JP2009158550A - Semiconductor light emitting element and display using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting element for suppressing a leakage current by reducing the thickness of a depletion layer, and to provide a display using the same. <P>SOLUTION: The semiconductor light emitting element includes a supporting substrate having a p-side electrode layer 12, a p-type contact layer 14, a p-type clad layer 16, an active layer 18, an n-type clad layer 20, an n-type contact layer 24 and an n-side electrode layer 26, wherein the n-side electrode layer is stacked so as to contact the n-type contact layer and the n-type clad layer, an ohmic junction is formed with the n-type contact layer and a Schottky junction is formed with the n-type clad layer. When a reverse bias voltage is applied, a depletion layer 22 is formed on the n-type clad layer below the n-type contact layer, the depletion layer is expanded as the increase in the reverse bias voltage, and a leakage current is suppressed. The n-type contact layer includes a diameter of ≤20 μm. The semiconductor light emitting elements are arranged in two-dimensional matrix to form a display, and the semiconductor light emitting elements are driven in a simple matrix. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device capable of suppressing leakage current by controlling the thickness of a depletion layer in a Schottky junction and a display device using the same.

  A semiconductor light emitting device having an active layer made of a compound semiconductor can realize a light emission wavelength in a wide range from ultraviolet to infrared by controlling the band gap energy by the mixed crystal composition and thickness of the active layer. Semiconductor light-emitting elements capable of emitting various colors have been developed, and these are arranged in a two-dimensional matrix and are used for applications such as image display devices and illumination devices.

  Various element structures have been studied in order to suppress the leakage current in the semiconductor light emitting element or increase the current density in the active layer. For example, a structure for preventing a reactive current from flowing, a structure for flowing a current so as to limit a light emitting portion by changing an area in which the current flows are being studied.

  Patent Document 1 below entitled “Semiconductor Light Emitting Element” has the following description.

  In the semiconductor light emitting device of the invention of Patent Document 1, a first conductive type semiconductor layer is formed below the active layer, and a second conductive type semiconductor layer is formed above the active layer. In a semiconductor light emitting device having a current confinement structure in which a current blocking layer of a first conductivity type is formed on or inside the semiconductor layer, and a current path region is formed in the current blocking layer, a reverse bias applied to the current blocking layer It is characterized in that the effective area of the current path region is made variable by changing the spread of the depletion layer extending from the current blocking layer into the second semiconductor layer by controlling the voltage.

  In the invention of Patent Document 1, the spread of the depletion layer extending from the current blocking layer into the second semiconductor layer can be changed by controlling the reverse bias voltage applied to the current blocking layer. The effective area of the current path region formed in the blocking layer can be changed.

  Accordingly, the current density per unit area can be changed by changing the effective area of the current path region (that is, the area through which the current flows), thereby changing the light emission output of the semiconductor light emitting device. Further, since the emission diameter also changes, the spot diameter of the emitted light beam can be controlled.

  FIG. 10 is a cross-sectional view showing a light emitting diode, which is shown in FIG.

  On the p-type GaAs substrate 101, a p-type AlGaAs lower clad layer 102, a GaAs active layer 103, an n-type AlGaAs inner clad layer 104, and a p-type GaAs current blocking layer 105 are successively grown by a first crystal growth process. ing. The current blocking layer 105 has an opening that becomes the current path region 111 by photolithography or the like.

  In addition, an n-type AlGaAs outer cladding layer 106 is regrown on the current blocking layer 105 having the opening formed by a second crystal growth process. Here, the carrier concentration of the current blocking layer 105 is sufficiently higher than the carrier concentration of the inner and outer cladding layers 104 and 106, and the depletion layer 110 is formed in the inner and outer cladding layers 104 and 106 from the current blocking layer 105. It has spread.

  Furthermore, wires 107 and 109 are bonded to the upper surface of the outer cladding layer 106 and the lower surface of the substrate 101, and when a drive voltage is applied to both the wires 107 and 109, electrons are injected into the active layer 103 through the current path region 111. Then, light is emitted from the injection region of the active layer 103.

  A wire 108 is bonded to a portion of the current blocking layer 105 exposed from the outer cladding layer 106. When a reverse bias voltage lower than the voltage applied to the wire 7 is applied to the wire 108, the depletion layer 110 increases in accordance with the magnitude of the reverse bias voltage. Therefore, the current blocking layer is adjusted by adjusting the magnitude of the reverse bias voltage. The spread of the depletion layer 110 extending from the inner layer 105 into the inner and outer cladding layers 104 and 106 can be controlled.

  That is, when the depletion layer 110 spreads, the area through which the current flowing out from the active layer 103 (or the electrons injected into the active layer 103) passes (the effective area of the current path region 111) is narrowed. At the same time, the current density per unit area increases and the current injection into the active layer 103 can be efficiently performed, so that the light emission output increases. Conversely, when the depletion layer 110 contracts, the effective area of the current path region 111 increases and the emission diameter in the active layer 103 increases, and at the same time, the current density per unit area decreases and the emission output decreases. Therefore, according to the invention of Patent Document 1, the light emission diameter and the light emission output can be controlled simultaneously only by adjusting the potential applied to the wire 108.

  Here, since the voltage applied to the wire 108 is on the order of several volts to several tens of volts, it is at a level that is easy to control, and the light emission output can be easily controlled. In addition, since the light emission output can be controlled by changing only the reverse bias voltage of the wire 108 while keeping the drive voltage between the wires 107 and 109 constant, the light emission diameter is independent of the drive of the light emitting diode. And the light output can be controlled.

  In order to make the emission diameter sensitive to the size of the depletion layer 110, the inner cladding layer 104 should be thinned to about 0.5 to 1 μm, for example, and the depletion layer 110 can be efficiently formed in the lateral direction. In order to widen, it is desirable that the carrier concentration of the outer cladding layer 106 is lower than the carrier concentration of the inner cladding layer 104.

  Patent Document 2 below titled “Semiconductor Light-Emitting Element and Driving Method Thereof” has the following description.

  11A and 11B are diagrams illustrating a configuration of a semiconductor laser. FIG. 11A is a cross-sectional view, FIG. 11B is a plan view, and FIGS.

  FIG. 12 is a cross-sectional view for explaining the operation of the semiconductor laser shown in FIG. 11, and is FIG.

  FIG. 11A shows a stacked structure of the surface emitting semiconductor laser 10A according to the first embodiment of the present invention disclosed in Patent Document 2, and is taken along the line AA in FIG. 11B. FIG. In this semiconductor laser 210A, a p-type contact layer 212, a p-type DBR layer (Distributed Bragg Reflector) 213, and an active layer (light emitting layer) 214 are laminated in this order on a substrate 211. An AlGaAs layer 215 is formed on the active layer 214, and a current confinement portion 219 is provided on the AlGaAs layer 215. The current confinement part 219 has a current injection region 216 having a circular shape surrounded by an insulating film 217 (insulating films 217A and 217B), for example. In this embodiment mode, a ring-shaped control electrode 218 is provided in the insulating film 217 so as to surround the current injection region 216. FIG. 11B shows a planar configuration of the control electrode 218. A predetermined potential is applied to the control electrode 218 through the gate 218A.

  On the current confinement part 219, an n-type DBR layer 220 and an n-type contact layer 221 are formed in this order. The n-type DBR layer 220 and the n-type contact layer 221 are formed in a cylindrical mesa structure using an RIE (Reactive Ion Etching) method or the like. Further, an n-side electrode (main electrode) 223 is formed on the n-type contact layer 221 together with the light output window 222. On the other hand, a p-side electrode (main electrode) 224 is provided on the back surface of the substrate 211.

The current injection region 216 concentrates the drive current I ₁ injected by the main electrode (n-side electrode 223, p-side electrode 224) on the active layer 214, and suppresses the disturbance of the light output distribution, etc. For example, it is made of the same semiconductor material as the AlGaAs layer 215 and has a similar stacked structure.

