JP2006287120A - Light emitting element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting element whose light emitting efficiency is high and can be manufactured through a simple process. <P>SOLUTION: The light emitting element includes a light emitting layer 3 having a first surface and second surface, a first electrode 4 which is formed on a part of the first surface of the light emitting element layer 3, and a second electrode 8 which is formed on a part of the second surface of the light emitting element layer 3, where the first electrode 4 and the second electrode 8 are located, dislocated from each other. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light emitting device and a method for manufacturing the same.

  Among the LED elements, a double hetero structure having a laminated structure in which an active layer is sandwiched between an n-type clad layer and a p-type clad layer whose composition and material are set so as to be larger than the band gap of the active layer is an LED element. It is effective in increasing the luminous efficiency inside the. For the formation of high-brightness LED elements, it is important not only to improve the internal luminous efficiency, but also to realize effective light extraction outside by improving absorption inside the element, shielding by electrodes, etc. . Carrier injection into the light emitting part is performed through a metal electrode formed on the surface of the element. However, light emitted directly under the metal electrode and light traveling to the electrode side is blocked by the metal electrode and is difficult to extract effectively. is there.

  In order to improve the light extraction efficiency, an example of increasing the light extraction efficiency by preventing current from flowing under the electrode by providing a current blocking layer of a different conductivity type in the current diffusion layer under the electrode is disclosed in Patent Document 1. It is described in.

Furthermore, Patent Document 2 describes an example in which a part of the current diffusion layer under the electrode is removed to prevent the current from flowing under the electrode and the light extraction efficiency is increased.
JP-A-4-229665 JP-A-8-335717

  However, in order to improve the light extraction efficiency of the conventional LED element, a process such as removal of the current confinement structure, the current blocking layer, and the current diffusion layer is required, and the number of manufacturing steps increases.

  The present invention has been made on the basis of recognition of the problems in the prior art described above. For example, the present invention provides a light-emitting element that has a high light extraction efficiency and can be manufactured by a simple process, and has a high light extraction efficiency. An object is to manufacture a light-emitting element by a simple process.

A first aspect of the present invention relates to a light emitting element, and the light emitting element includes a light emitting element layer having a first surface and a second surface, and a first portion formed on a part of the first surface of the light emitting element layer. 1 electrode and the 2nd electrode formed in a part of said 2nd surface of the said light emitting element layer, Here, the said 1st electrode and the said 2nd electrode are arrange | positioned mutually shifted.
According to a preferred embodiment of the present invention, it is preferable that the first electrode and the second electrode are arranged so as not to overlap each other.

According to a preferred embodiment of the present invention, the light emitting element layer includes a pn junction surface, and light generated at the pn junction surface is extracted to the outside through the second surface, and the first surface and the pn junction surface The first distance is shorter than the second distance between the second surface and the pn junction surface.
According to a preferred embodiment of the present invention, the light emitting element layer includes an active layer, and light generated in the active layer is extracted to the outside through the second surface, and the first surface and the active layer are It is preferable that one distance is shorter than a second distance between the second surface and the active layer.

According to a preferred embodiment of the present invention, the light emitting element layer includes a well layer, and light generated in the well layer is extracted to the outside through the second surface, and the first surface and the well layer It is preferable that one distance is shorter than a second distance between the second surface and the well layer.
Can be.

According to a second aspect of the present invention, there is provided a method for manufacturing a light emitting device, the manufacturing method comprising: forming a light emitting device layer having a first surface and a second surface; and forming the first surface of the light emitting device layer. Forming a first electrode on a part thereof, and forming a second electrode on a part of the second surface of the light emitting element layer, wherein the first electrode and the second electrode comprise: They are formed with their positions shifted from each other.
According to a preferred embodiment of the present invention, the light emitting element layer has a stacked structure made of a material selected from the group consisting of GaN, InGaN, AlGaN, GaAs, AlGaAs, InGaAs, InGaAsP, InP, and InGaP. It is preferable.
According to a preferred embodiment of the present invention, the seed substrate is preferably formed of any material selected from the group consisting of Al ₂ O ₃ , SiC, GaAs, InP, Ge, and Si.

