JP2004247681A - Oxide semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide semiconductor light emitting device that is high in electrostatic withstanding voltage and excellent in reliability. <P>SOLUTION: In this oxide semiconductor light emitting device, an n-type ZnO buffer layer 102 is formed between an n-type ZnO single-crystal substrate 101 and an n-type Mg<SB>0.1</SB>Zn<SB>0.9</SB>O clad layer 103. The carrier concentration in the ZnO buffer layer 102 is maintained within the range from 1×10<SP>18</SP>cm<SP>-3</SP>to 1×10<SP>21</SP>cm<SP>-3</SP>. Consequently, the electrical resistance between the n-type ZnO single-crystal substrate 101 and n-type Mg<SB>0.1</SB>Zn<SB>0.9</SB>O clad layer 103 is reduced, and the electrostatic withstanding voltage of this light emitting device can be improved. <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 device and a semiconductor laser device, and more particularly, to an oxide semiconductor light emitting device having a high electrostatic breakdown voltage and excellent reliability.
[0002]
[Prior art]
Zinc oxide (ZnO) is a direct transition semiconductor having a band gap energy of about 3.4 eV. The exciton binding energy is as high as 60 meV. The raw material is inexpensive. There is a possibility that a light emitting device having high efficiency, low power consumption, and excellent environmental performance can be realized.
[0003]
Conventionally, it has been difficult to control the p-type conductivity of ZnO due to a self-compensation effect caused by strong ionicity. However, by using nitrogen (N) as an acceptor impurity, the p-type is realized, and ZnO-based semiconductors can be used. Many studies have been made to produce a highly efficient light-emitting element by using the light-emitting element.
[0004]
By the way, it is known that a semiconductor light emitting device having a minute and complicated structure such as a semiconductor laser device is deteriorated or destroyed by an excessive surge current due to static electricity or the like. Therefore, improvement of the electrostatic withstand voltage in the semiconductor light emitting device is an important issue in view of the reliability and cost reduction of the semiconductor light emitting device and the electronic device using the same.
[0005]
For example, a technology for improving the electrostatic withstand voltage of a semiconductor light emitting device is disclosed in Japanese Patent No. 3063757 (Patent Document 1). In Patent Document 1, an n-side multilayer clad layer and a p-side clad layer are formed so as to sandwich an active layer having a multiple quantum well structure. Here, the luminous efficiency and the electrostatic breakdown voltage are improved by making the layer configuration of the n-side multilayer cladding layer undoped / n-type impurity doped / undoped.
[0006]
[Patent Document 1]
Japanese Patent No. 3063757
[0007]
[Problems to be solved by the invention]
However, since the technique disclosed in Patent Document 1 is used for a nitride semiconductor device, it is possible to improve the electrostatic breakdown voltage of the oxide semiconductor light-emitting device even when applied to an oxide semiconductor light-emitting device. I can't. More specifically, when the present inventors applied the technique of Patent Document 1 to an oxide semiconductor light emitting element, the electrostatic breakdown voltage of the oxide semiconductor light emitting element was 50 V or less, and the electrostatic breakdown voltage was improved. The effect of was not fully obtained.
[0008]
In addition, the present inventors have searched for a technique for improving the electrostatic breakdown voltage of an oxide semiconductor light-emitting element, and such technique has not been disclosed in any literature.
[0009]
Therefore, an object of the present invention is to provide an oxide semiconductor light emitting device having high electrostatic withstand voltage and excellent reliability.
[0010]
[Means for Solving the Problems]
The low electrostatic breakdown voltage of the oxide semiconductor light-emitting element is considered mainly due to the high electric resistance between the substrate and the ZnO-based semiconductor layer stacked over the substrate. The inventors of the present invention have intensively studied a method for reducing the electric resistance, and have reached the present invention.
[0011]
In the oxide semiconductor light emitting device of the present invention, at least a first conductivity type clad layer, an active layer, a second conductivity type clad layer and a second conductivity type contact layer are sequentially laminated on a substrate,
The first conductivity type clad layer, the active layer, the second conductivity type clad layer, and the second conductivity type contact layer are made of a ZnO-based semiconductor;
The carrier concentration between the substrate and the first conductivity type cladding layer is 1 × 10 ¹⁸ cm ^-3 ~ 1 × 10 ²¹ cm ^-3 Is characterized in that a first conductivity type ZnO layer within the range described above is formed.
[0012]
Here, the phrase “at least” means that a light guide layer, an etching stop layer, a planarizing layer, a cap layer, and the like on both sides of the active layer may be provided.
[0013]
In this specification, the first conductivity type means p-type or n-type. The second conductivity type means n-type when the first conductivity type is p-type and p-type when the first conductivity type is n-type.
[0014]
Further, in this specification, a ZnO-based semiconductor includes ZnO and a mixed crystal represented by MgZnO, CdZnO, or the like using the same as a host.
[0015]
The oxide semiconductor light emitting device having the above configuration has a carrier concentration of 1 × 10 between the substrate and the first conductivity type cladding layer. ¹⁸ cm ^-3 ~ 1 × 10 ²¹ cm ^-3 Is formed, the electrical resistance between the substrate and the first conductivity type cladding layer is reduced. As a result, the electrostatic withstand voltage can be improved, and the reliability can be improved. That is, an oxide semiconductor light-emitting element having high electrostatic withstand voltage and excellent reliability can be obtained.
[0016]
The carrier concentration of the first conductivity type ZnO layer is 1 × 10 ¹⁸ cm ^-3 If it is less than 1, the electrical resistance of the ZnO layer of the first conductivity type increases, and the electrostatic breakdown voltage decreases.
[0017]
The carrier concentration of the first conductivity type ZnO layer is 1 × 10 ²¹ cm ^-3 If the ratio exceeds 1, the crystallinity of the ZnO layer of the first conductivity type deteriorates, and the electrostatic breakdown voltage decreases.
