JP2004214434A - Oxide semiconductor light emitting element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide semiconductor light emitting element that is applicable for a light emitting diode or a semiconductor laser element and is superior in light emission and the saving of electric power. <P>SOLUTION: The oxide semiconductor light emitting element includes at least an n-type ZnO-based semiconductor clad layer, a ZnO-based semiconductor light emitting layer, a p-type ZnO-based semiconductor clad layer, and a p-type ZnO-based semiconductor contact layer that are stacked in sequence on a substrate. A transition metal oxide is used to form in a p-type ZnO-based semiconductor contact layer an ohmic electrode that has a high adhesion to a ZnO-based semiconductor layer and a low resistance. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
[Field of the Invention]
The present invention relates to a semiconductor light emitting device such as a light emitting diode device and a semiconductor laser device, and more particularly, to an oxide semiconductor light emitting device using an ohmic electrode having a low resistance to a p-type oxide semiconductor. Furthermore, the present invention relates to a method for manufacturing the above oxide semiconductor light emitting device.
[0002]
[Prior art]
Oxide materials have many functions, such as dielectric properties, magnetism, and superconductivity, which cannot be realized by conventional semiconductor materials, and also have the potential to supplement the characteristics of existing materials as semiconductor materials.
Recently, zinc oxide (ZnO), which is a Group II oxide semiconductor, has been regarded as a promising material for light emitting devices in the blue or ultraviolet region.
ZnO is a direct transition semiconductor having a band gap energy of about 3.4 eV. Further, since ZnO has an extremely high exciton binding energy of about 60 meV, there is a possibility that a highly efficient light emitting device with low power consumption and excellent environmental properties may be realized, and furthermore, the raw material is inexpensive and harmless to the environment and the human body. And that the film forming technique is simple.
[0003]
Hereinafter, when the term "ZnO-based" semiconductor is used in this specification, it includes ZnO and mixed crystals represented by MgZnO, CdZnO, or the like using the same as a host. Further, in the present specification, when a compound is indicated without specifying a composition, for example, “MgZnO” is simply described only by an element symbol, and when a composition is specified, for example, “MgZnO” is used._0.1Zn_0.9O ".
[0004]
Conventionally, it has been difficult to control the p-type conductivity type of ZnO due to a self-compensation effect caused by strong ionicity. However, by using nitrogen (N) as an acceptor impurity, a p-type conductivity is realized (for example, “Japanese”).・ Journal of Applied Physics ”, Vol. 36, 1997, p. Many studies have been carried out to produce (e.g., "Japanese Journal of Applied Physics", Vol. 40, 2001, p. L177-180; See Non-Patent Document 2).
[0005]
However, the acceptor level in ZnO is very deep, and even an N acceptor capable of realizing p-type requires ionization energy of 200 to 300 meV, so that it is difficult to obtain a low resistance layer.
[0006]
JP-A-2001-48698 (Patent Document 1) and JP-A-2001-68707 (Patent Document 2) disclose the use of ZnO for an ultraviolet semiconductor laser diode required for high-density recording and transmission of a large amount of information. Discloses a so-called "simultaneous doping technique" in which a p-type dopant and an n-type dopant are simultaneously doped into ZnO to produce a low-resistance p-type ZnO single crystal thin film. This “simultaneous doping technique” is characterized in that doping is performed so that the p-type dopant concentration becomes higher than the n-type dopant concentration. By combining low-resistance p-type ZnO obtained by this technique with n-type ZnO obtained by doping impurities such as Ga, a pn junction can be realized in ZnO, which is the same semiconductor compound.
[0007]
Further, a technique of forming a low-resistance ohmic electrode on a p-type ZnO-based semiconductor is extremely important for uniformly and efficiently injecting carriers into an active layer. As a conventional technique related to an ohmic electrode of a p-type ZnO-based semiconductor layer, for example, a first metal layer containing Ni, Ph, Pt, or Pd or an alloy thereof, and a metal or alloy different from the first metal layer are included. A technique for forming an ohmic electrode made of a second metal layer is disclosed in Japanese Patent Application Laid-Open No. 2001-168392 (Patent Document 3).
[0008]
[Patent Document 1]
JP 2001-48698 A
[0009]
[Patent Document 2]
JP 2001-68707 A
[0010]
[Patent Document 3]
JP 2001-168392 A
[0011]
[Non-patent document 1]
"Japanese Journal of Applied Physics", Vol. 36, 1997, p. L1453-1455
[0012]
[Non-patent document 2]
"Japanese Journal of Applied Physics", Vol. 40, 2001, p. L177-180
[0013]
[Problems to be solved by the invention]
However, according to the study of the present inventor, an oxide semiconductor has poor adhesion to a metal layer, and an ohmic electrode formed by a conventional method with excellent productivity such as a vacuum deposition method or a sputtering method using the metal of the related art is not suitable. In many cases, peeling or deterioration occurs during wire bonding or energization, which has a problem in reliability.
Thus, in view of the above problems, the present invention provides an oxide semiconductor light emitting device that has excellent adhesion to a p-type oxide semiconductor and realizes excellent light emitting characteristics using a low-resistance ohmic electrode. Aim.
[0014]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on the material, structure, and manufacturing method of an ohmic electrode that achieves both adhesion and low resistance to a p-type layer of an oxide semiconductor light-emitting element. As a result, Ni, Cu, and Ag metal oxides were obtained. It has been found that the object can be attained by using as a ohmic electrode, and the present invention has been made.
[0015]
Hereinafter, in this specification, a layer that controls light emission in a semiconductor light emitting device is referred to as a “light emitting layer”, but in the case of a semiconductor laser device, the term “active layer” may be used in the same sense. However, since the functions of the two are substantially the same, no distinction is made.
[0016]
According to the present invention, at least an n-type ZnO-based semiconductor clad layer, a ZnO-based semiconductor light-emitting layer, a p-type ZnO-based semiconductor clad layer, and a p-type ZnO-based semiconductor contact layer are formed on a substrate. There is provided an oxide semiconductor light-emitting element on which a p-type ohmic electrode containing at least one oxide of a transition metal selected from the group consisting of Ni, Cu and Ag is formed.
[0017]
Since the transition metal oxide has better adhesion to the oxide than the metal, the ohmic resistance using the transition metal oxide does not peel off by wire bonding or energization. In particular, oxides of Ni, Cu, and Ag exhibit p-type semiconductor properties and have low-resistance conductivity, and thus are suitable as ohmic electrodes for p-type oxide semiconductors. Thus, an oxide semiconductor light-emitting element having excellent reliability and low operating voltage can be manufactured.
[0018]
If the p-type cladding layer has a low resistance, the light extraction efficiency can be improved. However, it is difficult to obtain a low-resistance p-type layer with a ZnO-based semiconductor. It is effective to be translucent.
When the thickness of the ohmic electrode is 1 to 100 nm, ohmic contact with sufficiently low resistance can be ensured, and the transmissivity is high with respect to the emission wavelength from the light emitting layer, and the light extraction efficiency is improved.
