JP4030513B2 - Ohmic electrode structure, compound semiconductor light emitting device and LED lamp provided with the same - Google Patents

Description

  The present invention relates to a p-type ohmic electrode structure provided in contact with the surface of a boron phosphide-based semiconductor layer exhibiting p-type conduction, and a compound semiconductor device using the p-type ohmic electrode structure. The present invention relates to a technique for configuring an element.

  2. Description of the Related Art Conventionally, there is a technology for forming a boron phosphide-based semiconductor element such as a light emitting diode (English abbreviation: LED) using boron phosphide (chemical formula: BP), which is a kind of III-V group compound semiconductor, and mixed crystals thereof. It is disclosed (for example, see Patent Document 1). For example, a boron phosphide (chemical formula: BP) layer of a p-type conductive monomer is used as a barrier layer constituting a light emitting portion of a pn junction type double hetero (DH) junction structure type (for example, Patent Document 2). A boron phosphide-based semiconductor light-emitting diode is configured, for example, by providing a p-type ohmic electrode on the surface of a p-type clad layer made of a boron phosphide layer. In the prior art, for example, for a p-type boron phosphide layer, an example in which a p-type ohmic electrode is formed from aluminum (Al) is known (for example, Non-Patent Document 1).

  Boron phosphide is supposed to obtain a low resistance n-type or p-type semiconductor layer without intentional addition of impurities (for example, see Non-Patent Document 1). Accordingly, an ohmic electrode can be formed on, for example, a clad layer or a contact layer made of a conductive boron phosphide layer. In a conventional compound semiconductor light emitting device having a p-type boron phosphide layer added with magnesium (element symbol: Mg) as a contact layer, it is composed of gold (element symbol: Au) and zinc (element symbol: Zn). An example is disclosed (for example, see Patent Document 2).

  However, an ohmic electrode that exhibits good ohmic contact with p-type boron phosphide has not been stably formed from the metal as described above. For this reason, the input resistance when the current for operating the light emitting element (element driving current) is allowed to flow is easily increased, resulting in a LED having a high forward voltage (Vf). . Further, it is inconvenient for obtaining a laser diode (LD) having a low threshold voltage (Vth).

See US Pat. No. 6,069,021 See JP-A-2-288388 K. Shono et al., J. Crystal Growth, 24/25, 1974 (Netherlands), p. 193.

  In the present invention, a p-type ohmic electrode provided in contact with the surface of a p-type boron phosphide-based semiconductor layer containing boron (B) and phosphorus (P) as constituent elements provides good ohmic contact. The structure of the electrode to be applied is presented. A p-type ohmic electrode refers to a positive (positive) electrode provided in a p-type semiconductor layer. Moreover, the compound semiconductor light-emitting device provided with the p-type ohmic electrode which consists of a structure concerning this invention is provided.

