JP2006013475A - Positive electrode structure and gallium nitride based compound semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode structure which is excellent in current diffusivity having better translucency and low contact resistance that does not require heat treatment nor heat treatment for alloying in an oxygen atmosphere, nor the like, and also to provide a semiconductor light emitting device which is higher in luminescent efficiency using the positive electrode. <P>SOLUTION: The positive electrode structure is related to the transparent positive electrode of the compound semiconductor light emitting device, wherein the structure comprises: a contact metal layer consisting of a thin film of at least one kind of metal chosen from a platinum group, a current diffusion layer consisting of at least one kind of metal chosen from a group consisting of gold, silver or copper, or an alloy including at least one kind of these; and a bonding pad. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gallium nitride-based compound semiconductor light-emitting device having a light-transmitting positive electrode, and more particularly to a positive-electrode structure and a light-emitting device with little decrease in output when the light-emitting layer has an element structure containing In.

  In recent years, GaN-based compound semiconductor materials have attracted attention as semiconductor materials for short wavelength light emitting devices. GaN-based compound semiconductors include sapphire single crystals, various oxide substrates, and III-V group compounds as substrates, and then metalorganic vapor phase chemical reaction method (MOCVD method) and molecular beam epitaxy method (MBE method). And so on.

  A characteristic of the GaN-based compound semiconductor material is that current diffusion in the lateral direction is small. The cause is thought to be the presence of dislocations penetrating from the substrate present in the epitaxial crystal to the surface, but the details are not known. Furthermore, the resistivity of the p-type GaN-based compound semiconductor is higher than that of the n-type GaN-based compound semiconductor, and there is almost no spread of lateral current in the p-layer just by stacking metal on the surface. In the case of an LED structure having a pn junction, light is emitted only directly below the positive electrode.

  Therefore, a structure has been adopted in which a light-transmitting electrode is formed as a positive electrode and light emission is extracted to the outside through the electrode. In the case of this structure, the electrode has a function of diffusing current. For example, Ni and Au are each deposited on the p layer by several tens of nanometers and alloyed in an oxygen atmosphere to promote the reduction of the resistance of the p layer and to form a positive electrode having translucency and ohmic properties. (For example, refer to Patent Document 1).

In addition, it has been proposed to form a Pt layer on the p layer as a positive electrode and heat-treat in an oxygen-containing atmosphere to simultaneously reduce the resistance of the p layer and perform alloying treatment (see, for example, Patent Document 2). .
However, since this method is also heat-treated in an oxygen atmosphere, it has the same problem as described above. Furthermore, in order to make a good transparent electrode with Pt alone, it must be made quite thin (for example, 5 nm or less), but as a result, the electrical resistance of the Pt layer is increased and the resistance of the Pt layer is lowered by heat treatment. Even if this is the case, the spread of current is poor, resulting in non-uniform light emission, leading to an increase in forward voltage (VF) and a decrease in light emission intensity.

Moreover, it has been found that the heat treatment has an influence on the semiconductor multilayer structure. In particular, when the light emitting layer has a structure containing In, the gallium nitride-based compound semiconductor crystal containing In deteriorates due to heat, which causes adverse effects such as a decrease in light emission output and a decrease in reverse voltage. Even when the initial characteristics are good, a material that has undergone a thermal history is likely to be deteriorated by aging. For this reason, in the case of an element having a light-emitting layer containing In, it is desirable that heat treatment be avoided as much as possible in the manufacturing process.
Japanese Patent No. 2803742 JP 11-186605 A

An object of the present invention is to solve the above-described problems, and in an element structure having a light-emitting layer containing In, it does not require heat treatment or alloying heat treatment in an oxygen atmosphere, and has good light-transmitting properties. It is to provide a positive electrode structure having a low contact resistance and excellent current diffusivity, and further to provide a semiconductor light emitting device having a high light emission efficiency using the positive electrode.
In the present invention, translucency means translucency with respect to light in a wavelength region of 300 to 600 nm, and does not mean colorless and transparent.

The present invention provides the following inventions.
(1) A transparent positive electrode of a gallium nitride-based compound semiconductor light-emitting element containing In, a contact metal layer made of a thin film of at least one metal selected from the platinum group, and a metal other than the metal constituting the contact metal layer Alternatively, a positive electrode structure comprising two types of current diffusion layers made of an alloy thin film and a bonding pad.