[0019]
In the oxide semiconductor light emitting device of the present invention, a pad electrode is formed on the p-type ohmic electrode using Au.
Au is suitable as a pad electrode for bonding a wire with low resistance, and does not act as a donor impurity for an oxide semiconductor. Therefore, even if formed on a p-type ohmic electrode, the electrode does not increase in resistance.
[0020]
In another aspect of the oxide semiconductor light-emitting device of the present invention, between the ohmic electrode and the pad electrode, selected from the group consisting of Ru, Os, Rh, Ir, Ni, Pd, Pt, Cu, and Ag. An intermediate layer containing at least one element is formed.
By including the intermediate layer, the adhesion between the p-type ohmic electrode and the pad electrode is improved. Further, when the intermediate layer is formed of a metal thin film, it is possible to reflect light emitted from the light-transmitting electrode without absorbing it, and to further reduce the resistance of the electrode.
The intermediate layer having such features is realized by including at least one element selected from the group consisting of Ru, Os, Rh, Ir, Ni, Pt, Cu, and Ag.
[0021]
When the p-type ohmic electrode and the intermediate layer formed on and in contact with the p-type ohmic electrode contain donor impurities and an n-type ohmic electrode material, these elements diffuse into the p-type ohmic electrode and the p-type ZnO contact layer, thereby increasing the resistance. Will occur.
Therefore, in the oxide semiconductor light emitting device of the present invention, the constituent elements of the p-type ohmic electrode and the intermediate layer do not include Al, In, Ga, Ti, and Cr.
[0022]
Further, the present invention forms at least an n-type ZnO-based semiconductor clad layer, a ZnO-based semiconductor light-emitting layer, a p-type ZnO-based semiconductor clad layer, and a p-type ZnO-based semiconductor contact layer on a substrate; Provided is a method for manufacturing an oxide semiconductor light-emitting device in which a p-type ohmic electrode made of a transition metal oxide is formed on a base semiconductor contact layer.
[0023]
In the first aspect of the method for manufacturing an oxide semiconductor light-emitting device of the present invention, a p-type transition metal oxide is formed using at least one transition metal oxide selected from the group consisting of Ni, Cu, and Ag. An ohmic electrode is formed.
By using a transition metal oxide as a raw material for an electrode thin film, O₂There is no need to introduce a gas, and a transition metal oxide p-type ohmic electrode can be easily manufactured.
[0024]
In the second aspect of the method for manufacturing an oxide semiconductor light-emitting device of the present invention, a transition metal oxide is formed in the presence of oxygen using at least one transition metal selected from the group consisting of Ni, Cu, and Ag. A p-type ohmic electrode is formed.
Since an elemental metal can be obtained at a low cost as a raw material having high purity, an electrode having excellent characteristics can be manufactured at a low cost by using the raw material as a raw material for an electrode thin film. Further, an oxide thin film can be easily formed by vapor deposition in an oxygen atmosphere, so that an ohmic electrode having excellent adhesion and low resistance can be formed.
[0025]
The p-type ohmic electrode made of the above transition metal oxide is formed by using any one of thin film forming methods of an electron beam evaporation method, a sputtering method, and a laser ablation method. The above-described thin film formation method is a film formation method which has high mass productivity and can easily form a high-quality oxide thin film, and can manufacture a light-emitting element having excellent characteristics at low cost.
[0026]
In the method for manufacturing an oxide semiconductor light-emitting device of the present invention, after forming the p-type ohmic electrode, a heat treatment is performed in an oxygen atmosphere or the air to improve the adhesion and ohmic characteristics of the electrode. In particular, by performing the annealing treatment in an oxygen atmosphere, it is possible to suppress the escape of oxygen from the electrode and improve the adhesion while maintaining a low ohmic resistance.
[0027]
The heat treatment is performed at a temperature in the range of 300 to 450 ° C. When the temperature is 300 ° C. or higher, the effects of improving the adhesion of the electrode and reducing the resistance are high.
[0028]
In the present invention, an n-type ZnO-based semiconductor clad layer, a ZnO-based semiconductor light-emitting layer, a p-type ZnO-based semiconductor clad layer, a p-type ZnO-based semiconductor contact layer, and an ohmic electrode can be directly laminated on the substrate in this order. Another layer may be formed between the layers for the purpose of improving the characteristics of the semiconductor light emitting device. For example, a buffer layer can be first formed on a substrate in order to obtain a growth layer having good crystallinity. In the semiconductor laser device, an optical guide layer is formed between the ZnO-based semiconductor light-emitting layer and the n-type and p-type ZnO-based semiconductor clad layers in order to improve the light confinement rate of light emitted from the light-emitting layer. You can also.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments to which the oxide semiconductor light emitting device of the present invention is applied will be specifically described with reference to the drawings.
[0030]
First embodiment
The oxide semiconductor light-emitting device according to the first embodiment of the present invention is a light-emitting diode device having at least an n-type MgZnO cladding layer, a CdZnO light-emitting layer, a p-type MgZnO cladding layer, and a p-type ZnO contact layer on a substrate. This light emitting diode element is characterized in that a p-type ohmic electrode containing an oxide of a transition metal is formed on the p-type ZnO contact layer.
[0031]
FIG. 1 shows a perspective view (A) and a sectional view (B) of the light emitting diode element 1. In the light-emitting diode element 1, an n-type MgZnO cladding layer 102, a non-doped CdZnO light-emitting layer 103, a p-type MgZnO cladding layer 104, and a p-type contact layer 105 are stacked on an n-type ZnO substrate 101 having a zinc surface as a main surface. It is constituted by that.
[0032]
On the entire main surface of the p-type MgZnO contact layer 105, a p-type ohmic electrode 106 that is transparent to light emitted from the light emitting layer is laminated. Further, the translucent p-type ohmic electrode 106 is formed of an oxide of at least one transition metal selected from the group consisting of Ni, Cu and Ag, for example, NiO, Cu₂O or Ag₂It is formed using O. Further, a bonding pad electrode 107 is formed on the translucent p-type ohmic electrode 106 with an area smaller than that of the translucent p-type ohmic electrode 106.
On the back surface of the ZnO substrate 101, an n-type ohmic electrode 108 is laminated.
[0033]
In the oxide semiconductor light emitting device of the present invention, the material of the substrate 101 may be sapphire, spinel, LiGaO₂Or a conductive substrate such as SiC or GaN.
FIGS. 2A and 2B are perspective views of a light emitting diode element 1 ′ using sapphire as an insulator for the substrate 101.
In the case of using an insulating substrate, as shown in FIG. 2A, a part of the growth layer is etched to expose the n-type MgZnO cladding layer 102, and the n-type ohmic electrode 108 may be formed thereon. In addition, as shown in FIG. 2B, in order to obtain a growth layer with good crystallinity, first, an n-type ZnO buffer layer 109 is formed on the substrate, and further, the contact resistance of the n-type ohmic electrode 108 is reduced. May be formed with an n-type ZnO contact layer 110.