That is, the present invention is as follows.
(1) An ohmic electrode structure in which an ohmic electrode is provided in contact with the surface of a conductive boron phosphide-based semiconductor layer exhibiting p-type conduction and containing boron and phosphorus as constituent elements. An ohmic electrode structure characterized in that at least the bottom surface of an electrode in contact with the surface of a boron-based semiconductor layer is made of a lanthanide element or an alloy containing a lanthanide element.
(2) The ohmic structure as described in (1) above, wherein the bottom surface contacting the surface of the p-type boron phosphide-based semiconductor layer is made of an alloy of lanthanum and an element having a work function of 4.5 eV or less. Electrode structure.
(3) The ohmic electrode structure as described in (1) or (2) above, wherein the bottom surface contacting the surface of the p-type boron phosphide-based semiconductor layer is made of an alloy of lanthanum and aluminum.
(4) The ohmic electrode structure as described in (1) or (2) above, wherein the bottom surface in contact with the surface of the p-type boron phosphide-based semiconductor layer is made of an alloy of lanthanum and silicon.
(5) The p-type monomer phosphide in which the p-type boron phosphide-based semiconductor layer is undoped without intentionally adding impurities and has a forbidden band width of 2.8 eV to 5.4 eV at room temperature 6. A compound semiconductor device including an ohmic electrode structure according to any one of (1) to (4), wherein the compound semiconductor device is boron.
(6) A compound semiconductor light emitting element comprising the compound semiconductor device according to (5).
(7) a substrate made of an insulating or conductive crystal, a light emitting layer made of a compound semiconductor layer formed on the crystal substrate, boron and phosphorus exhibiting p-type conductivity provided on the light emitting layer, And a p-type ohmic electrode in contact with the p-type boron phosphide semiconductor layer in contact with the p-type boron phosphide semiconductor layer. A compound semiconductor light emitting device, wherein at least the bottom surface of the p-type ohmic electrode in contact with the surface of the boron phosphide-based semiconductor layer is composed of a lanthanide element or an alloy containing a lanthanide element.
(8) The compound semiconductor light-emitting element according to (7), wherein the bottom surface of the p-type ohmic electrode is made of an alloy of lanthanum and an element having a work function of 4.5 eV or less.
(9) The compound semiconductor light-emitting element according to (7) or (8) above, wherein the bottom surface of the p-type ohmic electrode is made of an alloy of lanthanum and aluminum.
(10) The compound semiconductor light-emitting element according to the above (7) or (8), wherein the bottom surface of the p-type ohmic electrode is made of an alloy of lanthanum and silicon.
(11) The compound semiconductor light-emitting element according to any one of (7) to (10), wherein the compound semiconductor layer is made of a III-V group compound semiconductor.
(12) The compound semiconductor layer is composed of gallium nitride indium (composition formula Ga _x In _1-x N: 0 ≦ X ≦ 1) or gallium nitride phosphide (composition formula GaN _1-Y P _Y : 0 ≦ Y ≦ 1). The compound semiconductor light-emitting element according to any one of (7) to (11) above, wherein
(13) The bottom portion of the p-type ohmic electrode made of a lanthanide element or an alloy containing a lanthanide element has, as a planar shape, a shape of a connection base electrode and a mesh portion formed adjacent thereto. The compound semiconductor light-emitting element according to any one of (7) to (12) above,
(14) The p-type monomer phosphide in which the p-type boron phosphide-based semiconductor layer is undoped without intentionally adding impurities and has a forbidden band width of 2.8 eV to 5.4 eV at room temperature The compound semiconductor light-emitting element according to any one of (7) to (13), wherein the compound semiconductor light-emitting element is boron.
(15) An LED lamp using the compound semiconductor element according to any one of (7) to (14) above.

  According to the present invention, since the p-type ohmic electrode provided in contact with the surface of the p-type boron phosphide-based semiconductor layer is composed of a lanthanoid element or an alloy film thereof, an electrode with low contact resistance can be formed. Therefore, the supplied element driving current is efficiently used for light emission, and therefore, it is effective to provide a compound semiconductor light emitting element with high light emission intensity. Furthermore, a high-intensity LED lamp can be produced by connecting a conducting wire to the compound semiconductor light-emitting device of the present invention and encapsulating it in a resin.

The present invention relates to an electrode structure that provides excellent ohmic contact to a p-type boron phosphide-based semiconductor layer.
In the present invention, a boron phosphide-based semiconductor is a compound semiconductor containing boron (B) and phosphorus (P) as constituent elements. For example, B _α Al _β Ga _γ In _1-α-β-γ P _{1- δ} As _δ (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 ≦ δ <1). Also, for example, B _α Al _β Ga _γ In _1-α-β-γ P _1-δ N _δ (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 ≦ δ <1). For example, monomeric boron phosphide (BP), boron phosphide / gallium / indium (compositional formula B _α Ga _γ In _1-α-γ P: 0 <α ≦ 1, 0 ≦ γ <1), It is a mixed crystal containing a plurality of group V elements such as boron nitride phosphide (composition formula BP _1-δ N _δ : 0 ≦ δ <1) and boron arsenide phosphide (composition formula BP _1-δ As _δ ). For example, in the case of BP _1-δ N _δ , BP _1-δ As _δ, etc., the preferred lower limit composition ratio (1-δ) of phosphorus (P) is 0.50 or more, more preferably 0.75. That's it.

