JP2004228318A - Oxide semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide semiconductor light emitting element exhibiting excellent emission characteristics and reliability and applicable to a light emitting diode or a semiconductor laser element. <P>SOLUTION: The lattice constant of a substrate is controlled by changing the composition of group I elements or group III elements using an oxide substrate having a composition represented by Li<SB>1-(x+y)</SB>Na<SB>x</SB>K<SB>y</SB>Al<SB>1-z</SB>Ga<SB>z</SB>O<SB>2</SB>(0≤x, y, z≤1, 0≤x+y≤1). Consequently, crystal defects and strain in the epitaxial layer of an oxide semiconductor light emitting element are reduced. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor light emitting device such as a light emitting diode and a semiconductor laser, and more particularly, to an oxide semiconductor light emitting device which reduces distortion in a semiconductor crystal and has excellent light emitting characteristics and reliability.
[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]
ZnO has the same wurtzite crystal structure as a group III nitride semiconductor such as GaN that has already been put to practical use as a light emitting device in the blue to ultraviolet region, and has a thermal expansion coefficient and a lattice constant that are extremely close to GaN. Studies have been made on stacking an epitaxial thin film on a substrate such as sapphire or Si used in a group III nitride semiconductor device to produce a light emitting device.
[0005]
For example, Japanese Patent Application Laid-Open No. 2001-44499 (Patent Document 1) discloses a technique in which a silicon nitride film is formed on a Si substrate, and a ZnO-based semiconductor thin film is grown thereon. In addition, Japanese Patent Application Laid-Open No. 2001-44500 (Patent Document 2) discloses a technique in which an A-plane (11-20) of a sapphire substrate is used as a main surface, and a ZnO-based semiconductor thin film is crystal-grown thereon. .
[0006]
[Patent Document 1]
JP 2001-44499 A
[0007]
[Patent Document 2]
JP 2001-44500 A
[0008]
[Problems to be solved by the invention]
Although Si and sapphire are low in cost and can obtain very high quality substrate crystals, the difference in lattice constant from the ZnO-based semiconductor is as large as more than 10%, and even if a buffer layer is formed, good crystallinity can be obtained. It is difficult to obtain a ZnO-based semiconductor epitaxial layer having the following. In particular, on a Si substrate, Si reacts with oxygen to easily form a SiOx layer. For this reason, many crystal defects are generated in the epitaxial crystal, and a large lattice strain is inherent therein, so that there is a problem that luminous efficiency and reliability are not sufficient.
Thus, an object of the present invention is to provide an oxide semiconductor light emitting device having reduced reliability of an epitaxial layer and high reliability and luminous efficiency in view of the above problems.
[0009]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on a substrate material capable of epitaxially growing a ZnO-based semiconductor layer having excellent crystallinity. As a result, an oxide having an excellent affinity for a ZnO-based semiconductor and capable of controlling a lattice constant by composition has The present inventors have found that the object can be attained by using as a substrate, and have reached the present invention.
[0010]
In a first aspect, the present invention provides at least an n-type ZnO-based semiconductor cladding layer, a ZnO-based semiconductor active layer, and a p-type ZnO-based semiconductor cladding layer formed on an oxide substrate, wherein the oxide The substrate is Li_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂Provided is an oxide semiconductor light emitting device having a composition represented by (0 ≦ x, y, z ≦ 1, 0 ≦ x + y ≦ 1).
Li of the present invention_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂The substrate has a crystal structure similar to that of the ZnO-based semiconductor, and can epitaxially grow the ZnO-based semiconductor. Further, by controlling the composition, the lattice constant can be controlled in a range very close to that of the ZnO-based semiconductor.
Therefore, by using the oxide substrate of the present invention, a ZnO-based semiconductor epitaxial layer having almost no distortion can be obtained, and a highly reliable oxide semiconductor light-emitting element can be manufactured.
[0011]
In particular, the oxide substrate is Li_1-aNa_aAlO₂, Li_1-bNa_bGaO₂, LiAl_1-cGa_cO₂, And NaAl_1-dGa_dO₂(0 ≦ a, b, c, d ≦ 1)
Said oxide is the Li of the present invention._{1- (x + y)}Na_xK_yAl_1-zGa_zO₂Among them, the lattice constant difference from the ZnO-based semiconductor is particularly small, and the composition can be easily controlled. By using this as a substrate, an oxide semiconductor light-emitting element with particularly excellent reliability can be manufactured.
[0012]
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.
[0013]
In a second aspect, the present invention provides an oxide semiconductor light-emitting device having excellent reliability and light-emitting characteristics by controlling a main growth surface of an oxide substrate.
As one specific example of the oxide semiconductor light emitting device of the present invention, the main growth surface of the oxide substrate is a (001) metal surface, and the main growth surface of the ZnO-based semiconductor epitaxially grown on the oxide substrate is It is a (0001) zinc surface.