  The control electrode 218 is made of, for example, a metal such as gold (Au) or aluminum (Al), and a potential having the same polarity as that of the n-side electrode 223 is applied through the gate 218 </ b> A in the current injection region 216. Then, a depletion region (depletion layer) 215A is generated to change the diameter (current confinement diameter) of the current injection region 216 so as to be narrower than the intended size. The control electrode 218 is driven independently of the main electrode (n-side electrode 223, p-side electrode 224).

The insulating film 217 is made of an insulating material such as silicon dioxide (SiO ₂ ). The insulating film 217 is formed to a thickness of, for example, about 5 nm so that a depletion region 215A having a thickness of about 500 nm is generated with a control voltage of about 1-2 V, for example.

  Next, a method for driving the surface emitting semiconductor laser 210A will be described.

In this semiconductor laser 210 </ b> A, when a predetermined voltage is applied between the n-side electrode 223 and the p-side electrode 224, as shown in FIG. 11A, the driving current is supplied to the active layer 214 through the current injection region 216. I ₁ is injected, light is emitted from the active layer 214, and laser resonance occurs between the p-type DBR layer 213 and the n-type DBR layer 220, that is, in a direction perpendicular to the substrate 211. The output light h ₁ is extracted from the light output window 222 formed on the n-side electrode 223.

At this time, a voltage (control voltage) is applied to the control electrode 218 independently of the main electrode (n-side electrode 223 and p-side electrode 224) through the gate 218A, and the width of the current confinement portion 219 in the current injection region 216 is applied. (Current confinement diameter) is controlled. Current confinement diameter is applied state of voltage to the control electrode 218, i.e., depending on the size of the depletion region 215A induced by an electric field generated at this time, the magnitude of the current confinement diameter, the driving current I ₁ The amount of passage is controlled.

Specifically, as shown in FIG. 12A, when no potential is applied to the control electrode 218, the current confinement diameter is the current confinement diameter of the initial size of the current injection region 216. D ₁ , light emission corresponding to the drive current I ₂ (= I ₁ ) passing through the current confinement diameter D ₁ occurs, and is emitted as output light h ₂ (= h ₁ ). The output light h ₂ has optical characteristics such as a transverse mode property and a modulation degree corresponding to the drive current I ₂ passing through the current confinement diameter D ₁ .

On the other hand, as shown in FIG. 12B, when a voltage having the same polarity as the n-side electrode 223 (here, a negative potential) is applied to the control electrode 218, the current injection region 216 has a peripheral edge. An electric field is generated, and induced by this electric field, a depletion region 215A is generated in the AlGaAs layer 215 and the current injection region 216. The size of the depletion region 215A changes depending on the magnitude of the voltage applied to the control electrode 218. In particular, the current injection region 216 is narrowed by the depletion region 215A extending into the current injection region 216, and the current confinement is reduced. diameter D ₂ is determined. Then, a drive current I ₃ (<I ₂ ) corresponding to the current confinement diameter D ₂ is injected into the active layer 214 to emit light, and is emitted as output light h ₃ (<h ₂ ). This output light h ₃ has optical characteristics such as a transverse mode property and a modulation degree depending on the drive current I ₃ that has passed through the current confinement diameter D ₂ .

  Patent Document 3 below titled “Semiconductor Laser and its Manufacturing Method” has the following description.

  The width of the depletion layer can be changed by an external electric field by applying a reverse bias to a current blocking layer having a conductivity type different from that of the second cladding layer and the cap layer on both sides of the active layer serving as the light emitting region. It is possible to control the injection width, in other words, the injection carrier density. Furthermore, carriers flowing in the passage are focused by the electric field, the injection efficiency into the active layer is increased, the leakage current component that does not contribute to light emission is reduced, and the internal light emission efficiency of the semiconductor laser diode is improved. Therefore, the threshold value itself can be controlled at the same time as the laser oscillation threshold level is reduced. This further promotes the low current operation of the semiconductor laser diode.

  Patent Document 4 below entitled “Semiconductor Light Emitting Element” has the following description.

  The semiconductor light emitting device includes a substrate crystal, an active layer, and a junction. The joint portion is disposed in the vicinity of the active layer. Further, the junction is configured to generate a depletion region that restricts the flow of carriers to the active layer. The semiconductor light emitting device further includes a control region made of a first conductivity type semiconductor and a gate region made of a second conductivity type semiconductor. The junction is formed by joining the control region and the gate region. The control region is disposed on a flow path of a current flowing into the active layer. In the semiconductor light emitting device, a third electrode for applying a voltage to the gate region is electrically connected to the gate region.

  According to the semiconductor light emitting device of the invention of Patent Document 4, the flow path of the drive current can be regulated by the depletion region generated by the junction. Thereby, the width | variety of the waveguide as a gain waveguide can be narrowed. Furthermore, the width of the waveguide can be dynamically controlled by applying a voltage to the gate region constituting the junction. That is, laser oscillation can be controlled by voltage.

  Patent Document 5 described below entitled “Compound Semiconductor Light-Emitting Device” includes the following description.

  The light emitting element body is erected in a part of the area, and the surface of the conductive layer between the positive and negative electrodes, including its side surfaces, is covered with an insulating film, so that the damage between the positive and negative electrodes and the conductive layer between the positive and negative electrodes Occurrence of leakage current that does not contribute to light emission through dirt adhered to the film was suppressed, that is, current confinement was realized, and the current density in the light emitting layer could be increased.

  Patent Document 6 below titled “Current-Confined Light-Emitting Diode and Light-Emitting Device” has the following description.

  The LED chip is formed by sequentially laminating a first n-type cladding layer which is a light emitting surface, an active layer, and a p-type cladding layer on the mounting surface side on the second n-type cladding layer, and on the mounting surface side. The chamfered portion provided at the peripheral edge is chamfered in a concave shape so as to incline outward, and is formed so that the depth reaches the middle of the first n-type cladding layer. The surface of the p-type cladding layer In addition, an insulating film is formed on the surface of the chamfered portion, the p-side electrode is partially removed on the insulating film, and the p-side electrode and the p-type cladding layer are connected to confine the current in this portion. It has become.

  Patent Document 7 described later entitled “Surface Emitting Laser Device” includes a current confinement layer having an Al oxide layer formed by oxidation treatment on the outer periphery, and includes an outer edge of the mesa post and an exposed surface of the quantum well active layer. Is a surface emitting laser element in which is coated with a dielectric film (SiN or the like).

  Moreover, the above-mentioned patent document 2 has the following description.

A surface emitting semiconductor laser has a constriction structure (AlAs layer) for efficiently injecting current into a minute volume, and a drive current flowing between the n-side electrode and the p-side electrode is a current injection region ( It passes through the current confinement diameter and is injected into the active layer, whereby light emission occurs and this light emission is emitted. As a method for forming a confined structure (AlAs layer) of a surface emitting semiconductor laser, the AlAs layer is selectively oxidized from the outer periphery to the center to a certain depth to be insulated, and a current injection region (current) is formed in the central portion of the AlAs layer. A method of forming a constriction diameter (selective oxidation method), or a current confinement method (proton injection method) in which protons (H ⁺ ) are implanted from around the DBR and the injection region is insulated, and a band is formed in the DBR layer. A method of confining current by embedding a semiconductor having a large gap and a low refractive index in the periphery (embedding method) is used. By using these methods, a current injection region having a size that generates the desired output light is formed.

  As an example of the current blocking type structure, Japanese Patent Application Laid-Open No. 2004-228620 entitled “Light Emitting Diode” includes the following description.

  A light-emitting diode is formed by sequentially forming a current blocking portion made of a second conductive type or high resistance semiconductor, a light emitting portion layer having an active layer, and a second conductive type current spreading layer on a first conductive type substrate. The current blocking portion is a layer formed by diffusing a dopant or implanting ions into the substrate. When a current blocking portion whose conductivity type is reversed or increased in resistance is formed by diffusing a dopant or ion-implanting into a position corresponding to a position almost immediately below the surface electrode on the surface of the substrate, the current blocking portion and the surface electrode are formed. Since no light emission occurs in the light emitting layer between the two, the useless light blocked by the surface electrode is eliminated, and the luminance of the entire light emitting unit is improved.

