal type; The surface of the group III nitride semiconductor layer is a (0.0.0.1.) Crystal plane, and the boron phosphide layer is (0.0.0.1.) Of the group III nitride semiconductor layer. {111} -boron phosphide layer having {111} crystal planes stacked parallel to the crystal planes on the crystal planes [2 .. of the (0.0.0.1.) Crystal plane of the group III nitride semiconductor layer. -1. -1.0. The crystal orientation is parallel to the <110> crystal orientation of the {111} crystal plane of the boron phosphide layer. A boron phosphide-based compound semiconductor device,
( 2 ) On the (0.0.0.1.) Crystal plane of the group III nitride semiconductor layer [2. -1. -1.0. There are two <110> crystal orientations of the boron phosphide layer parallel to the crystal orientation, and the angle formed by these is 180 ° ( 1 ) Boron phosphide-based compound semiconductor device,
( 3 ) On the (0.0.0.1.) Crystal plane of the group III nitride semiconductor layer [2. -1. -1.0. The <110> crystal orientation of the boron phosphide layer parallel to the crystal orientation is [1. -1.0. ] And [-1.1.0. ] ( 2 ) Boron phosphide-based compound semiconductor device,
( 4 ) The group III nitride semiconductor layer is a (0.0.0.1.)-Gallium nitride layer, and the boron phosphide layer includes stacking faults and / or twins in the <111> crystal orientation {111} -A boron phosphide layer, characterized in that (1) to ( 3 ) A boron phosphide-based compound semiconductor device according to any one of
( 5 The boron phosphide layer has a dislocation density smaller than that of the group III nitride semiconductor layer (1) to (1) 4 The boron phosphide-based compound semiconductor device according to any one of items 1 to 3).
[0009]
The present invention also provides:
( 6 ) In a method for manufacturing a boron phosphide-based compound semiconductor device having a heterojunction structure composed of a group III nitride semiconductor layer and a boron phosphide layer, the surface is a (0.0.0.1.) Crystal plane. Wurtzite crystal type A boron-containing compound and a phosphorus-containing compound are supplied to the vapor phase growth region with the group III nitride semiconductor layer as a base, and the (0.0.0.1.) Crystal plane of the group III nitride semiconductor layer is In parallel {111} -boron phosphide layer having {111} crystal planes In addition, the [0.0.0.1.] Crystal plane of the group III nitride semiconductor layer [2. -1. -1.0. The <110> crystal orientation of the {111} crystal plane of the boron phosphide layer is parallel to the crystal orientation. A process for producing a boron phosphide-based compound semiconductor device comprising a step of vapor-phase growth,
( 7 ) The boron phosphide layer is vapor-phase grown at a temperature of 750 ° C. to 1200 ° C. ( 6 ) A process for producing a boron phosphide-based compound semiconductor device according to claim 1,
( 8 ) The boron phosphide layer is vapor grown at a V / III ratio of 600 or more ( 6 Or ( 7 ). The method for producing a boron phosphide-based compound semiconductor device according to).
In the present specification, “V / III ratio” means the concentration of phosphorus atoms in the phosphorus-containing compound (phosphorus raw material) relative to the concentration of boron atoms in the boron-containing compound (boron raw material) supplied to the vapor phase growth region. It means the ratio of
[0010]
The present invention also provides:
( 9 ) In a light emitting diode including a laminate formed by sequentially laminating a lower clad layer, a light emitting layer, a protective layer protecting the light emitting layer, and an upper clad layer, the protective layer has a surface of (0.0 .0.1.) A group III nitride semiconductor layer having a crystal plane, and the upper cladding layer is parallel to the crystal plane on the (0.0.0.1.) Crystal plane of the protective layer A light emitting diode comprising a {111} -boron phosphide layer having stacked {111} crystal faces.
[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 has a heterogeneous junction structure composed of a group III nitride semiconductor layer and a boron phosphide layer, and the crystallinity of the group III nitride semiconductor layer and the boron phosphide layer. The structure is characteristic.