  According to a preferred embodiment of the present invention, the separation structure preferably includes a separation layer made of a material having a lattice constant and / or a thermal expansion coefficient different from that of the seed substrate.

According to the present invention, it is possible to provide a light emitting device that has a high light extraction efficiency and can be manufactured by a simple process.
According to the present invention, a light emitting device with high light extraction efficiency can be manufactured by a simple process.

  Hereinafter, a method for manufacturing a light emitting device according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

  1 to 7 are conceptual diagrams illustrating a method for manufacturing a light emitting device according to a preferred embodiment of the present invention.

  First, in the process shown in FIG. 1, a separation layer 2 as a separation structure is formed on a seed substrate 1 having crystallinity such as a germanium (Ge) substrate. The isolation layer 2 can be configured by heteroepitaxially growing a material such as InGaAs having a lattice constant and / or a thermal expansion coefficient different from those of the substrate 1 on the seed substrate 1 directly or via another layer.

  Here, the separation structure may include a buffer layer and / or a separation auxiliary membrane in addition to the separation layer 2. The structure for separation is the inside thereof (for example, the inside of the separation layer 2, the interface between the separation layer 2 and the buffer layer, the interface between the separation layer 2 and the separation auxiliary layer), and / or the structure for separation and the top Strain energy due to lattice constant and / or thermal expansion coefficient mismatch is concentrated at the interface with the light emitting element layer 3 and / or at the interface between the separation structure and the seed substrate 1. Let

  Next, a light emitting element layer (LED layer) 3 made of a compound semiconductor such as GaAs is formed on the separation layer 2. The light emitting element layer 3 can be configured as, for example, a single heterostructure, a double heterostructure, or a single quantum well structure.

  Next, in the process shown in FIG. 2, a first metal electrode (lower electrode) 4 for carrier injection is formed on a part of the first surface of the light emitting element layer 3.

Next, in the process shown in FIG. 3, an insulator such as a plasma oxide film is formed on the entire surface of the substrate on which the metal electrode 4 is formed by CVD or the like, and then the surface of the metal electrode 4 is exposed. The insulating film is polished by a process such as CMP, and the surface of the substrate is planarized to form the insulating layer 5. Accordingly, the substrate having the separation layer 2 as the separation structure on the seed substrate 1, the light emitting element layer 3 on the separation layer 2, and the first metal electrode 4 and the insulating layer 5 on the separation layer 2 (hereinafter, referred to as the “separation structure”) 10) (referred to as donor substrate). Here, instead of disposing the insulating layer 5, a portion of the insulating layer 5 may be a gap.
Next, in the step shown in FIG. 4, the composite member 20 is formed by bonding the donor substrate 10 (seed substrate 1) to the handle substrate (support) 6 so that the first metal electrode 4 and the insulating layer 5 are inside. . As the handle substrate 6, for example, a Si substrate can be adopted.
Next, in the step shown in FIG. 5, the composite member 20 is divided using the separation structure (separation layer 2). Specifically, by applying a force or energy for inducing division of the composite member 20 to the composite member 20 (more specifically, a portion where strain energy is generated), the composite member 20 is separated. (For example, the inside of the separation layer 2, the interface between the separation layer 2 and the buffer layer, the interface between the separation layer 2 and the separation auxiliary layer) and / or the interface between the structure for separation and the light emitting element layer 3. And / or a crack spreading in the surface direction is generated at the interface between the separation structure and the seed substrate 1 to divide the composite member 20 into two members. In such a dividing step, it is preferable to induce the division by driving a fluid into the separation structure of the composite member 20 or in the vicinity thereof.

  By this division step, the light emitting element layer 3 is transferred from the seed substrate 1 (donor substrate 10) to the handle substrate 6, and as shown in FIG. 6, the metal electrode 4 and the insulating layer 4 (or A substrate having a layer composed of voids) and a light emitting element layer 3 is obtained.

