JP2004342732A - Oxide semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide semiconductor light emitting device which is excellent in light emitting properties, simple in structure, and manufacturable at a low cost. <P>SOLUTION: An n-type ZnO layer 2 doped with Ga, a ZnO light emitting layer 3 which is doped with Ga and 10 μm in thickness, and a p-type ZnO layer 4 doped with N, are formed on a ZnO substrate 1. A non-doped region of thickness 0.5 μm is provided to the ZnO light emitting layer 3 at a point located nearly at a center but closer to the p-type ZnO layer 4 than to the n-type ZnO layer 2 in the direction of thickness. A Ga impurity level in the doped region of the light emitting layer 3 is excited by exciton emission that is preferentially generated in the non-doped region to induce emission of light through an impurity level for carrying out multiple emission of light. Without using a multi-quantum well structure, light can be emitted from nearly all the light emitting layer 3 that is comparatively large in thickness, so that the oxide semiconductor light emitting device which is simple in structure, manufactured at a low cost, and high in luminous efficiency can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an oxide semiconductor light emitting device using, for example, a ZnO-based semiconductor.
[0002]
[Prior art]
For example, wide-gap semiconductors represented by group III nitrides have many characteristics that are extremely high in industrial application value over conventional semiconductor materials, and recently, including blue to ultraviolet short-wavelength light-emitting elements, Application to electronic devices has been proposed.
[0003]
Zinc oxide (hereinafter referred to as ZnO), which is one of such wide gap semiconductors, is a direct transition semiconductor having a band gap energy of about 3.4 eV, has an extremely high exciton binding energy of 60 meV, and furthermore, It has features such as inexpensive raw materials, harmlessness to the environment and the human body, and simple film forming method, so that it is possible to realize a light-emitting element with high efficiency, low power consumption, and little impact on the environment. .
[0004]
In this specification, the ZnO-based semiconductor includes ZnO and a mixed crystal such as MgZnO (magnesium / zinc oxide) or CdZnO (cadmium / zinc oxide) using the same as a host.
[0005]
In order to produce a light-emitting element utilizing the characteristics of the wide-gap semiconductor, such as short-wavelength light emission, a thin-film fabrication technique for strictly controlling the layer thickness and band gap, such as a quantum well or a double heterostructure, is required. Many are used.
[0006]
However, the wide gap semiconductor has a problem that it is difficult to control crystal growth and processing due to high stability, and is inferior to a conventional semiconductor material in terms of yield and cost.
[0007]
In order to solve such a problem, research on the above-described thin film manufacturing technology has been advanced, and attempts have been made to manufacture a light emitting element having a simple configuration and sufficiently high efficiency.
[0008]
Regarding a semiconductor light emitting device having such a simple configuration and high efficiency, the present inventors have formed a light emitting layer having a thickness of 5 μm or more in a pn junction type light emitting diode using silicon carbide (hereinafter referred to as SiC). Thus, a technique has been proposed in which a donor-acceptor (hereinafter, referred to as DA) pair is caused to undergo multi-stage transition to improve the emission intensity (Japanese Patent Laid-Open No. Hei 6-334214: Patent Document 1).
[0009]
Conventionally, there has been proposed a semiconductor light emitting device including an n-type GaN clad layer, an InGaN quantum well light-emitting layer, a p-type AlGaN clad layer, and a p-type GaN contact layer and capable of obtaining high brightness with a minimum configuration (Patent). No. 31,35041: Patent Document 2).
[0010]
In addition, conventionally, a method for manufacturing an oxide semiconductor light emitting device using a ZnO-based semiconductor has been proposed (International Patent Publication No. WO 00/16411: Patent Document 3).
[0011]
[Patent Document 1]
JP-A-6-334214 (FIG. 1)
[Patent Document 2]
Japanese Patent No. 3135041 (FIG. 1)
[Patent Document 3]
WO 00/16411 pamphlet (Fig. 1)
[0012]
[Problems to be solved by the invention]
However, the light emitting diode using SiC has a problem that the light emission intensity is insufficient because SiC is an indirect transition type semiconductor.
[0013]
In addition, the technique of manufacturing a quantum well structure and the technique of controlling a composition ratio for controlling a band gap as in the conventional InGaN-based semiconductor light-emitting element described above are not sufficiently applied to a ZnO-based semiconductor. However, there is a problem that the quantum well structure cannot be manufactured with a high yield.
[0014]
According to tests by the present inventors, the conventional oxide semiconductor light-emitting device using the ZnO-based semiconductor cannot improve the light-emitting intensity only by forming the light-emitting layer thicker, and the light-emitting layer thickness is 3 μm. It has been found that when the thickness exceeds the above range, there arises a problem that the emission intensity cannot be effectively increased even if the thickness is increased.
[0015]
Therefore, an object of the present invention is to provide an oxide semiconductor light-emitting element having excellent light-emitting characteristics, a simple structure, and which can be manufactured at low cost.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, an oxide semiconductor light emitting device of the present invention includes at least a first conductivity type layer, a light emitting layer, and a second conductivity type layer on a substrate,
The light emitting layer is characterized in that it has a doped region doped with impurities and a non-doped region not doped with impurities.
[0017]
The present inventor has found that the mechanism of exciton emission in a wide gap semiconductor such as a ZnO-based semiconductor is different from the emission mechanism using only a DA pair such as the conventional SiC described above, in addition to the thickness of the emission layer. It has been found that the structure of the impurities doped with GaAs is correlated with the emission intensity, and based on this, the present invention has been accomplished.
[0018]
According to the above configuration, exciton emission occurs preferentially in the non-doped region of the light emitting layer due to the carriers confined in the light emitting layer by the first conductivity type layer and the second conductivity type layer. Next, light emission via the impurity level is promoted in the doped region by the exciton light emission. As described above, by providing the non-doped region in the light emitting layer, multi-step light emission using exciton light emission can be effectively performed. The light emission intensity is dramatically increased as compared with the element. In particular, when, for example, a ZnO-based semiconductor is used for the light-emitting layer, exciton light emission is a light emission mechanism having a large transition energy next to inter-band light emission, so that carriers are easily excited to impurity levels to perform multi-step light emission. Can do it. Therefore, high-efficiency and high-intensity light emission can be realized with a simple structure without using a multiple quantum well structure having a complicated structure.