(2) The positive electrode structure according to (1), wherein the contact metal layer has a thickness of 0.1 to 7.5 nm.
(3) The positive electrode structure according to (1), wherein the contact metal layer has a thickness of 0.1 to 5 nm.
(4) The positive electrode structure according to (1), wherein the contact metal layer has a thickness of 0.5 to 2.5 nm.
(5) Any one of (1) to (4), wherein the platinum group metal constituting the contact metal layer includes at least one kind of metal selected from platinum, iridium, rhodium, and ruthenium. The positive electrode structure described in 1.
(6) The positive electrode structure according to any one of (1) to (5), wherein the contact metal layer includes platinum.

(7) The current spreading layer is a thin film of at least one metal selected from gold, silver and copper, or a thin film of an alloy containing at least one metal. (1) to (6) The positive electrode structure according to any one of the above.
(8) The positive electrode structure according to any one of (1) to (7), wherein the current diffusion layer is gold.
(9) The positive electrode structure according to any one of (1) to (8), wherein the current diffusion layer has a thickness of 1 to 20 nm.
(10) The positive electrode structure according to any one of (1) to (8), wherein the current diffusion layer has a thickness of 10 nm or less.
(11) The positive electrode structure according to any one of (1) to (8), wherein the current diffusion layer has a thickness of 3 to 6 nm.

(12) A light emitting layer having a quantum well structure made of a gallium nitride compound semiconductor containing In and having the positive electrode structure according to any one of (1) to (11). Gallium nitride compound semiconductor light emitting device.
(13) The gallium nitride compound semiconductor light-emitting element according to (12), wherein the light-emitting layer has a multiple quantum well structure including a plurality of well layers and a plurality of barrier layers.

  The present invention provides a light-transmitting electrode made of only a metal as an electrode for a light-emitting element having a light-emitting layer containing In, and does not perform heat treatment in the manufacturing process, thereby reducing the emission intensity and the reverse breakdown voltage. A light-emitting element with little aging deterioration can be manufactured without incurring.

Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following embodiments, and for example, the constituent elements of these embodiments may be appropriately combined.
FIG. 1 is a schematic view showing a cross section of a light-emitting element having a translucent positive electrode according to the present invention. In a compound semiconductor light emitting device 100 of the present invention, a GaN-based compound semiconductor layer 2 is formed on a substrate 1 with a buffer layer 6 interposed therebetween, and a light-transmitting positive electrode 10 of the present invention is formed thereon.
The GaN-based compound semiconductor layer 2 has a heterojunction structure including, for example, an n-type semiconductor layer 3, a light emitting layer 4, and a p-type semiconductor layer 5. The light emitting layer 4 contains In. The light emitting layer 4 may have a multiple quantum well structure including a well layer containing In and a barrier layer not containing In.
A negative electrode 20 is formed on a part of the n-type semiconductor layer 3, and a translucent positive electrode 10 is formed on a part of the p-type semiconductor layer 5.
The translucent positive electrode 10 is composed of three layers: a contact metal layer 11, a current diffusion layer 12, and a bonding pad layer 13.

  As the performance required for the contact metal layer 11, it is essential that the contact resistance with the p layer is small. Further, a face-up mount type light emitting element that takes out light from the light emitting layer from the electrode surface side is required to have excellent light transmittance.

  The material of the contact metal layer 11 is platinum (Pt), ruthenium (Ru), osmium (Os), rhodium (Rh), iridium (from the viewpoint that good contact resistance can be obtained without performing heat treatment. A platinum group metal such as Ir) or palladium (Pd) is preferred. Among these, Pt is particularly preferable because it has a high work function and can obtain a good ohmic contact even with a relatively high resistance p-type GaN compound semiconductor layer that has not been subjected to high-temperature heat treatment.

  When the contact metal layer 11 is made of a platinum group metal, it is necessary to make the thickness very thin from the viewpoint of light transmittance. The thickness of the contact metal layer 11 is preferably in the range of 0.1 to 7.5 nm. If it is less than 0.1 nm, it is difficult to obtain a stable thin layer. If it exceeds 7.5 nm, the translucency is lowered, so that it is more preferably 5 nm or less. In consideration of a decrease in translucency due to subsequent lamination of the current diffusion layer 12 and stability of film formation, a range of 0.5 to 2.5 nm is particularly preferable.