  Next, as shown in FIG. 7, on the second surface of the light emitting element layer 3, a position shifted from the position of the first metal electrode 4 in the plane direction (preferably, the second metal electrode (upper electrode) 8 A second metal electrode (upper electrode) 8 is formed at a position where the region does not overlap the region of the first metal electrode (lower electrode) 3.

  If the light emitting element layer 3, the first metal electrode 4 and the second metal electrode 8 have a single hetero structure, the thickness from the pn junction surface to the first metal electrode 4 is from the pn junction surface. It is preferable to be configured to be sufficiently small with respect to the thickness up to the second metal electrode 8. The thickness from the pn junction surface to the first metal electrode 4 is preferably in the range of 10 to 1 μm, for example.

  The light emitting element layer 3, the first metal electrode 4, and the second metal electrode 8 have a thickness from the active layer to the first metal electrode 4 if the light emitting element layer 3 is a double hetero structure or a single quantum well structure. It is preferable to be configured to be sufficiently small with respect to the thickness from the active layer to the second metal electrode 8. The thickness from the active layer to the first metal electrode 4 is preferably in the range of 10 to 1 μm, for example.

  The first metal electrode 4 is configured as an anode when a semiconductor layer in contact with the first metal electrode 4 among the plurality of semiconductor layers included in the light emitting element layer 3 is p-type, and the semiconductor in contact with the first metal electrode 4 When the layer is n-type, it is configured as a cathode.

  The LED element emits light in which electrons and holes diffused in the current diffusion layer and the cladding layer are recombined in the active layer or the well layer. Recombination occurs in the vicinity of the carrier injection position if the light emission location is close to the carrier injection position.

  In a general LED element, one electrode (light extraction side (front side) electrode) is formed in a part of the region on the LED element layer, and the other electrode is formed over the entire back surface of the substrate. Alternatively, a uniform voltage is applied to the semiconductor layer on the substrate side. Therefore, in a general LED element, recombination frequently occurs in the vicinity of the light extraction side electrode. In this case, the light extraction efficiency is inevitably lowered due to optical shielding by the electrode on the light extraction side.

  On the other hand, in this embodiment, carrier recombination in the light emitting region close to the first metal electrode 4 becomes dominant, and light emission can be concentrated directly on the first metal electrode 4 located on the handle substrate side.

  Further, by arranging the second metal electrode 8 at a position shifted from the first metal electrode 4 in the plane direction, preferably at a position not overlapping the first metal electrode 4, an overlapping portion of the light emitting portion and the light extraction side electrode. Can be reduced, preferably without overlapping, and the influence of optical shielding can be greatly reduced.

The seed substrate 1 is preferably composed of a material having a single crystal structure, and is composed of a material selected from the group consisting of, for example, Al ₂ O ₃ , SiC, GaAs, InP, and Si in addition to a Ge substrate. A substrate is preferred.

  The separation layer 2 is preferably made of a material having a lattice constant and / or a thermal expansion coefficient different from that of the seed substrate 1. In addition to InGaAs, for example, GaN, InGaN, AlGaN, AlN, AlAs, AlGaAs, InAlAs, InGaAlP. A compound semiconductor material selected from the group consisting of InGaAsP and InGaP is preferred.

  The light emitting element layer 3 is a compound semiconductor including at least one material selected from the group consisting of GaN, AlGaAs, InP, InGaN, AlGaN, AlN, AlAs, InGaAs, InAlAs, InGaAlP, InGaAsP, and InGaP in addition to GaAs. Composed of materials.