When the main growth surface of the oxide substrate is a (001) metal surface, the growth plane orientation of the ZnO-based semiconductor can be a (0001) zinc surface. A ZnO-based semiconductor whose main growth surface is a (0001) zinc surface is excellent in doping characteristics of a special acceptor impurity and has a reduced operating voltage. Thus, an oxide semiconductor light-emitting element having excellent power saving properties and reliability can be manufactured.
[0014]
As another specific example of the oxide semiconductor light-emitting device of the present invention, the crystal growth main surface of the oxide substrate is a surface inclined at an off angle of 15 ° or less from the (001) plane. It is characterized by.
Generally, when forming a semiconductor light emitting device, a “just substrate” having a crystal growth main surface of a low index surface such as a (001) plane is used, but the surface orientation of the substrate is inclined from the low index surface. The “off-substrate” has steps and terraces formed on the main growth surface, so that “step flow growth” in which material atoms are taken into the steps and two-dimensionally grow, is likely to occur, and a ZnO-based semiconductor layer excellent in flatness is obtained. Can be
According to the present invention, since the “off substrate” having the crystal growth main surface is a surface inclined at a predetermined off angle from the (001) plane of the substrate, the oxide semiconductor light emitting with excellent luminous efficiency and reliability is used. An element can be manufactured.
[0015]
Furthermore, in a third aspect, the present invention provides a method for manufacturing a semiconductor device, comprising the steps of:_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂Provided is an oxide semiconductor light-emitting element in which a buffer layer including (0 <x, y, z <1, 0 <x + y <1) is formed.
Even when the oxide substrate has a lattice mismatch with a ZnO-based semiconductor layer grown thereon, a buffer layer made of the same material as that of the present invention is formed, and the composition of the buffer layer is controlled to reduce lattice distortion. Can be eased. Therefore, a ZnO-based semiconductor epitaxial layer having high crystallinity can be obtained, and an oxide semiconductor light-emitting element having excellent reliability can be manufactured.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which the oxide semiconductor light emitting device of the present invention is applied to a light emitting diode device and a semiconductor laser device will be specifically described with reference to the drawings.
First embodiment
The oxide semiconductor light emitting device according to the first embodiment of the present invention has at least an n-type ZnO-based semiconductor clad layer, a ZnO-based semiconductor light-emitting layer, and a p-type ZnO-based semiconductor clad layer formed on an oxide substrate, Here, the oxide substrate is Li_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂It is a light emitting diode element having a composition represented by (0 ≦ x, y, z ≦ 1, 0 ≦ x + y ≦ 1).
According to the present invention, as the substrate, Li having excellent affinity with the ZnO-based semiconductor layer is used._{1- (x + y)}Na_xK_yAl_1-zGa_zO₂Since an oxide is used, an epitaxial layer having good crystallinity can be obtained, and a lattice constant can be controlled by changing its composition.
Thus, a light-emitting diode element having excellent light-emitting characteristics and reliability can be obtained.
[0017]
FIG. 1 shows a perspective view (A) and a sectional view (B) of the light emitting diode element 1. The light emitting diode element 1 is made of LiGaO having a (001) metal surface as a main surface.₂An n-type ZnO contact layer 102, an n-type MgZnO cladding layer 103, a quantum well light emitting layer 104, a p-type MgZnO cladding layer 105, and a p-type ZnO contact layer 106 are stacked on a single crystal substrate 101. .
[0018]
The quantum well light emitting layer 104 has a multi-well structure in which one or a plurality of ZnO barrier layers and one or a plurality of CdZnO well layers are alternately stacked.
On the entire main surface of the p-type ZnO contact layer 106, a p-type ohmic electrode 107 that is transparent to light emitted from the light-emitting layer is laminated. Further, a bonding pad electrode 108 is formed on the translucent ohmic electrode 107 with an area smaller than that of the translucent p-type ohmic electrode 107.
Further, the epitaxial layer from the n-type MgZnO cladding layer 103 to the p-type ZnO contact layer 106 is partially etched, and an n-type ohmic electrode 109 is laminated on the exposed surface of the n-type ZnO contact layer 102.
[0019]
Hereinafter, other configurations for maximizing the effects of the present invention will be described, but they may be used in any combination in other embodiments.
[0020]
Insulator oxide LiGaO used as a substrate in the present invention₂2 is shown in FIG. 2 in comparison with ZnO.
XYO₂The orthorhombic oxide having the following structure has a crystal structure similar to the wurtzite structure of a ZnO-based semiconductor. In particular, the in-plane lattice constant of the orthorhombic oxide in which the element X contains any of Li, Na, or K and the element Y contains any of Al or Ga is the lattice constant of ZnO (3.25 °). , It is possible to obtain a ZnO-based semiconductor epitaxial layer having extremely small lattice distortion.
[0021]
In the case of manufacturing a light-emitting diode element, 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 incident light, since light extraction efficiency is improved, which is preferable.
[0022]
As a donor impurity to be doped into the n-type ZnO buffer layer 102 and the n-type MgZnO cladding layer 103, a group III element such as B, Al, Ga, or In may be used because the activation rate in the ZnO-based semiconductor is high. Preferably, Ga or Al is particularly preferred.