  However, by reducing the thickness of the contact metal layer 11, the electrical resistance in the surface direction of the contact metal layer 11 is increased, and only the peripheral portion of the pad layer, which is the current injection portion, is combined with the p layer having a relatively high resistance. The current does not spread, resulting in a non-uniform light emission pattern, and the light emission output decreases.

  Therefore, by disposing a current diffusion layer 12 made of a metal thin film having a high light transmittance and a high conductivity as a means for supplementing the current diffusibility of the contact metal layer 11, low contact resistance of the platinum group metal is provided. In addition, the current can be spread uniformly without greatly impairing the light transmittance, and as a result, a light emitting element having a high light emission output can be obtained.

The current diffusion layer 12 is made of a thin film of metal or alloy other than the metal constituting the contact metal layer 11.
The material of the current spreading layer 12 is preferably a metal having a high conductivity, for example, a metal selected from the group consisting of gold (Au), silver (Ag), and copper (Cu), or an alloy containing at least one of them. Of these, gold is most preferable because of its high light transmittance when it is made into a thin film.

  The thickness of the current spreading layer 12 is preferably 1 to 20 nm. If it is less than 1 nm, the current diffusion effect is not sufficiently exhibited. If the thickness exceeds 20 nm, the light transmission of the current diffusion layer 12 is significantly lowered, and the light emission output may be lowered. More preferably, it is 10 nm or less. Further, by setting the thickness in the range of 3 to 6 nm, the balance between the light transmittance of the current diffusion layer 12 and the effect of current diffusion becomes the best, and by combining with the contact metal layer 11 above, the entire surface on the positive electrode can be evenly distributed. Light emission and high output light emission can be obtained.

  The method for forming the contact metal layer 11 and the current diffusion layer 12 is not particularly limited, and a known vacuum deposition method or sputtering method can be used. Among these, the vapor deposition method with little thermal damage is suitable as a method for forming an electrode on an element having the light emitting layer 4 containing In.

  As the bonding pad layer 13 constituting the bonding pad portion, those having various structures using various materials are known, and these known materials can be used without particular limitation. However, it is desirable to use a material having good adhesion to the current diffusion layer 12, and the thickness needs to be sufficiently thick so as not to damage the contact metal layer 11 or the current diffusion layer 12 due to stress during bonding. . The outermost layer is preferably made of a material having good adhesion to the bonding ball.

The greatest advantage of a translucent electrode made of only metal as proposed in the present invention is that it can be produced without including heat treatment in the production process. The fact that the manufacturing process does not include heat treatment is very advantageous for suppressing the accumulation of thermal damage to the light emitting layer 4 as compared with the conventionally known gallium nitride compound semiconductor light emitting device in which the light emitting layer 4 contains In. A translucent electrode including an oxide layer that cannot be formed without a conventional heat treatment step, or a metal translucent electrode that has been subjected to a heat treatment for ohmic contact, is composed of InGaN or the like. A portion where the crystal was thermally decomposed and metallized was observed in the light emitting layer 4 containing In. Further, even when such a clear fracture mark is not observed, the breakage may be manifested by aging. However, such an inconvenience is solved when an electrode not subjected to a heat treatment step is used.
This is an advantage generally found in a gallium nitride-based compound semiconductor light-emitting element having a light-emitting layer 4 containing In. In addition, the effect is particularly remarkable in the quantum well structure in which the InGaN layer is thinned and the lattice strain is applied. In particular, when the multiple quantum well structure is used, the effect of suppressing the destruction of the light emitting layer 4 is further remarkable.

The substrate 1 includes a sapphire single crystal (Al ₂ O ₃ ; A plane, C plane, M plane, R plane), spinel single crystal (MgAl ₂ O ₄ ), ZnO single crystal, LiAlO ₂ single crystal, LiGaO ₂ single crystal. Known substrate materials such as oxide single crystals such as MgO single crystal, Si single crystal, SiC single crystal, GaAs single crystal, AlN single crystal, GaN single crystal, and boride single crystals such as ZrB ₂ are used without any limitation. be able to. The plane orientation of the substrate is not particularly limited. Moreover, a just board | substrate may be sufficient and the board | substrate which provided the off angle may be sufficient.