The handle substrate 6 is preferably a semiconductor substrate such as Si, a metal substrate such as Al, Cu, or CuW, an insulating substrate such as glass, or a flexible substrate such as plastic. In particular, the Si substrate and the metal substrate are excellent in conductivity and thermal conductivity, and contribute to good light emission characteristics. Alternatively, the surface of the handle substrate 6 is one material selected from the group of Au, Pt, Cr, Ti, AuGe, Ni, AuSn, AuZn, and AuSb, or a laminated structure of at least two materials selected from the group It is preferable to coat with. Such a metal coating film can function as a reflection film. Further, the bonding strength between the donor substrate and the handle substrate can be increased by using an Au-based eutectic material as the coating film and performing a heat treatment at 250 ° C. or the like.
The handle substrate 6 is preferably provided with a drive circuit for driving the light emitting elements formed in the light emitting element layer 3. In this case, the light emitting element formed on the light emitting element layer 3 and the drive circuit formed on the handle substrate 6 are electrically connected.

  According to this embodiment, since the first electrode formed on the light emitting element layer 3 in the production of the donor substrate is disposed close to the pn junction or the active layer, the first electrode and the positive electrode in the vicinity of the first electrode are positive. The recombination probability (that is, light emission) of the holes is increased, and the first electrode and the second electrode are arranged so that their positions (positions in the plane direction) are shifted from each other, so that the light shielding by the second electrode is greatly reduced. The light extraction efficiency can be improved.

In this regard, on the light extraction side (the second surface side of the light emitting element layer), it is only necessary to form the second electrode by shifting the position from the first electrode, so that the increase in the number of processes can be minimized. be able to.
In this embodiment, the first electrode is formed on the first surface (surface on the handle substrate side) of the light emitting element layer, and the second electrode is formed on the second surface (surface on the light extraction side) that is the opposite surface. It is necessary to align the second electrode with respect to the first electrode. However, high accuracy is not necessary for the alignment. For example, when forming the first electrode, a hole penetrating the separation structure is formed by etching or the like, and after the first electrode and the light emitting element layer are transferred to the handle substrate, the second electrode is formed. This can be done by using the holes as alignment marks.
The seed substrate can be reused after being processed as necessary after the dividing step. Such reuse contributes to a reduction in the production cost of the light emitting element.

By supporting the light emitting element layer with the handle substrate, it is not necessary to support the light emitting element layer with a support film formed thick by epitaxial growth such as HVPE.
Hereinafter, exemplary embodiments of the present invention will be described by way of example.

[First embodiment]
8 to 10 are views showing a light emitting device and a method for manufacturing the same according to the first embodiment of the present invention. As shown in FIG. 8, an AlAs layer (separation auxiliary layer) 10 and an InGaAs layer (separation layer) 11 are formed on a Ge substrate (seed substrate) 9, and then an n-type GaAs layer 12, as a light emitting element layer, An n-type AlxGa1-xAs layer 13, a p-type AlyGa1-yAs layer 14, a p-type AlxGa1-xAs layer 15, and a p-type GaAs layer 16 (y <x) are sequentially epitaxially grown.

  Although the impurity concentration and thickness of the epitaxial growth layer depend on the design of the device, the light emission in the vicinity of the first metal electrode becomes dominant and the structure suitable for the present invention in which the light emission efficiency is improved is double. In the terror-type LED element, for example, it is as follows.

n-type GaAs layer 12: 0.5 μm; Si-doped n-type Al0.15 Ga0.85 As layer 13: 1 μm; Si-doped p-type Al0.13 Ga0.87 As layer 14: 0.3 μm; Zn-doped p-type Al0.23 Ga0.77 As layer 15: 0.3 μm; Zn doping p-type GaAs layer 16: 0.1 μm; Zn doping Si doping can be performed so that the carrier concentration is, for example, about 10 ¹⁷ / cm ³ .

  Note that a p-type electrode is brought close to the p-type AlyGa1-yAs layer 14 as the active layer, and the injection of holes from the p-type electrode is the electron-positive in the p-type AlyGa1-yAs layer 14 as the active layer. The p-type Al0.23Ga0.77As layer 15 and the p-type GaAs layer 16 are made thin, and the n-type GaAs layer 12 and the n-type Al0.15Ga0.85As layer 13 are designed so as to be dominant in hole recombination. It is preferable.