A p-type boron phosphide-based semiconductor layer for providing a p-type ohmic electrode can be formed by a halogen method, a hydride method, or a MOCVD (metal organic chemical vapor deposition) method. It can also be formed by molecular beam epitaxy (see J. Solid State Chem., 133 (1997), pages 269-272). For example, a p-type monomeric boron phosphide layer can be formed by MOCVD using triethylboron (molecular formula: (C ₂ H ₅ ) ₃ B) and phosphine (molecular formula: PH ₃ ) as raw materials. As the formation temperature of the p-type BP layer, a temperature of 1000 ° C. to 1200 ° C. is suitable. The raw material supply ratio (= PH ₃ / (C ₂ H ₅ ) ₃ B) at the time of formation is suitably 10-50. A so-called undoped BP layer in which impurities are not intentionally added is effective in avoiding the modification of other layers due to the diffusion of impurities. If the formation rate is precisely controlled in addition to the formation temperature and the V / III ratio, a boron phosphide-based semiconductor layer having a large forbidden band can be formed (see Japanese Patent Application No. 2002-158282).

In particular, a p-type boron phosphide-based semiconductor layer having a forbidden band width at room temperature of 2.8 electron volts (unit: eV) to 5.4 eV can be preferably used. More preferably, the p-type boron phosphide-based semiconductor layer having a wide band gap of 2.8 eV to 3.2 eV is in a compound semiconductor light emitting device, such as a p-type cladding layer. It can be used as a barrier layer having a barrier action. Further, p-type boron-phosphide-based semiconductor layer having a wider bandgap, gallium indium nitride (compositional formula _{Ga X In 1-X N:} 0 ≦ X ≦ 1) or gallium nitride phosphide (compositional formula GaN _1-Y P _It is suitable for constituting a window layer for transmitting visible light such as blue light or green light from the light emitting layer composed of _Y : 0 ≦ Y ≦ 1) to the outside of the light emitting element. When the forbidden band width exceeds 5.4 eV, the barrier difference from the light emitting layer becomes large, which is disadvantageous for obtaining a compound semiconductor light emitting device having a low forward voltage or low threshold voltage. For example, the p-type cladding layer can be suitably formed from a low-resistance boron phosphide layer having a carrier concentration at room temperature of 1 × 10 ¹⁹ cm ⁻³ or more and a resistivity of 5 × 10 ⁻² Ω · cm or less. . The thickness of the p-type boron phosphide constituting the p-type cladding layer is suitably 500 nanometers (unit: nm) or more and 5000 nm or less. When the p-type ohmic electrode is provided in contact with the p-type cladding layer and the p-type cladding layer is unnecessarily thin, the device driving current supplied via the ohmic electrode is transmitted to the entire light emitting layer. This is inconvenient because it cannot diffuse evenly and flatly.
A typical example of a compound semiconductor device using such a p-type boron phosphide-based semiconductor layer is, but not limited to, a boron phosphide-based compound semiconductor LED. In particular, as described above, a gallium indium nitride (compositional formula _{Ga X In 1-X N:} 0 ≦ X ≦ 1): composed of or gallium phosphide nitride (0 ≦ Y ≦ 1 formula GaN _1-Y P Y) It is suitably combined with the light emitting layer. In addition, the present invention can also be applied to a compound semiconductor light emitting element such as a laser diode (LD).

In the present invention, the bottom portion of the p-type ohmic electrode provided in contact with the surface of the p-type boron phosphide-based semiconductor layer forming the cladding layer or the electrode-forming contact layer is a lanthanide element film or an element thereof. It is comprised from the alloy film containing.
Lanthanide elements are elements from lanthanum (La) with atomic number 57 to lutesium (element symbol: Lu) with atomic number 71 (JAE Duffy, "Inorganic Chemistry", Yodogawa Shoten, Showa) Issued April 15, 1946, 5th edition, see page 262). Cerium (Ce; atomic number 58), praseodymium (Pr; atomic number 59), neodymium (Nd; atomic number 60), holmium (Ho; atomic number 67) and the like are lanthanoids (the above “inorganic chemistry”). "See page 263). In particular, in the present invention, it is preferable that the bottom surface portion of the p-type ohmic electrode is composed of lanthanum (La) and its alloy. This is because, among lanthanoids, lanthanum and its alloys provide good ohmic contact with the p-type boron phosphide-based semiconductor layer. In addition, the adhesion to the boron phosphide-based semiconductor layer is excellent in wealth among lanthanoids, and therefore, a firmly attached bottom surface portion can be formed.