[0018]
The “active layer” is referred to as a “light-emitting layer” in the light-emitting diode element, but has the same meaning as a layer that controls light emission, and is not particularly distinguished below.
[0019]
In one embodiment, the first conductive ZnO layer has a carrier concentration of 1 × 10 3. ¹⁹ cm ^-3 ~ 1 × 10 ²⁰ cm ^-3 Is within the range.
[0020]
In the oxide semiconductor light emitting device of the above embodiment, the carrier concentration of the first conductivity type ZnO layer is 1 × 10 ¹⁹ cm ^-3 ~ 1 × 10 ²⁰ cm ^-3 , The electrical resistance between the substrate and the first conductivity type cladding layer is further reduced. As a result, the electrostatic withstand voltage can be further improved, and the reliability can be further improved.
[0021]
In one embodiment, the substrate is a conductive substrate.
[0022]
According to the oxide semiconductor light emitting device of the embodiment, since the substrate is a conductive substrate, an electrode can be formed on the back surface of the substrate (the surface opposite to the active layer). Therefore, the manufacturing process can be simplified and the operating voltage can be reduced.
[0023]
In one embodiment, the conductive substrate is a ZnO single crystal substrate.
[0024]
In the oxide semiconductor light emitting device of the embodiment, since the conductive substrate is a ZnO single crystal substrate, the affinity of the conductive substrate for the first conductivity type ZnO layer is improved. As a result, distortion and defects generated in the first conductivity type ZnO layer can be extremely reduced.
[0025]
In one embodiment, the main growth surface of the ZnO single crystal substrate is a zinc surface.
[0026]
In the oxide semiconductor light emitting device of the embodiment, when a p-type layer is formed on the ZnO single crystal substrate, the carrier activation rate of the p-type layer is determined by setting the main growth surface of the ZnO single crystal substrate to a zinc surface. And a p-type layer having low electric resistance is easily obtained.
[0027]
In one embodiment, the thickness of the first conductivity type ZnO layer is in the range of 10 nm to 10 μm.
[0028]
In the oxide semiconductor light emitting device of the embodiment, when the thickness of the first conductivity type ZnO layer is in the range of 10 nm to 10 μm, the electric resistance between the substrate and the first conductivity type clad layer is sufficiently low. Become. Therefore, the operating voltage can be reduced.
[0029]
If the thickness of the first conductivity type ZnO layer is less than 10 nm, the operating voltage increases and the electrostatic breakdown voltage also decreases.
[0030]
When the thickness of the first conductivity type ZnO layer exceeds 10 μm, the electrostatic withstand voltage can be improved, but the operating voltage increases.
[0031]
In one embodiment, the substrate is an insulating substrate, a part of the first conductivity type ZnO layer is exposed, and a first conductivity type ohmic electrode is formed on the part. Have been.
[0032]
According to the oxide semiconductor light emitting device of the above embodiment, since the substrate is an insulating substrate, no electrode can be provided on the substrate, and the electric resistance of the device tends to increase, and the electrostatic breakdown voltage tends to increase. However, since the first conductivity type ohmic electrode is formed on the exposed part of the first conductivity type ZnO layer, the first conductivity type ZnO layer can be used as the contact layer. As a result, an increase in the element electrical resistance can be prevented.
[0033]
Further, a sapphire substrate as an example of the insulating substrate is preferable because of its low cost and high quality.
[0034]
LiGaO as an example of the insulating substrate ₂ The substrate is preferable because of its high lattice matching with the ZnO-based semiconductor.
[0035]
In one embodiment, the thickness of the first conductivity type ZnO layer is in the range of 100 nm to 20 μm.
[0036]
In the oxide semiconductor light emitting device of the embodiment, when the thickness of the first conductivity type ZnO layer is in the range of 100 nm to 20 μm, the electric resistance between the substrate and the first conductivity type clad layer is sufficiently low. Become. Therefore, the operating voltage can be reduced.
[0037]
If the thickness of the first conductivity type ZnO layer is less than 100 nm, the operating voltage increases and the electrostatic breakdown voltage also decreases.
[0038]
When the thickness of the first conductivity type ZnO layer exceeds 20 μm, the electrostatic withstand voltage can be improved, but the operating voltage increases.
[0039]
When an insulating substrate is used as the substrate, it is preferable to use a first conductivity type ZnO layer as a contact layer in order to prevent an increase in element electrical resistance. As described above, when the first conductivity type ZnO layer is used as a contact layer, a current flows in the first conductivity type ZnO layer in a lateral direction (a direction along the surface of the first conductivity type ZnO layer). It is necessary to increase the thickness of the first conductivity type ZnO layer as compared with the case where a conductive substrate is used.
[0040]
In one embodiment, the in-plane lattice constant of the insulating substrate is within a range of (100 ± 3)% of the in-plane lattice constant of ZnO.
[0041]
In this specification, the in-plane lattice constant refers to a distance between lattice points on a two-dimensional plane perpendicular to a crystal growth direction (a direction in which semiconductor layers are stacked).
[0042]
In the oxide semiconductor light emitting device of the above embodiment, the in-plane lattice constant of the insulating substrate falls within the range of (100 ± 3)% with respect to the in-plane lattice constant of ZnO. A crystal structure with less crystallinity can be obtained on an insulating substrate.
[0043]
In one embodiment, a buffer layer is formed between the insulating substrate and the first conductivity type ZnO layer, and the material of the buffer layer is based on the in-plane lattice constant of ZnO. (100 ± 3)%.
[0044]
According to the oxide semiconductor light emitting device of the above embodiment, the in-plane lattice constant of (100 ± 3)% of the in-plane lattice constant of ZnO is provided between the insulating substrate and the first conductivity type ZnO layer. Since the second first conductivity type ZnO layer is formed, even when an insulating substrate having a large in-plane lattice constant difference from ZnO such as sapphire is used, an element structure having excellent crystallinity with few distortions and defects can be obtained. It can be obtained on the insulating substrate.