[0019]
Here, when the first conductivity type is p-type, the second conductivity type is n-type. On the other hand, when the first conductivity type is n-type, the second conductivity type is p-type.
[0020]
Note that a part of the first conductivity type layer and the second conductivity type layer may also serve as a light emitting layer.
[0021]
In one embodiment, the light-emitting layer has a thickness of 3 μm or more and 30 μm or less.
[0022]
According to the above embodiment, since the thickness of the light emitting layer is 3 μm or more and 30 μm or less, the multi-step light emission can be sufficiently performed, and the light emission intensity is effectively increased.
Here, when the thickness of the light emitting layer is smaller than 3 μm, it is difficult to perform multi-step light emission using excitons. On the other hand, when the thickness of the light emitting layer is larger than 30 μm, the rate of increase in light emission intensity decreases.
[0023]
In one embodiment, the thickness of the light emitting layer is 5 μm or more and 15 μm or less.
[0024]
According to the embodiment, since the thickness of the light emitting layer is 5 μm or more, light of relatively high intensity can be obtained by multi-step light emission using excitons. Further, since the thickness of the light emitting layer is 15 μm or less, an increase in manufacturing cost can be suppressed. Here, if the thickness of the light emitting layer is smaller than 5 μm, the effect of increasing the light emission intensity becomes relatively small. On the other hand, if the thickness of the light emitting layer is larger than 15 μm, the film formation cost increases and the manufacturing cost of the oxide semiconductor light emitting device increases.
[0025]
In one embodiment, the first conductivity type layer, the light emitting layer, and the second conductivity type layer are all made of ZnO.
[0026]
According to the embodiment, the first conductivity type layer, the light emitting layer, and the second conductivity type layer are all made of ZnO, and can be stacked under substantially the same crystal growth conditions. Therefore, unlike a conventional semiconductor light emitting device having a multiple quantum well active layer in a light emitting layer, it is not necessary to form an MgZnO layer or a CdZnO layer having different crystal growth conditions, and the fabrication can be performed by an extremely simple manufacturing process. As a result, cost performance and yield are significantly improved.
[0027]
In one embodiment, the first conductivity type layer and the second conductivity type layer are made of a ZnO-based semiconductor having a larger band gap than the light emitting layer.
[0028]
According to the above embodiment, when the light emitting layer is relatively thin, a double hetero structure can be formed by the light emitting layer, the first conductivity type layer and the second conductivity type layer, so that the carrier confinement efficiency can be improved. The luminous efficiency can be further improved.
[0029]
In one embodiment, the first conductivity type layer and the second conductivity type layer are made of Mg. _x Zn _1-x O (0 <x <1).
[0030]
According to the embodiment, by using MgZnO mixed crystal for the first conductivity type layer and the second conductivity type layer, the hetero barrier to the light emitting layer is increased, and the carrier confinement efficiency in the light emitting layer is improved. As a result, the luminous efficiency can be further improved.
[0031]
In one embodiment, in the oxide semiconductor light emitting device, the light emitting layer includes Cd _y Zn _1-y O (0 <y <1).
[0032]
According to the embodiment, by using CdZnO for the light emitting layer, the band gap is reduced, and visible light emission having high industrial value is obtained.
[0033]
In one embodiment, the impurity doped in the light emitting layer includes one or more elements selected from Li, Na, K, Rb, Cu, Ag, and Au.
[0034]
According to the above embodiment, in the light emitting layer, the element replaces, for example, Zn and becomes an acceptor, and forms an impurity level at an energy position of about 100 to 400 meV from the valence band. Therefore, light emission having a wavelength component corresponding to energy of about 3 eV or less can be obtained. When two or more of the above impurities are contained, the respective impurity levels are different, so that the emission spectrum width in the light emitting layer is widened, and the light emission intensity is effectively increased.
[0035]
In one embodiment, the impurity doped in the light emitting layer includes at least one element selected from B, Al, Ga, In, Sc, Y, La, and Ce.
[0036]
According to the embodiment, in the light emitting layer, the element replaces, for example, Zn and becomes a donor, and forms an impurity level at an energy position of about 10 to 50 meV from the conduction band. Therefore, light emission having a wavelength component corresponding to energy of about 3.3 eV or less can be obtained. Further, when two or more of the above impurities are contained or when the above-mentioned group I element is further contained, the respective impurity levels are different, so that the emission spectrum width in the light emitting layer is widened. The emission intensity is effectively increased.
[0037]
In one embodiment, the impurity doped in the light-emitting layer includes one or more elements selected from N, P, As, Sb, Bi, V, Nb, and Ta.
[0038]
According to the embodiment, in the light-emitting layer, the element replaces, for example, O to become an acceptor, and forms an impurity level at an energy position of about 100 to 400 meV from the conduction band. Therefore, light emission having a wavelength component corresponding to energy of about 3 eV or less can be obtained. When two or more of the above impurities are contained, or when the above-mentioned group I element and group III element are further contained, the respective impurity levels are different, so that the emission spectrum width in the light emitting layer is increased. This effectively increases the light emission intensity.
[0039]
In one embodiment, the impurity doped in the light emitting layer includes at least one element selected from F, Cl, Br, I, Mn, and Re.
[0040]
According to the embodiment, in the light emitting layer, the element replaces, for example, O and becomes a donor, and forms an impurity level at an energy position of about 50 to 100 meV from the conduction band. Therefore, light emission having a wavelength component corresponding to energy of about 3.2 eV or less can be obtained. When two or more of the above impurities are contained, or when the above-mentioned group I element, group III element and group V element are further contained, the respective impurity levels are different. The spectrum width is broadened, thereby effectively increasing the emission intensity.
[0041]
In one embodiment, the impurity doped in the light emitting layer includes at least one element selected from C, Si, Ge, Sn, Ti, Zr, and Hf.
[0042]
According to the above embodiment, a relatively deep impurity level is formed by the element in the light emitting layer, and the wavelength of light emitted through the impurity level is relatively long. Thereby, emission of visible light wavelength is obtained. When two or more of the above impurities are contained, or when the above-mentioned group I element, group III element, group V element and group VII element are further contained, the respective impurity levels are different. The emission spectrum width in the emission layer is broadened, and the emission intensity is further increased.