[0012]
Examples of the compound constituting the group III nitride semiconductor layer that forms the base of the boron phosphide layer include gallium nitride (GaN), aluminum nitride / gallium (Al _X Ga _1-X Composition formula Al such as N: 0 ≦ X ≦ 1) _X Ga _Y In _Z A compound represented by N (0 ≦ X, Y, Z ≦ 1, X + Y + Z = 1) is preferable. Further, in addition to nitrogen (N), other group V elements (for example, phosphorus (P), arsenic (As), etc.), for example, a composition formula Al _X Ga _Y In _Z N _Q M _1-Q A compound represented by (0 ≦ X, Y, Z ≦ 1, X + Y + Z = 1, 0 <Q ≦ 1, M is a Group V element other than nitrogen) is also suitable.
[0013]
In the boron phosphide-based compound semiconductor element of the present invention, the surface of the group III nitride semiconductor layer is a (0.0.0.1.) Crystal plane, and the boron phosphide layer is bonded to the crystal plane. It has been done. Further, in the present invention, the boron phosphide layer has {111} -phosphorus having {111} crystal planes stacked in parallel with the (0.0.0.1.) Crystal plane of the group III nitride semiconductor layer. It is a boron fluoride layer. By adopting such a configuration, a high-quality boron phosphide layer with few misfit dislocations and the like can be obtained.
This is because the {110} crystal lattice spacing (lattice spacing) of the boron phosphide monomer and the a-axis lattice constant of the (0.0.0.1.) Crystal plane of the group III nitride semiconductor Therefore, on the (0.0.0.1.) Crystal plane of the group III nitride semiconductor layer, a high-quality {111} -boron phosphide layer with few misfit dislocations caused by lattice mismatch is formed. This is because it can be grown.
For example, while the lattice spacing of monomeric boron phosphide crystal is 0.320 nm, the a-axis lattice constant of gallium nitride (GaN) is 0.318 nm, and the a-axis lattice constant of aluminum nitride (AlN) is (For the a-axis lattice constant, see Teramoto Satoshi, “Introduction to Semiconductor Devices”, first edition, Baifukan Co., Ltd., March 30, 1995, p. 28). Thus, the lattice mismatch between the a-axis lattice constant of the (0.0.0.1.) Crystal plane of the group III nitride semiconductor and the lattice spacing of the {110} crystal plane of boron phosphide is AlN is almost 2.8% even with AlN, and a high-quality boron phosphide layer can be grown on the (0.0.0.1.) Crystal plane of the group III nitride semiconductor.
[0014]
Based on FIG. 1, the present invention will be specifically described by taking up a case where the group III nitride semiconductor layer is made of a wurtzite crystal type gallium nitride single crystal. FIG. 1 is a plan view schematically showing the (0.0.0.1.) Crystal plane of a wurtzite crystal type gallium nitride single crystal and the state of arrangement of boron phosphide crystals formed thereon. is there.
The (0.0.0.1.) Crystal plane 1 of the gallium nitride single crystal is formed by densely arranging a large number of regular hexagonal unit cells (unitary plane crystal lattice) 1a in plan view. In the present invention, {111} crystals 2 (2a and 2b) of boron phosphide are stacked on the crystal plane 1 in parallel with the crystal plane 1, and a good lattice is obtained between gallium nitride and boron phosphide. Try to demonstrate matching.
The best lattice matching between gallium nitride and boron phosphide is that the <110> crystal orientation in the {111} crystal plane of boron phosphide is (0.0.0.1.) Of gallium nitride. [2. -1. -1.0. This is the case where the {111} crystal face of boron phosphide is arranged so as to be parallel to the crystal orientation. This is because the a-axis lattice constant in the (0.0.0.1.) Crystal plane 1 of gallium nitride (indicated by symbol a in FIG. 1) and {110} in the {111} crystal plane of boron phosphide. } This is because the lattice plane spacing is almost the same.