[0045]
In one embodiment, the first conductivity type ZnO layer is an n-type ZnO layer, and the impurity doped in the first conductivity type ZnO layer contains Ga or Al.
[0046]
In the oxide semiconductor light emitting device of the above embodiment, the impurity doped in the first conductivity type ZnO layer contains Ga or Al, so that the activation rate of the impurity can be increased. As a result, the electric resistance of the first conductivity type ZnO layer can be reduced, and the crystallinity of the first conductivity type ZnO layer can be improved.
[0047]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the oxide semiconductor light emitting device of the present invention will be described in detail with reference to the illustrated embodiments.
[0048]
(Embodiment 1)
In Embodiment 1, a light-emitting diode element as an example of the oxide semiconductor light-emitting element of the present invention will be described. The light emitting diode is manufactured using a ZnO substrate.
[0049]
FIG. 1 shows a schematic sectional view of the light emitting diode element.
[0050]
In the light emitting diode element, Ga is 1 × 10 5 on an n-type ZnO single crystal substrate 101 whose main growth surface is a zinc surface. ¹⁹ cm ^-3 N-type ZnO buffer layer 102 doped with a concentration of 0.5 μm and having a Ga content of 3 × 10 ¹⁸ cm ^-3 1 μm thick n-type Mg doped at a concentration of _0.1 Zn _0.9 O-cladding layer 103, non-doped 0.5 μm thick Cd _0.05 Zn _0.95 O light emitting layer 104, N is 5 × 10 ¹⁹ cm ^-3 P-type Mg doped at a concentration of 1 μm _0.1 Zn _0.9 O cladding layer 105, N is 1 × 10 ²⁰ cm ^-3 The p-type ZnO contact layer 106 having a thickness of 0.5 μm and doped at a concentration of 0.5 μm is stacked in this order.
[0051]
Here, the n-type ZnO single crystal substrate 101 is an example of a conductive substrate, and the n-type ZnO buffer layer 102 is an example of a first conductivity type ZnO layer. _0.1 Zn _0.9 The O-clad layer 103 is an example of the first conductivity type clad layer, _0.05 Zn _0.95 O-emitting layer 104 is an example of an active layer, _0.1 Zn _0.9 The O-cladding layer 105 corresponds to an example of a second conductivity type cladding layer, and the p-type ZnO contact layer 106 corresponds to an example of a second conductivity type contact layer.
[0052]
On the entire main surface of the p-type contact layer 106, a 15-nm-thick Ni p-type ohmic electrode 107 is laminated. On the p-type ohmic electrode 107, a bonding Au pad electrode 108 having a thickness of 100 nm is formed with a smaller area than the p-type ohmic electrode 107.
[0053]
An n-type ohmic electrode 109 made of Al having a thickness of 100 nm is provided on the back surface (the lower surface in the figure) of the ZnO substrate 101.
[0054]
After the stacked structure as described above is formed on the n-type ZnO single-crystal substrate 101, the n-type ZnO single-crystal substrate 101 is separated into chips to obtain the light-emitting diode element of the first embodiment. When this light emitting diode was mounted on a lead frame with an Ag paste and molded to emit light, blue light emission having an emission peak wavelength of 400 nm was obtained.
[0055]
FIG. 2 shows the relationship between the carrier concentration of the n-type ZnO buffer layer 102 and the reverse withstand voltage of the light emitting diode element (a voltage that causes breakdown when a reverse bias voltage is applied) by a solid line.
[0056]
The carrier concentration of the n-type ZnO buffer layer 102 is 1 × 10 ¹⁸ cm ^-3 If it is less than 0, the reverse breakdown voltage will decrease due to an increase in the electrical resistance of the n-type ZnO buffer layer 102. Further, the carrier concentration of the n-type ZnO buffer layer 102 is 1 × 10 ²¹ cm ^-3 In the case where n exceeds 3, the crystallinity of the n-type ZnO buffer layer 102 deteriorates, and the reverse breakdown voltage decreases.
[0057]
Therefore, the carrier concentration of the n-type ZnO buffer layer 102 is set to 1 × 10 ¹⁸ cm ^-3 ~ 1 × 10 ²¹ cm ^-3 Is preferably within the range.
[0058]
Further, in FIG. 2, the above relationship in the case where an n-type ZnO single crystal substrate whose growth main surface is an oxygen surface is used instead of the n-type ZnO single crystal substrate 101 is indicated by a dotted line.
[0059]
As can be seen by comparing the solid line and the dotted line in the figure, the reverse breakdown voltage can be increased by using the zinc surface as the main growth surface rather than using the oxygen surface as the main growth surface. As described above, the reason why the reverse breakdown voltage is increased by using the n-type ZnO single crystal substrate 101 in which the zinc surface is the main growth surface is that the carrier activation rate of the p-type layer is improved and the p-type layer having a low electric resistance is low. It is presumed that it becomes easier to obtain
[0060]
FIG. 3 shows the relationship between the layer thickness of the n-type ZnO buffer layer 102 and the operating voltage and reverse breakdown voltage of the light emitting diode device. The dotted line in the figure shows the relationship between the thickness of the n-type ZnO buffer layer 102 and the operating voltage of the light emitting diode device. The solid line in the figure shows the relationship between the thickness of the n-type ZnO buffer layer 102 and the reverse breakdown voltage of the light emitting diode element. The reverse withstand voltage refers to a voltage that causes breakdown when a reverse bias voltage is applied to the light emitting diode element.
[0061]
FIG. 3 shows that when the layer thickness of the n-type ZnO buffer layer 102 is 10 nm or more and 10 μm or less, the operating voltage is reduced and the reverse breakdown voltage is increased. Therefore, it is preferable that the thickness of the n-type ZnO buffer layer 102 be 10 nm or more and 10 μm or less.