[0043]
In one embodiment, the impurity doped in the light-emitting layer includes a plurality of elements.
[0044]
According to the above embodiment, exciton light emission and light emission between impurity levels at various energy levels can be obtained by including a plurality of elements in the impurity doped into the light emitting layer. By combining the plurality of wavelength components, it is possible to improve light emission characteristics such as an increase in light emission intensity.
[0045]
In one embodiment, the impurity doped in the light-emitting layer is formed by randomly dispersing the plurality of elements.
[0046]
According to the embodiment, the impurity doped in the light emitting layer is generated by dispersing a plurality of elements in a random manner, so that light emission based on different activation energies is uniformly mixed in the doped region. You. As a result, light with a wide spectrum width can be obtained, so that the emission intensity increases.
[0047]
In one embodiment, the light-emitting layer has the non-doped region on the p-type conductivity type layer side of the first conductivity type layer or the second conductivity type layer with respect to the center in the thickness direction. .
[0048]
According to the above embodiment, the electrons supplied from the n-type layer of the first conductivity type layer and the second conductivity type layer and the p-type layer of the first conductivity type layer and the second conductivity type layer With respect to the holes supplied from, the diffusion length in the light emitting layer is longer for electrons than for holes. Therefore, in the non-doped region formed closer to the p-type conductivity type layer than the center in the thickness direction of the light emitting layer, light recombination due to the electrons and holes efficiently occurs, and free exciton emission is preferentially performed. Occurs. As a result, the doped region of the light emitting layer is efficiently photoexcited by the free exciton light emission, and visible light is generated with high efficiency.
[0049]
In one embodiment, the doped region of the light emitting layer has an activation energy of an impurity doped in a portion near the non-doped region and an impurity doped in a portion near the first conductivity type layer. And the activation energy of the impurity doped in the portion near the second conductivity type layer.
[0050]
According to the above-described embodiment, the exciton emission generated in the non-doped region excites the carrier to the impurity level in the portion of the doped region near the non-doped region, and emits light via the impurity level. The impurity doped in the portion near the first conductivity type layer and the impurity doped in the portion near the second conductivity type layer have an activation energy of activating the impurity doped in the portion near the non-doped region. Since the energy is larger than the energy, carriers are effectively excited by light emitted from a portion of the doped region near the non-doped region, and light is emitted via an impurity level. Therefore, in the light emitting layer, excitation and light emission are effectively performed from a portion near the non-doped region to a portion near the first conductivity type layer and a portion near the second conductivity type layer. Luminous efficiency is obtained.
[0051]
In the doped region, the activation energy of impurities between the portion near the non-doped region, the portion near the first conductivity type layer, and the portion near the second conductivity type layer changes continuously. It does not need to be, and may change stepwise.
[0052]
In one embodiment, the doped region of the light emitting layer has an activation energy from a portion near the non-doped region toward the first conductivity type layer and the second conductivity type layer. The impurity is doped so as to increase the size.
[0053]
According to the above-described embodiment, the impurity in the doped region of the light-emitting layer is changed from the portion near the non-doped region to the first conductive type layer and the second conductive type layer as the transition between the impurity levels proceeds. Doping is performed so as to reduce energy. That is, an impurity level is formed such that the transition energy is gradually reduced from the portion near the non-doped region toward the first conductivity type layer and the second conductivity type layer. Therefore, the exciton emission generated in the non-doped region excites the carrier to the impurity level in the portion of the doped region near the non-doped region, and emits light via the impurity level. The energy of light emission via the impurity level in the vicinity of the non-doped region is larger than the transition energy of the impurities on the first conductivity type layer side and the second conductivity type layer side. Carriers are excited to impurity levels on the conductivity type layer side, and light emission occurs through the impurity levels. Thus, in the doped region of the light emitting layer, carriers are sequentially excited to the impurity level from the portion near the non-doped region, and light is emitted up to the boundary on the first conductivity type layer side and the boundary on the second conductivity type layer side. . As a result, light having a wavelength ranging from the ultraviolet to the visible region is efficiently generated in the light emitting layer.
[0054]
In one embodiment, the substrate is a ZnO substrate.
[0055]
According to the above-described embodiment, the ZnO substrate has excellent affinity with the ZnO-based semiconductor layer. Therefore, a favorable ZnO-based semiconductor layer having extremely few crystal defects can be formed on the ZnO substrate by, for example, epitaxial growth. Since the ZnO is conductive, an n-type electrode can be directly formed on the back surface of the ZnO substrate. Therefore, this oxide semiconductor light emitting device has low resistance and can simplify the production process, and as a result, an oxide semiconductor light emitting device having excellent luminous efficiency and production efficiency can be realized.
[0056]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
[0057]
(1st Embodiment)
In the first embodiment, an example of an oxide semiconductor light-emitting element including only ZnO will be described.
[0058]
FIG. 1 is a sectional view showing a light emitting diode 10 as an oxide semiconductor light emitting device of the first embodiment. The light emitting diode 10 of the present embodiment has a carrier concentration of 5 × 10 ¹⁸ cm ^-3 N-type ZnO layer 2 having a thickness of 1 μm, ZnO light-emitting layer 3 having a thickness of 10 μm doped with Ga, and a carrier concentration of 1 × 10 ¹⁸ cm ^-3 And a p-type ZnO layer 4 having a thickness of 1 μm. The n-type ZnO layer 2 is a first conductivity type layer, and the p-type ZnO layer 4 is a second conductivity type layer.
[0059]
The ZnO light emitting layer 3 has a non-doped region where impurities are not doped, which is located closer to the p-type ZnO layer 4 than the center in the thickness direction. This non-doped region has a thickness of 0.5 μm, and a carrier concentration of 1 × 10 ¹⁷ cm ^-3 Ga is uniformly doped so that
[0060]
FIG. 1 also shows a doping profile representing the doping concentration at each position from the n-type ZnO layer 2 to the p-type ZnO layer 4.
[0061]
On the back surface of the ZnO substrate 1, Al having a thickness of 1000 ° is formed as an n-type ohmic electrode 5.