[0023]
Although the light emitting layer may have a single layer structure, it is preferable that the light emitting layer has a quantum well structure because the optical gain is improved in a semiconductor laser device and the light emitting efficiency is also improved in a light emitting diode device.
[0024]
As an acceptor impurity to be doped into the p-type MgZnO layer 105 and the p-type ZnO contact layer 106, 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.
[0025]
In order to improve the efficiency of the light emitting diode element, the MgZnO mixed crystal has a lower impurity activation rate than ZnO, so that the p-type ohmic electrode 107 is not directly formed on the p-type MgZnO cladding layer 105, and the p-type It is preferable to provide a contact layer 106 to reduce the resistance.
As the contact layer material, it is preferable to use ZnO which has excellent crystallinity and can increase the carrier concentration. If the p-type ZnO contact layer 106 is excessively doped with an acceptor impurity, the crystallinity deteriorates remarkably, and the effect of the present invention is reduced.¹⁶~ 5 × 10¹⁹cm^-3It is preferable to dope so that the carrier concentration is within the above range.
[0026]
ZnO is suitable for the n-type contact layer 102 as in the case of the p-type contact layer 106, and the doping concentration of the donor impurity is 1 × 10¹⁸~ 1 × 10²¹cm^-3Is more preferable, and 5 × 10¹⁹~ 5 × 10²⁰cm^-3Is preferably adjusted within the range described above. Further, the film thickness is preferably adjusted to a range of 0.001 to 1 μm, preferably 0.005 to 0.5 μm, and more preferably 0.01 to 0.1 μm.
[0027]
For the p-type ohmic electrode 107, a metal material such as Ni, Pt, Pd, and Au can be used. The metal material forms a low-resistance ohmic contact with the p-type ZnO-based semiconductor layer and has excellent adhesion to the ZnO-based semiconductor. Therefore, a light-emitting element with excellent reliability and low operating voltage can be realized. Among them, Ni having low resistance and good adhesion is preferable. An electrode may be formed by alloying a plurality of the metal materials.
[0028]
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 107 is formed so as to transmit light emitted from the light-emitting layer. It is preferable to improve the extraction efficiency.
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 5 to 200 nm, more preferably in the range of 30 to 100 nm.
It is preferable to perform an annealing treatment after the formation of the p-type ohmic electrode 107, 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 400 ° C. The atmosphere in the annealing process is O₂Or in an air atmosphere;₂Then, on the contrary, the resistance increases.
[0029]
In order to easily perform wiring to a lead frame, it is effective to provide a pad electrode 108 for wire bonding on the p-type ohmic electrode 107. If the pad electrode 108 is formed on a part of the translucent p-type ohmic electrode 107 with a smaller area than the p-type ohmic electrode 107, 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 108, a metal material that 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.
Further, another metal layer may be formed between the p-type ohmic electrode 107 and the pad electrode 108 for the purpose of improving adhesion and light reflectivity.
[0030]
For the n-type ohmic electrode 109, 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.
[0031]
Other configurations are arbitrary and are not limited to only the configurations described in this specification.
[0032]
The oxide semiconductor light emitting device of the present invention can be 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.
[0033]
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.
[0034]
Second embodiment
The oxide semiconductor light emitting device of the second embodiment according to the present invention is configured similarly to the oxide semiconductor light emitting device of the first embodiment,₂Li between the substrate 101 and the n-type ZnO contact layer 102_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂This is a light emitting diode element (not shown) in which a buffer layer 201 including (0 <x, y, z <1, 0 <x + y <1) is formed.
According to the present invention, first, Li_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂Since the buffer layer 201 is formed, by controlling the composition of the group I element and the group III element, the LiGaO₂The lattice mismatch between the substrate 101 and the n-type ZnO contact layer 102 can be reduced, and the characteristics as a light emitting diode element can be further improved.
[0035]
Third embodiment
In the oxide semiconductor light emitting device of the third embodiment according to the present invention, at least an n-type ZnO-based semiconductor clad layer, a ZnO-based semiconductor active layer, and a p-type ZnO-based semiconductor clad layer are formed on an oxide substrate, The p-type ZnO-based semiconductor cladding layer is processed into a ridge stripe shape._{1- (x + y)}Na_xK_yAl_1-zGa_zO₂A semiconductor laser device having a composition represented by (0 ≦ x, y, z ≦ 1, 0 ≦ x + y ≦ 1).
According to the present invention, as the substrate, Li having excellent affinity with the ZnO-based semiconductor layer is used._{1- (x + y)}Na_xK_yAl_1-zGa_zO₂Since an oxide is used, an epitaxial layer having good crystallinity can be obtained, and a lattice constant can be controlled by changing its composition.
Thus, a semiconductor laser device excellent in reliability and luminous efficiency can be obtained.