[0015]
In particular, [2. -1. -1.0] crystal orientation and [1. -1.0. ] Or [-1.1.0. When the {111} -crystals 2a and 2b of boron phosphide having a regular triangular shape in plan view are arranged so that the crystal orientations are parallel, an excellent quality {111} -boron phosphide layer can be obtained. it can. Here, [1. -1.0. ] Crystal orientation and [-1.1.0. The crystal orientations are directions different from each other by 180 ° in angle. In FIG. 1, [2. -1. -1.0] crystal orientation, and [1. -1.0. The boron phosphide crystal body 2a has a parallel relationship with the crystal orientation, and [2. -1. -1.0] crystal orientation, and [-1.1.0. It is the boron phosphide crystal body 2b that has a parallel relationship with the crystal orientation. Matching with the (0.0.0.1.) Crystal plane of gallium nitride by combining {111} -crystals 2a and 2b that have apexes 180 degrees different from each other and assembled together, a plane as a whole A {111} -boron phosphide crystal layer exhibiting a regular hexagonal shape can be formed.
[0016]
[Method of Manufacturing Boron Phosphide Compound Semiconductor Device]
The boron phosphide-based compound semiconductor device of the present invention described above includes, for example, a group III nitride semiconductor layer as a base, a boron-containing compound and a phosphorus-containing compound are supplied to a vapor phase growth region, and a specific condition is obtained by a vapor phase growth method. It can be produced by growing a boron phosphide layer underneath. Examples of the vapor phase growth method include a metal organic vapor phase epitaxy (MOVPE) method, a halogen VPE method, a hydride VPE method, and a molecular beam epitaxy (MBE) method.
[0017]
Here, the hexagonal group III nitride semiconductor crystal has a regular hexagonal unit cell shape that conforms to the shape of the regular hexagonal unit cell constituting the (0.0.0.1.) Crystal plane. In order to obtain a {111} boron phosphide crystal layer composed of a large number of {111} crystals arranged in a regular manner in a plan view, it is preferable to satisfy the following conditions (A) to (G).
[0018]
(A) When vapor-phase-growing the {111} -boron phosphide crystal layer, the surface of the underlying group III nitride semiconductor layer (eg, gallium nitride crystal layer) is (0.0.0.1.) It must be a single crystal plane composed of crystal planes.
[0019]
(B) The inclination angle of the (0.0.0.1.) Single crystal surface of the group III nitride semiconductor layer is within ± 5 ° with the (0.0.0.1.) Crystal plane as the horizontal plane. It is preferable that (0.0.0.1.) On the single crystal surface inclined more than 5 ° from the crystal plane, the distance between the arrangement of atoms constituting the crystal and the {110} lattice plane of the {111} -boron phosphide crystal Since the difference increases, it is difficult to stably form a {111} -boron phosphide crystal layer in which {111} -boron phosphide crystals having a regular triangular shape in plan view are regularly and regularly arranged as shown in FIG. It becomes.
[0020]
(C) In order to effectively function the boron phosphide crystal layer as an underlayer for vapor phase growth, it is preferable to maintain the surface of the group III nitride semiconductor layer in a composition that is almost stoichiometrically balanced. For example, when the group III nitride semiconductor layer is kept at a high temperature during the vapor phase growth of the boron phosphide crystal layer, the group V element constituting the group III nitride semiconductor layer is volatilized, and the group III nitride semiconductor layer In order to maintain a stoichiometrically balanced (0.0.0.1.) Crystal surface when the Group III element is richer than the Group V element on the surface of Group III nitride semiconductor layer is made of ammonia ₃ ) And hydrazine (N ₂ H ₂ It is preferable to take measures such as raising the temperature in an atmosphere containing an excessive amount of nitrogen-containing compounds such as).