Japanese Patent Laid-Open No. 5-55629 (paragraphs 0008 to 0017, FIG. 1) JP-A-2005-243900 ((paragraphs 0003 to 0005, paragraphs 0017 to 0018, paragraphs 0025 to 0027, paragraphs 0039 to 0042, FIGS. 1, 2, 5, and 7) JP-A-6-29616 (paragraph 00017, FIG. 1) JP 2006-80427 A (paragraph 0029, paragraph 0035, paragraph 0041, paragraph 0043, FIG. 3, FIG. 9) JP-A-11-220175 (paragraphs 0076 to 0079, FIG. 16) Japanese Unexamined Patent Publication No. 2000-244008 (paragraphs 0011 to 0016, FIGS. 3, 4, and 5) JP 2003-115634 A (paragraphs 0006 to 0013, paragraphs 0035 to 0042, FIGS. 1 and 7) JP 2003-37285 A (paragraphs 0003 to 0015, paragraphs 0018 to 0022, paragraph 0054, FIGS. 1 to 6)

  The LED display of the simple matrix driving type (also referred to as passive matrix driving type) has an advantage of simple structure and low cost. However, when driving two-dimensionally arranged LEDs, reverse leakage inside the LEDs is obtained. There is a problem that crosstalk occurs due to the current and the reverse current passing through the short-circuited LED, and another LED emits light at a place other than the arbitrarily addressed LED.

  The carriers excited in the semiconductor emit energy by a relaxation process of luminescence recombination accompanied by light emission and a relaxation process of non-radiative recombination without light emission. The non-radiative recombination of carriers reduces the light emission of the LED and causes the light emission efficiency with respect to the injection current to decrease. From the voltage value at which current begins to flow to the LED to the voltage value exceeding the emission threshold, the leakage current generated in the carrier relaxation process due to non-radiative recombination does not contribute to light emission, resulting in high power consumption. It was. For example, carriers injected into the light emitting layer are diffused to the end face of the device, and carriers are non-radiatively recombined through the surface level, resulting in a decrease in light emission efficiency with respect to the injected current.

  Conventionally, in order to make the LED drive current rise sharply, a small amount of the end face of the active layer that is likely to cause non-radiative recombination, chemical treatment for the purpose of reducing the region where non-radiative recombination occurs, treatment with a protective film, There is a window structure that prevents current from flowing near the end face of the active layer by making it p-type by doping. In surface-emitting lasers, etc., a current confinement structure that oxidizes the Al-containing layer to narrow the current flow area so that the current does not spread to the vicinity of the end face of the active layer where non-radiative recombination is likely to occur. May be provided. However, such a method does not fundamentally cut off the leakage current at the time of start-up, and there is a possibility that the characteristics are deteriorated by applying a load to the LED by performing various processes.

  In the technique related to the formation of the depletion layer described in Patent Documents 1 to 4, the third electrode for control is required in addition to the n-side electrode and the p-side electrode, and a complicated configuration is required. There is.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a semiconductor light-emitting device capable of suppressing leakage current by controlling the thickness of a depletion layer in a Schottky junction. And providing a display device using the same.

  That is, the present invention relates to a substrate, a p-side electrode layer and a p-type cladding layer formed on the substrate, an active layer made of a compound semiconductor, an n-type cladding layer, an n-type contact layer, and an n-side electrode layer. The n-side electrode layer is in contact with and stacked on the n-type contact layer and the n-type cladding layer, and the n-side electrode layer forms an ohmic junction with the n-type contact layer, It is configured to form a Schottky junction with the n-type cladding layer, and when a reverse bias voltage is applied between the n-side electrode layer and the p-side electrode layer, the region below the n-type contact layer The present invention relates to a semiconductor light emitting device in which a depletion layer is formed in an n-type cladding layer.

  The present invention also relates to a display device in which semiconductor light emitting elements are arranged in a two-dimensional matrix and the arranged semiconductor light emitting elements are driven in a simple matrix.

  According to the semiconductor light emitting device of the present invention, the n-side electrode layer is laminated in contact with the n-type contact layer and the n-type cladding layer, and the n-side electrode layer is in ohmic contact with the n-type contact layer. And forming a Schottky junction with the n-type cladding layer, and when a reverse bias voltage is applied between the n-side electrode layer and the p-side electrode layer, Since a depletion layer is formed in the n-type cladding layer in the lower region, in addition to the n-side electrode layer, the p-side electrode layer, and a power source for applying a voltage applied therebetween, a leakage current is generated. It is possible to control the formation of a depletion layer by a voltage applied between the n-side electrode layer and the p-side electrode layer with a simple configuration without requiring a control electrode and a power source for suppression. By suppressing the current That.

  According to the display device of the present invention, the semiconductor light-emitting elements are arranged in a two-dimensional matrix, and the arranged semiconductor light-emitting elements are driven in a simple matrix. Formation of a depletion layer can be controlled by a voltage applied between the p-side electrode layers, and leakage current and crosstalk can be suppressed.

  In the semiconductor light emitting device of the present invention, it is preferable that the region of the depletion layer is enlarged as the reverse bias voltage increases, and current flowing from the p-side electrode layer to the n-side electrode layer is suppressed. According to this configuration, the region of the depletion layer is enlarged as the reverse bias voltage increases, and the current flowing from the p-side electrode layer to the n-side electrode layer is suppressed, so that leakage current can be suppressed. .

  The depletion layer region may be reduced by applying a forward bias voltage between the n-side electrode layer and the p-side electrode layer. Since a region of the depletion layer is reduced by applying a forward bias voltage between the n-side electrode layer and the p-side electrode layer, current can be injected from the n-side electrode layer into the active layer. it can.

  In addition, when the forward bias voltage is increased to reach a certain voltage, a current flows from the n-type contact layer to the n-type cladding layer, and light is emitted from the active layer. According to such a configuration, by applying a forward bias voltage between the n-side electrode layer and the p-side electrode layer, the region of the depletion layer is reduced so that the n-type contact layer and the n-type cladding layer are reduced. When a current flows into the active layer and current is injected into the active layer to increase the forward bias voltage and reach a certain voltage, light is emitted from the active layer.

  The diameter of the n-type contact layer is preferably 20 μm or less. According to such a configuration, since the diameter of the n-type contact layer is 20 μm or less and the n-side electrode layer and the n-type contact layer form an ohmic junction, the Schottky junction is applied when a reverse bias is applied. As a result, the depletion layer formed sufficiently spreads and the leakage current can be suppressed.

  In the LED according to the present invention, a part of the n-side electrode layer is in ohmic contact with the n-type contact layer, and the other region of the n-side electrode layer is joined with the n-type cladding layer. Configured to form. In a Schottky junction, when a negative voltage (forward bias) is applied to the n-side electrode layer, the depletion layer shrinks and current flows easily, and a positive voltage (reverse voltage, reverse bias) is applied to the n-side electrode layer. Then, the depletion layer expands and current does not flow easily. When applying a reverse bias, if the depletion region is sufficiently expanded in the n-type cladding layer, a reverse current such as a minute leak (reverse bias leak) can be cut off. When a forward bias is applied, the depletion region is reduced, so that current flows from the n-type contact layer to the n-type cladding layer, and current is injected into the active layer (light emitting layer).

  When forming the n-side electrode layer in the LED of the present invention, the n-type contact layer is formed so that the n-type cladding layer is exposed, and the n-side electrode is formed on both layer surfaces of the n-type contact layer and the exposed n-type cladding layer. A metal layer to be a layer is formed (area of n-type contact layer <area of n-side electrode layer ≦ area of n-type cladding layer). The metal layer is in ohmic contact with the n-type contact layer. The n-type cladding layer has an equal ping concentration so as to form a Schottky junction with the metal layer, and a depletion region is formed in the n-type cladding layer by applying a reverse bias.