An alloy of lanthanum and a material having a work function of 4.5 eV or less is convenient for forming a bottom surface portion of a p-type ohmic electrode in contact with the surface of the p-type boron phosphide-based semiconductor layer. is there. When the work function exceeds 4.5 eV, the barrier with the p-type boron phosphide-based semiconductor layer increases rapidly, which is disadvantageous for forming a p-type ohmic electrode. In addition to a small work function, an alloy with a substance having a high melting point is suitable for forming a p-type ohmic electrode having excellent heat resistance. Therefore, the melting point is lower than that of an alloy with gallium (work function = 4.0 eV, melting point = 29.8 ° C.) or indium (work function = 3.8 eV, melting point = 156 ° C.) having a low work function but low melting point. A high alloy is suitable. For example, from the lanthanum and aluminum (work function = 4.3 eV, melting point = 660 ° C.) or the alloy of lanthanum and silicon (work function = 4.0 eV, melting point = 1414 ° C.), the bottom surface portion exhibits good ohmic contact. Can be constructed conveniently. The content of aluminum (Al) or silicon (Si) in mass percentage (mass%) is suitably 1% or more and less than 50%. The lanthanum alloy film can be formed by means such as vacuum vapor deposition, electron beam vapor deposition, and high-frequency sputtering. If the alloy film is patterned using a well-known photolithography technique, a bottom surface having a desired shape such as a circular shape or a square shape can be formed. In addition, for example, lanthanum telluride (compositional formula: La ₂ Te ₃ ) which is an alloy of lanthanum and tellurium (element symbol: Te, work function = 4.3 eV, melting point = 450 ° C.), nickel (element symbol) : Ni, work function = 4.5 eV, melting point = 1453 ° C.) and lanthanum nickel (compositional formula LaNi ₅ ) alloy.

The characteristics of the p-type ohmic electrode including the bottom surface portion made of lanthanum or an alloy thereof according to the present invention can be investigated from, for example, general current-voltage (IV) characteristics. As an example, the IV characteristics of a p-type ohmic electrode composed of a lanthanum-aluminum alloy (composition formula: LaAl ₂ ) are illustrated in FIG. 1 in comparison with the characteristics of a conventional electrode. The IV characteristics are those between adjacent p-type ohmic electrodes at an interval of 350 μm. Moreover, it is the characteristic measured using the p-type boron phosphide layer which has the same resistance, Therefore The low resistance reflects the low contact resistance. As illustrated in FIG. 1, in the LaAl ₂ electrode according to the present invention, compared with a conventional aluminum (Al) simple substance or a gold (Au) / zinc (Zn) or gold (Au) / beryllium (Be) alloy electrode, Many currents can flow at the same applied voltage, resulting in a p-ohmic electrode with lower contact resistance.

The p-type ohmic electrode, particularly the bottom surface thereof, is preferably composed of a continuous film having no pores in order to make good contact with the p-type boron phosphide-based semiconductor layer. For this reason, it is suitable that the bottom portion is composed of a film containing lanthanum having a thickness of 10 nm or more. More preferred is 100 nm or more and 300 nm or less .
An ohmic electrode having a multilayer structure can be formed by further layering another metal film on the surface of the bottom surface portion. For example, a titanium (Ti) film and a gold (Au) film are sequentially stacked on a bottom surface of a circular plane made of a lanthanum (95% by mass) / aluminum (5% by mass) alloy having a thickness of 120 nm. Thus, a p-type ohmic electrode having a three-layer structure can be preferably configured. In constructing a p-type ohmic electrode having a multilayer structure, the uppermost layer is preferably composed of gold (Au) or aluminum (Al) in order to facilitate bonding. In the p-type ohmic electrode having a three-layer structure, the intermediate layer provided between the bottom surface portion and the uppermost layer is made of, for example, a transition metal such as titanium or molybdenum (Mo) or platinum (Pt). obtain.