[0062]
On the entire main surface of the p-type ZnO layer 4, a translucent ohmic electrode 6 formed by laminating Ni with a thickness of 150 ° is laminated. The Au pad electrode 7 is formed to have an area smaller than the translucent ohmic electrode 6.
[0063]
The light emitting diode 10 as the oxide semiconductor light emitting element of the present embodiment is characterized in that a non-doped region is formed in a part of the light emitting layer 3 and that the light emitting layer 3 has a thickness of 3 μm or more. .
[0064]
The light emitting diode 10 was mounted on a lead frame with an Ag paste, wired, molded, and emitted light. Blue light having a peak wavelength of 400 nm was obtained.
[0065]
FIG. 2 is a diagram showing the relationship between the thickness of the ZnO light emitting layer 3 and the light emission intensity of the light emitting diode 10 of the present embodiment.
[0066]
FIG. 2 shows, as a comparative example, a 6H-SiC light emitting diode (Comparative Example 1) in which an Al acceptor and an N donor are doped in a light emitting layer and has no non-doped region, and a Si donor is doped. A GaN-based light emitting diode having a non-doped region similar to the present invention (Comparative Example 2) and a ZnO-based semiconductor light emitting diode having a multiple quantum well light emitting layer including a MgZnO barrier layer and a CdZnO well layer (Comparative Example 3) The relationship between the light emitting layer thickness and the light emitting intensity is shown.
[0067]
In FIG. 2, the horizontal axis is the light emitting layer thickness (μm), and the vertical axis is the light emission intensity (relative intensity). The luminous intensity on the vertical axis does not take luminosity into account.
[0068]
The SiC light emitting diode of Comparative Example 1 is of an indirect transition type and has a relatively small light emission intensity. However, since it performs multi-step light emission of DA versus transition, light emission from a light emitting layer thickness of 5 μm to about 10 μm is obtained. The emission intensity increases with an increase in the layer thickness.
[0069]
Since the GaN-based light-emitting diode of Comparative Example 2 is a direct transition type, the light-emitting intensity is relatively large, and even when the light-emitting layer thickness is increased to about 12 μm, the light-emitting intensity increases with the light-emitting layer thickness. Increases, and has the same effect as the present invention.
[0070]
In contrast to these comparative examples, the ZnO light emitting diode 10 according to the present embodiment has the luminous intensity with the increase in the thickness of the light emitting layer 3 even when the thickness of the light emitting layer 3 is increased from about 10 μm to about 30 μm. Increase. That is, as shown in FIG. 2, the light emitting layer 3 of the present embodiment has a light emission substantially equivalent to that of the semiconductor light emitting device of Comparative Example 3 having a high light emitting efficiency and a carrier confinement effect by using a multiple quantum well structure in the light emitting layer. Strength is obtained.
[0071]
Although the reason is not clear, it is presumed to be related to the fact that the exciton binding energy of ZnO is as high as 60 meV. FIG. 3 shows a light emitting mechanism in the light emitting diode 10 of the present embodiment. In the present embodiment, since the n-type layer, the light-emitting layer, and the p-type layer are made of a ZnO-based semiconductor, compared with Comparative Example 1 in which the light-emitting layer is formed of GaN (exciton binding energy is about 24 meV), Exciton emission from the non-doped region of the layer 3 is extremely strong. It is considered that the strong exciton light emission excites carriers at the impurity level in the doped region adjacent to the non-doped region in the light emitting layer 3 and significantly promotes light emission via this impurity level.
[0072]
As can be seen from FIG. 2, the thickness of the light emitting layer 3 is preferably 3 μm or more and 30 μm or less in that the light emission intensity can be increased with the increase in the thickness of the light emitting layer 3. However, if the light emitting layer 3 is excessively thick, the manufacturing cost increases. Therefore, it is more preferable that the light emitting layer 3 has a thickness of 5 μm or more and 15 μm or less, at which sufficient emission intensity is obtained.
[0073]
The oxide semiconductor light-emitting device of the present embodiment includes a molecular beam epitaxy (hereinafter, referred to as MBE) method, a pulse laser deposition (hereinafter, referred to as PLD) method using a solid material or a gaseous material, and a metal organic chemical vapor deposition (hereinafter, referred to as MOCVD). ) Method.
[0074]
FIGS. 4A and 4B show the ZnO-based light-emitting diode 10 of the first embodiment and the ZnO-based light-emitting diode having a multiple quantum well light-emitting layer of Comparative Example 3 in which the vicinity of the light-emitting layer is formed by MBE. FIG. 4 is a diagram showing a growth temperature control and a raw material supply sequence in the case of performing the above.
[0075]
As shown in FIG. 4B, in Comparative Example 3, when forming the n-type and p-type MgZnO cladding layers and the multiple quantum well light emitting layer, the vapor pressures of the group II elements Mg, Cd and Zn which are the raw materials are used. Therefore, it is necessary to control the growth temperature according to the composition ratio of the layer to be formed. In particular, when CdZnO and MgZnO are alternately stacked a plurality of times to form a quantum well light emitting layer, it is necessary to control so that the growth temperature is frequently changed between different values. In addition, it is necessary to frequently open and close a plurality of cell shutters for supplying a raw material.
[0076]
On the other hand, in the present embodiment, since MgZnO mixed crystal or CdZnO mixed crystal is not laminated, as shown in FIG. 4A, temperature control and opening / closing of a cell shutter are almost unnecessary. Therefore, the light emitting diode of the present embodiment greatly simplifies the manufacturing process, thereby greatly improving the yield.
[0077]
As a lamination method used in the manufacturing process of the light emitting diode of the present embodiment, a molecular beam epitaxy (laser MBE) method, which is one of the PLD methods, is particularly preferable in the following points. That is, the composition deviation between the raw material target and the thin film to be laminated is small, and an unintended by-product (ZnGa ₂ O ₄ Etc.) can be suppressed. Also, it is obvious that, even when the laser MBE method is used, according to the light emitting diode of the present embodiment, simplification of the process and improvement of the yield can be effectively realized.
[0078]
In the present embodiment, if a non-doped region is formed in the light emitting layer 3, the effects of the present invention can be obtained. However, the carrier diffusion length in the light emitting layer 3 is longer for electrons than holes, so that exciton emission generated by injected carriers preferentially occurs on the side closer to the p-type ZnO layer 4 that supplies holes. Occurs. Therefore, the non-doped region is preferably formed closer to the p-type ZnO layer 4 than the center of the light emitting layer 3 in the thickness direction.