The n-type semiconductor layer 3, the light emitting layer 4, and the p-type semiconductor layer 5 are known in various structures, and these known materials can be used without any limitation. In particular, the carrier concentration of the p-type semiconductor layer 5 is a common concentration, but the translucent positive electrode of the present invention is also applied to a p-type semiconductor layer having a relatively low carrier concentration, for example, about 1 × 10 ¹⁷ cm ^−3. Is applicable.

As a gallium nitride compound semiconductor constituting them, semiconductors of various compositions represented by the general formula Al _x In _y Ga _1-xy N (0 ≦ x <1, 0 ≦ y <1, 0 ≦ x + y <1) Is known, and the gallium nitride-based compound semiconductor constituting the n-type semiconductor layer 3 and the p-type semiconductor layer 5 in the present invention is also represented by the general formula Al _x In _y Ga _1-xy N (0 ≦ x <1, Semiconductors having various compositions represented by 0 ≦ y <1, 0 ≦ x + y <1) can be used without any limitation. The gallium nitride-based compound semiconductor constituting the light emitting layer 4 is represented by the general formula Al _x In _y Ga _1-xy N (0 ≦ x <1, 0 <y <1, 0 <x + y <1) including In. The semiconductors represented can be used without any limitation.

The growth method of these gallium nitride-based compound semiconductors is not particularly limited. Group III nitride semiconductors such as metal organic chemical vapor deposition (MOCVD), hydride vapor deposition (HVPE), molecular beam epitaxy (MBE), etc. All methods known to grow can be applied. A preferred growth method is the MOCVD method from the viewpoint of film thickness controllability and mass productivity.
In the MOCVD method, hydrogen (H ₂ ) or nitrogen (N ₂ ) as a carrier gas, trimethyl gallium (TMG) or triethyl gallium (TEG) as a Ga source which is a group III source, trimethyl aluminum (TMA) or triethyl aluminum as an Al source (TEA), trimethylindium (TMI) or triethylindium (TEI) as an In source, ammonia (NH ₃ ), hydrazine (N ₂ H ₄ ), or the like as an N source as a group V source. As dopants, monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ) is used as a Si raw material for n-type, germane (GeH ₄ ) is used as a Ge raw material, and biscyclohexane is used as an Mg raw material for p-type. Pentadienyl magnesium (Cp ₂ Mg) or bisethylcyclopentadienyl magnesium ((EtCp) ₂ Mg) is used.

  In order to form the negative electrode 20 in contact with the n-type semiconductor layer 3 of the gallium nitride-based compound semiconductor in which the n-type semiconductor layer 3, the light-emitting layer 4 and the p-type semiconductor layer 5 are sequentially stacked on the substrate 1, A part of the p-type semiconductor layer 5 is removed to expose the n-type semiconductor layer 3. Thereafter, the translucent positive electrode of the present invention is formed on the remaining p-type semiconductor layer 5, and the negative electrode 20 is formed on the exposed n-type semiconductor layer 3. As the negative electrode 20, negative electrodes having various compositions and structures are known, and these known negative electrodes can be used without any limitation.

In the present invention, it is assumed that the light emitting layer (active layer) 4 contains indium (In). The light emitting layer 4 may be composed of a single layer such as InGaN, or may have a quantum well structure, but the effect of the present invention is particularly remarkable when a quantum well structure is employed.
The quantum well structure may be a single quantum well structure composed of a single layer, but a multiple quantum well structure in which a plurality of well layers and barrier layers as active layers are alternately stacked improves the light emission output. Therefore, it is preferable. The number of lamination is preferably about 3 to 10 times, more preferably about 3 to 6 times. In the case of a multiple quantum well structure, it is not necessary that all well layers (active layers) have a thick film portion and a thin film portion, and the dimensions and area ratios of the thick film portion and the thin film portion are changed depending on each layer. May be. In the case of a multiple quantum well structure, the whole of the well layer (active layer) and the barrier layer together is referred to as a light emitting layer in this specification.

  The thickness of the barrier layer is preferably 70 mm or more, and more preferably 140 mm or more. If the thickness of the barrier layer is thin, the flattening of the upper surface of the barrier layer is hindered, and the light emission efficiency and aging characteristics are reduced. Moreover, when the film thickness is too thick, it causes an increase in driving voltage and a decrease in light emission. For this reason, the thickness of the barrier layer is preferably 500 mm or less.

  In the case of a multiple quantum structure, the barrier layer can be formed of InGaN having a smaller In ratio than InGaN constituting the well layer (active layer) in addition to GaN and AlGaN. Among these, GaN is preferable.