[0036]
FIG. 3 shows a perspective view (A) and a sectional view (B) of the ZnO-based semiconductor laser device 3. The semiconductor laser device 3 is made of NaAlO having a (001) metal surface as a main surface.₂On a substrate 301, Li_1-aNa_aAlO₂Buffer layer 302, n-type ZnO contact layer 303, n-type MgZnO cladding layer 304, n-type ZnO light guiding layer 305, non-doped quantum well active layer 306, p-type ZnO light guiding layer 307, p-type MgZnO cladding layer 308, and p It is configured by laminating type ZnO contact layers 309.
The quantum well active layer 306 has a multiple quantum well structure formed by alternately stacking one or more ZnO barrier layers and one or more CdZnO well layers.
[0037]
Further, the p-type ZnO contact layer 309 and the p-type MgZnO cladding layer 308 are etched into a ridge stripe shape, and the side surfaces of the ridge stripe are buried by the n-type MgZnO current block layer 310.
A p-type ohmic electrode 312 is formed on the n-type MgZnO current block layer 310 and the p-type ZnO contact layer 309.
A part of the laminated structure from the n-type MgZnO cladding layer 304 to the n-type MgZnO current block layer 310 is partially etched, and an n-type ohmic electrode 311 is formed on the exposed n-type ZnO contact layer 303.
[0038]
Li_1-aNa_aAlO₂Buffer layer 302 is made of NaAlO₂In order to make lattice matching at the interface between the substrate 301 and the n-type ZnO contact layer 303, Li_1-aNa_aAlO₂By gradually changing the Na composition in the buffer layer in the growth direction of the epitaxial layer, crystal defects in the growth layer can be reduced and lattice distortion can be reduced.
[0039]
In order to improve the efficiency of the semiconductor laser device, the MgZnO mixed crystal has a lower impurity activation rate than ZnO, so that the p-type ohmic electrode 312 is not directly formed on the p-type MgZnO cladding layer 308, and the p-type It is preferable to provide a contact layer 309 to reduce resistance.
As the contact layer material, it is preferable to use ZnO which has excellent crystallinity and can increase the carrier concentration. If the p-type ZnO contact layer 309 is excessively doped with an acceptor impurity, crystallinity deterioration becomes remarkable, and the effect of the present invention is reduced.¹⁶~ 5 × 10¹⁹cm^-3It is preferable to dope so that the carrier concentration is within the above range.
[0040]
ZnO is suitable for the n-type contact layer 303 as in the case of the p-type contact layer 309, and the doping concentration of the donor impurity is 1 × 10¹⁸~ 1 × 10²¹cm^-3Is more preferable, and 5 × 10¹⁹~ 5 × 10²⁰cm^-3Is preferably adjusted within the range described above. Further, the film thickness is preferably adjusted to a range of 0.001 to 1 μm, preferably 0.005 to 0.5 μm, and more preferably 0.01 to 0.1 μm.
[0041]
【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 sectional view of the light emitting diode element 1. In this embodiment, LiGaO having a (001) metal surface as a main surface is used.₂On the single crystal substrate 101, 3 × 10 Ga¹⁸cm^-30.1 μm thick n-type ZnO contact layer 102 doped with¹⁸cm^-3N-type Mg doped at a concentration of 1 μm_0.1Zn_0.9O cladding layer 103, non-doped quantum well light emitting layer 104, N is 5 × 10¹⁹cm^-3P-type Mg doped at a concentration of 1 μm_0.1Zn_0.9O cladding layer 105 and N are 1 × 10²⁰cm^-3The p-type ZnO contact layer 106 having a thickness of 0.3 μm and doped with the above concentration was stacked to fabricate a light emitting diode element 1a.
[0042]
The quantum well light emitting layer 104 is composed of 11 ZnO barrier layers having a thickness of 5 nm and Cd having a thickness of 4 nm._0.2Zn_0.8It has a multi-well structure in which 10 O-well layers are alternately stacked.
n-type Mg_0.1Zn_0.9A part of the epitaxial layer from the O-cladding layer 103 to the p-type ZnO contact layer 106 is partially etched, and 100 nm thick Al is laminated as an n-type ohmic electrode 109 on the exposed surface of the n-type ZnO contact layer 102. .
On the entire main surface of the p-type ZnO contact layer 106, Ni having a thickness of 15 nm is laminated as a light-transmitting p-type ohmic electrode 107, and an area smaller than that of the light-transmitting p-type ohmic electrode 107 is formed thereon. An Au pad electrode 108 for bonding having a thickness of 100 nm is formed.
[0043]
The manufacturing method will be described below in order.
First, the washed LiGaO₂The substrate 101 was introduced into the laser MBE device 7 and heated at a temperature of 600 ° C. for 30 minutes to be cleaned.
Next, the substrate temperature was lowered to 500 ° C., and the non-doped ZnO single crystal and Ga₂O₃Is used as a raw material target, and the driving cycle of the target table by the rotation mechanism and the pulse irradiation cycle of the KrF excimer laser are synchronized by an external control device (not shown) at a ratio at which a desired Ga doping concentration can be obtained. The n-type ZnO contact layer 102 was grown by alternately ablating the two material targets.