[0034]
However, in order to obtain high luminous efficiency to the maximum, (1) a lattice-matched substrate having an in-plane lattice constant difference of 3% or less from ZnO, having excellent crystallinity of a grown layer and being a non-luminescent center It is preferable to use a substrate that can reduce defects, (2) has a low absorption coefficient corresponding to the emission wavelength, and (3) is conductive and can form an electrode on the back surface. A substrate made of ZnO single crystal is most preferable because it satisfies all the above conditions. The ZnO substrate is perfectly lattice-matched with the ZnO-based semiconductor light emitting device epitaxially grown thereon, and has a higher affinity than using a heterogeneous substrate. Thus, a light-emitting element having good crystallinity and extremely few non-light-emission centers can be manufactured.
[0035]
The use of a zinc surface as the main surface is preferable because the carrier activation rate of the p-type layer is improved and a p-type layer having low resistance is easily obtained.
In addition, it is preferable to form irregularities on the back surface of the substrate by a known method such as polishing or etching and irregularly reflect the emitted light, which improves the light extraction efficiency.
[0036]
As the donor impurity doped into the n-type MgZnO cladding layer 102, a group III element such as B, Al, Ga, or In is preferably used because the activation rate in the ZnO-based semiconductor is high, and Ga or Al is particularly preferable. preferable.
[0037]
The light-emitting layer 103 can be made n-type by doping a donor impurity, for example, a group III element such as B, Al, Ga, or In in an arbitrary amount. Alternatively, the light-emitting layer 103 can be made n-type by co-doping the above-described donor impurity and an acceptor impurity, for example, a group I or V element such as Li, Na, Cu, Ag, N, P, or As. . N and Ag are preferable because they are easily activated. N is N₂Is particularly preferable because high-concentration doping can be performed while maintaining good crystallinity by a method of irradiating during plasma growth with plasma. Thereby, the peak wavelength and the emission intensity can be controlled.
Further, the light emitting layer 103 may have a quantum well structure in which well layers and barrier layers are alternately stacked. In this case, only the well layer or only the barrier layer of the light emitting layer 103 can be doped with the donor impurity or the donor impurity and the acceptor impurity.
[0038]
As an acceptor impurity to be doped into the p-type MgZnO cladding layer 104 and the p-type contact layer 105, a Group I or V element such as Li, Na, Cu, Ag, N, P, As or the like can be used. N and Ag are preferable because they are easily activated. N is N₂Is particularly preferable because high-concentration doping can be performed while maintaining good crystallinity by a method of irradiating during plasma growth with plasma.
[0039]
As a material of the p-type contact layer 105, it is preferable to use ZnO which has excellent crystallinity and can increase the carrier concentration. If the p-type ZnO contact layer 105 is excessively doped with an acceptor impurity to increase the carrier concentration, the absorption loss increases and the crystallinity deteriorates significantly, and the light extraction efficiency decreases.¹⁶~ 5 × 10¹⁹cm^-3It is preferable to adjust the doping concentration so that the carrier concentration is within the above range.
[0040]
The p-type ohmic electrode 106 needs to have a large work function. In particular, a transition metal having a work function of 4 eV or more has stable ohmic characteristics. Among them, particularly, oxides of Ni, Cu and Ag exhibit low-resistance p-type semiconductor properties and are preferable as a p-type oxide ohmic electrode.
The p-type ohmic electrode 106 can be formed directly on the p-type MgZnO cladding layer 104. However, since the MgZnO mixed crystal has a lower impurity activation ratio than ZnO, the p-type ZnO contact layer 105 is formed. It is preferable to lower the resistance and to form it thereon, since the current spread can be made uniform.
[0041]
In order to obtain the high luminous efficiency and low operating voltage of the present invention with the maximum effect, the p-type ohmic electrode 106 is formed so as to have a light-transmitting property with respect to the light emitted from the light-emitting layer. It is preferable to improve the extraction efficiency. The effect is exhibited if the light transmittance is 0% or more, but it is preferably 30% or more, more preferably 60% or more with respect to the emission wavelength.
Since the transparent conductive film is formed on the entire main surface, the current spread becomes uniform and the external light extraction efficiency is improved. Therefore, an ultraviolet light emitting device having excellent luminous efficiency can be realized.
The thickness that achieves both good ohmic characteristics and high translucency is preferably in the range of 1 to 100 nm.
[0042]
After the formation of the p-type ohmic electrode 106, it is preferable to perform an annealing treatment because the adhesion is improved and the contact resistance is reduced. In order to obtain an annealing effect without causing defects in the ZnO crystal, the temperature is preferably 300 to 450 ° C. The atmosphere in the annealing process is O₂Or in an air atmosphere;₂Then, on the contrary, the resistance increases.
[0043]
If the pad electrode 107 is formed on a part of the translucent p-type ohmic electrode 106 with a smaller area than the p-type ohmic electrode 106, the mounting process on the lead frame is easy without impairing the effect of the translucent electrode. Is preferable.
As a material of the pad electrode 107, a metal material which is easy to bond and does not become a donor impurity even when diffused into a ZnO-based semiconductor is preferable, and Au is particularly preferable.
[0044]
For the n-type ohmic electrode 108, a metal material such as Ti, Cr, or Al can be used. Above all, Al with low resistance and low cost or Ti with good adhesion is preferable. An electrode may be formed by alloying a plurality of the metal materials.
Since Al has a high reflectance of blue to ultraviolet light, even if the n-type ohmic electrode 108 is formed on the entire back surface using Al, the light extraction efficiency is high, which is preferable.
Further, the n-type ohmic electrode 108 can be patterned into an arbitrary shape, and the exposed back surface of the substrate can be bonded to a lead frame with a conductive resin such as Ag paste. Since Ag has a higher reflectance of blue to ultraviolet light than Al, it is also preferable to bond the lead frame with an Ag paste.
When patterning the n-type ohmic electrode 108, an auxiliary electrode may be formed in order to prevent an increase in element resistance. If a metal having a high reflectance of blue to ultraviolet light, such as Ag or Pt, is used for the auxiliary electrode. More preferred.
Since the auxiliary electrode increases the contact area with the lead frame, the operating voltage does not increase even if the n-type electrode is patterned. Therefore, a light-emitting element with low operation voltage can be realized.
[0045]
Other configurations are arbitrary and are not limited to only the configurations described in this specification.
[0046]
The oxide semiconductor light emitting device of the present invention is manufactured by a crystal growth method such as a molecular beam epitaxy (MBE) method, a laser molecular beam epitaxy (laser MBE) method, and a metal organic chemical vapor deposition (MOCVD) method using a solid or gaseous raw material. Can be made.
In the laser MBE method, the composition deviation between the raw material target and the thin film is small, and for example, when ZnO is doped with Ga,₂O₄This is preferable because generation of unintended by-products such as the above can be suppressed.
When the present invention is applied to a light emitting diode element and a semiconductor laser element, a semiconductor laser element can be manufactured using the laser MBE device 7 shown in FIG.
In the laser MBE apparatus 7, a substrate holder 702 is disposed above a growth chamber 701 capable of being evacuated to an ultra-high vacuum, and a substrate 703 is fixed to the substrate holder 702. The back surface of the substrate holder 702 is heated by the heater 704 disposed above the substrate holder 702, and the substrate 703 is heated by the heat conduction.