When the active layer is constituted by a multiple quantum well structure and is undoped, the well layer can have a structure including a thick region and a thin region. By adopting this structure for the well layer, the drive voltage can be reduced.
Such a structure can be formed by growing a well layer at a relatively low temperature such as 600 to 900 degrees and then increasing the temperature while stopping the growth.

When doping the active layer with Si, an organic silicon raw material can be used as a dopant source in addition to silane (SiH ₄ ) and disilane (Si ₂ H ₆ ) which are generally well known. Silane (SiH ₄ ) and disilane (Si ₂ H ₆ ) may be supplied as 100% gas, but it is desirable to supply a diluted gas from a cylinder from the viewpoint of safety.

Similarly, when the active layer is doped with Ge, an organic germanium raw material can be used as a dopant source in addition to germanium (GeH ₄ ) which is generally well known. Although germane (GeH ₄ ) may be supplied as a 100% gas, it is desirable to supply a diluted gas from a cylinder from the viewpoint of safety.

When the n dopant is doped into the active layer, the entire region may be doped, or only a part of the region may be doped. In particular, doping the barrier layer with n dopant in a structure employing a quantum well structure has the effect of reducing the driving voltage of the device, so it is desirable to dope the barrier layer with n dopant. In this case, not only the entire barrier layer but also a part of the region may be doped. In particular, a high output and a low drive voltage can both be achieved by selectively doping the region immediately below the well layer.
The concentration at which the n-dopant is doped is preferably 5 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ¹⁹ cm ⁻³ or less. If the concentration is lower than this, the driving voltage cannot be reduced, and if it is higher than this, the crystallinity and flatness are lowered. More desirably, it is 1 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less, and 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ¹⁸ cm ⁻³ or less is most preferable.

  An n-clad layer is preferably provided between the contact layer and the light emitting layer. This is because the deterioration of flatness generated on the outermost surface of the n contact layer can be filled. The n-clad layer can be formed of AlGaN, GaN, InGaN or the like, but it goes without saying that in the case of using InGaN, it is desirable that the composition be larger than the band gap of InGaN in the active layer. The carrier concentration of the n-clad layer may be the same as that of the n-contact layer, or may be large or small. In order to improve the crystallinity of the active layer formed thereon, it is preferable to adjust the growth conditions such as the growth rate, the growth temperature, the growth pressure, and the doping amount as appropriate to obtain a highly flat surface.

  The n-clad layer may be formed by alternately laminating layers having different compositions and lattice constants. At that time, in addition to the composition, the amount and thickness of the dopant may be changed depending on the layer to be stacked.

EXAMPLES Next, although an Example demonstrates this invention still in detail, this invention is not limited only to these Examples.
(Example)
FIG. 2 is a schematic view showing a cross section of the gallium nitride compound semiconductor light emitting device 200 manufactured in this example, and FIG. 3 is a schematic view showing the plane thereof. On a substrate 1 made of sapphire, a base layer 3a made of undoped GaN having a thickness of 8 μm, a Ge-doped n-type GaN contact layer 3b having a thickness of 2 μm, and an n having a thickness of 0.03 μm, via a buffer layer 6 made of AlN. A type In _0.1 Ga _0.9 N cladding layer 3c, a 16 nm thick Si-doped GaN barrier layer, and a 3 nm thick In _0.2 Ga _0.8 N well layer are stacked five times, and finally a barrier layer is formed. The provided multi-quantum well structure light emitting layer 4, Mg-doped p-type Al _0.07 Ga _0.93 N cladding layer 5a having a thickness of 0.01 μm, and Mg-doped p-type AlGaN contact layer 5b having a thickness of 0.15 μm are sequentially arranged. Stacked to form a gallium nitride compound semiconductor. On the p-type AlGaN contact layer 5b, a Pt contact metal layer 11 having a thickness of 1.5 nm, an Au current diffusion layer 12 having a thickness of 5 nm, and an Au / Ti / Al / Ti / Au5 layer structure (thickness is 50/20, respectively). The positive electrode 10 made of the bonding pad layer 13 of / 10/100/200 nm was formed. FIG. 4 shows a cross-sectional structure of the light emitting layer 4 having a multiple quantum well structure. In the figure, 41-1 to 41-6 are barrier layers, and 42-1 to 42-5 are well layers.