If a p-type ohmic electrode having a structure according to the present invention is used, a compound semiconductor light emitting device having excellent electrical characteristics can be provided. For example, an LED having a low forward voltage (Vf) can be provided. A visible light LED having a low Vf includes, for example, a laminated structure including a sapphire substrate / n-type gallium nitride (GaN) cladding layer / n-type gallium nitride / indium (GaInN) light emitting layer / p-type boron phosphide (BP) cladding layer. The p-type ohmic electrode made of a lanthanum / aluminum alloy film can be provided on the surface of the p-type BP cladding layer. In an LED having a chip size of, for example, 300 μm to 350 μm, the bottom surface of the p-type ohmic electrode is preferably, for example, 90 μm to 150 μm in diameter. A compound semiconductor having higher emission intensity if it is composed of a Ga _x In _1-x N (0 <X <1) layer having a multiphase structure including a plurality of phases having different indium compositions (= 1−X) This is effective for forming an element (see Japanese Patent No. 3090057).

  For example, when an LED having a large planar area with a side length of 500 μm or more is constructed, means for arranging the LED over a wide range on the surface of the p-type boron phosphide-based semiconductor layer is effective. This is because the element driving current can be diffused over a wide range in a plane, which is advantageous for obtaining an LED having a high emission intensity or a large emission area. It is desirable that the ohmic electrode be arranged with a shape that allows uniform diffusion. For example, a p-type ohmic electrode made of a lanthanum-aluminum alloy in a lattice shape or a network shape is provided in contact with the surface of a p-type boron gallium phosphide mixed crystal layer on the light emitting layer. Further, a bottom portion made of lanthanum / silicon alloy provided in contact with the surface of the p-type boron phosphide-based semiconductor layer is electrically connected to the bottom portion while being branched or radially around the periphery of the chip. Extending to form a p-type ohmic electrode. In addition, a p-type ohmic electrode is composed of a plurality of concentric lanthanum / aluminum alloy films that are electrically connected to a pedestal electrode provided in the center of the p-type boron phosphide-based semiconductor layer. If the pedestal electrode is connected to the ohmic electrode of these shapes and the bottom surface is made of a material having a high ohmic contact resistance with respect to the p-type boron phosphide-based semiconductor layer, the element drive current is directly below the pedestal electrode. On the contrary, the device driving current can be diffused over a wide range to the light emitting region opened to the outside which is convenient for taking out the light emission to the outside.

In order to form a p-type ohmic electrode having a desired planar shape, for example, a lanthanum / aluminum alloy film, for example, is formed on the entire surface of the p-type boron phosphide-based semiconductor layer by, for example, a normal vacuum deposition method or an electron beam deposition method. Deposit by law or other means. Next, a desired shape is patterned using a known photolithography technique. It is preferable to pattern the p-type boron phosphide-based semiconductor layer so as to form an equipotential distribution. Next, an unnecessary alloy film is removed by means of a wet etching method or a plasma dry etching method using a halogen gas such as chlorine gas (molecular formula: Cl ₂ ). For wet etching of lanthanoid alloys, acid mixtures containing glacial acetic acid such as glacial acetic acid-hydrogen peroxide mixture can be used (Günter Pezzo, translated by Gentaro Matsumura, “Metal Etching Technology”, Agne Corporation) , September 10, 1977, first edition, first print), page 91).

  An electrode having a bottom surface in contact with the surface of the p-type boron phosphide-based semiconductor layer made of a lanthanide element or an alloy containing the element results in a p-type ohmic electrode exhibiting good ohmic characteristics for the p-type boron phosphide-based semiconductor layer. Has an effect.

  A p-type ohmic electrode having a bottom surface in contact with the surface of the p-type boron phosphide-based semiconductor layer made of a lanthanide element or an alloy containing the element has an action of diffusing an element driving current over a wide range of a light emitting region.

(First embodiment)
The present invention will be specifically described by taking as an example a case where a compound semiconductor LED is constructed by providing a p-type ohmic electrode made of lanthanum-aluminum alloy (LaAl ₂ ) on the surface of a p-type boron phosphide semiconductor layer.

FIG. 2 schematically shows a cross-sectional structure of a laminated structure used for manufacturing the LED 100 having a double hetero (DH) junction structure. The laminated structure includes a phosphorus (P) -doped n-type (111) -silicon (Si) single crystal substrate 101, an undoped lower clad layer 102 made of n-type boron phosphide (BP), n-type gallium nitride, A light emitting layer 103 having a multilayer quantum well structure in which an indium (Ga _0.90 In _0.10 N) well layer 103a and a gallium nitride (GaN) barrier layer 103b are stacked in five periods, and an upper cladding layer made of undoped p-type boron phosphide 104 were sequentially deposited.