[0079]
In addition, in order to obtain exciton light emission having sufficient intensity to cause multi-step light emission, the thickness of the non-doped region is preferably 3% or more of the total thickness of the light emitting layer 3. However, if the non-doped region is thicker than the doped region, it is difficult to effectively generate multi-step light emission and the operating voltage increases. Therefore, the thickness of the non-doped region is preferably 50% or less of the total thickness of the light-emitting layer 3, and more preferably 30% or less, in that light can be emitted at the same operating voltage as the conventional one.
[0080]
The impurity introduced into the doped region of the light emitting layer 3 has a carrier concentration lower than that of either the n-type ZnO layer 2 or the p-type ZnO layer 4 in order to suppress carrier overflow and absorption loss and to prevent an increase in operating voltage. And the doping concentration is 1 × 10 ¹⁶ ~ 1 × 10 ¹⁹ cm ^-3 Is preferably within the range. In particular, the doping concentration is 1 × 10 ¹⁷ ~ 1 × 10 ¹⁸ cm ^-3 Is more preferable in that the deterioration of crystallinity can be prevented.
[0081]
In the present embodiment, Ga, which is an n-type donor impurity, is used as an impurity to be introduced into the doped region of the ZnO light emitting layer 3, but is smaller than the free exciton emission (about 3.3 eV) of ZnO at room temperature. What is necessary is just to be able to form the impurity level which can take transition energy. Such impurities include, for example, the following four types.
[0082]
(1) The group I element replaces Zn and becomes an acceptor, and forms an impurity level at an energy position of about 100 to 400 meV from the valence band. Specifically, there are Li, Na, K, Rb, Cu, Ag, and Au. In particular, Li, Cu and Ag are preferable, and Ag is most preferable, since the activation energy is relatively small and the doping efficiency is high.
[0083]
(2) The group III element becomes a donor by replacing Zn, and forms an impurity level at an energy position of about 10 to 50 meV from the conduction band. Specifically, there are B, Al, Ga, In, Sc, Y, La and Ce. In particular, Al, Ga and In are preferable, and Ga and Al are most preferable, since the activation energy is relatively small and the doping efficiency is high.
[0084]
(3) The group V element becomes an acceptor by substituting O (oxygen) and forms an impurity level at an energy position of about 100 to 400 meV from the valence band. Specifically, there are N, P, As, Sb, Bi, V, Nb and Ta. In particular, N and P are preferable, and N is most preferable, since activation energy is relatively small and doping efficiency is high.
[0085]
(4) Group VII element replaces O (oxygen) and becomes a donor, and forms an impurity level at an energy position of about 50 to 100 meV from the conduction band. Specifically, there are F, Cl, Br, I, Mn and Re. F and Cl are particularly preferable because activation energy is relatively small and doping efficiency is high.
[0086]
(5) Since the group V element forms a deep impurity level, light of a long wavelength can be obtained through the impurity level. Specifically, there are C, Si, Ge, Sn, Ti, Zr and Hf. In terms of low cost and high doping efficiency, Si, Ti and Zr are preferred, and Si is most preferred.
[0087]
In the present embodiment, the p-type ZnO layer 4 is doped with N as an impurity. However, the impurities to be doped into the p-type ZnO layer 4 include Li, Cu, and Ag of a group I element, and N, of a group V element. As and P can be used. N and Ag are particularly preferred because of their low activation energy. ₂ Is particularly preferred by a method of irradiating during the crystal growth by turning into a plasma, since high-concentration doping can be performed while maintaining good crystallinity.
[0088]
In the present embodiment, it is preferable that the p-type ZnO layer 4 is doped with a p-type impurity at a high concentration to reduce the resistance in order to increase the luminous efficiency. However, if the doping concentration is excessive, the p-type ZnO layer 4 causes remarkable absorption loss and crystallinity deterioration. ¹⁶ ~ 5 × 10 ¹⁹ cm ^-3 It is preferable to set the doping concentration so that the carrier concentration falls within the range described above.
[0089]
As the n-type impurity to be doped into the n-type ZnO layer 2, a group III element such as B, Al, Ga, and In can be used. However, in view of a high activation rate in a ZnO-based semiconductor, Ga or Al is preferred.
[0090]
Further, in order to obtain the maximum luminous efficiency, it is preferable to use a material having a low absorption coefficient corresponding to the emission wavelength for the substrate 1. In the present embodiment, the single crystal ZnO used as the substrate 1 has the same material system as the layer grown thereon, so that the generation of crystal defects is extremely small and is most preferable. The use of a zinc surface is preferable because the carrier activation rate of the p-type ZnO layer 4 is improved and the resistance is reduced.
[0091]
The substrate 1 may be made of sapphire or LiGaO4 in addition to ZnO single crystal. ₂ Or an electrically conductive substrate such as SiC or GaN.
[0092]
In particular, when an insulating substrate is used as the substrate 1, a part of the growth layer thereon is etched to expose the n-type ZnO layer 2, and the n-type ohmic electrode 5 is formed on the exposed n-type ZnO layer 2. May be formed. In addition, a buffer layer may be provided on the substrate 1 in order to obtain a growth layer having good crystallinity.
[0093]
On the other hand, when a conductive substrate is used as the substrate 1, as shown in this embodiment, the n-type ohmic electrode 5 can be directly formed on the back surface of the substrate 1, so that the element resistance can be reduced and the manufacturing process can be simplified. Is preferable.
[0094]
In addition, it is preferable that the substrate 1 be provided with unevenness on the back surface thereof by a known method such as polishing or etching, because the emitted light is diffusely reflected to improve the light extraction efficiency.
[0095]
For the p-type ohmic electrode 6, Ni, Pt, Pd, Au, or the like can be used, and particularly, Ni having low resistance and good adhesion is preferable. Alternatively, the p-type electrode 6 may be formed by alloying the plurality of metal materials.