[0021]
(D) It is preferable to vapor-phase grow the boron phosphide crystal layer at a temperature of 750 ° C. or higher and 1200 ° C. or lower. If the film forming temperature (underlying temperature) is less than 750 ° C., it is difficult to stably obtain a {111} single crystal layer of boron phosphide. ₁₃ P ₂ It is difficult to stably obtain a monomeric boron phosphide due to the generation of boron phosphide multimers such as. When obtaining an n-type {111} -boron phosphide crystal layer, the film forming temperature is preferably 750 ° C. to about 1000 ° C. When obtaining a p-type {111} -boron phosphide crystal layer, The film forming temperature is preferably about 1000 ° C. to 1200 ° C.
[0022]
(E) The V / III ratio during vapor phase growth of the boron phosphide crystal layer is preferably 600 or more, and particularly preferably 1000 to 2000.
[0023]
(F) Before the vapor phase growth of the boron phosphide crystal layer, the source gas (boron-containing compound and phosphorus-containing compound) is passed through the vapor phase growth region in advance, and the surface of the portion in contact with the raw material gas in the vapor phase growth region It is preferable to form a film containing phosphorus and boron. The thickness of the coating is not particularly limited, but about 100 nm is sufficient.
[0024]
(G) When vapor-growing a boron phosphide crystal layer, a group III nitride semiconductor layer in which a boron-containing compound and a phosphorus-containing compound, which are source gases, are placed in the vapor phase growth region almost simultaneously in time It is preferably adjusted so as to reach the surface. The arrival time of the source gas to the group III nitride semiconductor layer can be adjusted by the flow rate of the carrier gas. The “carrier gas” is a gas that plays a role of transporting the raw material gas to the vapor phase growth region. ₂ ) And nitrogen (N ₂ ) And argon (Ar), and a mixed gas containing them. The allowable difference in the arrival time of the source gas is, for example, about 5 seconds when the {111} -boron phosphide crystal layer is vapor-phase grown at a growth rate of 50 nm / min. If the arrival times are almost the same but have a slight difference, the highly volatile Group V element material (phosphorus-containing compound) precedes the Group III element material (boron-containing compound) in terms of time. If the flow rate of the carrier gas is adjusted so as to reach the surface of the group III nitride semiconductor layer, the {111} -boron phosphide crystal layer is more easily formed.
[0025]
Whether or not the {111} -boron phosphide crystal layer having orientation is formed on the (0.0.0.1.) Crystal plane of the group III nitride semiconductor layer is determined by X-ray diffraction or electron beam. It can be determined from the diffraction image of the diffraction.
When the {111} -boron phosphide crystal layer is grown on the (0.0.0.1) crystal plane of the group III nitride semiconductor layer, the layer thickness of the {111} -boron phosphide crystal layer is particularly large Is a thin film layer of less than about 500 nm, the Bragg diffraction derived from the (0.0.0.1.) Crystal plane of the group III nitride semiconductor crystal and the {111} crystal plane of boron phosphide in the X-ray diffraction image A peak appears clearly.
In the electron diffraction pattern, the {111} crystal plane of the boron phosphide crystal layer is on a straight line connecting diffraction spots derived from the (0.0.0.1.) Crystal plane of the group III nitride semiconductor layer. Diffraction spots derived from. In addition, when the direction of the incident electron beam is <110>, {111} -boron phosphide crystal in which the direction of one vertex is different by 180 ° with respect to the angle, that is, bilaterally symmetric about the <110> crystal axis. From the oriented {111} -boron phosphide crystal, a reciprocal lattice image of the {110} crystal plane in a 180 ° inverted relationship is obtained.
[0026]
In the boron phosphide-based compound semiconductor device of the present invention, the boron phosphide crystal layer is vapor-phase grown with the (0.0.0.1.) Crystal plane of the group III nitride semiconductor layer as a base, and is regularly and regularly arranged. Since the {111} -boron phosphide crystal layer is provided, the effect of suppressing the propagation of dislocations from the underlayer is exhibited at a high level and stably. As a result, it is possible to provide a boron phosphide-based compound semiconductor element in which the boron phosphide crystal layer has a dislocation density smaller than that of the group III nitride semiconductor layer.