The undoped n-type and p-type boron phosphide layers 102 and 104 use triethyl boron (molecular formula: (C ₂ H ₅ ) ₃ B) as a boron (B) source and phosphine (molecular formula: PH ₃ ) as a phosphorus source. It was formed using an atmospheric pressure (substantially atmospheric pressure) organometallic vapor phase epitaxy (MOVPE) means. The n-type boron phosphide layer 102 was formed at 925 ° C., and the p-type boron phosphide layer 104 was formed at 1025 ° C. The light emitting layer 103 was formed at 800 ° C. by trimethylgallium (molecular formula: (CH ₃ ) ₃ Ga) / NH ₃ / H ₂ reaction system atmospheric pressure MOCVD means. The gallium nitride / indium layer constituting the well layer 103a is composed of a multiphase structure composed of a plurality of phases having different indium compositions, and the average indium composition is 0.10 (= 10 %)Met. The layer thicknesses of the well layer 103a and the barrier layer 103b were 5 nm and 10 nm, respectively.

The undoped p-type boron phosphide layer 104 forming the upper cladding layer 104 had a carrier (hole) concentration of 2 × 10 ¹⁹ cm ⁻³ and a layer thickness of 720 nm. The resistivity of the layer 104 at room temperature was 5 × 10 ⁻² Ω · cm. Further, since the p-type boron phosphide layer 104 has a forbidden band width at room temperature of 3.2 eV, the p-type boron phosphide layer 104 was used as a p-type cladding layer also serving as a window layer for transmitting light emitted from the light-emitting layer 103 to the outside.

A lanthanum-aluminum (LaAl ₂ ) alloy film 105, a titanium (Ti) film 106, an entire surface of the p-type boron phosphide layer 104 constituting the p-type upper clad layer, according to a normal vacuum vapor deposition method and an electron beam vapor deposition method, And a gold (Au) film 107 was deposited. Next, in order to leave the above three-layer multilayer electrode having the bottom surface portion of the LaAl ₂ alloy film 105 only in the region where the connection base electrode 108 is provided, patterning is selectively performed using a known photolithography technique. Was given. Next, the LaAl ₂ alloy film or the like in a region other than the base electrode 108 is removed by etching using an acid mixed solution such as glacial acetic acid / sulfuric acid, and the surface of the p-type boron phosphide layer 104 is removed. Exposed. After peeling off the photoresist material, selective patterning was performed again to provide lattice-like grooves for cutting into chips. Thereafter, the p-type boron phosphide layer 104 was selectively removed by etching, limited to the region subjected to the above patterning, by a plasma dry etching method using a halogen-based mixed gas containing chlorine.
On the other hand, an n-type ohmic electrode (negative electrode) 109 was formed on the entire back surface of the silicon single crystal substrate 101 by depositing a gold (Au) film by a general vacuum deposition method. A square that is cleaved along the above-described band-shaped groove hole with a line width of 50 μm provided parallel to the <110> crystal orientation orthogonal to the (111) -crystal surface of the Si single crystal substrate 101 and having a side of 350 μm LED chip.

In the present invention, since the bottom surface portion is composed of the lanthanum aluminum (LaAl ₂ ) alloy film 105 having excellent adhesion to the p-type boron phosphide layer forming the upper cladding layer 104, the p-type boron phosphide is used even during connection. A p-type ohmic electrode 108 that also serves as a pedestal electrode that does not peel from the layer 104 could be formed.
Between the p-type and n-type ohmic electrodes 108 and 109, an element drive current of 20 mA was passed in the forward direction, and the light emission characteristics of the LED chip 100 were confirmed. The LED 100 emitted blue band light having a central wavelength of 440 nm. The half-value width of the emission spectrum was 210 millielectron volts (unit: meV). The luminance in a chip state before the resin mold measured using a general integrating sphere was 11 millicandelas (mcd). Further, since the bottom surface portion of the p-type ohmic electrode 105 is made of a LaAl ₂ alloy film having a small contact resistance with respect to the p-type boron phosphide layer, the forward voltage (Vf) when the forward current is 20 mA is 3 The value was as low as 1V. On the other hand, the reverse voltage when the reverse current was 10 μA was a high value of 9.5V. Further, the upper cladding layer is composed of an undoped p-type boron phosphide layer having a high carrier concentration and a low resistance, and includes a lanthanum aluminum alloy film having a low contact resistance in contact with the surface of the p-type boron phosphide. Since the p-type ohmic electrode was provided, the device drive current was emitted from substantially the entire light emitting region other than the projection region of the base electrode.