A KrF excimer laser (wavelength: 248 nm, pulse number: 10 Hz, output 1 J / 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.
Next, a non-doped ZnO single crystal and Ga₂O₃The MgZnO sintered body to which n is added is used as a raw material target, and ablation is alternately performed at a ratio to obtain a desired Mg composition and a Ga doping concentration to obtain n-type Mg._0.1Zn_0.9An O-cladding layer 103 was grown.
Next, using a non-doped ZnO single crystal and a CdZnO sintered body as raw material targets, the ZnO barrier layer and the Cd_0.2Zn_0.8A quantum well active layer 104 composed of an O well layer was grown.
[0044]
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-cladding layer 105 was grown.
Next, N introduced through the gas introduction pipe 710b₂Ablation was performed using a non-doped ZnO single crystal as a raw material target while irradiating the gas with plasma generated in a radical cell 709 to grow a p-type ZnO contact layer 106.
[0045]
Next, the substrate 101 is taken out of the laser MBE device 7, a resist mask covering a part of the growth layer is formed, and the n-type MgO is removed from the p-type ZnO contact layer 106 using a 1% by weight nitric acid aqueous solution._0.1Zn_0.9The growth layer reaching the O-clad layer 103 was partially removed by etching.
Next, Al was vacuum-deposited as an n-type ohmic electrode 109 on the exposed n-type ZnO contact layer 102.
Next, a Ni thin film was vacuum-deposited as a p-type ohmic electrode 107 on the entire upper surface of the p-type ZnO contact layer 106. This Ni thin film has high translucency and transmits 80% at a blue emission wavelength.
Finally, Au having a thickness of 100 nm was vacuum-deposited on the p-type ohmic electrode 107 as a pad electrode.
[0046]
In this example, the Mg composition and the Ga doping concentration were controlled by alternately ablating two material targets of a ZnO single crystal and a Ga-doped MgZnO sintered body. The controllability of the doping concentration can be improved by using a method such as punching out three raw material targets of a Ga-doped ZnO sintered body.
Instead of using a MgZnO sintered body, a ZnO single crystal and a MgO single crystal may be alternately ablated to obtain a MgZnO mixed crystal having a desired composition.
Further, Ga₂O₃Instead of using the additive sintered body, metal Ga may be doped using an evaporation cell.
[0047]
The light-emitting diode element 1a was separated into chips, mounted on a lead frame, and resin-molded to emit light. As a result, blue light having an emission peak wavelength of 430 nm was obtained.
[0048]
For comparison, a light-emitting diode element 1b was fabricated in the same manner as the light-emitting diode element 1a, except that sapphire was used for the substrate 101.
In the same manner as described above, the light emitting diode element 1b was separated into chips, mounted on a lead frame, and resin-molded to emit light. As a result, blue light emission having an emission peak wavelength of 450 nm was obtained. It is considered that the reason why the emission wavelength was increased was that lattice stress was generated in the ZnO-based semiconductor epitaxial layer by stress from the substrate.
Also, as compared with the light emitting diode element 1a, the light emission intensity at an operation current of 20 mA is reduced to ／, and the element life (operating at an operation current of 20 mA, the light emission intensity is reduced to 50% of the initial value from the start of operation). Defined as the time to decrease.) Was 1/5.
It is considered that the large deterioration of the light emission intensity is caused by a decrease in the light emission efficiency due to the deterioration of the crystallinity.
[0049]
Further, a light emitting diode element 1c was fabricated in the same manner as the light emitting diode element 1a except that Si was used for the substrate 101.
In the same manner as described above, the light emitting diode element 1c was separated into chips, mounted on a lead frame, and resin-molded to emit light. As a result, blue light with a peak emission wavelength of 450 nm was obtained. It is considered that the reason why the emission wavelength was increased was that lattice stress was generated in the ZnO-based semiconductor epitaxial layer by stress from the substrate.
Also, as compared with the light emitting diode element 1a, the light emission intensity at an operation current of 20 mA is reduced to 1/10, and the element life (operated at an operation current of 20 mA, the light emission intensity is reduced to 50% of the initial value from the start of operation) (Defined by the time to decrease)) was 1/10.
It is considered that the significant deterioration of the light emission intensity is caused by the absorption loss in the Si substrate in addition to the decrease in the light emission efficiency due to the deterioration of the crystallinity.
[0050]
As shown above, Li_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂When a substrate is used, a ZnO-based semiconductor light-emitting element having high luminous efficiency and excellent reliability can be manufactured.
[0051]
Example 2
Next, in order to examine the influence of the growth main surface of the substrate on the characteristics of the light emitting diode, LiGaO₂A light emitting diode element 1d was fabricated in the same manner as the light emitting diode element 1a, except that the growth main surface of the single crystal substrate 101 was changed to the (00-1) oxygen plane.
As in the case of the first embodiment, the light emitting diode element 1d was separated into chips, mounted on a lead frame, and resin-molded to emit light. The operating voltage at an operating current of 20 mA was 0.5 V compared to the light emitting diode 1a. Increased.