  Next, Ti (10 nm), Pt (10 nm), and Au (50 nm) are sequentially sputtered on the p-type GaAs layer 16 and then patterned by a lift-off method to form an n-type metal electrode (first electrode) 17. To do. Thereafter, a plasma oxide film having a thickness of 300 nm is formed, planarized by CMP, and an insulating layer 18 is formed by exposing the upper surface of the metal electrode 17, and a Si substrate (handle substrate) 19 is bonded to this surface. The composite member 30 is formed.

  Next, as shown in FIG. 9, a high-pressure water stream (water jet) W that is finely squeezed onto the side surfaces of the AlAs layer (separation assisting layer) 10 and the InGaAs layer (separation layer 11) or the vicinity thereof is sprayed, so that the composite member 30 is The separation is performed at the interface between the (separation assisting layer) 10 and the Ge substrate (seed substrate) 9.

  Next, as shown in FIG. 10, a p-type metal electrode 22 is formed on the n-type GaAs layer 12 at a position that does not overlap the n-type metal electrode layer 17.

  In this way, a surface-emitting LED element with high emission extraction efficiency can be obtained.

  In this embodiment, the insulating film 18 is formed in the region where the metal electrode layer is removed. However, the donor substrate is formed on the Si substrate (handle substrate) 19 without forming the insulating film 18 after the electrode 17 is formed. They may be combined to form a composite member.

  In this embodiment, a Ge substrate is used as a seed substrate, but a GaAs substrate may be used as a seed substrate.

[Second Embodiment]
After cleaning and planarizing the Al ₂ O ₃ substrate by exposing it to hydrogen at a high temperature of 1000 ° C. or higher, the AlN layer is formed at 500 ° C. by MOCVD using Ga, Al organometallic compound and NH ₃ gas as the hydrogen carrier gas. To a thickness of 20 to 100 nm to form a buffer layer. Since this buffer layer has a microcrystalline grain boundary structure and is deposited at a low temperature of about 500 ° C., it can be deposited spatially uniformly and flatly as compared with the case of growing at a high temperature of about 1000 ° C. it can. In the case of AlN, the crystallite grain size is about a dozen nm.

Next, the substrate temperature of the Al ₂ O ₃ substrate is raised to about 1000 ° C., a GaN layer is formed on the buffer layer, and a PN junction multilayer structure for the active layer or well layer of the LED is further formed thereon. Form.

  The clad layers formed above and below the active layer or well layer have an upper clad of 0.3 μm and a lower clad of 1 μm, and their thicknesses are varied so that carrier injection from the upper electrode can be performed. Or it sets so that it may become dominant to the recombination in a well layer.

Next, after sequentially depositing a Pd film and an Au film on the LED multilayer structure on the Al ₂ O ₃ substrate, these are patterned by a lift-off method to form a metal electrode. In the region where the metal electrode layer is removed by patterning, an insulating film is formed as in the first embodiment.

  An Si substrate is prepared as a handle substrate, and an Al film and an Sn film are sequentially formed on the surface of the Si substrate to form a metal electrode layer.

  Then, the electrode layer on the LED multilayer structure and the electrode layer on the Si substrate are brought into close contact with each other, further heat-treated at 300 ° C., and fused by alloying Au / Sn at the bonding interface, A composite member in which the bonding strength at the bonding interface is remarkably enhanced is formed.

  Next, the composite member is immersed in a phosphoric acid solution, and an AlN buffer layer in which strain and crystal defects are concentrated is retracted from the end surface toward the center by several tens of microns along the entire outer peripheral end surface of the composite member. A recess is formed.

Next, a pure water converging fluid with a pressure of 0.3 N is injected into the recess while rotating about the axis passing through the composite member substantially vertically, and the inside of the AlN layer and / or the AlN layer At the interface between the GaN layer and the Al ₂ O ₃ substrate, the Al ₂ O ₃ substrate is separated without damaging the GaN layer. As a result, the multilayer film which is the LED structure formed on the upper part is transferred onto the Si substrate.

In this embodiment, Al ₂ O ₃ is used for the seed substrate, but a SiC substrate may be used instead.