In particular, the [0.0.0.1.] Crystal plane of the group III nitride semiconductor layer [2. -1. -1.0. The crystal orientation in which the crystal orientation is parallel to the <110> crystal orientation of the boron phosphide crystal layer matches well with the (0.0.0.1.) Crystal plane of the group III nitride semiconductor layer A {111} -boron phosphide crystal layer is obtained stably and is preferred.
[0027]
For example, the {111} -boron phosphide crystal layer provided on the (0.0.0.1.) Crystal plane of gallium nitride stops dislocation propagation from gallium nitride at the junction interface between the two layers. 1 × 10 ³ / Cm ² The crystal layer has the following low dislocation density. Such a low dislocation density boron phosphide crystal layer is characterized in that stacking faults and / or twinning are included in the <111> crystal orientation of boron phosphide. is there. It is thought that the dislocation density decreases as a result of stacking faults and twins absorbing dislocations.
[0028]
As described above, according to the present invention, the boron phosphide crystal layer can sufficiently and stably suppress the propagation of dislocations from the underlayer, so that the leakage current is small and good rectification characteristics can be expressed. A boron phosphide-based compound semiconductor device having excellent device characteristics can be provided.
In the boron phosphide-based compound semiconductor element of the present invention, the {111} -boron phosphide crystal layer having the above-described characteristics can be effectively used as a functional layer that can avoid a short circuit through dislocation of the element driving current. . For example, a low dislocation density {111} -boron phosphide crystal layer that forms a heterogeneous (hetero) junction with a group III nitride semiconductor layer is used to form an ohmic electrode that does not have a breakdown voltage failure due to a short circuit. It can be used as a contact layer. In addition, it can be used as a contact layer for forming a Schottky junction gate electrode in which short-circuit leakage of gate current is suppressed.
[0029]
【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 {111} -boron phosphide crystal layer is vapor-phase grown on the surface of a (0.0.0.1.)-Gallium nitride single crystal layer deposited on a sapphire substrate. Thus, a light emitting diode (LED) having a pn junction type double hetero (DH) junction structure was manufactured. A cross-sectional structure of the manufactured LED is schematically shown in FIG.
[0030]
First, on the surface of the sapphire substrate 101 having the (0.0.0.1.) Crystal plane as a surface, trimethylgallium ((CH ₃ ) ₃ Ga) / Ammonia (NH ₃ ) / Hydrogen (H ₂ ) A lower cladding layer 102 made of an n-type (0.0.0.1.)-Gallium nitride (GaN) single crystal layer was formed at 1050 ° C. by a reaction system normal pressure (substantially atmospheric pressure) MOCVD method. The carrier concentration of the n-type gallium nitride crystal layer forming the lower cladding layer 102 is about 2 × 10 ¹⁸ cm ^-3 The layer thickness was 3 μm.
[0031]
On the (0.0.0.1.) Crystal surface of the lower cladding layer 102, (CH ₃ ) ₃ Ga / trimethylindium ((CH ₃ ) ₃ In) / NH ₃ / H ₂ N-type (0.0.0.1.)-Gallium nitride indium (Ga) at 850 ° C. by a reaction system normal pressure (substantially atmospheric pressure) MOCVD method. _0.90 In _0.10 The light emitting layer 103 made of N) was vapor grown. The carrier concentration of the n-type gallium nitride / indium mixed crystal layer forming the light emitting layer 103 is about 8 × 10 ¹⁷ cm ^-3 The layer thickness was about 50 nm.
[0032]
Indium raw material ((CH ₃ ) ₃ After the supply of In) is stopped and the growth of the light emitting layer 103 is terminated, (CH ₃ ) ₃ Ga and NH ₃ And carrier gas H ₂ At the same time, it was continuously distributed to the vapor phase growth region. Thus, a protective layer 104 made of an undoped, high-resistance (0.0.0.1.)-Gallium nitride layer was formed on the light-emitting layer 103. The protective layer 104 is a layer for preventing a decrease in light emission intensity of the light emitting layer 103. The carrier concentration of the protective layer 104 is about 5 × 10. ¹⁷ cm ^-3 The layer thickness was about 12 nm.