[0062]
If the thickness of the n-type ZnO buffer layer 102 is less than 10 nm, the operating voltage increases and the reverse breakdown voltage also decreases.
[0063]
When the thickness of the n-type ZnO buffer layer 102 exceeds 10 μm, the reverse breakdown voltage is high, but the operating voltage is high.
[0064]
In the first embodiment, the substrate made of ZnO single crystal is used as the conductive substrate, but a substrate made of SiC, GaN, or the like may be used as the conductive substrate.
[0065]
In order to maximize the high luminous efficiency of the ZnO-based semiconductor, it is preferable to use a substrate satisfying the following conditions (a) to (c).
[0066]
(A) From the viewpoint of reducing defects serving as non-emission centers in the growth layer on the substrate, the in-plane lattice constant of the substrate is within (100 ± 3)% of the in-plane lattice constant of ZnO. I have.
[0067]
(B) The substrate has a low absorption coefficient corresponding to the emission wavelength.
[0068]
(C) From the viewpoint of providing electrodes under the back surface of the substrate, the substrate is a conductive substrate.
[0069]
The n-type ZnO single crystal substrate 101 used in the first embodiment satisfies all of the above conditions (a) to (c) and is most preferable.
[0070]
In addition, it is preferable to form irregularities on the back surface of the substrate by a known method such as polishing or etching, because light incident on the substrate is irregularly reflected, thereby improving light extraction efficiency.
[0071]
As the donor impurity to be doped into the n-type ZnO buffer layer 102, group III elements such as B, Al, Ga, and In can be used, but Ga or Al having a high activation rate in a ZnO-based semiconductor is preferable. . Of course, these donor impurities may be applied to n-type ZnO-based semiconductor layers other than the n-type ZnO buffer layer 102.
[0072]
Hereinafter, another configuration for maximizing the effects of the present invention in the first embodiment will be described. However, this configuration may be arbitrarily combined with the other embodiments.
[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 using a solid or gaseous raw material, a laser molecular beam epitaxy (laser MBE) method, and a metal organic chemical vapor deposition (MOCVD) method. Can be made. Among these crystal growth methods, the laser MBE method has a small composition deviation between a raw material target and a thin film and has a ZnGa ₂ O ₄ This is particularly preferable because generation of unintended by-products such as the above can be suppressed.
[0074]
As an acceptor impurity to be doped into the p-type ZnO-based semiconductor layer, a Group I element such as Li, Cu, or Ag, or a Group V element such as N, As, or P can be used, but the effect of the present invention is maximized. For obtaining N, Li and Ag, which have a high activation rate, are particularly preferable. When N is used as an acceptor impurity, N becomes N ₂ It is preferable to irradiate during the crystal growth by turning into plasma. By this method, high-concentration doping of N can be performed while maintaining good crystallinity.
[0075]
To improve the luminous efficiency of the light emitting diode element, p-type Mg _0.1 Zn _0.9 It is preferable to form the p-type ohmic electrode 107 on the p-type ZnO contact layer 106 without forming the p-type ohmic electrode 107 directly on the O-cladding layer 105. That is, p-type Mg _0.1 Zn _0.9 It is preferable to form a p-type ZnO contact layer 106 between the O-cladding layer 105 and the p-type ohmic electrode 107. The p-type ZnO contact layer 106 further reduces the element electrical resistance and makes the current spread uniform. Also, if the p-type ZnO contact layer 106 is excessively doped with an acceptor impurity, the crystallinity is remarkably deteriorated, and the effect of the present invention is reduced. ¹⁶ ~ 5 × 10 ¹⁹ cm ^-3 It is preferable to dope the p-type ZnO contact layer 106 so as to fall within the range described above. Note that, as in the case of the p-type ZnO contact layer 106, it is preferable to use ZnO, which has excellent crystallinity and can increase the carrier concentration, as a material for the p-type contact layer.
[0076]
In order to obtain high luminous efficiency, it is preferable to form the p-type ohmic electrode 107 so as to have a light-transmitting property as described in the first embodiment to improve the light extraction efficiency. As a material of the p-type ohmic electrode, Ni, Pt, Pd, Au, or the like can be used, and among them, Ni having low resistance and good adhesion is preferable. Further, an alloy of a plurality of the above metal materials may be used as the p-type ohmic electrode. Further, the thickness of the p-type ohmic electrode is preferably adjusted within a range of 5 to 200 nm, and more preferably within a range of 30 to 100 nm, from the viewpoint of achieving both good ohmic characteristics and high translucency. Is more preferred.
[0077]
It is preferable to perform an annealing treatment after forming the p-type electrode because the adhesion of the p-type electrode is improved and the contact resistance of the p-type electrode is reduced. In order to obtain an annealing effect without causing defects in the ZnO crystal on the substrate, the temperature of the annealing treatment is preferably adjusted within the range of 300 to 400 ° C. The atmosphere in the annealing treatment is O ₂ Alternatively, it is preferably an air atmosphere. The atmosphere in the annealing process is N ₂ In this case, the contact resistance of the p-type electrode increases.
[0078]
If the bonding Au pad electrode 108 is formed with a smaller area than the p-type ohmic electrode 107, that is, if the bonding Au pad electrode 108 is formed on a part of the p-type ohmic electrode 107, the p-type ohmic electrode 107 becomes transparent. This is preferable because the process of mounting on a lead frame is facilitated without significantly affecting optical properties. As a material of the pad electrode, Au which can be easily bonded and does not become a donor impurity even when diffused into ZnO is preferable. Further, another metal layer may be provided between the bonding Au pad electrode 108 and the p-type ohmic electrode 107 for the purpose of improving adhesion and light reflectivity.