A target table 705 is arranged directly below the substrate holder 702 at an appropriate distance, and a plurality of raw material targets 706 can be arranged on the target table 705.
The surface of the target 706 is ablated by a pulsed laser beam 708 radiated through a view port 707 provided on a side surface of the growth chamber 701, and a thin film grows by instantaneously evaporating the raw material of the target 706 on the substrate.
The target table 705 has a rotation mechanism, and by controlling the rotation in synchronization with the irradiation sequence of the pulsed laser beam 708, different target materials can be stacked on the thin film. A plurality of gas introduction tubes 710 are provided in the growth chamber so that a plurality of gases can be introduced, and the substrate 703 can be irradiated with an atomic beam activated by the radical cell 709.
[0047]
When forming a metal oxide ohmic electrode of the oxide semiconductor light emitting device of the present invention, a high-purity and inexpensive element metal of 99.99 to 99.999% and a high-purity O₂The oxide layer can be grown in a laser MBE apparatus using a gas. Since the layers from the growth layer to the electrode can be formed consistently in a vacuum growth chamber, it is possible to easily form a low-resistance oxide ohmic electrode with high purity.
[0048]
In the case where a metal oxide ohmic electrode is formed in the oxide semiconductor light-emitting element of the present invention, an electron beam evaporation method which is a film formation technique which has high productivity and can easily form a high-quality oxide thin film is used. By using this method, a light-emitting element having excellent characteristics can be manufactured at low cost.
[0049]
Further, it is difficult to obtain a metal oxide target or tablet having a high purity of 99.999% or more. However, when a very high-purity raw material is not required, a metal oxide can be used for the raw material tablet. , O in the device₂An oxide ohmic electrode can be formed without introducing a gas, which is excellent in simplicity of a manufacturing process and is suitable when a vacuum film-forming apparatus or the like which does not like oxygen is used.
[0050]
In addition, the sputtering method and the laser ablation method are also high in mass productivity and can easily form a high-quality oxide thin film similarly to the electron beam evaporation method, and a light emitting element with excellent characteristics can be manufactured at low cost. .
[0051]
Second embodiment
The oxide semiconductor light emitting device according to the second embodiment of the present invention is configured similarly to the semiconductor light emitting device according to the first embodiment, except that an intermediate layer 201 is provided between the p-type ohmic electrode 106 and the pad electrode 107. Are formed on the light-emitting diode element.
[0052]
FIG. 3 shows a sectional view of the light emitting diode element 2. In this figure, the same components as those of the light emitting diode element 1 are denoted by the same reference numerals as in FIG.
The light emitting diode element 2 is manufactured in the same manner as the light emitting diode element 1 except that the intermediate layer 201 is formed between the p-type ohmic electrode 106 and the pad electrode 107.
The pad electrode 107 can be formed directly on the p-type ohmic electrode 106. However, it is preferable to form the intermediate layer 201 and form it on the intermediate layer 201 because adhesion and light reflectivity are improved.
[0053]
When the p-type ohmic electrode 106 and the intermediate layer 201 formed on and in contact with the p-type ohmic electrode 106 contain donor impurities and an n-type ohmic electrode material, these elements diffuse into the p-type ohmic electrode and the p-type ZnO contact layer. Therefore, the p-type ohmic electrode and the intermediate layer are formed using elements other than Al, In, Ga, Ti, and Cr.
[0054]
Third embodiment
The oxide semiconductor light-emitting device according to the third embodiment of the present invention has at least an n-type MgZnO cladding layer, a quantum well active layer, a p-type MgZnO cladding layer, and a p-type ZnO contact layer on a substrate. This is a semiconductor laser device in which part of a p-type MgZnO cladding layer and a p-type ZnO contact layer are processed into a ridge stripe shape.
This semiconductor laser device is characterized in that a p-type ohmic electrode containing an oxide of a transition metal is formed on the p-type ZnO contact layer, and a pad electrode is formed thereon.
[0055]
FIG. 4 shows a perspective view (A) and a sectional view (B) of the ZnO-based semiconductor laser device 3. The semiconductor laser device 3 includes a ZnO buffer layer 302, an n-type MgZnO cladding layer 303, an n-type ZnO light guide layer 304, a quantum well active layer 305, The light guide layer 306, the p-type MgZnO clad layer 307, and the p-type ZnO contact layer 308 are stacked.
[0056]
A part of the p-type MgZnO cladding layer 307 and the p-type ZnO contact layer 308 are etched into a ridge stripe shape, and the n-type current blocking layer 309 buries the side surfaces of the ridge stripe.
[0057]
On the p-type ZnO contact layer 308 and the n-type current block layer 309, a p-type ohmic electrode 310 containing a transition metal oxide and having a width wider than the ridge stripe and smaller than the element is formed. Is formed.
An n-type ohmic electrode 312 is formed below the ZnO substrate 301.
[0058]
In the oxide semiconductor of the present invention, as a material of the substrate 301, sapphire, spinel, LiGaO₂Or a conductive substrate such as SiC or GaN.
As shown in FIG. 2 in the first embodiment, when an insulating substrate is used, a part of the growth layer is etched to expose the n-type MgZnO cladding layer 303, and the n-type ohmic electrode 312 is formed thereon. It may be formed. Further, in order to obtain a growth layer having good crystallinity, a buffer layer may be formed first on the substrate.
[0059]
However, in order to obtain high luminous efficiency to the maximum, (1) a lattice-matched substrate having an in-plane lattice constant difference of 3% or less from ZnO, having excellent crystallinity of a grown layer and being a non-luminescent center It is preferable to use a substrate that can reduce defects, (2) has a low absorption coefficient corresponding to the emission wavelength, and (3) is conductive and can form an electrode on the back surface. A substrate made of ZnO single crystal is most preferable because it satisfies all the above conditions. The ZnO substrate is perfectly lattice-matched with the ZnO-based semiconductor light emitting device epitaxially grown thereon, and has a higher affinity than using a heterogeneous substrate. Thus, a light-emitting element having good crystallinity and extremely few non-light-emission centers can be manufactured.
[0060]
The use of a zinc surface as the main surface is preferable because the carrier activation rate of the p-type layer is improved and a p-type layer having low resistance is easily obtained.
[0061]
The buffer layer 302 is preferably made of ZnO, which has better crystallinity than MgZnO. However, when a ZnO substrate is used, an MgZnO layer having an Mg composition intermediate between ZnO and MgZnO cladding layers may be used. May be provided.
In the case where an insulating substrate is used as the substrate, an effect is obtained even if a group III nitride such as GaN or AlGaN having the same crystal structure as ZnO and a similar lattice constant is used for the buffer layer.
It is preferable that the buffer layer be grown at a lower temperature than the n-type MgZnO cladding layer 303 because crystallinity above the n-type MgZnO cladding layer 303 is improved.