After completing the vapor phase growth of the protective layer 104, the temperature drop was started. Until the temperature is lowered to 600 ° C., ammonia continues to flow through the vapor phase growth region to prevent the volatilization of nitrogen from the (0.0.0.1.) Crystal surface of the protective layer 104. The stoichiometric composition can be maintained.
After cooling to room temperature, a laminate in which the lower clad layer 102, the light emitting layer 103, and the protective layer 104 were sequentially laminated on the substrate 101 was retracted from the vapor phase growth region into a chamber in which contact with the source gas was avoided. . While storing the laminate, hydrogen gas was allowed to flow through the chamber.
[0033]
While the laminate is retracted as described above, triethylboron ((C ₂ H ₅ ) ₃ B) Hydrogen gas accompanied by vapor and phosphine (PH ₃ ) To form a film containing boron and phosphorus on the inner wall of a quartz growth furnace in the vapor phase growth region. After a film having a thickness of about 1 μm was deposited at 1100 ° C., the temperature of the vapor phase growth region was lowered to a temperature near room temperature while flowing hydrogen gas.
[0034]
Thereafter, the stacked body that has been saved is returned to the vapor phase growth region, and ammonia (NH ₃ ) And hydrogen (H ₂ The temperature was raised from room temperature to 1025 ° C. in a mixed atmosphere. After temperature rise, NH ₃ Of phosphine (PH) as a phosphorus raw material at the same time ₃ ) And boron triethylboron ((C ₂ H ₅ ) ₃ B) was simultaneously distributed to the vapor phase growth region. In order to cause the phosphorus raw material and the boron raw material to simultaneously reach the (0.0.0.1.) Crystal plane of the protective layer 104, PH ₃ The flow rate of the hydrogen carrier gas for transporting the gas is 9 L / min, and (C ₂ H ₅ ) ₃ The flow rate of the hydrogen carrier gas carrying the vapor of B) was 7 L / min. Thereby, on the (0.0.0.1.)-Gallium nitride (GaN) crystal surface of the protective layer 104, (C ₂ H ₅ ) ₃ B / PH ₃ / H ₂ An upper cladding layer 105 made of an undoped p-type boron phosphide layer was formed by bonding using a reaction-type atmospheric pressure MOCVD method. V / III ratio (= PH) when growing the upper cladding layer 105 (boron phosphide layer) ₃ / (C ₂ H ₅ ) ₃ B concentration ratio) was 1000. The carrier concentration of the upper cladding layer 105 (boron phosphide layer) is 2 × 10 ¹⁹ cm ^-3 The layer thickness was 500 nm.
As described above, a laminated body 200 in which the lower clad layer 102, the light emitting layer 103, the protective layer 104, and the upper clad layer 105 were sequentially laminated on the substrate 101 was obtained.
[0035]
When the cross-section TEM observation of the thin piece of the laminated body 200 was performed and the crystal structure of the boron phosphide layer forming the upper cladding layer 105 was observed, the (0.0.0.1.) Crystal surface of the protective layer 104 was found inside. On the other hand, twins (stacking faults) were observed to be present in the direction of 70 ° in angle, that is, along the <111> crystal orientation of boron phosphide.
[0036]
Further, FIG. 3 shows a copy of an electron diffraction pattern from the gallium nitride layer forming the protective layer 104 and the boron phosphide layer forming the upper cladding layer 105. In FIG. 3, the diffraction points from the boron phosphide crystal are indicated by ◯, and the diffraction points from gallium nitride are indicated by ●. The part where these marks overlap indicates that the diffraction points from both crystals appear at the same position.
As shown in the figure, the direction in which diffraction occurs on the (0.0.0.1.) Crystal plane of gallium nitride is parallel to the direction in which diffraction points on the {111} crystal plane of boron phosphide appear. It was confirmed that the {111} -crystal face of boron phosphide was stacked on the (0.0.0.1.) Crystal face of gallium nitride.