[0096]
The p-type ohmic electrode 6 is preferably formed to have a light-transmitting property to improve the light extraction efficiency in order to effectively reduce the operating voltage and improve the luminous efficiency. The thickness of the p-type electrode 6 that achieves both good ohmic characteristics and high translucency is preferably in the range of 50 to 2000 °, and more preferably in the range of 300 to 1000 °.
[0097]
Further, it is preferable to perform an annealing treatment after the formation of the p-type ohmic electrode 6 because the adhesion to the underlying p-type ZnO layer 4 is improved and the contact resistance is reduced. In order to obtain an annealing effect without causing defects in the ZnO crystal forming each layer, the annealing temperature is preferably 300 to 400 ° C. The atmosphere in the annealing process is O ₂ Alternatively, it is preferably in an air atmosphere. ₂ In the atmosphere, the resistance increases conversely.
[0098]
If the pad electrode 7 is formed on a part of the translucent p-type ohmic electrode 6 with a smaller area than the p-type ohmic electrode 6, the pad electrode 7 can be connected to the lead without impairing the light transmission effect of the p-type ohmic electrode 6. This is preferable because the mounting process on the frame can be facilitated. The material of the pad electrode 7 is preferably Au, which can be easily bonded and does not become a donor impurity even when diffused into ZnO. Another metal layer may be interposed between the p-type ohmic electrode 6 and the pad electrode 7 in order to improve adhesion and light reflectivity.
[0099]
For the n-type ohmic electrode 5, a material such as Ti, Cr and Al can be used. In particular, Al with low resistance and low cost or Ti with good adhesion is preferable. Further, the n-type electrode 5 may be formed by alloying the plurality of metal materials. Since the n-type electrode 5 of the present embodiment is made of Al having a relatively high reflectance for blue to ultraviolet light, and is formed on the entire back surface of the substrate 1, good light extraction efficiency can be obtained. Alternatively, the n-type electrode 5 may be patterned into an arbitrary shape, and the exposed back surface of the substrate 1 may be bonded to a lead frame with an Ag paste or the like. In this case, Ag is preferable because it has a higher reflectance for blue to ultraviolet light than Al. When the n-type ohmic electrode 5 is patterned, an auxiliary electrode may be formed in order to prevent an increase in element resistance. The auxiliary electrode has a reflectance for blue to ultraviolet light such as Ag or Pt. It is more preferable to use a high metal.
[0100]
In the present embodiment, other configurations are optional and are not limited by the present embodiment.
[0101]
(2nd Embodiment)
The second embodiment is different from the first embodiment except that the ZnO light emitting layer 13 is doped with Ga and N, and the doping concentration in the doped region of the ZnO light emitting layer 13 becomes higher toward the vicinity of the non-doped region. Is the same as the above ZnO-based light emitting diode.
[0102]
FIG. 5 is a diagram showing a cross section and a doping profile of the light emitting diode of the present embodiment. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description is omitted.
[0103]
As shown in FIG. 5, the ZnO light emitting layer 13 has a non-doped region at a position closer to the p-type ZnO layer 4 than the center in the thickness direction, and the non-doped region is closer to the n-type ZnO layer 2 and to the p-type ZnO layer 4. On the side, there are doped regions doped with Ga and N, respectively. The concentration of Ga and N in the doped region is set highest in the portion adjacent to the non-doped region. The doping region has a doping profile in which the concentrations of Ga and N decrease from the portion adjacent to the non-doping region toward the n-type ZnO layer 2 and the p-type ZnO layer 4. That is, the impurity is doped from the portion adjacent to the non-doped region toward the n-type ZnO layer 2 and the p-type ZnO layer 4 so that the activation energy is reduced.
[0104]
In the present embodiment, Ga and N doped in the ZnO light emitting layer 13 are introduced to generate DA (donor / acceptor) pair light emission, and are disclosed as a technique for obtaining a low-resistance p-type ZnO layer. This is different from the so-called “co-doping technique”.
[0105]
When the light emitting diode of this embodiment was mounted on a lead frame with an Ag paste, and wiring and molding were performed to emit light, blue light with a peak wavelength of 420 nm was obtained. Further, the light emission intensity was improved by 50% with respect to the light emission intensity in the first embodiment.
[0106]
In the light emitting diode of the present embodiment, the emission wavelength is increased and the emission intensity is improved because a plurality of impurities doped into the ZnO light emitting layer 13 increase the spectral width of DA versus emission, and further increase the ZnO emission. This is probably because the doping profile of the light emitting layer 13 was optimized for the light emitting process.
[0107]
That is, in the light emission from the DA, as the doping concentration increases, the distance between the DA and the light becomes shorter, and the emission wavelength becomes shorter. Therefore, the exciton light emission in the non-doped region excites the carrier to a high concentration of impurity levels in the region adjacent to the non-doped region, so that a short-wavelength DA pair light emission is obtained. Due to this short-wavelength light, carriers are excited to an impurity level of a somewhat lower concentration in the n-type layer side and the p-type layer side than this area, and DA emission having a wavelength slightly longer than the short-wavelength light is emitted. can get. In this way, the carriers are sequentially excited to the impurity level in the doped region doped with impurities so that the concentration becomes lower toward the n-type layer side and the p-type layer side, and light is emitted. The entire layer emits light in a spectrum having a relatively wide width, so that the luminous efficiency can be improved and the luminous intensity can be increased.
[0108]
In the above embodiment, the doped region is doped with Ga and N, but may be doped with another impurity.
[0109]
Regarding the profile of the impurity introduced into the doped region of the light emitting layer 13, the impurity concentration in the portion near the non-doped region is higher than the impurity concentration in the portion near the n-type ZnO layer 2 and the portion near the p-type ZnO layer 4. If it is high, the density profile of the other portions may have any shape such as a linear shape, a curved shape, and a stepped shape.
[0110]
(Third embodiment)
FIG. 6 is a sectional view showing a light emitting diode of the third embodiment.
[0111]
The light emitting diode of the present embodiment has an n-type MgO layer between the n-type ZnO layer 2 and the ZnO light-emitting layer 3. _0.05 Zn _0.95 An O-cladding layer 8 is formed, and a p-type MgO layer is formed between the p-type ZnO layer 4 and the ZnO light emitting layer 3. _0.05 Zn _0.95 Except that the O clad layer 9 is formed, the ZnO-based light emitting diode of the first embodiment has the same configuration.