  Next, a light emitting device in which a negative electrode 20 having a two-layer structure of Ti / Au is formed on the n-type GaN contact layer 3b and the light extraction surface is the semiconductor side. The planar shapes of the positive electrode 10 and the negative electrode 20 are as shown in FIG.

In this light emitting device structure, the carrier concentration of the n-type GaN contact layer 3b is 5 × 10 ¹⁸ cm ⁻³ , the Si doping amount of the GaN barrier layer is 1 × 10 ¹⁸ cm ⁻³ , and the p-type AlGaN contact layer 5b The carrier concentration was 5 × 10 ¹⁸ cm ⁻³ , and the Mg doping amount of the p-type AlGaN cladding layer 5a was 5 × 10 ¹⁹ cm ⁻³ .

  Lamination of the gallium nitride compound semiconductor layers was performed by MOCVD under normal conditions well known in the art. Moreover, the positive electrode 10 and the negative electrode 20 were formed in the following procedure.

  First, the n-type GaN contact layer 3b where the negative electrode 20 is to be formed was exposed by the following procedure by the reactive ion etching method.

First, an etching mask was formed on the p-type semiconductor layer 5b. The formation procedure is as follows. After uniformly applying the resist over the entire surface, the resist was removed from a region that was slightly larger than the positive electrode region using a known lithography technique. It was set in a vacuum deposition apparatus, and Ni and Ti were laminated by an electron beam method at a pressure of 4 × 10 ⁻⁴ Pa or less so that the film thicknesses were about 50 nm and 300 nm, respectively. Thereafter, the metal film other than the positive electrode region was removed together with the resist by a lift-off technique.

Next, after placing the semiconductor laminated substrate on the electrode in the etching chamber of the reactive ion etching apparatus and reducing the etching chamber to 10 ⁻⁴ Pa, Cl ₂ is supplied as an etching gas to form the n-type GaN contact layer 3b. Etched until exposed. After the etching, it was taken out from the reactive ion etching apparatus, and the etching mask was removed with nitric acid and hydrofluoric acid.

  Next, the contact metal layer 11 made of Pt and the current diffusion layer 12 made of Au were formed only in the region where the positive electrode was formed on the p-type AlGaN contact layer 5b by using a known photolithography technique and lift-off technique. In the formation of the contact metal layer 11 and the current diffusion layer 12, first, the substrate 1 on which the gallium nitride compound semiconductor layer is stacked is placed in a vacuum deposition apparatus, and Pt is first deposited on the p-type AlGaN contact layer 5b at 1.5 nm, Next, 5 nm of Au was laminated. Subsequently, after taking out from the vacuum chamber, it is processed in accordance with a well-known procedure generally called lift-off, and further, a first layer made of Au and a second layer made of Ti are partially formed on the current diffusion layer 12 by a similar method. Then, a third layer made of Al, a fourth layer made of Ti, and a fifth layer made of Au were laminated in this order to form a bonding pad layer 13. In this way, the positive electrode 10 was formed on the p-type AlGaN contact layer 5b.

  The positive electrode 10 formed by this method showed translucency and had a light transmittance of 60% in the wavelength region of 470 nm. The light transmittance was measured by forming the same contact metal layer and current diffusion layer as described above in a size for measuring light transmittance.

  Next, the negative electrode 20 was formed on the exposed n-type GaN contact layer 3b by the following procedure. After uniformly applying the resist to the entire surface, the resist is removed from the negative electrode forming portion on the exposed n-type GaN contact layer 3b by using a known lithography technique, and Ti is sequentially applied from the semiconductor side by a commonly used vacuum deposition method. A negative electrode 20 having a thickness of 100 nm and Au of 200 nm was formed. Thereafter, the resist was removed by a known method.

  The wafer on which the positive electrode 10 and the negative electrode 20 are formed in this way is thinned and polished to 80 μm by grinding and polishing the back surface of the substrate, and a ruled line is inserted from the semiconductor lamination side using a laser scriber. Then, it was cut and cut into 350 μm square chips. Subsequently, when these chips were energized with a probe needle and the forward voltage was measured at a current application value of 20 mA, it was 2.9 V.

  After that, when mounted on a TO-18 can package and measured for light output by a tester, the light output at an applied current of 20 mA was 6 mW. Further, while the sample was mounted in a TO-18 can package, a current of 30 mA was continuously applied for 100 hr, and the light emission characteristics and electrical characteristics were measured by a tester. Then, no change was observed in the light emission output and the reverse voltage.