(Second embodiment)
The present invention will be specifically described by taking as an example a case where a compound semiconductor LED is formed by providing a p-type ohmic electrode containing a lanthanum / silicon alloy on a p-type boron phosphide / gallium mixed crystal layer. Since the basic structure of the compound semiconductor light emitting device is the same as that of the first embodiment, the same reference numerals are used for the same parts, and the cross-sectional structure is shown in FIG. 3 and the planar structure is shown in FIG.

An undoped p-type gallium phosphide / boron gallium mixed crystal (B _0.98 Ga _0.02 P) layer 204 was deposited on the light emitting layer 103 described in the first embodiment. The B _0.98 Ga _0.02 P layer 204 was formed at 850 ° C. by a (C ₂ H ₅ ) ₃ B / (CH ₃ ) ₃ Ga / PH ₃ -based reduced pressure MOCVD method. The layer thickness was 340 nm. The carrier concentration of the B _0.98 Ga _0.02 P layer 204 at room temperature was 8 × 10 ¹⁸ cm ⁻³ and the resistivity was 8 × 10 ⁻² Ω · cm.

Next, a lanthanum-silicon (La.Si) alloy film 205 was formed on the entire surface of the p-type B _0.98 Ga _0.02 P layer 204 by a normal vacuum deposition method. The thickness of the La · Si alloy film 205 was 540 nm. Next, patterning was performed using a known photolithography technique and plasma etching technique. Thereafter, an unnecessary alloy film is removed by a plasma dry etching method. As shown in FIG. 3, a circular 205 having a diameter of 150 .mu.m is formed at the center of the LED chip 200, and a p-type B _0.98 Ga _0.02 P around it. The La · Si alloy film was left on the network 210 in contact with the surface of the layer. An intermediate layer 206 and a gold film 207 were formed on the portion left to be circular, and the pedestal electrode 208 was completed.
On the other hand, a gold (Au) 99 mass% / antimony (Sb) 1 mass% alloy film 209 was deposited on the entire back surface of the silicon single crystal substrate 101 by a general vacuum deposition method.
After that, with the La / Si alloy film and the gold vapor deposition film subjected to the above patterning process applied, heat treatment (sinter) was performed at 450 ° C. for 10 minutes in a hydrogen stream to improve ohmic contact. . Thus, a p-type ohmic electrode 205 made of La · Si was formed on the surface of the p-type B _0.98 Ga _0.02 P layer 204, and an Au ohmic electrode 209 was formed on the back surface of the silicon single crystal substrate 101. The film thickness of the Au film forming the n-type ohmic electrode 209 was 2 μm.

Next, it separated and cut | disconnected to the individual LED chip along the cutting line formed in connection with etching process of said La * Si alloy film. The groove for cutting use is made of [1. -1.0] and [-1. -1.0] provided parallel to the crystal orientation. As a result, a rectangular LED chip 200 having one side of 500 μm and the other side of 600 μm was obtained. The emission center wavelength when a forward current of 20 mA was passed between the p-type and n-type ohmic electrodes 205 and 209 of the large LED chip 200 was 440 nm. Further, according to the near-field light emission image, it was confirmed that light emission with uniform intensity was caused from the light emission region other than the base electrode at the center of the chip 200. This is because the p-type ohmic electrode is arranged in such a shape that the device operating current can be uniformly diffused over a wide range in the p-type B _0.98 Ga _0.02 P layer. When the forward current was 20 mA, the forward voltage was 3.4 V, and when the reverse current was 10 μA, the reverse voltage was 8.3 V.

It is a figure which shows the electric current and voltage characteristic about this invention and the conventional material. It is a schematic diagram which shows the cross-section of LED as described in 1st Example. It is a schematic diagram which shows the cross-section of LED as described in 2nd Example. It is a schematic diagram which shows the planar structure of LED as described in 2nd Example.