[0079]
As the material of the n-type ohmic electrode, Ti, Cr, Al, or the like can be used. Among Ti, Cr, Al and the like, Al with low electric resistance and low cost or Ti with good adhesion is preferable. Further, an alloy of a plurality of metal materials such as Ti, Cr, and Al may be used as the n-type ohmic electrode. Since the n-type ohmic electrode made of Al has a high reflectance with respect to blue to ultraviolet light, the light extraction efficiency is high even if it is formed on the entire back surface. Alternatively, an n-type ohmic electrode made of Al may be patterned into an arbitrary shape, and the exposed back surface of the substrate may be bonded to a lead frame with an Ag paste or the like. Ag is preferable because the reflectivity of blue to ultraviolet light is higher than that of Al.
[0080]
Other configurations are arbitrary and are not limited by the present embodiment.
[0081]
(Embodiment 2)
In Embodiment 2, a light-emitting diode element as an example of the oxide semiconductor light-emitting element of the present invention will be described. Note that the light emitting diode is LiGaO ₂ It is manufactured using a substrate.
[0082]
FIG. 4 shows a schematic sectional view of the light emitting diode element.
[0083]
The light emitting diode element is LiGaO ₂ Ga is 1 × 10 on the (111) plane of the substrate 201. ¹⁹ cm ^-3 0.5 μm thick n-type ZnO contact layer 202 doped with a concentration of ¹⁸ cm ^-3 1 μm thick n-type Mg doped at a concentration of _0.1 Zn _0.9 O-cladding layer 203, non-doped Cd 0.5 μm thick _0.05 Zn _0.95 O light emitting layer 204, N is 5 × 10 ¹⁹ cm ^-3 P-type Mg doped at a concentration of 1 μm _0.1 Zn _0.9 O cladding layer 205, N is 1 × 10 ²⁰ cm ^-3 The p-type ZnO contact layer 206 having a thickness of 0.5 μm and doped at a concentration of 0.1 μm is stacked in this order.
[0084]
Here, the above-mentioned LiGaO ₂ The substrate 201 is an example of an insulating substrate, and the n-type ZnO contact layer 202 is an example of a first conductivity type ZnO layer. _0.1 Zn _0.9 The O-clad layer 203 is an example of a first-conductivity-type clad layer, _0.05 Zn _0.95 The O light emitting layer 204 is an example of an active layer, _0.1 Zn _0.9 The O clad layer 205 corresponds to an example of a second conductive type clad layer, and the p-type ZnO contact layer 206 corresponds to an example of a second conductive type contact layer.
[0085]
The n-type Mg _0.1 Zn _0.9 A part of the layered structure to be formed from the O-clad layer 203 to the p-type ZnO contact layer 206 upward in the drawing is etched to expose a part of the n-type ZnO contact layer 202. On an exposed part of the n-type ZnO contact layer 202, an n-type ohmic electrode 209 as an example of a first conductivity type ohmic electrode is formed. This n-type ohmic electrode 209 is made of Al having a thickness of 100 nm.
[0086]
On the entire main surface of the p-type ZnO contact layer 206, a 15-nm-thick Ni p-type ohmic electrode 207 is laminated. On the p-type ohmic electrode 207, a bonding Au pad electrode 208 having a thickness of 100 nm is formed with an area smaller than that of the p-type ohmic electrode 207.
[0087]
The above-described laminated structure is made of LiGaO ₂ After being formed on the substrate 201, LiGaO ₂ By separating the substrate 201 into chips, the light emitting diode element of Embodiment 2 is obtained. When this light emitting diode was mounted on a lead frame with an Ag paste and molded to emit light, blue light emission having an emission peak wavelength of 400 nm was obtained.
[0088]
In the light emitting diode device having the above configuration, the carrier concentration of the n-type ZnO contact layer 202 is set to 1 × 10 ¹⁸ cm ^-3 ~ 1 × 10 ²¹ cm ^-3 Within the range of LiGaO ₂ Substrate 201 and p-type Mg _0.1 Zn _0.9 The electric resistance between the O-clad layer 205 and the O-clad layer 205 can be reduced. As a result, the electrostatic withstand voltage can be improved, and the reliability can be improved.
[0089]
The n-type ZnO contact layer 202 also functions as a low electric resistance buffer layer for improving electrostatic withstand voltage.
[0090]
FIG. 5 shows the relationship between the layer thickness of the n-type ZnO contact layer 202 and the operating voltage and reverse breakdown voltage of the light emitting diode device. The dotted line in the figure shows the relationship between the thickness of the n-type ZnO contact layer 202 and the operating voltage of the light emitting diode device. The solid line in the figure shows the relationship between the thickness of the n-type ZnO contact layer 202 and the reverse breakdown voltage of the light emitting diode device. The reverse withstand voltage refers to a voltage that causes breakdown when a reverse bias voltage is applied to the light emitting diode element.
[0091]
FIG. 5 shows that when the thickness of the n-type ZnO contact layer 202 is 100 nm or more and 20 μm or less, the operating voltage is reduced and the reverse breakdown voltage is increased. Therefore, it is preferable that the layer thickness of the n-type ZnO contact layer 202 be 100 nm or more and 20 μm or less.
[0092]
If the thickness of the n-type ZnO contact layer 202 is less than 100 nm, the operating voltage increases and the reverse breakdown voltage decreases.
[0093]
When the thickness of the n-type ZnO contact layer 202 exceeds 20 μm, the reverse breakdown voltage is high, but the operating voltage is high.
[0094]
As described above, the preferable thickness of the n-type ZnO contact layer 202 is larger than the preferable thickness of the n-type ZnO buffer layer 102 in the first embodiment because the n-type ZnO contact layer 202 is formed in the lateral direction (n This is because a current flows in the direction along the surface of the type ZnO contact layer 202).