(Comparative Example 1)
A gallium nitride-based compound semiconductor light-emitting device was fabricated in the same manner as in Example 1 except that the electrode had a conventional Au / NiO structure. When producing the Au / NiO translucent electrode, heat treatment was performed at a temperature of 450 ° C. in an oxygen atmosphere. The forward voltage and light emission output of this light emitting device were 2.9 V and 3.7 mW, respectively. When the state of luminescence was confirmed with a microscope, it was found that dark spots were seen in some places. This seems to indicate that the light emitting layer was deteriorated by the heat treatment during the production of the translucent electrode.

(Comparative Example 2)
A gallium nitride-based compound semiconductor light-emitting device was fabricated in the same manner as in Example 1 except that the electrode was made of Pt only and was subjected to heat treatment. The forward voltage and light emission output of this light emitting device were 2.9 V and 4.5 mW, respectively. When this sample was subjected to an aging test while energizing a current of 30 mA for 100 hr, the reverse voltage at a reverse current of 10 μA was 20 V or more before the test, but decreased to 5 V after the test. This seems to be due to damage to the light emitting layer accumulated by the heat treatment at the time of forming the translucent electrode.

  The electrode for a gallium nitride-based compound semiconductor light-emitting device provided by the present invention is useful as a positive electrode of a translucent gallium nitride-based compound semiconductor light-emitting device.

It is the schematic diagram which showed the cross-section of the compound semiconductor light-emitting device of this invention. It is the schematic diagram which showed the cross-section of the compound semiconductor light-emitting device of an Example. It is the schematic diagram which showed the plane of the compound semiconductor light-emitting device of an Example. It is a figure which shows the cross-section of the light emitting layer of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... GaN-based compound semiconductor layer, 3 ... n-type semiconductor layer, 3a ... Underlayer, 3c ... Cladding layer, 4 ... Light emitting layer, 5 ... p-type semiconductor layer, 5a ... cladding layer, 5b ... contact layer, 6 ... buffer layer, 10 ... positive electrode, 11 ... contact metal layer, 12 ... current diffusion layer, 13. .... Bonding pad layer, 20 ... negative electrode, 41-1 to 41-6 ... barrier layer, 42-1 to 41-5 ... well layer, 100, 200 ... gallium nitride compound semiconductor light emission element

Claims (13)

  A transparent positive electrode of a gallium nitride-based compound semiconductor light-emitting element containing In, comprising a contact metal layer made of a thin film of at least one metal selected from the platinum group, and a metal or alloy other than a metal constituting the contact metal layer A positive electrode structure comprising two types of current diffusion layers made of a thin film and a bonding pad.   The positive electrode structure according to claim 1, wherein a thickness of the contact metal layer is 0.1 to 7.5 nm.   The positive electrode structure according to claim 1, wherein a thickness of the contact metal layer is 0.1 to 5 nm.   The positive electrode structure according to claim 1, wherein a thickness of the contact metal layer is 0.5 to 2.5 nm.   The platinum group metal constituting the contact metal layer contains at least one kind of metal selected from the group consisting of platinum, iridium, rhodium, and ruthenium, according to any one of claims 1 to 4. The positive electrode structure.   The positive electrode structure according to claim 1, wherein the contact metal layer contains platinum.   The current spreading layer is a thin film of at least one metal selected from gold, silver and copper, or a thin film of an alloy containing at least one metal. 2. The positive electrode structure according to item 1.   The positive electrode structure according to claim 1, wherein the current diffusion layer is gold.   The positive electrode structure according to any one of claims 1 to 8, wherein the current diffusion layer has a thickness of 1 to 20 nm.   The positive electrode structure according to claim 1, wherein a thickness of the current diffusion layer is 10 nm or less.   The positive electrode structure according to any one of claims 1 to 8, wherein the current diffusion layer has a thickness of 3 to 6 nm.   12. A gallium nitride system comprising a light emitting layer having a quantum well structure made of a gallium nitride compound semiconductor containing In and comprising the positive electrode structure according to claim 1. Compound semiconductor light emitting device. The gallium nitride-based compound semiconductor light-emitting device according to claim 12, wherein the light-emitting layer has a multiple quantum well structure including a plurality of well layers and a plurality of barrier layers.

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