[0112]
In the drawings, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description is omitted.
[0113]
When the light emitting diode of this embodiment was mounted on a lead frame with an Ag paste, wired, and molded to emit light, blue light having a peak wavelength of 400 nm was obtained.
[0114]
FIG. 7 is a diagram showing the relationship between the thickness of the ZnO light emitting layer 3 and the light emission intensity in the light emitting diode of the present embodiment. In FIG. 7, the horizontal axis is the light emitting layer thickness (μm), and the vertical axis is the light emission intensity (relative intensity). FIG. 7 also shows the relationship in the light emitting diode of the first embodiment.
[0115]
As can be seen from FIG. 7, according to the present embodiment, when the ZnO light emitting layer 3 has a layer thickness of up to about 5 μm, the present embodiment having the double hetero structure has a better structure than the first embodiment having the homo structure. However, the emission intensity is high. However, when the thickness of the light-emitting layer is larger than that, the light-emitting intensity of the present embodiment is substantially the same as the light-emitting intensity of the first embodiment. Therefore, it is considered that there is not much advantage in confining carriers by the hetero barrier. Therefore, when the thickness of the light emitting layer is 5 μm or less and cannot be increased further, it is preferable to form a double hetero structure using MgZnO mixed crystal.
[0116]
In order to obtain a sufficient carrier confinement effect while maintaining the crystallinity of the cladding layers 8 and 9, it is necessary to use Mg. _x Zn _1-x The composition ratio x of Mg in O is preferably 0.01 or more and 0.5 or less, and more preferably 0.03 or more and 0.33 or less.
[0117]
The light emitting layer 3 is made of Cd _y Zn _1-y Even when the emission wavelength is further increased as an O mixed crystal, the same effect as in the present embodiment can be obtained. In this case, in order to maintain the crystallinity and increase the emission wavelength, Cd _y Zn _1-y The composition ratio y of Cd of O is preferably 0.02 or more and 0.3 or less, more preferably 0.05 or more and 0.25 or less.
[0118]
(Fourth embodiment)
The light emitting diode of the fourth embodiment has the same configuration as the light emitting diode of the first embodiment, except that Ga, N, and Si as impurities are uniformly and simultaneously doped in the doped region of the light emitting layer. The same components as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0119]
In the doped region of the light emitting layer, Ga, N, and Si as the uniformly and simultaneously doped impurities are randomly distributed.
[0120]
When the light emitting diode of the above embodiment was mounted on a lead frame with an Ag paste, wired, and molded to emit light, blue light having a peak wavelength of 420 nm was obtained. The emission light of the light emitting diode of the present embodiment has an emission spectrum width that is twice or more that of the first embodiment, and the luminance in consideration of the visibility is improved by 60%.
[0121]
In the light emitting diode of the present embodiment, Ga, N, and Si form impurity levels different from each other in the band gap energy in the doped region. Carriers are excited to the different impurity levels by the exciton emission generated in the non-doped region, thereby generating light of a plurality of wavelengths corresponding to a plurality of transition energies. As a result, light of a plurality of wavelengths overlaps, and light emission of a relatively wide spectrum width is obtained. Further, since Si among the impurities forms a deep level, the spectrum has a longer wavelength.
[0122]
According to the light emitting diode of this embodiment, although the color purity is inferior due to the expansion of the spectrum width, an extremely high emission intensity can be obtained. Therefore, for example, when used as a phosphor excitation light source, it is possible to form a multicolor light emitting element having better light emission intensity and power saving than before.
[0123]
The impurity introduced into the doped region of the light emitting layer is not limited to Ga, N, and Si, and an element may be added or changed according to the emission intensity or spectrum width to be generated.
[0124]
(Fifth embodiment)
The light-emitting diode according to the fifth embodiment divides the two doped regions of the light-emitting layer 23 into four regions, respectively, and, in order from a region adjacent to the non-doped region, a region doped only with Ga and a region doped only with N. The structure is the same as that of the first embodiment except that a region doped with Ga, N, and a region doped with Ga, N, and Si are provided. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description is omitted.
[0125]
FIG. 8 is a diagram illustrating a cross section of the light emitting diode of the present embodiment and doping profiles of the n-type ZnO layer 2, the ZnO light-emitting layer 23, and the p-type ZnO layer 4 of the light-emitting diode. As shown in FIG. 8, the light emitting layer 23 has two doped regions formed on the upper side and the lower side of the non-doped region, the Ga-doped region, the N-doped region, Ga and N-doped regions, Ga, N and Si-doped regions are formed respectively.
[0126]
When the light emitting diode of this embodiment was mounted on a lead frame with an Ag paste, wiring and molding to emit light, blue light having a peak wavelength of 450 nm was obtained. In addition, the light emission intensity without considering the visibility was improved by 30% with respect to the light emission intensity of the light emitting diode of the fourth embodiment.
[0127]
FIGS. 9A and 9B are diagrams for explaining the light emitting mechanism of the light emitting diode of the present embodiment in comparison with that of the fourth embodiment. FIG. 9A shows a light emitting mechanism of the light emitting diode of the fourth embodiment, and FIG. 9B shows a light emitting mechanism of the light emitting diode of the fifth embodiment.
[0128]
The light emitting diode of the present embodiment is the same as the light emitting diode of the fourth embodiment in that it has a plurality of impurity levels in the doped region. However, in the fourth embodiment, a plurality of impurity levels are randomly dispersed in the doped region, whereas in the present embodiment, the impurity levels are sequentially changed from the non-doped region side and the transition energy is They are arranged in descending order. Therefore, as shown in FIG. 9B, the exciton emission generated in the non-doped region causes the N impurity level, Ga and N impurity levels, Ga, For N and Si impurity levels, carriers are reliably excited, and light having a wavelength corresponding to each transition energy is generated. As a result, the light emitting layer 23 can emit light in a spectrum ranging from ultraviolet to blue with high efficiency, despite having a relatively large thickness.
[0129]
The impurities to be introduced into the doped region of the light emitting layer 23 are not limited to Ga, N, Ga and N, and Ga, N and Si, and elements may be added according to the emission intensity or spectrum width to be generated. May be changed. The point is that the impurities may be doped in order from the non-doped region side in order of increasing transition energy of the impurity level.