[0062]
As a donor impurity to be doped into the n-type MgZnO cladding layer 303, a group III element such as B, Al, Ga, In, or the like is preferably used because the activation rate in the ZnO-based semiconductor is high, and Ga or Al is particularly preferable. preferable.
[0063]
The quantum well active layer 305 has a multiple quantum well structure formed by alternately stacking one or more ZnO-based semiconductor barrier layers and one or more ZnO-based semiconductor well layers.
The barrier layer has a function of confining carriers in the well layer, and is preferably made of ZnO, CdZnO or MgZnO having a larger band gap energy than the well layer. The well layer is preferably made of ZnO, CdZnO or MgZnO having a band gap energy corresponding to a desired oscillation wavelength.
Further, the entire quantum well active layer 305 can be doped with a donor impurity, for example, a group III element such as B, Al, Ga, and In. Alternatively, the quantum well active layer 305 may be made n-type by co-doping the donor impurity and an acceptor impurity, for example, a group I or V element such as Li, Na, Cu, Ag, N, P, or As. it can. Thereby, the peak wavelength and the emission intensity can be controlled.
Further, only the well layer or only the barrier layer of the quantum well active layer 305 can be doped with the donor impurity or the donor impurity and the acceptor impurity.
[0064]
The n-type light guide layer 304 and the p-type light guide layer 306 are preferably made of ZnO, but may be made of MgZnO or CdZnO as long as they have a refractive index that provides a light confinement effect. Further, the layer thickness and composition ratio of the n-type light guide layer 304 and the p-type light guide layer 306 may be different, or only one of them may be formed. Further, a stacked structure of two or more layers having different refractive indices may be used.
[0065]
As an acceptor impurity to be doped into the p-type MgZnO cladding layer 307 and the p-type ZnO contact layer 308, a group I or V element such as Li, Na, Cu, Ag, N, P, As or the like can be used. N, Li and Ag are preferred because they are easily activated. N is N₂Is particularly preferable because high-concentration doping can be performed while maintaining good crystallinity by a method of irradiating during plasma growth with plasma.
[0066]
The n-type current block layer 309 is made of MgZnO doped with a donor impurity, for example, a group III element such as B, Al, Ga, and In.
[0067]
The p-type ohmic electrode 310 needs to have a large work function. In particular, a transition metal having a work function of 4 eV or more has stable ohmic characteristics. Among them, particularly, oxides of Ni, Cu and Ag exhibit low-resistance p-type semiconductor properties and are preferable as a p-type oxide ohmic electrode.
The p-type ohmic electrode 310 can be formed directly on the p-type MgZnO cladding layer 307. However, since the MgZnO mixed crystal has a lower impurity activation rate than ZnO, a p-type ZnO contact layer 308 is formed. It is preferable to lower the resistance and to form it thereon, since the current spread can be made uniform.
In addition, since the semiconductor laser element 3 is an edge emitting type, the ohmic electrode 310 does not need to be translucent, and is preferably formed thick to sufficiently reduce ohmic resistance.
[0068]
It is preferable to perform an annealing treatment after the formation of the p-type ohmic electrode 310 because the adhesion is improved and the contact resistance is reduced. In order to obtain an annealing effect without causing defects in the ZnO crystal, the temperature is preferably 300 to 450 ° C. The atmosphere in the annealing process is O₂Or in an air atmosphere;₂Then, on the contrary, the resistance increases.
[0069]
Also, the narrower the ridge stripe width is, the higher the carrier injection efficiency is, and the kink level can be improved by cutting off the higher-order transverse mode. On the other hand, the operating voltage is increased and the reliability is deteriorated. It is preferable to control appropriately within a range of 5 μm or more and 5 μm or less.
[0070]
As a material for the pad electrode 311, a metal material which is easy to bond and does not become a donor impurity even when diffused into a ZnO-based semiconductor is preferable, and Au is particularly preferable.
[0071]
For the n-type ohmic electrode 312, a metal material such as Ti, Cr, or Al can be used. Above all, Al with low resistance and low cost or Ti with good adhesion is preferable. An electrode may be formed by alloying a plurality of the metal materials.
[0072]
Other configurations are arbitrary and are not limited to only the configurations described in this specification.
[0073]
The oxide semiconductor light emitting device of the present invention is manufactured by a crystal growth method such as a molecular beam epitaxy (MBE) method, a laser molecular beam epitaxy (laser MBE) method, and a metal organic chemical vapor deposition (MOCVD) method using a solid or gaseous raw material. Can be made.
In the laser MBE method, the composition deviation between the raw material target and the thin film is small, and for example, when ZnO is doped with Ga,₂O₄This is preferable because generation of unintended by-products such as the above can be suppressed.
When the present invention is applied to a semiconductor laser device, a semiconductor laser device can be manufactured using the laser MBE device 7 shown in FIG.
In the laser MBE apparatus 7, a substrate holder 702 is disposed above a growth chamber 701 capable of being evacuated to an ultra-high vacuum, and a substrate 703 is fixed to the substrate holder 702. The back surface of the substrate holder 702 is heated by the heater 704 disposed above the substrate holder 702, and the substrate 703 is heated by the heat conduction.
A target table 705 is arranged directly below the substrate holder 702 at an appropriate distance, and a plurality of raw material targets 706 can be arranged on the target table 705.
The surface of the target 706 is ablated by a pulsed laser beam 708 radiated through a view port 707 provided on a side surface of the growth chamber 701, and a thin film grows by instantaneously evaporating the raw material of the target 706 on the substrate.
The target table 705 has a rotation mechanism, and by controlling the rotation in synchronization with the irradiation sequence of the pulsed laser beam 708, different target materials can be stacked on the thin film. A plurality of gas introduction tubes 710 are provided in the growth chamber so that a plurality of gases can be introduced, and the substrate 703 can be irradiated with an atomic beam activated by the radical cell 709.
[0074]
When forming a metal oxide ohmic electrode of the oxide semiconductor light emitting device of the present invention, a high-purity and inexpensive element metal of 99.99 to 99.999% and a high-purity O₂The oxide layer can be grown in a laser MBE apparatus using a gas. Since the layers from the growth layer to the electrode can be formed consistently in a vacuum growth chamber, it is possible to easily form a low-resistance oxide ohmic electrode with high purity.
[0075]
In the case where a metal oxide ohmic electrode is formed in the oxide semiconductor light-emitting element of the present invention, an electron beam evaporation method which is a film formation technique which has high productivity and can easily form a high-quality oxide thin film is used. By using this method, a light-emitting element having excellent characteristics can be manufactured at low cost.
[0076]
Further, it is difficult to obtain a metal oxide target or tablet having a high purity of 99.999% or more. However, when a very high-purity raw material is not required, a metal oxide can be used for the raw material tablet. , O in the device₂An oxide ohmic electrode can be formed without introducing a gas, which is excellent in simplicity of a manufacturing process and is suitable when a vacuum film-forming apparatus or the like which does not like oxygen is used.
[0077]
Furthermore, the sputtering method and the laser ablation method are also high in mass productivity and can easily form a high-quality oxide thin film similarly to the electron beam evaporation method, and a light emitting element with excellent characteristics can be manufactured at low cost. .