  When the reverse bias is increased, a region where the n-type contact layer and the n-type cladding layer are in contact with each other is covered by the depletion region, and a current flowing between the n-type contact layer and the n-type cladding layer is cut off.

  In addition, when a depletion layer is formed, when a forward bias of a certain level or more is applied, the area of the depletion region remaining after the depletion layer shrinks is equal to the region where the n-type contact layer and the n-type cladding layer are in contact with each other. The LED becomes smaller than the area, current flows from the n-type contact layer to the n-type cladding layer, and is injected into the active layer, so that the LED emits light.

The area of the region where the n-type contact layer and the n-type cladding layer are in contact (ie, the area of the n-type contact layer) is S _c , and the region where the n-type contact layer and the n-type cladding layer are in contact (ie, the n-type contact) The area where no depletion region is formed in the region below the layer is defined as S _d .

When a reverse bias is applied so as to satisfy S _d = 0 (that is, a depletion region is formed in the entire area S _c ), the n-type contact layer and the n-type cladding layer Current flowing between them is blocked by the depletion region.

0 <When the forward bias to satisfy S _d ≦ S _e is applied, by application of a certain or more forward biased with, it is injected into the active layer current flows from the n-type contact layer to the n-type cladding layer LED emits light.

  As a result, when a reverse bias is applied in which a depletion region is formed in the entire region below the n-type contact layer, the current is interrupted by the depletion region, so that the ratio of the current flowing by non-radiative recombination is relatively high. A current that does not contribute to light emission in a low voltage region (leakage current (leakage current)) can be cut off. In addition, by preventing reverse current flowing in the reverse direction, crosstalk in an LED array driven by a simple matrix method can be prevented.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings.

Embodiment FIG. 1 is a cross-sectional view illustrating a schematic configuration of an LED and control of formation of a depletion layer in an embodiment of the present invention. FIG. 1A illustrates formation of a depletion layer by applying a reverse bias. FIG. 1B shows a state in which the depletion layer is reduced by forward / reverse bias application and a current flows through the active layer, and FIG. 1C shows a state in which the depletion layer is enlarged by reverse bias application and current flows in the active layer. It is a figure which shows the state which stopped flowing.

  FIG. 2 is a diagram for explaining the schematic configuration of the LED in the embodiment of the present invention and for explaining the area of the depletion layer formed by applying a reverse bias. FIG. 2 shows the state shown in FIG. 2A is a cross-sectional view, and FIG. 2B is a plan view.

  As shown in FIG. 1, the LED includes a supporting substrate (for example, a sapphire substrate (not shown)), a p-side electrode layer 12, a p-type contact layer 14, a p-type cladding layer 16 composed of a compound semiconductor layer, and a compound. It has an active layer (light emitting layer) 18 made of a semiconductor layer, an n-type cladding layer 20 made of a compound semiconductor layer, an n-type contact layer 24 made of a compound semiconductor layer, and an n-side electrode layer 26. The p-side electrode layer 12 and the n-side electrode layer 26 are layers for connecting to a power source, and the n-type contact layer 24 is a layer for connecting the n-type cladding layer 20 and the n-side electrode layer 26 to form a metal electrode layer. The n-type cladding layer 20 is a layer for supplying electrons, the p-type cladding layer 16 is a layer for supplying holes, and the active layer (light emitting layer) 18 is recombined with injected carriers (electrons and holes). And a layer for emitting light.

  An n-side electrode layer 26 is laminated on and in contact with the n-type contact layer 24 and the n-type cladding layer 20, and a partial region of the n-side electrode layer 26 is in ohmic contact with the n-type contact layer 24 and n The type cladding layer 20 has a doping concentration so as to form a Schottky junction with other regions of the n-side electrode layer 26, and the other regions of the n-side electrode layer 26 join with the n-type cladding layer 20 to form a Schottky junction. is doing.

  The n-type contact layer 24 is formed so that the n-type cladding layer 20 is exposed, and the n-type contact layer 24 and a metal layer that becomes the n-side electrode layer 26 are formed on both layer surfaces of the exposed n-type cladding layer 20. ing. The area of the n-type contact layer 24 <the area of the n-side electrode layer 26 ≦ the area of the n-type cladding layer 20.

  As shown in FIG. 1A, when a reverse bias is applied between the n-side electrode layer 26 and the p-side electrode layer 12, a depletion region 22 is formed in the n-type cladding layer 20. That is, in the Schottky junction formed by the n-side electrode layer 26 and the n-type cladding layer 20, a depletion region 22 is formed when a positive voltage (reverse bias), that is, a reverse voltage is applied to the n-side electrode layer 26.

Figure 2 shows the state shown in FIG. 1 (A), 2L _e represents the one side dimension of the n-type contact layer 24 constituting the square, 2L _c is a region that is not the depletion region 22 is formed When a forward bias of a certain level or more is applied, current flows from the n-type contact layer 24 to the n-type cladding layer 20 and further, the dimension of one side of a square region where current can flow to the active layer 18 is shown. Yes.

  As shown in FIG. 1C, when the reverse bias is increased following the state shown in FIG. 1A, when the depletion region 22 is sufficiently expanded to the n-type cladding layer 20, n Since the current flowing between the n-type contact layer and the n-type clad layer is difficult to flow, reverse current (reverse bias leak) such as minute leak can be cut off (current OFF).

  As shown in FIG. 1B, the depletion region 22 is reduced when a negative voltage (forward bias), that is, a forward voltage is applied to the n-side electrode layer 26 following the state shown in FIG. I will do it. When the forward bias is increased, when a forward bias exceeding a certain level is applied, a current flows from the n-type contact layer 24 to the n-type cladding layer 20 (current ON), and the current is injected into the active layer (active layer) 18. The LED will emit light.

  The depletion layer generated when the reverse bias is applied is generated not only in the vertical direction of FIG. 1 but also with a three-dimensional spread due to the interaction of electrons. Therefore, when the reverse bias is increased, the n-type contact layer 24 and A region in contact with the n-type cladding layer 20 is covered by the depletion region 22, and a current flowing between the n-type contact layer 24 and the n-type cladding layer 20 is cut off.

  Further, when the depletion region 22 is formed, when a forward bias of a certain level or more is applied, the area of the depletion region 22 that remains after the depletion region 22 is reduced is determined by the n-type contact layer 24 and the n-type cladding layer 20. It becomes smaller than the area of the contact region, current flows from the n-type contact layer 24 to the n-type cladding layer 20 and is injected into the active layer 18, and the LED emits light.

Here, the area of the region where the n-type contact layer 24 and the n-type cladding layer 20 are in contact, that is, the area of the n-type contact layer 24 is S _c , and the n-type contact layer 25 and the n-type cladding layer 20 are in contact with each other. The area where the depletion region 22 is not formed in the region, that is, the region below the n-type contact layer 24 is defined as S _d .

When a reverse bias is applied so as to satisfy S _d = 0 (that is, a depletion region is formed in the entire area S _c ), as shown in FIG. The current flowing between the type contact layer 24 and the n-type cladding layer 20 is blocked by the depletion region 22.

0 <S when a forward bias to satisfy _d ≦ S _e is applied, by application of the above certain forward bias, as shown in FIG. 1 (B), n-type cladding from the n-type contact layer Current flows through the layer and is injected into the active layer, causing the LED to emit light.

  As shown in FIG. 1C, when a reverse bias is applied in which the depletion region 22 is formed in the entire region below the n-type contact layer 24, the current is cut off by the depletion region 22. A current that does not contribute to light emission (leakage current (leakage current)) in a low-voltage region where the ratio of the current flowing through the coupling is relatively high can be cut off. Further, by blocking reverse current flowing in the reverse direction, crosstalk can be prevented in an LED array driven by a simple matrix method.