[0130]
【The invention's effect】
As is clear from the above, according to the oxide semiconductor light emitting device of the present invention, at least the first conductivity type layer, the light emitting layer, and the second conductivity type layer are provided on the substrate, and the light emitting layer is doped with impurities. And a non-doped region in which impurities are not doped, so that exciton luminescence that occurs preferentially in the non-doped region results in multi-step luminescence that promotes luminescence through the impurity level in the doped region. Thus, light emission can be obtained over substantially the entire light emitting layer without using a multiple quantum well structure or the like. As a result, high efficiency and high intensity light emission can be realized with a simple structure.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a light emitting diode as an oxide semiconductor light emitting device according to a first embodiment.
FIG. 2 is a diagram showing a relationship between a layer thickness of a light emitting layer and light emission intensity in the light emitting diode of the first embodiment.
FIG. 3 shows a light emitting mechanism in the light emitting diode of the first embodiment.
FIG. 4 (a) shows the light emitting diode of the first embodiment, and FIG. 4 (b) shows the light emitting diode of Comparative Example 3 when controlling the growth temperature and material supply when forming the vicinity of the light emitting layer by the MBE method. It is a figure which shows a sequence each.
FIG. 5 is a diagram illustrating a cross section and a doping profile of a light emitting diode according to a second embodiment.
FIG. 6 is a sectional view showing a light emitting diode of a third embodiment.
FIG. 7 is a diagram illustrating a relationship between a layer thickness of a light emitting layer and light emission intensity in a light emitting diode according to a third embodiment.
FIG. 8 is a diagram showing a cross section and a doping profile of a light emitting diode according to a fifth embodiment.
FIG. 9A illustrates a light emitting mechanism of a light emitting diode according to a fourth embodiment, and FIG. 9B illustrates a light emitting mechanism of a light emitting diode according to a fifth embodiment.
[Explanation of symbols]
1 ZnO substrate
2 n-type ZnO layer
3 ZnO light emitting layer
4 p-type ZnO layer
5 n-type ohmic electrode
6 Transparent ohmic electrode
7 Au pad electrode
10. Light emitting diode

Claims (18)

On the substrate, at least a first conductivity type layer, a light emitting layer and a second conductivity type layer are provided,
An oxide semiconductor light emitting device, wherein the light emitting layer has a doped region doped with an impurity and a non-doped region not doped with an impurity. The oxide semiconductor light emitting device according to claim 1,
An oxide semiconductor light emitting device, wherein the light emitting layer has a thickness of 3 μm or more and 30 μm or less. The oxide semiconductor light emitting device according to claim 2,
An oxide semiconductor light emitting device, wherein the light emitting layer has a thickness of 5 μm or more and 15 μm or less. The oxide semiconductor light emitting device according to claim 1,
An oxide semiconductor light emitting device, wherein the first conductivity type layer, the light emitting layer, and the second conductivity type layer are all made of ZnO. The oxide semiconductor light emitting device according to claim 1,
An oxide semiconductor light emitting device, wherein the first conductivity type layer and the second conductivity type layer are made of a ZnO-based semiconductor having a band gap larger than that of the light emitting layer. The oxide semiconductor light emitting device according to claim 5,
The first conductive layer and a second conductivity type _layer, oxide semiconductor light-emitting device characterized by comprising a _{Mg x Zn 1-x O (} 0 <x <1). The oxide semiconductor light emitting device according to claim 1, 2, 3, 5, or 6,
The light emitting _layer, Cd _{y Zn 1-y} O oxide semiconductor light-emitting device characterized in that it consists of (0 <y <1). The oxide semiconductor light-emitting device according to any one of claims 1 to 7,
An oxide semiconductor light-emitting element, wherein the impurity doped in the light-emitting layer includes one or more elements selected from Li, Na, K, Rb, Cu, Ag, and Au. The oxide semiconductor light emitting device according to claim 1,
An oxide semiconductor light-emitting element, wherein the impurity doped in the light-emitting layer includes one or more elements selected from B, Al, Ga, In, Sc, Y, La, and Ce. The oxide semiconductor light emitting device according to any one of claims 1 to 9,
An oxide semiconductor light emitting device, wherein the impurity doped in the light emitting layer contains one or more elements selected from N, P, As, Sb, Bi, V, Nb and Ta. The oxide semiconductor light emitting device according to any one of claims 1 to 10,
An oxide semiconductor light-emitting element, wherein the impurity doped in the light-emitting layer contains one or more elements selected from F, Cl, Br, I, Mn, and Re. The oxide semiconductor light emitting device according to any one of claims 1 to 11,
An oxide semiconductor light emitting device, wherein the impurity doped in the light emitting layer includes one or more elements selected from C, Si, Ge, Sn, Ti, Zr, and Hf. The oxide semiconductor light emitting device according to any one of claims 1 to 12,
An oxide semiconductor light-emitting element, wherein the impurity doped in the light-emitting layer includes a plurality of elements. The oxide semiconductor light emitting device according to claim 13,
An oxide semiconductor light-emitting element, wherein the plurality of elements are randomly dispersed in the impurity doped in the light-emitting layer. The oxide semiconductor light emitting device according to any one of claims 1 to 14,
The oxide semiconductor light emitting device, wherein the light emitting layer has the non-doped region closer to the p-type conductive layer of the first conductive layer or the second conductive layer than the center in the thickness direction. The oxide semiconductor light emitting device according to any one of claims 1 to 15,
In the doped region of the light emitting layer, the activation energy of the impurity doped in the portion near the non-doped region is the activation energy of the impurity doped in the portion near the first conductivity type layer and the second conduction type. An oxide semiconductor light emitting device, wherein the activation energy of an impurity doped in a portion near a mold layer is smaller than the activation energy. The oxide semiconductor light emitting device according to claim 16,
The doped region of the light emitting layer is doped with the impurity such that activation energy increases from a portion near the non-doped region toward the first conductivity type layer and the second conductivity type layer. An oxide semiconductor light emitting device, comprising: The oxide semiconductor light emitting device according to any one of claims 1 to 17,
An oxide semiconductor light-emitting element, wherein the substrate is a ZnO substrate.

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