[0095]
In the second embodiment, LiGaO ₂ Although a substrate made of sapphire or spinel is used as the insulating substrate, a substrate made of sapphire or spinel may be used as the insulating substrate. LiGaO ₂ Has an in-plane lattice constant of (100 ± 3)% with respect to the in-plane lattice constant of the ZnO-based semiconductor, so that it can be easily lattice-matched with the ZnO-based semiconductor. Therefore, LiGaO ₂ When a ZnO-based semiconductor layer is formed on a substrate made of, the crystallinity of the ZnO-based semiconductor layer can be extremely increased.
[0096]
As an insulating substrate having high lattice matching with a ZnO-based semiconductor, LiGaO ₂ In addition to the substrate, LiAlO ₂ , NaGaO ₂ , NaAlO ₂ And substrates composed of these mixed crystals.
[0097]
(Embodiment 3)
In Embodiment 3, a Fabry-Perot ZnO-based semiconductor laser device as an example of the oxide semiconductor light-emitting device of the present invention will be described. The semiconductor laser device is manufactured using a ZnO substrate.
[0098]
FIG. 6 is a schematic perspective view of the semiconductor laser device.
[0099]
In the semiconductor laser device, Ga is 1 × 10 5 on an n-type ZnO single crystal substrate 301 having a zinc surface as a main growth surface. ¹⁹ cm ^-3 0.3 μm thick n-type ZnO buffer layer 302 doped with a concentration of ¹⁸ cm ^-3 1 μm thick n-type Mg doped at a concentration of _0.1 Zn _0.9 O cladding layer 303, Ga is 5 × 10 ¹⁷ cm ^-3 30 nm thick n-type ZnO light guide layer 304, non-doped quantum well active layer 305 doped with a concentration of ¹⁸ cm ^-3 P-type ZnO light guide layer 306 doped with a concentration of 30 nm and having a thickness of 5 × 10 ¹⁹ cm ^-3 1.2 μm thick p-type Mg doped at a concentration of _0.1 Zn _0.9 O cladding layer 307, N is 1 × 10 ²⁰ cm ^-3 A p-type ZnO contact layer 308 doped with a concentration of 0.5 μm and having a thickness of 0.5 μm is stacked in this order.
[0100]
Here, the n-type ZnO single crystal substrate 301 is an example of a conductive substrate, and the n-type ZnO buffer layer 302 is an example of a first conductivity type ZnO layer. _0.1 Zn _0.9 The O-cladding layer 303 is an example of a first conductivity type cladding layer, and the quantum well active layer 305 is an example of an active layer. _0.1 Zn _0.9 The O clad layer 307 corresponds to an example of a second conductive type clad layer, and the p-type ZnO contact layer 308 corresponds to an example of a second conductive type contact layer.
[0101]
The quantum well active layer 305 includes a ZnO barrier layer having a thickness of 5 nm and a Cd layer having a thickness of 6 nm. _0.1 Zn _0.9 O well layers are alternately stacked. There are two ZnO barrier layers, Cd _0.1 Zn _0.9 There are three O well layers.
[0102]
A part of the p-type MgZnO cladding layer 307 and the p-type ZnO contact layer 308 are etched in a ridge stripe shape. The side surface of a part of the ridge stripe in the p-type MgZnO cladding layer 307 and the side surface of the p-type ZnO contact layer 308 have Ga of 3 × 10 3. ¹⁸ cm ^-3 -Type Mg doped at a concentration of _0.2 Zn _0.8 It is embedded by the O current block layer 309.
[0103]
An n-type ohmic electrode 310 is formed below the n-type ZnO single crystal substrate 301, and a p-type ZnO contact layer 308 and an n-type MgO _0.2 Zn _0.8 On the O current block layer 309, a p-type ohmic electrode 311 is formed.
[0104]
After a pair of end face mirrors are formed by cleaving the n-type ZnO single crystal substrate 301 having the above-described laminated structure, a protective film is vacuum-deposited on the end face mirrors. Then, device isolation is performed to obtain a semiconductor laser device having a width of 300 μm. When a current was applied to this semiconductor laser device, blue oscillation light having a wavelength of 400 nm was obtained from the end face.
[0105]
In the light emitting diode device having the above configuration, the carrier concentration of the n-type ZnO buffer layer 302 is set to 1 × 10 ¹⁸ cm ^-3 ~ 1 × 10 ²¹ cm ^-3 , The n-type ZnO single crystal substrate 301 and the n-type Mg _0.1 Zn _0.9 The electric resistance between the O-clad layer 303 and the O-clad layer 303 can be reduced. As a result, the electrostatic withstand voltage can be improved, and the reliability can be improved. Specifically, the reverse withstand voltage can be made 170 V or more.
[0106]
As a comparative example, a semiconductor laser device was manufactured in the same manner as in Embodiment 3 except that the n-type ZnO buffer layer 302 was not formed. The oscillation wavelength and oscillation threshold current of the semiconductor laser device of this comparative example were the same as those of the third embodiment, but the reverse breakdown voltage of the semiconductor laser device of the comparative example was lower than that of the third embodiment and was 100 V or less. .
[0107]
As described above, even when the present invention is applied to a Fabry-Perot semiconductor laser device using a conductive substrate, an effect of reducing electrostatic withstand voltage can be obtained.
[0108]
(Embodiment 4)
Embodiment 4 describes a ZnO-based semiconductor laser device as an example of the oxide semiconductor light-emitting device of the present invention. The semiconductor laser device is manufactured using a sapphire substrate.
[0109]
FIG. 7 is a schematic perspective view of the semiconductor laser device.