  In the technology related to the formation of the depletion layer described in Patent Documents 1 to 4, a third electrode for control is required in addition to the n-side electrode layer and the p-side electrode layer, and a complicated configuration is required. However, in the configuration of the LED according to the present invention, the third electrode for control and the power source are not required, and the depletion layer is applied by the voltage applied between the n-side electrode layer 26 and the p-side electrode layer 12 with a simple configuration. Can be controlled, and leakage current and crosstalk can be suppressed.

  The configuration shown in FIG. 1 and FIG. 2 has a current concentration in which a side or diameter of the n-type contact layer 24 has a micro size of 5 μm to 8 μm, and current is injected from the micro size region into the active layer at a high density. It is suitable for high luminous efficiency LEDs having a type electrode structure. For example, the area of the n-type contact layer 24, that is, the area of the ohmic contact is reduced to, for example, 20 μm or less in diameter, the barrier potential viewed from the electron side of the n-side cladding layer 20, the doping concentration, the dielectric constant, By appropriately selecting the work function of the material of the n-side electrode layer 26, it is possible to form a depletion layer extending not only in the vertical direction of FIG. 1 but also in the horizontal direction of FIG. 1 and in the direction perpendicular to the paper surface of FIG. The depletion region 22 formed by the Schottky contact with the n-side electrode layer 26 and the n-side cladding layer 20 is expanded to the region below the n-type contact layer 24 as shown in FIG. Can do. As a result, the leakage current that flows when the reverse bias is applied can be cut off.

  The LED can be formed of various compound semiconductor materials, and each layer shown in FIGS. 1 and 2 can have, for example, the following configuration.

(A) GaN LED
The GaN-based LED includes, for example, a supporting substrate (for example, a sapphire substrate (not shown)), a p-type GaN layer (p-type cladding layer 16), an InGaN-based active layer (active layer 18), and an n-type GaN layer ( An n-type cladding layer 20), an n-type GaN layer (n-type contact layer 24), an Ag / Au electrode (p-side electrode layer 12), and Ti / Au (n-side electrode layer 26) are included.

  The InGaN-based active layer has a multiple quantum well (MQW) structure in which a well layer made of InGaN and a barrier layer made of GaN are alternately stacked and is composed of a number of well layers sandwiched between the barrier layers. is doing. The InGaN-based compound material constituting the well layer can obtain light emission from blue violet to red by changing these ratios as a ternary or quaternary mixed crystal with InN or AlN added centering on GaN.

The wavelength of the light emitted from the well layer made of InGaN changes depending on the change in the composition ratio of In and Ga in the well layer. The smaller the In ratio, the shorter the emission wavelength, and the larger the In ratio, the light emission. The wavelength becomes a long wavelength. For example, if the well layer composition is In _0.23 Ga _0.77 N, green light emission with a wavelength of 510 nm to 520 nm can be obtained, and if In _0.17 Ga _0.83 N is used, blue light emission with a wavelength of 450 nm to 470 nm can be obtained.

(B) AlGaInP LED
The AlGaInP-based LED includes, for example, a support substrate (for example, a sapphire substrate (not shown)), a p-type AlGaInP clad layer (p-type clad layer 16), an AlGaInP active layer (active layer 18), and an n-type AlGaInP clad layer. (N-type cladding layer 20), n-type GaAs layer (n-type contact layer 24), AuZn (p-side electrode layer 12), AuGe (n-side electrode layer 26), and emits light from green to red Obtainable. For example, if the active layer is (Al _0.05 Ga _0.95 ) _0.5 In _0.5 P, red light emission can be obtained, and if the active layer is (Al _0.45 Ga _0.55 ) _0.5 In _0.5 P, green light emission can be obtained.

(C) AlGaAs LED
The AlGaAs LED includes, for example, a supporting substrate (for example, a sapphire substrate (not shown)), a p-type AlGaAs cladding layer (p-type cladding layer 16), a GaAs active layer (active layer 18), and an n-type AlGaAs cladding layer. (N-type cladding layer 20), n-type AlGaAs contact layer (n-type contact layer 24), AuZn (p-side electrode layer 12), AuGe (n-side electrode layer 26), and the active layer is Ga _0.65 Al _{If it is 0.35} As, red light emission can be obtained.

  In the configuration shown in FIGS. 1 and 2, the metal material forming the n-side electrode layer 26 forms an ohmic junction with the n-type contact layer 24 and forms a Schottky junction with the n-type cladding layer 20. The p-side and n-side electrode layers 12 and 26 may be composed of a single layer or a plurality of layers. In the following description, elements are represented as A, B, C,..., And the layer structure is represented as A / B, A / B / C,..., And the elements are semiconductors in the order of elements A, B, C,. Indicates that the layers are stacked. That is, the element A described before the first symbol “/” means that it is formed in close contact with the p-type layer or the n-type layer.

The n-side electrode layer 26 includes, for example, Al, Sc, Ti, Zr, Mo, Ta, W, Ni, Cr, Cu, Ag, Au, Pd, Pt, Hf, etc., and is formed from a single metal layer. Or a plurality of layers in which metals (which may include alloys) are laminated, such as Ti / Au, Ti / Al, Ti / Pt / Au, Ni / AuGe alloy / Au, or the like.
When light is extracted from the transparent p-type electrode layer 12 side, the light reflection efficiency of the n-side electrode layer 26 is enhanced by using a high-light reflective material such as Ag or Al to improve the light extraction efficiency from the inside of the LED. Is possible.

  The p-side electrode layer 12 includes, for example, Pd, Pt, Ag, Au, Ni, In, Cr, Ti, etc., and is composed of a single metal layer, or Ag / Au, Ag / Ni. , Ni / Au, Ag / Pt / Au, Ni / Pt / Au, etc., and a plurality of layers in which metals (which may include alloys) are laminated. In the case where light is extracted from the n-side electrode layer 26 side, the p-side electrode layer 12 is constituted by a light-reflective metal layer so that it also functions as a light reflecting layer that increases the light emission efficiency. Yes.

  Next, an AlGaInP-based LED that emits a central wavelength of 635 nm will be described as an example.

  In order to confine carriers in an active layer that emits light, an active layer has a double heterostructure sandwiched between cladding layers (p-type and n-type AlGaInP layers) having p-polarity and n-polarity, respectively, by impurity doping. Generally have. This n-type cladding layer material is difficult to be doped with impurities to generate high-concentration carriers, and does not reach a carrier concentration that provides an ohmic contact with a metal to be an n-side electrode layer. Further, since the n-type cladding layer is adjacent to the active layer, it is difficult to perform high-concentration impurity doping in order to prioritize crystallinity. This is common to most high-efficiency LED and laser structures.

  Therefore, in general, in order to obtain ohmic contact with the electrode material for the purpose of ohmic contact with the metal material of the n-side electrode layer, the n-type contact layer doped at a high concentration is provided on the n-type cladding layer. Is done.

  Since this n-type contact layer is made of a material (GaAs) suitable for high-concentration doping, it is easy to obtain an ohmic contact with the metal material of the n-side electrode layer, and the film thickness of the n-type contact layer is crystallized by impurity doping. The n-type cladding layer is relatively thin so as not to increase defects.

  Hereinafter, a specific configuration of the AlGaInP-based LED will be described.

First layer: AuZn (thickness 0.2 μm) is provided as a p-side electrode layer 12 on the surface of a supporting substrate (for example, a sapphire substrate (not shown)),
Second layer: A p-type GaAs buffer layer (thickness 0.5 μm, Zn or Mg is doped with 1 × 10 ¹⁸ / cm ³ ) on the other surface of the p-type GaAs wafer.
Third layer: p-type AlGaInP cladding layer ((Al _0.65 Ga _0.35 ) _0.5 In _0.5 P, thickness 0.5 μm, Zn or Mg is doped with 1 × 10 ¹⁸ / cm ³ ).
Fourth layer: p-type GaAs layer (thickness 0.05 μm, doped with Zn or Mg at 5 × 10 ¹⁹ / cm ³ .