When the cause was investigated, the growth main surface of the ZnO-based semiconductor layer was an oxygen surface (000-1), and p-type Mg_0.1Zn_0.9It was found that the resistivity of the O clad layer 105 and the p-type ZnO contact layer 106 was increased.
[0052]
Therefore, the Li of the present invention_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂When a (001) metal plane is selected as the main growth plane of the substrate, the ZnO-based semiconductor layer epitaxially grown thereon becomes a (0001) zinc plane. If the zinc plane is the main growth plane, the carrier activation rate of the p-type layer is increased. Is improved, and a p-type ZnO-based semiconductor layer having low resistance is easily obtained, which is preferable.
[0053]
Example 3
In order to investigate the influence of the orientation of the crystal growth main surface of the substrate on the characteristics of the light emitting diode element, LiGaO having a crystal plane direction inclined from the (001) plane to the [100] direction was used as the substrate main growth surface.₂Various light-emitting diode elements were manufactured in the same manner as the light-emitting diode element 1a except that a single-crystal off-substrate was used.
FIG. 5 shows the relationship between the off angle of the substrate and the light emission intensity.
[0054]
When the off angle is 15 ° or less, the luminous intensity increases as compared with the “just substrate” having no inclination, but when the off angle exceeds 15 °, the luminous intensity sharply decreases. That is, it is preferable to use an “off substrate” whose main growth surface is inclined at an off angle of 15 ° or less from (001).
Although FIG. 5 shows the case where the substrate has a tilt in the [100] direction, similar results were obtained using an off-substrate tilted in the [010] direction.
[0055]
The reason why the emission intensity is increased when the “off substrate” is used is that “step flow growth” in which material atoms are incorporated into the steps and two-dimensional growth occurs, and the crystallinity and flatness of the ZnO-based semiconductor layer are improved. In particular, if the off-substrate has an off-angle of up to 15 °, the growth layer has excellent flatness because it has an appropriate step height and a wide terrace.
Further, in this embodiment, the results are shown only for the off-substrate inclined in the [100] direction and the [010] direction. The off-substrate used in the present invention is not limited in inclination direction because it has an atomic plane step.
[0056]
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.
In this example, LiGaO₂Between the substrate 101 and the n-type ZnO contact layer 102, a 30 nm-thick Li_0.75Na_0.25GaO₂A light emitting diode element 2a was fabricated in the same manner as the light emitting diode element 1a except that the buffer layer 201 was formed (not shown).
[0057]
As in Example 1, the light emitting diode element 2a was separated into chips, mounted on a lead frame, resin-molded, and emitted light. As a result, blue light emission having an emission peak wavelength of 430 nm was obtained. Also, as compared with the light emitting diode element 1a, the light emission intensity at an operating current of 20 mA was increased by 30%, and the element life was doubled.
[0058]
The reason why the characteristics of the light emitting diode element 2a are improved as compared with the light emitting diode element 1a is that the Li layer formed as the buffer layer 201_0.75Na_0.25GaO₂The layer is LiGaO₂This is probably because the lattice mismatch between the substrate 101 and the n-type ZnO contact layer 102 was reduced.
[0059]
In this example, LiGaO₂Li of a single composition on substrate 101_0.75Na_0.25GaO₂Although the buffer layer is formed, when the composition is changed so that the lattice mismatch is reduced on the substrate side and on the ZnO-based semiconductor side, crystal defects and lattice distortion are further relaxed, and the oxide semiconductor light emitting element has extremely excellent characteristics. Is preferable since it can be produced.
[0060]
Reference Example 1
Li of the present invention_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂The substrate can be lattice-matched to the ZnO-based semiconductor by controlling the lattice constant by appropriately selecting the composition of the constituent elements. In particular, Li_1-bNa_bGaO₂Besides Li_1-aNa_aAlO₂, LiAl_1-cGa_cO₂, NaAl_1-dGa_dO₂For example, an oxide in which either the group IA or the group IIIA is composed of two elements is preferable because the composition can be easily controlled.
[0061]
FIG. 6 shows the result of obtaining the effective lattice constant represented by the average oxygen-oxygen distance for the four oxides in this reference example. Here, the "effective lattice constant" is defined as a regular hexagon having the same area as a hexagon composed of six oxygen atoms in the same plane, and defined as an oxygen-oxygen atom distance forming one side of the regular hexagon. .
[0062]
From this, with respect to ZnO, -4% (LiAlO₂Is used; effective lattice constant = 3.12 °) to + 6% (NaGaO₂Is used; an effective lattice constant of 3.44 °) can be controlled._1-aNa_aAlO₂In the case where the Na composition x is 0.4 to 0.6;_1-bNa_bGaO₂In the case where the Na composition x is 0.15 to 0.35, the difference in lattice constant with ZnO is extremely small as ± 0.75%, and it is preferable._0.5Na_0.5AlO₂Or Li_0.75Na_0.25GaO₂In this case, the effective lattice constant is 3.25 °, which indicates that a ZnO-based semiconductor layer that is almost perfectly lattice-matched with ZnO and has no distortion and excellent crystallinity can be epitaxially grown.