Further, the direction of the incident electron beam is changed to [2. -1. -1.0. ] When the crystal orientation is taken, a reciprocal lattice image of zincblende crystal-type boron phosphide appears from the <110> crystal direction of boron phosphide. From this, [0.0.0.1.] Of [2. -1. -1.0. The crystal orientation and the <110> crystal orientation of boron phosphide were shown to be parallel.
Further, since the reciprocal lattice images (rectangles c and d shown by broken lines in FIG. 3) viewed from the <110> crystal orientation of boron phosphide appear at positions rotated by 180 °, {111} -phosphorus It has been shown that the boron phosphide layer is composed of {111} -boron phosphide crystals whose orientations differ from each other by 180 °.
[0037]
The dislocation density of the upper cladding layer 105 made of a boron phosphide layer is 1 × 10 ³ cm ^-3 Was less than. This occurs due to a lattice mismatch with the sapphire substrate 101, and dislocations propagated from the inside of the lower cladding layer 102 made of the n-type gallium nitride layer through the light emitting layer 103 and the protective layer 104 are boron phosphide. This is because it is blocked at the junction interface between the upper clad layer 105 made of a layer and the protective layer 104.
[0038]
After the above evaluation, a p-type ohmic electrode 106 having a diameter of 130 μm in a plan view and made of gold / beryllium alloy (Au 99 mass% · Be 1 mass%) was disposed at the center of the surface of the upper clad layer 105. On the other hand, the upper clad layer 105, the protective layer 104, and the light emitting layer 103 are partially removed to expose the lower clad layer 102 made of an n-type gallium nitride layer, and the n-type ohmic electrode 107 is disposed on the exposed surface. . The n-type ohmic electrode 107 was composed of a two-layer electrode having a lower layer made of titanium (Ti) and an upper layer made of aluminum (Al).
[0039]
As described above, a square pn junction type DH structure LED having a side of about 300 μm in a plan view was manufactured. The light emission characteristics when an operating current of 20 mA was passed in the forward direction between the p-type and n-type ohmic electrodes 106 and 107 of this LED were as follows.
(1) Luminous color: Blue purple
(2) Emission center wavelength: about 430 nm
(3) Luminance (chip state): about 7 mcd
(4) Forward voltage: about 3.6V
The reverse voltage when a current of 10 μA was passed in the reverse direction between the p-type and n-type ohmic electrodes 106 and 107 was 10V.
[0040]
In this embodiment, the upper clad layer 105 is formed as a protective layer 104 (0.0.0.1.)-A low resistance p-type {111} -phosphide regularly and regularly arranged on the gallium nitride crystal surface. Since it is composed of a boron layer, the device operating current can be diffused over a wide area of the light emitting layer 103. In addition, almost no occurrence of local breakdown (local breakdown) was observed through {111} -dislocations having a low dislocation density. For this reason, light emission luminescent spots due to short-circuit distribution of element operating current via dislocations are not generated sparsely, and from a near-field light emission image, light emission with uniform intensity is obtained from substantially the entire surface of the light emitting layer 103. It was confirmed that As described above, in this example, it was possible to obtain a short wavelength visible light emitting diode excellent in device characteristics, having excellent withstand voltage characteristics and uniform emission intensity.
[0041]
【The invention's effect】
As described above in detail, according to the present invention, there is provided a boron phosphide-based compound semiconductor device excellent in device characteristics in which propagation of misfit dislocations from the group III nitride semiconductor layer is sufficiently and stably suppressed. can do.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the arrangement of {111} -boron phosphide crystals on the (0.0.0.1.) Crystal surface of a wurtzite crystal-type gallium nitride single crystal.
FIG. 2 is a schematic diagram showing a cross-sectional structure of a pn junction type LED manufactured in an example according to the present invention.