Fifth layer: p-type AlGaInP layer ((Al _0.65 Ga _0.35 ) _0.5 In _0.5 P, thickness 1.0 μm, Zn or Mg is doped with 1 × 10 ¹⁸ / cm ³ ),
Sixth layer: undoped AlGaInP layer ((Al _0.6 Ga _0.4 ) _0.5 In _0.5 P, thickness 0.05 μm, impurity concentration 7 × 10 ¹⁵ cm ³ or less),
Seventh layer: undoped GaInP layer (well layer, Ga _0.5 In _0.5 P, thickness 0.01 μm, impurity concentration 7 × 10 ¹⁵ cm ³ or less) and undoped AlGaInP layer (barrier layer, (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P, a thickness of 0.042 μm, an impurity concentration of 7 × 10 ¹⁵ cm ³ or less), a multiple quantum well active layer (15 well layers and 14 barrier layers are sequentially stacked),
Eighth layer: undoped AlGaInP layer ((Al _0.6 Ga _0.4 ) _0.5 In _0.5 P, thickness 0.05 μm, impurity concentration 7 × 10 ¹⁵ cm ³ or less),
Ninth layer: n-type AlGaInP cladding layer ((Al _0.65 Ga _0.35 ) _0.5 In _0.5 P, thickness 1.0 μm, doped with Si or Se at 1 × 10 ¹⁸ / cm ³ )
Tenth layer: An n-type GaAs layer (thickness 0.05 μm, Si or Se doped at 5 × 10 ¹⁸ / cm ³ ) is laminated in this order.

  The LED element composed of the above layers is, for example, 20 μm × 20 μm in size, and the area of the n-type contact layer is, for example, 8 μm × 8 μm in size.

  It has a larger area than the n-type contact layer, for example, 12 μm × 12 μm, and has AuGe (thickness 0.2 μm) as an n-side electrode layer that contacts both the n-type contact layer and the exposed n-type cladding layer ing.

  The metal material constituting the n-side electrode layer forms an ohmic contact with the n-type electrode layer in which the n-side electrode layer is highly doped, and the n-side electrode layer forms a Schottky contact with the n-type cladding layer Anything can be used. When forming the n-side electrode layer, a difference in eutectic temperature for alloying the metal constituting the n-side electrode layer can be utilized, so that the n-side electrode layer and the n-type cladding layer (n-type AlGaInP) A Schottky contact can be selectively formed between them, and an ohmic contact can be selectively formed between the n-side electrode layer and the n-type contact layer (n-type GaAs).

  The surface of the n-type cladding layer in contact with the n-side electrode layer is electrically Schottky contact, and the n-type electrode layer is in contact with the n-side electrode layer in a reverse bias state where a positive voltage is applied to the n-side electrode layer. A carrier depletion region is generated inside the n-type cladding layer starting from the surface of the cladding layer. This depletion region also extends under the n-type contact layer, and when the depletion region is sufficiently expanded, current flowing from the n-type cladding layer to the n-type contact layer is blocked. That is, when a reverse bias is applied, the depletion region increases, and when the depletion region is formed in all the regions below the n-type contact layer, the current flowing in the reverse direction, that is, from the n-type cladding layer to n Leakage current flowing in the mold contact layer is cut off.

  The depletion region has a property of being reduced by setting a forward bias state in which a negative voltage is applied to the n-side electrode layer. The depletion region is reduced and a depletion region is formed below the n-type contact layer. When there is no region, current flows from the n-type contact layer to the n-type cladding layer.

  When the depletion region shrinks and the voltage value at which current begins to flow from the n-type contact layer to the n-type cladding layer is made close to the voltage value (voltage threshold) at which the LED emits light, it is consumed before the LED emits light. The power that is used can be eliminated.

  Next, a simple matrix drive type LED display (image display device using LEDs) in which LEDs according to the present invention are two-dimensionally arranged will be described.

  The LED display has a red LED, a green LED, and a blue LED, and is configured as a display capable of displaying a full color by mixing color of RGB three primary colors. Each LED forms a row array in which LEDs having the same emission color are arranged in a row, and is arranged so as to form a two-dimensional matrix as a whole.

  In the LED display of the simple matrix drive type, the n electrode of each LED is electrically connected to the n side wiring, the p electrode is electrically connected to the p side wiring, and the row driving circuit is connected to the n side wiring. The column drive circuit is connected to the p-side wiring.

  In an LED display, LEDs are arranged so as to emit a common color in the Y direction, and LEDs that emit R (red light), G (green light), and B (blue light) to the right in the column direction. Are arranged to repeat. For example, LEDs that emit R (red light) are arranged on the row wirings (n, n + 3, n + 6,...), And LEDs that emit G (green light) on the row wirings (n + 1, n + 4, n + 7,...). Are arranged, and LEDs that emit B (blue light) are arranged on the row wirings (n + 2, n + 5, n + 8,...).

Note that all of the LEDs that emit R (red light), G (green light), and B (blue light) can be, for example, GaN LEDs, but G (green light), B (blue light) The LED that emits light can be formed of a GaN-based LED, and the LED that emits R (red light) can be formed of an AlGaInP-based LED. As the red LED, the red LED having the configuration described with reference to FIGS. 1 and 2 is used. Red emitting LED is, for example, the supporting substrate (e.g., sapphire substrate) on having p-type AlGaInP cladding layer, AlGaInP active layer, n-type AlGaInP cladding layer, an n-type GaAs contact layer, an active layer (Al _0.05 Ga _0.95 ) _0.5 In _0.5 P layer.

  The p-electrodes of the plurality of LEDs arranged in each row are connected to the common wiring of each row, the n-electrodes of the plurality of LEDs arranged in each column are connected to the common wiring of each column, and each LED is driven in a simple matrix . In the simple matrix driving method, column wirings and row wirings are formed, and by applying a voltage to the column wirings and the row wirings, LEDs connected to the column wirings and the row wirings at the places where the column wirings and the row wirings cross each other. Driven. The simple matrix system has an advantage that the structure is simple and the yield is low and the yield is good. When driving a large number of LEDs by a simple matrix method, it is essential to pay attention to the leakage current and suppress it.

  When an LED is driven by a simple matrix method, an LED that is not driven is held so as not to emit light by applying a reverse bias, and thus a leakage current in each LED that occurs when a reverse bias is applied becomes a problem. come.

In the simple matrix method, since the column wiring and the row wiring are common wiring for the LEDs arranged in a two-dimensional matrix, the leakage current for each LED is also the whole of the LEDs in which the leakage current of one LED is arranged. It is close to the product multiplied by the total number. In an ideal LED, no current flows when the voltage is 0 V or less. However, in an actual LED, there is a reverse leakage current (leakage current). For example, even if the reverse leakage current is 0.1 μA. If the total number of LEDs arranged is 10 ⁴ , the current will flow to one place with a reverse leakage current of about 10 mA as a whole, and the supplied power will be wasted, increasing the power consumption. Will be invited. In an image display device using an LED and having a very large number of pixels, the presence of reverse leakage current causes not only an increase in power consumption but also a decrease in image quality due to crosstalk or the like.

For example, the total number of arranged LEDs is 10 ⁴ , and the drive current density (the value obtained by dividing the drive current for driving the LED by the area of the active layer (light emitting layer)) is 10 A / cm ^{2 to} 100 A / In the case of cm ² , the leakage current density per LED when a reverse bias is applied is about (10 to 100) (A / cm ² ) / 20000 = (0.5 to 5) mA / cm ² . If the leakage current density per LED when a reverse bias is applied is greater than about (0.5 to 5) mA / cm ² , all of the supplied current is wasted and desired light emission is performed. Will not be able to. Therefore, it is necessary to suppress the leakage current density to about 2 × 10 ⁴ or less than the driving current density.