Explanation of symbols

100, 200 ... LED
DESCRIPTION OF SYMBOLS 101 ... Silicon single-crystal substrate 102 ... n-type clad layer 103 ... n-type light emitting layer 104, 204 ... p-type clad layer 105, 205 ... p-type ohmic electrode 106, 206 ... intermediate layer 107, 207 ... pedestal metal 108 for connection 208: Pedestal electrode 109, 209: n-type ohmic electrode 210: network portion of p-type ohmic electrode

Claims (15)

  An ohmic electrode structure in which an ohmic electrode is provided in contact with the surface of a conductive boron phosphide-based semiconductor layer exhibiting p-type conductivity and containing boron and phosphorus as constituent elements, the p-type boron phosphide-based semiconductor An ohmic electrode structure characterized in that at least the bottom surface of the electrode in contact with the surface of the layer is composed of a lanthanide element or an alloy containing a lanthanide element.   2. The ohmic electrode structure according to claim 1, wherein the bottom surface in contact with the surface of the p-type boron phosphide-based semiconductor layer is made of an alloy of lanthanum and an element having a work function of 4.5 eV or less.   The ohmic electrode structure according to claim 1 or 2, wherein a bottom surface in contact with the surface of the p-type boron phosphide-based semiconductor layer is made of an alloy of lanthanum and aluminum.   The ohmic electrode structure according to claim 1 or 2, wherein a bottom surface in contact with the surface of the p-type boron phosphide-based semiconductor layer is made of an alloy of lanthanum and silicon.   The p-type boron phosphide-based semiconductor layer is a p-type monomer boron phosphide that is undoped without intentionally adding impurities and has a forbidden band width of 2.8 eV to 5.4 eV at room temperature. The compound semiconductor device containing the ohmic electrode structure of any one of Claims 1-4 characterized by the above-mentioned.   A compound semiconductor light emitting device comprising the compound semiconductor device according to claim 5.   Constituent elements comprising a substrate made of an insulating or conductive crystal, a light emitting layer made of a compound semiconductor layer formed on the crystal substrate, and boron and phosphorus having p-type conductivity provided on the light emitting layer A compound semiconductor light emitting device comprising: a conductive boron phosphide-based semiconductor layer contained in the substrate; and an ohmic contact p-type ohmic electrode in contact with the p-type boron phosphide-based semiconductor layer. A compound semiconductor light-emitting element, wherein at least the bottom surface of the p-type ohmic electrode in contact with the surface of the boron bromide-based semiconductor layer is composed of a lanthanide element or an alloy containing a lanthanide element.   8. The compound semiconductor light emitting device according to claim 7, wherein the bottom surface of the p-type ohmic electrode is made of an alloy of lanthanum and an element having a work function of 4.5 eV or less.   9. The compound semiconductor light-emitting element according to claim 7, wherein a bottom surface of the p-type ohmic electrode is made of an alloy of lanthanum and aluminum.   9. The compound semiconductor light-emitting element according to claim 7, wherein the bottom surface of the p-type ohmic electrode is made of an alloy of lanthanum and silicon.   11. The compound semiconductor light-emitting element according to claim 7, wherein the compound semiconductor layer is made of a group III-V compound semiconductor. The compound semiconductor layer is made of gallium nitride indium (composition formula Ga _x In _1-x N: 0 ≦ X ≦ 1) or gallium nitride phosphide (composition formula GaN _1-Y P _Y : 0 ≦ Y ≦ 1). The compound semiconductor light-emitting element according to claim 7, wherein   The bottom portion of the p-type ohmic electrode composed of a lanthanide element or an alloy containing a lanthanide element has, as a planar shape, the shape of a connection base electrode and a mesh portion formed adjacent thereto. The compound semiconductor light-emitting element according to claim 7.   The p-type boron phosphide-based semiconductor layer is a p-type monomer boron phosphide layer that is undoped without intentionally adding impurities and has a forbidden band width of 2.8 eV to 5.4 eV at room temperature. The compound semiconductor light-emitting element according to claim 7, wherein the compound semiconductor light-emitting element is provided. The LED lamp using the compound semiconductor element of any one of Claims 7-14.

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