[0063]
Example 5
Example 3 This example describes an oxide semiconductor light emitting device of a third embodiment in which the present invention is applied to a semiconductor laser device.
FIG. 3 shows a perspective view (A) and a sectional view (B) of the ZnO-based semiconductor laser device 3. In this embodiment, NaAlO having a (001) metal surface as a main surface is used.₂On a substrate 301, a 30 nm-thick Li_1-aNa_aAlO₂Buffer layer 302, Ga is 1 × 10¹⁹cm^-30.3 μm thick n-type ZnO contact layer 303 doped with a concentration of¹⁸cm^-3N-type Mg doped at a concentration of 1 μm_0.1Zn_0.9O cladding layer 304, Ga is 5 × 10¹⁷cm^-330 nm thick n-type ZnO light guide layer 305, undoped quantum well active layer 306, and N¹⁸cm^-330 nm thick p-type ZnO light guide layer 307 doped with a concentration of¹⁹cm^-31.2 μm thick p-type Mg doped at a concentration of_0.1Zn_0.9O cladding layer 308 and N²⁰cm^-3A 0.5 μm-thick p-type ZnO contact layer 309 doped with the above-described concentration was stacked to fabricate a semiconductor laser device 3a.
[0064]
The quantum well active layer 306 includes two ZnO barrier layers each having a thickness of 5 nm and Cd having a thickness of 6 nm._0.1Zn_0.9It is formed by alternately stacking three O well layers.
p-type ZnO contact layer 309 and p-type Mg_0.1Zn_0.9The O-clad layer 308 is etched into a ridge stripe shape, and Ga is 3 × 10 on the side surfaces of the ridge stripe.¹⁸cm^-3-Type Mg doped at a concentration of_0.2Zn_0.8It is buried by the O current block layer 310.
n-type Mg_0.1Zn_0.9From the O cladding layer 304 to n-type Mg_0.2Zn_0.8The laminated structure reaching the O current block layer 310 is partially etched, and an n-type ohmic electrode 311 is formed on the exposed n-type ZnO contact layer 303.
n-type Mg_0.2Zn_0.8A p-type ohmic electrode 312 is formed on the O current block layer 310 and the p-type ZnO contact layer 309.
[0065]
Li_1-aNa_aAlO₂The buffer layer 302 is formed of NaAlO from the substrate 301 side toward the ZnO contact layer 303 side.₂(Na composition a = 1) to Li_0.5Na_0.5AlO₂(Na composition a = 0.5).₂Lattice matching is performed at the interface between the substrate 301 and the n-type ZnO contact layer 303.
[0066]
After the fabrication of the semiconductor laser device 3a, a protective film was vacuum-deposited on the mirror end surface perpendicular to the ridge stripe, and then the device was separated into 300 μm square chips.
When a current was applied to the semiconductor laser device 3a, blue oscillation light having a wavelength of 405 nm was obtained from the end face.
The oscillation threshold current is 35 mA, the operating voltage at an optical output of 5 mW is 4 V, and the element life (continuous oscillation at an optical output of 5 mW at 60 ° C., from the start of oscillation until the operating current increases by 20% from the initial value) Is 10,000 hours.
[0067]
For comparison, a semiconductor laser device 3b was fabricated in the same manner as the semiconductor light emitting device 3a except that a sapphire (0001) plane was used for the substrate.
When the semiconductor laser device 3b was made to emit light in the same manner as above, the oscillation threshold current increased to 45 mA, and the device life was about 1,000 hours.
[0068]
From the above, Li of the present invention_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂It has been found that even when the substrate is applied to a semiconductor laser device, it is effective in reducing the oscillation threshold current and improving the reliability.
[0069]
Furthermore, Li_1-aNa_aAlO₂A semiconductor laser device 3c was fabricated in the same manner as the semiconductor laser device 3a, except that the buffer layer was not formed.
When the semiconductor laser device 3c was made to emit light in the same manner as described above, the oscillation threshold current was increased to 40 mA, and the device life was about 3,500 hours.
[0070]
Furthermore, Li_1-aNa_aAlO₂A semiconductor laser device 3d was fabricated in the same manner as the semiconductor laser device 3a, except that the buffer layer had a single composition of a = 0.5.
When the semiconductor laser element 3d was made to emit light in the same manner as described above, the oscillation threshold current was almost the same as that of the semiconductor laser element 3a, but the element life was about 8,000 hours.
[0071]
From the above, as in the present invention, Li_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂Li on the substrate_1-aNa_aAlO₂In the case of forming the buffer layer, by changing the Na composition in the buffer layer and controlling the lattice constant of the buffer layer, the lattice strain of the ZnO-based semiconductor layer can be reduced, and the oxide having excellent reliability can be obtained. It was found that a semiconductor light emitting device could be manufactured.