FIG. 3 is a copy of an electron diffraction pattern from a (0.0.0.1.)-Gallium nitride / {111} -boron phosphide junction structure of a laminate obtained in an example according to the present invention. is there.
[Explanation of symbols]
1 (0.0.0.1) crystal plane of gallium nitride
2 {111} -Boron Phosphide Crystal
101 Sapphire substrate
102 Lower cladding layer
103 Light emitting layer
104 Protective layer
105 Upper cladding layer
106 p-type ohmic electrode
107 n-type ohmic electrode

Claims (9)

In a boron phosphide-based compound semiconductor device having a heterogeneous junction structure composed of a group III nitride semiconductor layer and a boron phosphide layer,
The group III nitride semiconductor layer is a wurtzite crystal type, and the surface of the group III nitride semiconductor layer is a (0.0.0.1.) Crystal plane;
The boron phosphide layer has {111}-crystal planes stacked in parallel with the crystal plane on the (0.0.0.1.) Crystal plane of the group III nitride semiconductor layer. It is a boron phosphide layer , [2. -1. -1.0. A boron phosphide-based compound semiconductor device , wherein a crystal orientation and a <110> crystal orientation of a {111} crystal plane of the boron phosphide layer are parallel to each other .   The [2.0.0.] Crystal plane of the group III nitride semiconductor layer [2. -1. -1.0. 2. The boron phosphide-based compound semiconductor device according to claim 1, wherein there are two <110> crystal orientations of the boron phosphide layer parallel to the crystal orientation, and an angle formed by these two orientations is 180 °. .   The [2.0.0.] Crystal plane of the group III nitride semiconductor layer [2. -1. -1.0. The <110> crystal orientation of the boron phosphide layer parallel to the crystal orientation is [1. -1.0. ] And [-1.1.0. The boron phosphide-based compound semiconductor device according to claim 2, wherein   The group III nitride semiconductor layer is a (0.0.0.1.)-Gallium nitride layer, and the boron phosphide layer includes a stacking fault and / or a twin crystal in the <111> crystal orientation. The boron phosphide-based compound semiconductor device according to any one of claims 1 to 3, wherein the boron phosphide layer is a boron phosphide layer.   5. The boron phosphide-based compound semiconductor device according to claim 1, wherein the boron phosphide layer has a dislocation density smaller than that of the group III nitride semiconductor layer. In a method for manufacturing a boron phosphide-based compound semiconductor element having a heterogeneous junction structure comprising a group III nitride semiconductor layer and a boron phosphide layer,
A boron-containing compound and a phosphorus-containing compound are supplied to a vapor phase growth region using a wurtzite crystal group III nitride semiconductor layer having a (0.0.0.1.) Crystal plane as a base, and the III A {111} -boron phosphide layer having a {111} crystal plane parallel to the (0.0.0.1.) Crystal plane of the group nitride semiconductor layer is stacked; (0.0.0.1.) [2. -1. -1.0. A boron phosphide-based compound semiconductor device comprising a step of vapor-phase growth so that the <110> crystal orientation of the {111} crystal plane of the boron phosphide layer is parallel to the crystal orientation . Production method.   The method for manufacturing a boron phosphide-based compound semiconductor device according to claim 6, wherein the boron phosphide layer is vapor-phase grown at a temperature of 750 ° C to 1200 ° C.   The method for manufacturing a boron phosphide-based compound semiconductor device according to claim 6 or 7, wherein the boron phosphide layer is vapor-phase grown at a V / III ratio of 600 or more. In a light emitting diode including a laminate formed by sequentially laminating a lower clad layer, a light emitting layer, a protective layer protecting the light emitting layer, and an upper clad layer,
The protective layer is composed of a group III nitride semiconductor layer having a (0.0.0.1.) Crystal plane on the surface, and the upper cladding layer is (0.0.0.1. (1) A light emitting diode comprising a {111} -boron phosphide layer having a {111} crystal plane formed on the crystal plane so as to be stacked on the crystal plane.

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