[0078]
【Example】
Example 1
Example 1 This example describes an oxide semiconductor light emitting device of the first embodiment in which the present invention is applied to a light emitting diode device.
FIG. 1 shows a perspective view (A) and a sectional view (B) of the light emitting diode element 1. In this embodiment, 3 × 10 Ga is formed on an n-type ZnO substrate 101 having a (0001) zinc plane as a main surface.¹⁸cm^-3N-type Mg doped at a concentration of 1 μm_0.1Zn_0.9O-clad layer 102, non-doped Cd having a thickness of 0.1 μm_0.1Zn_0.9O light emitting layer 103, 1 × 10 N²⁰cm^-3P-type Mg doped at a concentration of 1 μm_0.1Zn_0.9O cladding layer 104 and N = 5 × 10²⁰cm^-3The p-type ZnO contact layer 105 having a thickness of 0.3 μm and doped with the above concentration was laminated to produce a light emitting diode element 1a.
On the entire main surface of the p-type ZnO contact layer 105, a 10 nm-thick NiO is laminated as a light-transmitting p-type ohmic electrode 106, and a bonding Au pad having a diameter of 100 μm and a thickness of 500 nm is formed thereon. The electrode 107 was formed.
Further, on the back surface of the ZnO substrate 101, Al having a thickness of 100 nm was laminated as an n-type ohmic electrode.
[0079]
The manufacturing method will be described below in order.
First, the cleaned ZnO substrate 101 is introduced into the laser MBE device 7, and₂The pressure in the growth chamber 701 was increased by 5 × 10^-3The pressure was adjusted to Pa, and the sample was heated at a temperature of 600 ° C. for 30 minutes for cleaning.
Next, the substrate temperature was lowered to 550 ° C., and the non-doped ZnO single crystal and Ga₂O₃Is used as a raw material target, and a driving cycle of a target table by a rotating mechanism and a pulse irradiation cycle of a KrF excimer laser are synchronized by an external control device (not shown), so that the raw material target has a desired Mg composition. N-type Mg is alternately ablated at a ratio to obtain Ga doping concentration._0.1Zn_0.9An O clad layer 102 was obtained. A KrF excimer laser (wavelength: 248 nm, pulse number: 10 Hz, output 1 mJ / cm) is used as a pulse laser for ablation.²) Was used. During growth, O gas is introduced through the gas introduction pipe 710a.₂Gas was introduced.
[0080]
Next, alternate ablation is performed using a non-doped ZnO single crystal and a non-doped CdO single crystal as raw material targets, and Cd_0.1Zn_0.9An O light emitting layer 103 was grown.
Next, N introduced through the gas introduction pipe 710b₂Alternating ablation is performed using a non-doped ZnO single crystal and a non-doped MgZnO sintered body as a raw material target while irradiating the gas with plasma generated in a radical cell 709 to obtain p-type Mg._0.1Zn_0.9An O-clad layer 104 was grown.
[0081]
Next, N introduced through the gas introduction pipe 710b₂Ablation was performed by using a non-doped ZnO single crystal as a raw material target while irradiating the gas with plasma in a radical cell 709 to grow a p-type ZnO contact layer 105.
[0082]
Next, O₂The pressure in the growth chamber 701 is adjusted to 1 × 10^-3The pressure was adjusted to Pa, ablation was performed using Ni as a raw material target, and a NiO ohmic electrode 106 was formed. At this time, the metal Ni evaporated by the ablation causes O in the growth chamber.₂The gas changes to NiO. The formed NiO has a thickness of 10 nm and transmits 705 of light emitted from the light-emitting layer.
[0083]
Next, O₂The introduction of gas was stopped and the pressure in the growth chamber 701 was reduced to 1 × 10^-4The pressure was adjusted to Pa, ablation was performed using Au as a raw material, and an Au pad electrode 107 was formed.
[0084]
Next, the ZnO substrate 101 was taken out of the laser MBE device 7, and the Au pad electrode 107 was processed to a diameter of 100 μm by etching.
Next, the ZnO substrate 101 is introduced into an annealing furnace (not shown),₂Annealing was performed at 350 ° C. for 1 minute at normal pressure while flowing gas.
Next, the ZnO substrate 101 was introduced into a vacuum evaporation apparatus (not shown), and electron beam evaporation was performed on the back surface of the ZnO substrate 101 using Al as a raw material to form an n-type ohmic electrode 108.
[0085]
The light emitting diode element 1a is separated into a chip shape of 300 μm square, an Ag paste is applied to the back surface of the substrate, the n-type ohmic electrode 108 is connected to one side of a lead frame (not shown), and the Au pad electrode 107 is connected to the other side of the lead frame. After molding with resin and emitting light, blue emission having an emission peak wavelength of 410 nm was obtained, and the operating voltage at an operating current of 20 mA was 3.6 V.
[0086]
When 100 chips of the light emitting diode element 1a were mounted on the lead frame, no electrode peeling occurred when the Au pad electrode 107 was wire-bonded to the lead frame.
[0087]
For comparison, O₂A light emitting diode element 1b was fabricated in the same manner as the light emitting diode element 1a, except that the NiO ohmic electrode 106 was changed to a Ni metal electrode by ablating Ni without flowing gas. When 100 chips were mounted on a lead frame, 25 electrodes peeled off during wire bonding, and the operating voltage of 20 chips was 5 V or more.
That is, since the adhesion between the metal electrode and the oxide semiconductor is weak, the production yield is low in the light-emitting diode element 1b, whereas the adhesion is small in the light-emitting diode element 1a because the ohmic electrode is made of metal oxide. It was confirmed that the reliability was dramatically improved.
[0088]
For comparison, a light-emitting diode element 1c was fabricated in the same manner as the light-emitting diode element 1a, except that the Au pad electrode 107 was not formed. When 100 chips were mounted on the lead frame, 60 wires could not be wire-bonded, and 20 wires were disconnected from the NiO ohmic electrode 106 during energization.
That is, it was confirmed that it is preferable to form a pad electrode and perform wire bonding in order to maximize the effects of the low ohmic resistance and the strong adhesion of the present invention.
[0089]
Further, for comparison, a light emitting diode element 1d was manufactured in the same manner as the light emitting diode element 1a, except that the annealing treatment was not performed after the formation of the p-type ohmic electrode 106. When 100 chips were mounted on a lead frame, 15 electrodes peeled off during wire bonding, and the operating voltage of 10 chips was 5 V or more.
That is, it was confirmed that the annealing treatment significantly improved the adhesion between the oxide semiconductor and the electrode and the ohmic characteristics.
[0090]
It has been confirmed that when the temperature of the annealing treatment is 300 ° C. or higher, the effect of improving the adhesion and the resistance reduction is high, and when the temperature is 450 ° C. or lower, it is confirmed that the oxide semiconductor element is hardly deteriorated. Therefore, it is preferable to perform the annealing at a temperature in the range of 300 to 450 ° C.
The atmosphere in the annealing process is O₂Or in an air atmosphere;₂On the contrary, it was confirmed that the resistance increased.