[0110]
In the semiconductor laser device, a non-doped 0.1 μm thick ZnO first buffer layer 402 and a non-doped 0.1 μm thick Li _0.35 Na _0.65 GaO ₂ Second buffer layer 403, Ga is 1 × 10 ¹⁹ cm ^-3 0.3 μm-thick n-type ZnO contact layer 404 doped with a concentration of ¹⁸ cm ^-3 1 μm thick n-type Mg doped at a concentration of _0.1 Zn _0.9 O cladding layer 405, Ga is 5 × 10 ¹⁷ cm ^-3 N-type ZnO light guide layer 406 doped with a concentration of 30 nm and a non-doped quantum well active layer 407; ¹⁸ cm ^-3 P-type ZnO light guide layer 408 doped with a concentration of 30 nm and having a thickness of 5 × 10 ¹⁹ cm ^-3 1.2 μm thick p-type Mg doped at a concentration of _0.1 Zn _0.9 O cladding layer 409, N is 1 × 10 ²⁰ cm ^-3 A p-type ZnO contact layer 410 having a thickness of 0.5 μm and doped at a concentration of 0.5 μm is stacked in this order.
[0111]
Here, the sapphire substrate 401 is an example of an insulating substrate, _0.35 Na _0.65 GaO ₂ The second buffer layer 403 is an example of a buffer layer, and the n-type ZnO contact layer 404 is an example of a first conductivity type ZnO layer. _0.1 Zn _0.9 The O-cladding layer 405 is an example of a first conductivity type cladding layer, and the non-doped quantum well active layer 407 is an example of an active layer. _0.1 Zn _0.9 The O clad layer 409 corresponds to an example of a second conductive type clad layer, and the p-type ZnO contact layer 410 corresponds to an example of a second conductive type clad layer.
[0112]
The quantum well active layer 407 includes a ZnO barrier layer having a thickness of 5 nm and a Cd layer having a thickness of 6 nm. _0.1 Zn _0.9 O well layers are alternately stacked. There are two ZnO barrier layers, Cd _0.1 Zn _0.9 There are three O well layers.
[0113]
A part of the p-type MgZnO cladding layer 409 is etched in a ridge stripe shape. The side surface of a part of the ridge stripe in the p-type MgZnO cladding layer 409 has Ga of 3 × 10 ¹⁸ cm ^-3 -Type Mg doped at a concentration of _0.2 Zn _0.8 It is buried by the O current blocking layer 411.
[0114]
Further, a part of the laminated structure to be formed from the n-type MgZnO cladding layer 405 to the p-type ZnO contact layer 410 upward in the drawing is etched to expose a part of the n-type ZnO contact layer 404. I have. On an exposed part of the n-type ZnO contact layer 404, an n-type ohmic electrode 412 as an example of a first conductivity type ohmic electrode is formed.
[0115]
On the p-type ZnO contact layer 410, a p-type ohmic electrode 413 is formed.
[0116]
By cleaving the sapphire substrate 401 having the above-described laminated structure, a pair of end face mirrors perpendicular to the ridge stripe are formed, and then a protective film is deposited on the end face mirror. Then, device isolation is performed to obtain a semiconductor laser device having a width of 300 μm. When a current was applied to this semiconductor laser device, blue light emission of 400 nm was obtained from the end face.
[0117]
In the light emitting diode device having the above configuration, the carrier concentration of the n-type ZnO contact layer 404 is set to 1 × 10 ¹⁸ cm ^-3 ~ 1 × 10 ²¹ cm ^-3 Sapphire substrate 401 and n-type Mg _0.1 Zn _0.9 The electric resistance between the O clad layer 405 and the O clad layer 405 can be reduced. As a result, the electrostatic withstand voltage can be improved, and the reliability can be improved. Specifically, the reverse withstand voltage can be set to 150 V or more.
[0118]
Further, the n-type ZnO contact layer 404 also functions as a low electric resistance buffer layer for improving the electrostatic withstand voltage.
[0119]
In addition, the above Li _0.35 Na _0.65 GaO ₂ Li as a material of the second buffer layer 403 _0.35 Na _0.65 GaO ₂ Is substantially lattice-matched with ZnO. Specifically, Li _0.35 Na _0.65 GaO ₂ Has an in-plane lattice constant of (100 ± 3) with respect to the in-plane lattice constant of ZnO. Therefore, the above Li _0.35 Na _0.65 GaO ₂ Since the second buffer layer 403 is formed between the sapphire substrate 401 and the n-type ZnO contact layer 404, a ZnO-based semiconductor layer having extremely high crystallinity can be formed on the sapphire substrate 401.
[0120]
Also, Li _0.35 Na _0.65 GaO ₂ When a ZnO-based semiconductor layer is formed on a buffer layer formed on a substrate after forming the buffer layer on the substrate, even if the substrate is an insulating substrate having a large lattice mismatch such as a sapphire substrate, the An extremely high ZnO-based semiconductor layer can be formed over a substrate.
[0121]
Although the ZnO first buffer layer 402 has no effect of improving the electrostatic withstand voltage, the sapphire substrate 401 _0.35 Na _0.65 GaO ₂ The affinity with the second buffer layer 403 is improved. Therefore, Li on the sapphire substrate 401 _0.35 Na _0.65 GaO ₂ Compared to the case where the second buffer layer 403 is directly formed, Li _0.35 Na _0.65 GaO ₂ The crystallinity of the second buffer layer 403 is significantly improved.
[0122]
As Comparative Example 1, a semiconductor laser device was manufactured in the same manner as in Embodiment 4 except that the n-type ZnO contact layer 404 was not formed. The semiconductor laser device of Comparative Example 1 had the same oscillation wavelength and oscillation threshold current as those of the fourth embodiment, but had a reverse breakdown voltage of 100 V or less, which was lower than that of the fourth embodiment.
[0123]
As Comparative Example 2, a semiconductor laser device was manufactured in the same manner as in the present embodiment except that the n-type ZnO first buffer layer 402 was not formed. In the semiconductor laser device of Comparative Example 2, the oscillation threshold current was increased by 40% as compared with Embodiment 4, and the reverse breakdown voltage was 80 V or lower, which was lower than that of Embodiment 4.