It is a figure which shows typically the process of forming the structure for isolation | separation and a light emitting element layer on a seed substrate. It is a figure which shows typically the process of forming a 1st electrode in a part on 1st surface of a light emitting element layer. It is a figure which shows typically the process of forming an insulating layer in the area | region between 1st electrodes. It is a figure which shows typically the process of couple | bonding the board | substrate (donor board | substrate) which has a 1st electrode and an insulating layer with a handle substrate, and forming a composite member. It is a figure which shows typically the process of dividing | segmenting a composite member using the structure for isolation | separation. It is a figure which shows typically the handle substrate in which the 1st electrode and the insulating layer were moved from the seed substrate. It is a figure which shows typically the process of forming a 2nd electrode in the position on the 2nd surface of a light emitting element layer after the division | segmentation of a composite member. A separation structure (separation auxiliary layer, separation layer), a light emitting element layer, and a first electrode are sequentially formed on a seed substrate to form a donor substrate, and the donor substrate and the handle substrate are combined to form a composite member. It is a figure which shows the process to do typically. It is a figure which shows typically the process of dividing | segmenting a composite member using the structure for isolation | separation. It is a figure which shows typically the process of forming a 2nd electrode in the position on the 2nd surface of a light emitting element layer after the division | segmentation of a composite member.

Explanation of symbols

1 Seed substrate 2 Utilization structure (separation layer)
3 Light-Emitting Element Layer 4 First Electrode 5 Insulating Layer 6 Handle Substrate 8 Second Electrode 10 Donor Substrate 20 Composite Member 17 First Electrode 18 Insulating Layer 19 Handle Substrate 22 Second Electrode

Claims (9)

A light emitting element layer having a first surface and a second surface;
A first electrode formed on a part of the first surface of the light emitting element layer;
A second electrode formed on a part of the second surface of the light emitting element layer;
And the first electrode and the second electrode are arranged to be shifted from each other,
A light emitting element characterized by the above.   The light emitting device according to claim 1, wherein the first electrode and the second electrode are arranged so as not to overlap each other. The light emitting element layer includes a pn junction surface, and light generated at the pn junction surface is extracted to the outside through the second surface;
A first distance between the first surface and the pn junction surface is shorter than a second distance between the second surface and the pn junction surface;
The light-emitting element according to claim 1 or 2. The light emitting element layer includes an active layer, and light generated in the active layer is extracted to the outside through the second surface,
A first distance between the first surface and the active layer is shorter than a second distance between the second surface and the active layer;
The light-emitting element according to claim 1 or 2. The light emitting element layer includes a well layer, and light generated in the well layer is extracted to the outside through the second surface;
A first distance between the first surface and the well layer is shorter than a second distance between the second surface and the well layer;
The light-emitting element according to claim 1 or 2. A method of manufacturing a light emitting device,
Forming a separation structure on the seed substrate;
Forming a light emitting element layer on the separation structure;
Forming a first electrode on a part of the first surface which is an exposed surface of the light emitting element layer;
Forming a composite member by bonding a support to the seed substrate such that the first electrode is on the inside;
Dividing the composite member using the separation structure and transferring the light emitting element layer and the first electrode from the seed substrate to the support;
Forming a second electrode on a part of the second surface which is an exposed surface of the light emitting element layer after the transfer;
The first electrode and the second electrode are formed so as to be displaced from each other,
A method for manufacturing a light-emitting element.   The light emitting element layer has a stacked structure made of a material selected from the group consisting of GaN, InGaN, AlGaN, GaAs, AlGaAs, InGaAs, InGaAsP, InP, and InGaP. Manufacturing method of light emitting element. The light emitting device according to claim 6, wherein the seed substrate is made of any material selected from the group consisting of Al ₂ O ₃ , SiC, GaAs, InP, Ge, and Si. Method.   The light emitting device manufacturing method according to claim 6, wherein the isolation structure includes an isolation layer made of a material having a lattice constant and / or a thermal expansion coefficient different from that of the seed substrate.

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