Further, when an easily oxidizable metal such as Al is used for the n-type ohmic electrode, annealing is performed in an air atmosphere, or after annealing the p-type ohmic electrode first as in this embodiment, n It was found that it was preferable to form a type ohmic electrode.
[0091]
Example 2
FIG. 6 shows the relationship between the thickness of the NiO ohmic electrode layer 106, the operating voltage of the light emitting diode element 1, and the light emission intensity.
Various light emitting diode elements were manufactured in the same manner as the light emitting diode element 1a except that the layer thickness of the NiO ohmic electrode 106 was changed.
As can be seen from FIG. 6, when the thickness of the NiO ohmic electrode layer 106 is 1 nm or more, the operating voltage sharply decreases, and when it exceeds 10 nm, the operating voltage becomes almost constant.
On the other hand, when the thickness exceeds 100 nm, the emission intensity sharply decreases. It is considered that when the electrode layer thickness was too high, the translucency was lowered.
From the above results, the thickness of the metal electrode layer is preferably 1 nm or more and 100 nm or less, more preferably 10 nm or more and 100 nm or less, in order to keep the operating voltage of the light emitting diode element low and achieve high light emission intensity.
[0092]
Example 3
Cu as the p-type ohmic electrode 106₂Cu by electron beam evaporation using an O tablet₂A light emitting diode element 1e was fabricated in the same manner as the light emitting diode element 1a except that O was formed.
The light emitting diode element 1e was mounted on a lead frame in the same manner as in Example 1 and emitted light. As a result, blue light emission having an emission peak wavelength of 410 nm was obtained. The operating voltage and the emission intensity at an operating current of 20 mA were almost the same as those of the light emitting diode element 1a.
When 100 chips were mounted on a lead frame, no electrode peeling occurred during wire bonding.
[0093]
Example 4
Example 2 This example describes an oxide semiconductor light emitting device of a second embodiment in which the present invention is applied to a light emitting diode device. The oxide semiconductor light emitting device of the second embodiment is a light emitting diode device in which an Ag intermediate layer 201 is formed between a NiO ohmic electrode 106 and an Au pad electrode 107.
[0094]
FIG. 3 shows a sectional view of the light emitting diode element 2. In this example, a light emitting diode element 2a was fabricated in the same manner as the light emitting diode element 1a, except that an Ag intermediate layer 201 having a thickness of 50 nm was formed between the NiO ohmic electrode 106 and the Au pad electrode 107. In this figure, the same components as those of the light emitting element 1a are denoted by the same reference numerals as those of FIG.
[0095]
The light-emitting diode element 2a was mounted on a lead frame in the same manner as in Example 1 and emitted light. As a result, blue light emission having an emission peak wavelength of 410 nm was obtained.
[0096]
When 100 chips of the light emitting diode element 2a were mounted on a lead frame, no electrode peeling occurred during wire bonding. The operating voltage was 3.3 V, which was lower than that of the light emitting diode element 1a.
That is, it was confirmed that the adhesion between the oxide ohmic electrode and the pad electrode can be improved by forming the intermediate layer 201 with a metal thin film such as Ag between the p-type ohmic electrode 106 and the pad electrode 107. Was.
Furthermore, the emission intensity increased by 10%. This is probably because light emitted immediately below the Au pad electrode was reflected by the Ag intermediate layer 201 having a high reflectance and extracted from the side surface of the chip.
[0097]
For comparison, a light emitting diode element 2b was fabricated in the same manner as the light emitting diode element 2a except that the intermediate layer 201 was formed using Ga, and mounted on a lead frame by the same method as described above. At this time, no electrode peeling occurred, but the operating voltage was 5 V or more.
That is, the adhesion between the oxide ohmic electrode and the pad electrode can be improved by forming the intermediate layer 201 with an element used as a donor impurity such as Ga between the p-type ohmic electrode 106 and the pad electrode 107. Was confirmed.
However, the operating voltage of the light emitting diode element 2b to which the Ga intermediate layer was applied increased compared to the light emitting diode element 2a to which the Ag intermediate layer was applied. This is presumably because Ga acts as a donor impurity in the ZnO semiconductor, and thus diffuses into the p-type ohmic electrode and the p-type ZnO layer, thereby inhibiting electrical conduction.
Therefore, the intermediate layer may be formed of a conductive oxide such as Ga. However, if the intermediate layer is formed of a metal thin film such as Ag, it is possible to reflect light emitted from the light-transmitting electrode without absorbing the light, It was confirmed that the electrode was preferable because the resistance was further reduced.
[0098]
From the above results, Ru, Os, Rh, Ir, Ni, Pd can be used as the intermediate layer material for improving the adhesion between the p-type ohmic electrode 106 and the pad electrode 107 and reducing the ohmic resistance. , Pt, Cu, and Ag are preferred.
As described above, it is preferable that the p-type ohmic electrode and the intermediate layer do not contain Al, Ga and In which are donor impurities, and further that they do not contain Ti and Cr which are n-type ohmic electrode materials.
[0099]
Example 5
This example describes a semiconductor light emitting device of a third embodiment in which the present invention is applied to a semiconductor laser device.
FIG. 4 shows a perspective view (A) and a sectional view (B) of the ZnO-based semiconductor laser device 3. In this embodiment, a Ga doping concentration of 1 × 10 3 was formed on an n-type ZnO single crystal substrate 301 having a zinc surface as a main surface.¹⁸cm^-3Buffer layer 302 having a thickness of 0.1 μm and a Ga doping concentration of 3 × 10¹⁸cm^-31.0μm thick n-type Mg_0.1Zn_0.9O cladding layer 303, Ga doping concentration is 5 × 10¹⁷cm^-330 nm thick n-type ZnO light guide layer 304, non-doped quantum well active layer 305, N doping concentration of 5 × 10¹⁸cm^-3And a p-type ZnO light guide layer 306 having a thickness of 30 nm and an N doping concentration of 1 × 10²⁰cm^-31.2μm thick p-type Mg_0.1Zn_0.9O cladding layer 307, N doping concentration is 1 × 10²⁰cm^-3Then, a 0.5 μm-thick p-type ZnO contact layer 308 was laminated to produce a semiconductor laser device 3a.
The quantum well active layer 305 includes two 5 nm thick ZnO barrier layers and 6 nm thick Cd_0.1Zn_0.9It is formed by alternately stacking three O well layers.
p-type ZnO contact layer 308 and p-type Mg_0.1Zn_0.9A part of the O-clad layer 307 is etched into a ridge stripe shape, and Ga is 1 × 10 on the side surface.¹⁸cm^-3-Type Mg doped at a concentration of_0.3Zn_0.7It is embedded by the O current block layer 309.
p-type ZnO contact layer 308 and n-type Mg_0.3Zn_0.7On the O current block layer 309, an Ag having a width wider than the ridge stripe and smaller than the element and having a thickness of 100 nm is formed.₂An O ohmic electrode 310 is formed, and an Au pad electrode 311 having a thickness of 500 nm is formed on the entire uppermost surface.