Further, 1 the contrast ratio: Assuming that 500 or more is required, less than one-about ¹⁰⁷ minutes the leakage current density with respect to the drive current density, i.e., necessary to suppress the (1~10) μA / cm ² There is. It goes without saying that the leakage current density needs to be reduced as the total number of LEDs arranged increases.

  Since the LED according to the present embodiment can prevent reverse leakage current, it can be particularly suitably used for a simple matrix drive type LED display in which a very large number of LEDs are two-dimensionally arranged. In addition to an increase in power consumption due to leakage current, the problem of image quality degradation due to crosstalk or the like can be solved. Therefore, the image quality can be improved and the power consumption can be reduced.

  FIG. 3 is an equivalent circuit diagram for explaining the problems of the simple matrix drive type LED display in the embodiment of the present invention.

  In the LED display shown in FIG. 3, when an i-th row n-side wiring 44 and a j-th column p-side wiring 45 are selected by a row driving circuit and a column driving circuit, respectively, the LED (i, j ), A forward voltage is applied only to 51, normal current 52 flows through LED 51, and only LED 51 is lit.

  However, for example, the LED (i−1, j−1) at the intersection of the (i−1) -th row n-side wiring 44 and the (j−1) -th column p-side wiring 45 is the defective LED 53. If the reverse leakage current is too large or the p-pole side and the n-pole side are short-circuited, the abnormal current 54 flows through the path indicated by the arrow 1-2-3-4-5 in the figure. Become. Similarly, if the LED (i−2, j + 1) is a defective LED 55, an abnormal current 56 is generated in the illustrated path 6-7-8-9-10. In this way, in the case of a simple matrix drive type LED display composed of an enormous number of LEDs, if a large number of LEDs with large reverse leakage current are included, an abnormal current is generated in an unspecified number of paths. To do.

  As described above, in the simple matrix drive type LED display having the structure shown in FIG. 3, the presence of a large reverse leakage current of the LED and the occurrence of a short circuit state can be a very serious problem. For this reason, as an LED used for a simple matrix drive type LED display, an LED which prevents the presence of a large reverse leakage current and the occurrence of a short-circuit state is required. In the present embodiment, for example, the LED described above with reference to FIGS. 1 and 2 is used as the red LED. Therefore, in the LED arranged in a two-dimensional matrix, the reverse direction passes through the internal crystal leakage and the short path (short circuit). The flowing current can be blocked by the formation of the depletion region, and a simple matrix driven display with high reliability and long life can be realized.

Embodiment First, a depletion layer generated by a Schottky junction consisting of an n-side electrode layer and an n-type cladding layer will be described.

Based on the one-dimensional model in which the n-side electrode layer and the n-type cladding layer are stacked, the thickness W of the depletion layer in the stacking direction was determined by W ² = 2ε (φ _bs −V) / (qN). Here, ε is the dielectric constant of the n-type cladding layer, φ _bs is the barrier potential seen from the electron side of the n-type cladding layer, V is the applied voltage (the applied voltage is negative in the reverse direction), and N is The doping concentration of the n-type cladding layer, q is the amount of element.

FIG. 4 shows the material of the n-side electrode layer when the N (nitrogen) doping concentration in the n-type cladding layer 20 (n-type AlGaInP) is 2 × 10 ¹⁸ (atoms / cm ³ ) in the embodiment of the present invention. FIG. 9 is a diagram for explaining a change in the bias voltage dependency of the depletion layer thickness due to the graph, where graph (a) shows the electrode material as Au and graph (b) shows the depletion layer thickness as a function of bias voltage when the electrode material is Pd. Showing gender.

Note that, when ε of n-type AlGaInP is 10 and the electrode materials are Au and Pd, φ _bs (eV) is 1.32 eV (Au) and 0.317 eV (Pd), respectively.

  As can be seen from FIG. 4, at a constant reverse bias, the thickness W of the depletion layer is larger when Au is used as the electrode, and W is larger as the work function of the electrode material is smaller.

  From the results shown in FIG. 4, in the case of the junction between Pd constituting the n-side electrode layer 26 and the n-type cladding layer 20 (n-type AlGaInP), a depletion region is generated at a voltage of 0.18 V or less, and the n-type contact layer 24 Since it spreads around the ohmic junction of the n-type cladding layer 20, the depletion region is expanded by reverse bias, and the reverse current is suppressed. Therefore, by controlling the formation of the depletion region 22, it is possible to suppress the leak current flowing in the reverse direction.

  If a forward bias of 0.18 V or higher is not applied, no current flows from the n-type contact layer 24 to the n-type cladding layer 20 and is not injected into the active layer, and the LED does not emit light.

FIG. 5 shows the change in the bias voltage dependency of the depletion layer thickness depending on the N (nitrogen) doping concentration in the n-type cladding layer 20 (n-type AlGaInP) when the electrode material is Au in the embodiment of the present invention. It is a figure explaining, a graph (a) is doping concentration = N (nitrogen) doping 5 × 10 ¹⁸ (atoms / cm ³ ), a graph (b) is a doping concentration = 2 × 10 ¹⁸ (atoms / cm ³ ), a graph (C) shows the bias voltage dependence of the thickness of the depletion layer when doping = 5 × 10 ¹⁷ (atoms / cm ³ ).

  As is clear from FIG. 5, with a constant reverse bias, the depletion layer thickness is larger when the doping concentration is smaller.

  Next, the result of evaluating the depletion layer generated by the Schottky junction by the n-side electrode layer and the n-type cladding layer by experiment will be described.

  FIG. 6 is a diagram for explaining a method for evaluating the formation of a depletion layer generated by a Schottky junction in the embodiment of the present invention. FIG. 6A is a cross-sectional view for explaining a material for an evaluation experiment, and FIG. ) Is a cross-sectional view and a plan view for explaining the formation of electrodes, and FIG. 6C is a plan view for explaining an electrode arrangement for measuring current-voltage (IV) characteristics.

As shown in FIG. 6A, as a material substrate for the evaluation experiment, an n-type GaAs substrate 30 is formed by sequentially forming an n-type AlGaInP epitaxially grown layer 31 and an n-type GaAs epitaxially grown layer 32. used. The n-type GaAs substrate 30 has a thickness of 350 μm and is doped with Si at 2 × 10 ¹⁸ / cm ³ . The n-type AlGaInP epitaxial growth layer 31 has a thickness of 0.5 μm and is doped with Si of 0.8 × 10 ¹⁸ / cm ³ . The n-type GaAs epitaxial growth layer 32 has a thickness of 0.05 μm and is doped with Si at 6 × 10 ¹⁸ / cm ³ .

  The electrode shown in FIG. 6B is formed using the material substrate shown in FIG. First, a multilayer electrode 33 (thickness 300 μm) made of Pd / (Au—Ge alloy) / Au sequentially formed from the lower layer is formed on the n-type GaAs epitaxial growth layer 32 in a predetermined size by vapor deposition (lift-off method). . After deposition, the n-type GaAs epitaxial growth layer 32 outside the multilayer electrode 33 is removed by wet etching (dilute hydrochloric acid + hydrogen peroxide solution) using the multilayer electrode 33 as a mask. Next, an Au electrode (thickness: 200 μm) is formed by sputtering so as to cover the multilayer electrode 33 and the n-type AlGaInP epitaxial growth layer 31 in a region of a predetermined size outside the multilayer electrode 33. Next, Pd of the multilayer electrode 33 and the n-type GaAs epitaxial growth layer 32 are alloyed so that the n-type GaAs epitaxial growth layer 32 and the multilayer electrode 33 are in ohmic contact. The diameter of the Au electrode was set to the diameter of the n-type GaAs epitaxial growth layer 32 (substantially equal to the diameter of the multilayer electrode 33) +2 μm.