[0124]
As Comparative Example 3, the n-type ZnO first buffer layer 402 and Li _0.35 Na _0.65 GaO ₂ A semiconductor laser device was manufactured in the same manner as in Embodiment 4 except that the second buffer layer 403 was not formed. In the semiconductor laser device of Comparative Example 3, the oscillation threshold current was increased by 60% as compared with the fourth embodiment, and the reverse breakdown voltage was 50 V or less, which was lower than that of the fourth embodiment.
[0125]
As described above in Embodiments 1 to 4, the n-type ZnO layer between the substrate and the n-type cladding layer has a carrier concentration of 1 × 10 ¹⁸ cm ^-3 ~ 1 × 10 ²¹ cm ^-3 Is preferably within the range. The carrier concentration is 1 × 10 4 from the viewpoint of further improving the electrostatic withstand voltage. ¹⁹ cm ^-3 ~ 1 × 10 ²⁰ cm ^-3 Is preferably within the range.
[0126]
In the first to fourth embodiments, the n-type cladding layer, the active layer, and the p-type cladding layer are laminated on the substrate in this order. The layers may be stacked in this order.
[0127]
Further, the n-type clad layer, the light-emitting layer, the p-type clad layer and the p-type ZnO contact layer may be composed of ZnO and a mixed crystal represented by MgZnO, CdZnO or the like based on ZnO.
[0128]
【The invention's effect】
As is clear from the above, the oxide semiconductor light emitting device of the present invention has a carrier concentration of 1 × 10 3 between the substrate and the first conductivity type cladding layer. ¹⁸ cm ^-3 ~ 1 × 10 ²¹ cm ^-3 Is formed, the electrical resistance between the substrate and the first conductivity type cladding layer is reduced, and the electrostatic breakdown voltage can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a light-emitting diode element according to Embodiment 1 of the present invention.
FIG. 2 is a diagram illustrating a relationship between a carrier concentration of an n-type ZnO buffer layer of the light emitting diode element according to the first embodiment and a reverse breakdown voltage of the light emitting diode element.
FIG. 3 is a diagram illustrating a relationship between a layer thickness of an n-type ZnO buffer layer of the light emitting diode according to the first embodiment and an operating voltage and a reverse breakdown voltage of the light emitting diode element.
FIG. 4 is a schematic cross-sectional view of a light-emitting diode element according to Embodiment 2 of the present invention.
FIG. 5 shows the relationship between the layer thickness of the n-type ZnO contact layer of Embodiment 2 and the operating voltage and reverse breakdown voltage of the light emitting diode element.
FIG. 6 is a schematic perspective view of a Fabry-Perot ZnO-based semiconductor laser device according to a third embodiment of the present invention.
FIG. 7 is a schematic perspective view of a ZnO-based semiconductor laser device according to a fourth embodiment of the present invention.
[Explanation of symbols]
101,301 n-type ZnO single crystal substrate
102,302 n-type ZnO buffer layer
103, 203, 303, 405 n-type Mg _0.1 Zn _0.9 O clad layer
104,204 Cd _0.05 Zn _0.95 O light emitting layer
105, 205, 307, 409 p-type Mg _0.1 Zn _0.9 O clad layer
106, 206, 308, 410 p-type ZnO contact layer
201 LiGaO ₂ substrate
202,404 n-type ZnO contact layer
305,407 Quantum well active layer
401 Sapphire substrate

Claims (11)

On the substrate, at least a first conductivity type clad layer, an active layer, a second conductivity type clad layer and a second conductivity type contact layer are sequentially laminated,
The first conductivity type clad layer, the active layer, the second conductivity type clad layer, and the second conductivity type contact layer are made of a ZnO-based semiconductor;
A first conductivity type ZnO layer having a carrier concentration within a range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ is formed between the substrate and the first conductivity type clad layer. An oxide semiconductor light emitting device characterized by the above-mentioned. The oxide semiconductor light emitting device according to claim 1,
An oxide semiconductor light-emitting element, wherein the first conductivity type ZnO layer has a carrier concentration in a range of 1 × 10 ¹⁹ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ . The oxide semiconductor light emitting device according to claim 1,
An oxide semiconductor light emitting device, wherein the substrate is a conductive substrate. The oxide semiconductor light emitting device according to claim 3,
An oxide semiconductor light emitting device, wherein the conductive substrate is a ZnO single crystal substrate. The oxide semiconductor light emitting device according to claim 4,
An oxide semiconductor light emitting device, wherein a main growth surface of the ZnO single crystal substrate is a zinc surface. The oxide semiconductor light emitting device according to claim 3,
An oxide semiconductor light emitting device, wherein the thickness of the first conductivity type ZnO layer is in the range of 10 nm to 10 μm. The oxide semiconductor light emitting device according to claim 1,
The substrate is an insulating substrate, and a part of the first conductivity type ZnO layer is exposed;
An oxide semiconductor light emitting device, wherein a first conductivity type ohmic electrode is formed on a part thereof. The oxide semiconductor light emitting device according to claim 7,
An oxide semiconductor light emitting device, wherein the thickness of the first conductivity type ZnO layer is in the range of 100 nm to 20 μm. The oxide semiconductor light emitting device according to claim 7,
An oxide semiconductor light-emitting device, wherein the in-plane lattice constant of the insulating substrate is within (100 ± 3)% of the in-plane lattice constant of ZnO. The oxide semiconductor light emitting device according to claim 7,
A buffer layer is formed between the insulating substrate and the first conductivity type ZnO layer,
An oxide semiconductor light emitting device, wherein the material of the buffer layer has an in-plane lattice constant of (100 ± 3)% with respect to the in-plane lattice constant of ZnO. The oxide semiconductor light emitting device according to claim 1,
The first semiconductor ZnO layer is an n-type ZnO layer, and the impurity doped in the first conductivity ZnO layer contains Ga or Al.

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