Since the semiconductor laser element 3a is of the edge emission type, Ag₂The O-ohmic electrode 310 does not need to be translucent, and is formed thick to sufficiently reduce ohmic resistance.
Below the n-type ZnO substrate 301, an n-type Al ohmic electrode 312 is formed.
[0100]
The manufacturing method will be described below in order.
The semiconductor laser element 3a performs crystal growth using the laser MBE device 7, and forms p-type Ag.₂The O ohmic electrode 310, the Au pad electrode 311 and the n-type Al ohmic electrode 312 are each made of Ag as a raw material target.₂It was formed by a sputtering method using O, Au and Al.
[0101]
After fabricating the semiconductor laser device 3a, the ZnO substrate 301 was cleaved to form an end face mirror, a protective film was vacuum-deposited, and the device was separated into chips of 300 μm square.
When a current was applied to the chip of the semiconductor laser element 3a, blue oscillation light having a wavelength of 405 nm was obtained from the end face, and the operating voltage and operating current were 3.5 V and 25 mA when the optical output was driven at 5 mW.
[0102]
For comparison, p-type Ag₂A semiconductor laser device 3b was manufactured in the same manner as the semiconductor laser device 3a, except that the O ohmic electrode 310 was formed of metal Ag. When the semiconductor laser device 3b was separated into chips and 100 chips were mounted, electrode peeling occurred when 30 devices were wire-bonded, and the operating voltage when 20 devices were driven at a light output of 5 mW was reduced. Exceeding 5 V, heat generation significantly reduced the element life.
[0103]
That is, it was confirmed that even when the oxide ohmic electrode was applied to the semiconductor laser device, it had a sufficient adhesion and a resistance reduction effect.
[0104]
【The invention's effect】
According to the present invention, a transition metal oxide ohmic electrode is formed on a p-type contact layer of an oxide semiconductor light emitting device by using at least one transition metal oxide selected from the group consisting of Ni, Cu, and Ag. Since it is formed, an ohmic electrode having excellent adhesion to the ZnO-based semiconductor layer, stable and low resistance can be formed, and an oxide semiconductor light-emitting element having high reliability and low operating voltage can be manufactured.
[Brief description of the drawings]
FIGS. 1A and 1B are a perspective view and a sectional view, respectively, showing an oxide semiconductor light emitting device (light emitting diode device) according to a first embodiment of the present invention.
FIG. 2 is a perspective view showing an oxide semiconductor light-emitting element (light-emitting diode) of the first embodiment using an insulating substrate.
FIG. 3 is a sectional view showing an oxide semiconductor light emitting device (light emitting diode device) according to a second embodiment of the present invention.
FIGS. 4A and 4B are a perspective view and a sectional view, respectively, showing an oxide semiconductor light emitting device (semiconductor laser device) according to a third embodiment of the present invention;
FIG. 5 is a schematic view of a laser molecular beam epitaxy apparatus.
FIG. 6 is a graph illustrating the relationship between the thickness of the NiO ohmic electrode layer, the operating voltage of the light emitting diode element, and the emission intensity.
[Explanation of symbols]
1 ... light emitting diode element
101 ... ZnO substrate,
102 ... n-type ZnO-based semiconductor layer,
103 ... light-emitting layer,
104 ... p-type ZnO-based semiconductor layer,
105 ... p-type ZnO-based semiconductor contact layer,
106 ... p-type ohmic electrode,
107 ... pad electrode,
108 ... n-type ohmic electrode,
109 ... n-type ZnO buffer layer,
110 ... n-type ZnO contact layer,
201 ... intermediate layer,
3 ... Semiconductor light emitting element,
301 ... ZnO substrate,
302... N-type ZnO buffer layer,
303 ... n-type ZnO-based semiconductor layer,
304 ... n-type ZnO light guide layer,
305 ・ ・ ・ Quantum well active layer,
306 ... p-type ZnO light guide layer,
307 ... p-type MgZnO cladding layer,
308 ... p-type ZnO contact layer,
309... N-type MgZnO current blocking layer,
310 ... p-type ohmic electrode,
311 ... pad electrode,
312 ... n-type ohmic electrode,
7 ... Laser MBE device,
701 ... growth room,
702: substrate holder,
703: substrate,
704: heater,
705: target table,
706: Raw material target,
707 ... viewport,
708: pulsed laser light (excimer laser),
709: radical cell,
710: gas introduction pipe.

Claims (10)

At least an n-type ZnO-based semiconductor clad layer, a ZnO-based semiconductor light-emitting layer, a p-type ZnO-based semiconductor clad layer, and a p-type ZnO-based semiconductor contact layer are formed on a substrate. , An oxide semiconductor light emitting device in which a p-type ohmic electrode containing at least one oxide of a transition metal selected from the group consisting of Cu and Ag is formed. 2. The oxide semiconductor light emitting device according to claim 1, wherein said p-type ohmic electrode has a thickness of 1 to 100 nm and has a light-transmitting property with respect to an emission wavelength from said light emitting layer. 2. The oxide semiconductor light emitting device according to claim 1, wherein a pad electrode containing Au is formed on said p-type ohmic electrode. An intermediate layer containing at least one element selected from the group consisting of Ru, Os, Rh, Ir, Ni, Pd, Pt, Cu and Ag was formed between the p-type ohmic electrode and the pad electrode. The oxide semiconductor light emitting device according to claim 3. 5. The oxide semiconductor light emitting device according to claim 1, wherein the constituent elements of the p-type ohmic electrode and the intermediate layer do not include Al, In, Ga, Ti, and Cr. Forming at least an n-type ZnO-based semiconductor clad layer, a ZnO-based semiconductor light-emitting layer, a p-type ZnO-based semiconductor clad layer, and a p-type ZnO-based semiconductor contact layer on the substrate; and then selecting from the group consisting of Ni, Cu and Ag A method for manufacturing an oxide semiconductor light emitting device, wherein a p-type ohmic electrode made of a transition metal oxide is formed on the p-type ZnO-based semiconductor contact layer using the obtained at least one transition metal oxide. Forming at least an n-type ZnO-based semiconductor clad layer, a ZnO-based semiconductor light-emitting layer, a p-type ZnO-based semiconductor clad layer, and a p-type ZnO-based semiconductor contact layer on the substrate; and then selecting from the group consisting of Ni, Cu and Ag A method for manufacturing an oxide semiconductor light emitting device, wherein a p-type ohmic electrode made of a transition metal oxide is formed on the p-type ZnO-based semiconductor contact layer in the presence of oxygen by using at least one transition metal thus obtained. 8. The method for manufacturing an oxide semiconductor light emitting device according to claim 6, wherein the transition metal oxide p-type ohmic electrode is formed by using an electron beam evaporation method, a sputtering method, or a laser ablation method. 8. The method for manufacturing an oxide semiconductor light emitting device according to claim 6, wherein a heat treatment is performed in an oxygen atmosphere or in the air after forming the transition metal oxide p-type ohmic electrode. The method according to claim 9, wherein the heat treatment is performed at a temperature in a range of 300 to 450 ° C. 10.

Images