[0072]
【The invention's effect】
According to the oxide semiconductor light emitting device of the present invention, Li_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂At least an n-type cladding layer, an active layer, and a p-type cladding layer composed of a ZnO-based semiconductor are formed on an oxide substrate having a composition represented by (0 ≦ x, y, z ≦ 1). Therefore, by controlling the composition of the substrate, the lattice constant could be controlled in a range very close to that of the ZnO-based semiconductor, and an oxide semiconductor light-emitting element having excellent reliability could be manufactured. In addition, the reliability of the oxide semiconductor light-emitting element could be further improved by using an off-substrate in which the main growth surface was inclined at a predetermined off-angle.
Also, Li_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂On the substrate, Li having a different composition from the oxide substrate_{1- (x + y)}Na_xK_yAl_1-zGa_zO₂By forming a buffer layer containing (0 <x, y, z <1) and controlling the composition of the buffer layer, lattice distortion can be reduced, and an oxide semiconductor light emitting device with even higher reliability can be obtained. Could be produced.
[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 shows ZnO and insulator oxide LiGaO₂FIG. 2 is a schematic diagram illustrating the crystal structure of FIG.
FIG. 3 is a sectional view showing an oxide semiconductor light emitting device (semiconductor laser device) according to a third embodiment of the present invention.
FIG. 4 is a schematic view of a laser molecular beam epitaxy apparatus.
FIG. 5 is a graph illustrating the relationship between the off-angle of the inclined substrate and the emission intensity of the light-emitting diode element.
FIG. 6 is a graph illustrating the relationship between the composition and the effective lattice constant represented by the average oxygen-oxygen distance for four oxides of the present invention.
[Explanation of symbols]
1 ... light emitting diode element
101 ... LiNaKAlGaO₂substrate,
102 ... n-type ZnO contact layer,
103 ... n-type MgZnO cladding layer,
104 light emitting layer,
105 ... p-type MgZnO cladding layer,
106 ... p-type ZnO contact layer,
107 ... p-type ohmic electrode,
108 ... pad electrode,
109 ... n-type ohmic electrode,
201 ... n-type LiNaKAlGaO₂Buffer layer,
3 ... Semiconductor laser device,
301 ・ ・ ・ LiNaKAlGaO₂substrate,
302 ・ ・ ・ LiNaKAlGaO₂Buffer layer,
303 ... n-type ZnO contact layer,
304 n-type MgZnO cladding layer,
305 ... n-type ZnO light guide layer,
306 ・ ・ ・ Quantum well active layer,
307 ... p-type ZnO light guide layer,
308: p-type MgZnO cladding layer,
309: p-type ZnO contact layer,
310 ... n-type MgZnO current block layer,
311 ... n-type ohmic electrode,
312 ... p-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 (9)

At least an n-type ZnO-based semiconductor clad layer, a ZnO-based semiconductor active layer, and a p-type ZnO-based semiconductor clad layer are formed on an oxide substrate, and the oxide substrate is formed of Li _{1- (x + y)} Na _{x K y Al 1-z Ga z} O 2 (0 ≦ x, y, z ≦ 1,0 ≦ x + y ≦ 1) oxide semiconductor light-emitting device having a composition represented by. Oxide _{substrate, Li 1-a Na a AlO} 2, Li 1-b Na b GaO 2, LiAl 1-c Ga c O 2, and _{NaAl 1-d Ga d O 2} (0 ≦ a, b, c , D ≦ 1). 3. The oxide substrate according to claim 1, wherein a main growth surface of the oxide substrate is a (001) metal surface, and a main growth surface of the ZnO-based semiconductor epitaxially grown on the oxide substrate is a (0001) zinc surface. An oxide semiconductor light-emitting element. The oxide semiconductor light emitting device according to claim 1, wherein a main crystal growth surface of the oxide substrate is a surface inclined at an off angle of 15 ° or less from a (001) plane. On the oxide substrate, a different composition from the oxide substrate _{Li 1- (x + y) Na} x K y Al 1-z Ga z O 2 (0 <x, y, z <1,0 <x + y <1 The oxide semiconductor device according to any one of claims 1 to 3, wherein a buffer layer containing (b) is formed. The composition of the end in the direction of growth of the composition or the buffer layer of the oxide substrate is a _{Li 1-a Na a AlO 2} , claim 1 of the Na composition a is in the range of 0.4-0.6 5. The oxide semiconductor device according to any one of 5. 7. The oxide semiconductor light-emitting device according to claim 6, wherein the composition of the oxide substrate or the composition of the terminal in the growth direction of the buffer layer is Li _0.5 Na _0.5 AlO ₂ . The composition of the end in the direction of growth of the composition or the buffer layer of the oxide substrate is a _{Li 1-b Na b GaO 2} , claim 1 of the Na composition b is in the range of 0.15 to 0.35 5. The oxide semiconductor device according to any one of 5. 9. The oxide semiconductor light emitting device according to claim 8, wherein the composition of the oxide substrate or the composition of the terminal in the growth direction of the buffer layer is Li _0.75 Na _0.25 GaO ₂ .

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