As shown in FIG. 6C, the electrodes shown in FIG. 6B have a plurality of the n-type GaAs epitaxial growth layers 32 having different diameters at equal intervals L ₁ (12 in FIG. 6C). To form.) Each electrode is formed with the n-side electrode pad 36 for connection, with pads 35a, 35 formed at a center-to-center distance L _3, it is used for I-V measurements. Incidentally, the distance between the centers of the pads 35a nearest the electrode is L _2, the interval L _1, L _2, L ₃ is about 15Myuemu～20myuemu.

7, 8, and 9 are diagrams illustrating evaluation results of a depletion layer generated by a Schottky junction in the example of the present invention, and are diagrams illustrating IV characteristics. FIG. 9 is an enlarged view in which the horizontal axis shown in FIG. 8 is a logarithmic scale, and the current of about 10 ⁻¹² A is the lower limit of measurement.

In FIG. 7, the graph (a) is between the n-side electrode pad 36 and the PAD (pad) 35 a connected to the electrode (diameter 5 μmφ) shown in FIG. 6 (B), and the graph (b) is FIG. 6 (B). Between the n-side electrode pad 36 and the PAD (pad) 35a connected to the electrode shown in FIG. 6 (diameter 8 μmφ), the graph (c) shows the n-side electrode connected to the electrode (diameter 10 μmφ) shown in FIG. The graph (d) shows the voltage between the n-side electrode pad 36 and the PAD (pad) 35a connected to the electrode (diameter 12 μmφ) shown in FIG. 6B, respectively, between the pad 36 and the PAD (pad) 35a. The IV characteristic obtained by applying is shown. The distance between the electrode (diameter 8 μmφ) and the pad 35a, the distance between the electrode (diameter 8 μmφ) and the pad 35a, the distance between the electrode (diameter 10 μmφ) and the pad 35a, and the graph (d) are the electrode (diameter 12 μmφ) and each distance between the pads 35a is different from the center distance L ₃ of the pad 35a, 35.

  As apparent from the graphs (a) and (b) shown in FIG. 7, when the electrode diameter shown in FIG. 6 (B) is 8 μmφ or less, the rising voltage is 0.8 V when forward bias (positive voltage) is applied, Generation of a Schottky barrier was confirmed, and when reverse bias (negative voltage) was applied, I (current) = 0, and it was confirmed that the reverse current was blocked by the depletion layer formed when reverse bias was applied. As described above, this is not limited to the vertical direction of FIG. 1, but the depletion layer has a three-dimensional expansion, and when the reverse bias is increased, the n-type contact layer 24 and the n-type cladding layer 20 It is experimentally shown that the region in contact with the n-type contact layer 24 is covered with the depletion region 22 and the current flowing between the n-type contact layer 24 and the n-type clad layer 20 is cut off. It clearly shows that the leakage current in can be prevented.

In FIG. 8, graph (e) is between PAD (pad) 35a and PAD (pad) 35b, and graph (f) is an n-side electrode connected to the electrode (diameter 5 μmφ) shown in FIG. 6 (B). The IV characteristics obtained by applying a voltage between the pad 36 and the PAD (pad) 35a are shown. The distance between the center distance L ₃ and the electrode (diameter 5Myuemufai) pads 35a of the pad 35a, 35 is approximately equal and are approximately 15Myuemu～20myuemu.

From the comparison between FIG. 7 and FIG. 8, the IV characteristics obtained in the case of the electrode (diameter 5 μmφ) are almost the same, and the distance L ₃ between the centers of the pads 35a and 35 and the electrode (diameter 5 μmφ) pad 35a. It is clear that the difference in distance does not affect the IV characteristics. Further, as shown in FIGS. 8 and 9, the conductive state of the pads 35a and 35 is substantially complete ohmic and does not affect the IV characteristics.

  As described above, the size of the electrode shown in FIG. 6B is an important factor in preventing leakage current when reverse bias is applied to the LED. By reducing the volume of the light-emitting element, the influence of current diffusion can be reduced, so that it can be driven with a very small current, and by increasing the current density, high-efficiency light emission can be obtained and low power consumption can be realized. Suitable for micro LED.

  As mentioned above, although this invention was demonstrated about embodiment, this invention is not limited to the above-mentioned embodiment, It cannot be overemphasized that various deformation | transformation based on the technical idea of this invention is possible. Absent.

  As described above, according to the present invention, it is possible to provide a semiconductor light emitting element capable of suppressing leakage current and crosstalk and a display device using the same.

It is sectional drawing explaining the outline structure of LED in embodiment of this invention, and control of formation of a depletion layer. It is a figure explaining schematic structure of LED same as the above, and is a sectional view explaining the area of the depletion layer formed by reverse bias application. It is an equivalent circuit diagram for demonstrating the problem of a simple matrix drive type LED display same as the above. It is a figure explaining the change of the bias voltage dependence of the thickness of a depletion layer by the material of an electrode layer in the Example of this invention. It is a figure explaining the change of the bias voltage dependence of the thickness of a depletion layer by the doping concentration of the carrier in a clad layer. It is a figure explaining the evaluation method of formation of the depletion layer produced by a Schottky junction same as the above. It is a figure which shows the evaluation result of the depletion layer produced by a Schottky junction same as the above, and is a figure which shows IV characteristic. It is a figure which shows the evaluation result of the depletion layer produced by a Schottky junction same as the above, and shows an IV characteristic. It is a figure which shows the evaluation result of the depletion layer produced by a Schottky junction same as the above, and shows an IV characteristic. It is sectional drawing which shows the light emitting diode in a prior art. It is a figure showing the structure of a semiconductor laser same as the above. It is sectional drawing for demonstrating the effect | action of a semiconductor laser same as the above.

Explanation of symbols

12 ... p-side electrode layer, 14 ... p-type contact layer, 16 ... p-type cladding layer,
18 ... active layer (light emitting layer), 20 ... n-type cladding layer, 22 ... depletion region,
24 ... n-type contact layer, 26 ... n-side electrode layer, 30 ... n-type GaAs substrate,
31 ... n-type AlGaInP epitaxial growth layer,
32 ... n-type GaAs epitaxial growth layer, 33 ... multilayer electrode, 34 ... Au electrode,
35a, 35b ... pads, 36 ... n-side electrode pads, 44 ... n-side wiring (row wiring),
45 ... p-side wiring (column wiring), 54, 56 ... abnormal current,
51 ... Selected LED (i, j), 52 ... Normal current, 53, 55 ... Bad LED

Claims (6)

A substrate,
A p-side electrode layer and a p-type cladding layer formed on the substrate;
An active layer made of a compound semiconductor;
an n-type cladding layer;
an n-type contact layer;
an n-side electrode layer, wherein the n-side electrode layer is laminated in contact with the n-type contact layer and the n-type cladding layer, and the n-side electrode layer forms an ohmic junction with the n-type contact layer. And forming a Schottky junction with the n-type cladding layer, and when a reverse bias voltage is applied between the n-side electrode layer and the p-side electrode layer, below the n-type contact layer A semiconductor light-emitting device in which a depletion layer is formed in the n-type cladding layer in the region.   2. The semiconductor light emitting element according to claim 1, wherein a region of the depletion layer is enlarged as the reverse bias voltage increases, and a current flowing from the p-side electrode layer to the n-side electrode layer is suppressed.   The semiconductor light emitting element according to claim 1, wherein a region of the depletion layer is reduced by applying a forward bias voltage between the n-side electrode layer and the p-side electrode layer.   4. The semiconductor light emitting device according to claim 3, wherein when the forward bias voltage is increased to reach a certain voltage, a current flows from the n-type contact layer to the n-type cladding layer, and light is emitted from the active layer. 5. element.   The semiconductor light emitting element according to claim 1, wherein the diameter of the n-type contact layer is 20 μm or less.   6. A display device, wherein the semiconductor light emitting elements according to claim 1 are arranged in a two-dimensional matrix, and the arranged semiconductor light emitting elements are driven in a simple matrix.

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