JP2001237461A - Semiconductor light emitting device - Google Patents

Abstract

[PROBLEMS] To provide a semiconductor light emitting device in which current is uniformly injected into an active layer, light emission from the active layer is made uniform, and uniformity of intensity distribution of a near-field image is improved. provide. SOLUTION: In a semiconductor light emitting device in which an active layer 18 is formed between a semiconductor substrate 10 and a transparent conductive film 28, an end of the transparent conductive film 28 is connected to an electrode pad 30 provided on the transparent conductive film 28. A thin wire electrode 32 extending to the vicinity is formed. By injecting a current from the fine wire electrode 32 into the active layer 18 through the transparent conductive film 28, the active layer 18
, The current can be injected uniformly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device using an oxide transparent conductive film.

[0002]

2. Description of the Related Art Referring to FIGS.
A conventional semiconductor light emitting device disclosed in Japanese Patent No. 3927 will be described. FIG. 8 is a diagram showing a cross section of a light emitting diode which is an example of a conventional semiconductor light emitting device, and FIG. 9 is a diagram showing a plane of the conventional light emitting diode viewed from a light emitting surface side. As shown in FIGS. 8 and 9, a lower clad layer 52, an active layer 54, an upper clad layer 56, and a transparent conductive film 58 are sequentially stacked on a semiconductor substrate 50. Also, the transparent conductive film 58
An electrode pad 60 is formed on the semiconductor substrate 5.
The lower electrode 62 is formed on the lower surface of the zero. here,
The transparent conductive film 58 is made of a light-transmitting material, and generally uses indium tin oxide (ITO film).

In such a light emitting diode, for example, a positive voltage is applied to the electrode pad 60, and a negative voltage is applied to the lower electrode 62. As a result, current is injected into the active layer 54 through the transparent conductive film 58 and the like, and the active layer 54 emits light. The emitted light passes through the transparent conductive film 58 and is emitted to the outside of the light emitting diode.

[0004]

However, the transparent conductive film 58 has a higher sheet resistivity than, for example, a metal film due to the material used. For this reason, when current is injected from the electrode pad 60 to the active layer 54 through the transparent conductive film 58, the current density distribution in the active layer 54 tends to be non-uniform. That is, the current value injected into the active layer 54 from the transparent conductive film 58 located in a region away from the electrode pad 60 is smaller than the current value injected into the active layer 54 from the transparent conductive film 58 near the electrode pad 60. It will be a low value.

[0005] The non-uniform distribution of the current density in the active layer 54 leads to the non-uniform distribution of the emission intensity in the active layer 54. As a result, the intensity distribution of the near-field image has become non-uniform. In particular, in the case of a high luminous flux light emitting diode that emits light of high intensity by injecting a large current, the intensity distribution of the near-field image becomes significantly uneven. Further, the uneven distribution of the light emission intensity in the active layer 54 also means that efficient light emission is not performed in the entire active layer.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and makes uniform light emission from an active layer by uniformly injecting current into the active layer, thereby achieving uniformity of intensity distribution of a near-field image and uniformity of intensity distribution. It is an object of the present invention to provide a semiconductor light emitting device having improved luminous efficiency over the entire active layer.

[0007]

To achieve the above object, a semiconductor light emitting device according to the present invention is a semiconductor light emitting device in which a light emitting layer is formed between a semiconductor substrate and a transparent conductive film. An electrode pad provided on a transparent conductive film, and a fine wire electrode provided on the transparent conductive film, connected to the electrode pad, and formed up to near an end on the transparent conductive film. Features.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A first embodiment of the present invention is characterized in that a thin line electrode composed of radial and lattice thin lines connected to an electrode pad on a transparent electrode is provided. This is to achieve uniform current injection into the layer.
The details will be described below with reference to the drawings.

FIG. 1 is a perspective view of a semiconductor light emitting device according to a first embodiment of the present invention. FIG. 2 is a sectional view of the semiconductor light emitting device according to the first embodiment of the present invention, and FIG. 3 is a plan view of the semiconductor light emitting device according to the first embodiment of the present invention viewed from the light emitting surface side.

As shown in FIGS. 1, 2 and 3, a buffer layer 12, a reflective layer 14, a lower clad layer 16, an active layer 18, an upper clad layer 20, an intermediate semiconductor layer 22, an ohmic layer A contact layer 24, a current blocking layer 26, and a transparent conductive film 28 are sequentially stacked. In this embodiment, the active layer 18 constitutes a light emitting layer. Then, an electrode pad 30 is formed on the transparent conductive film 28.
A thin wire electrode 32 connected to the electrode pad 30 is formed.

Here, as shown in FIG.
Is composed of a radial electrode 34 and a grid electrode 36.
The thin wire electrode 32 has an opening 38 in which the radial electrode 34 and the grid electrode 36 do not exist, and the transparent conductive film 28
Is directly exposed. Light is emitted to the outside from the part where the transparent conductive film 28 is directly exposed. On the other hand, as shown in FIG. 1 and FIG.
Are formed.

The current block layer 26 is formed below the electrode pad 30 on the ohmic contact layer 24. This current block layer 26 is
Has the role of diverting the current from the electrode pad 30 to the outside of the electrode pad 30. By diverting the current to the outside of the electrode pad 30 in this manner, it is possible to reduce the generation of light that is stopped by the electrode pad 30 without being emitted to the outside in the active layer 18.

The thin wire electrode 32 is composed of a radial electrode 34 formed of a thin wire extending in all directions from the center of the electrode pad 30 and a grid electrode 36 formed of square sides along the vicinity of the outer periphery of the transparent conductive film 28. The radial electrode 34 is connected to the electrode pad 30 and the grid electrode 36 is
It connects at two vertices and the center of four sides.

Next, the constituent materials, film thickness and the like in the present embodiment will be described in detail. The semiconductor substrate 10 has a thickness of about 1
The buffer layer 12 is made of a 50 μm n-GaAs substrate, and the buffer layer 12 is made of a 0.5 μm-thick n-GaAs substrate. The reflection layer 14 is made of n-In _0.5 Al
It is composed of a multilayer film in which 10 pairs of _0.5 P and n-GaAs layers are alternately laminated.

The lower cladding layer 16 has a thickness of 0.6 μm.
-In _0.5 Al _0.5 P, and the active layer 18 has a Zn-doped In _0.5 (Ga
_0.7 Al _0.3 ) _0.5 P. The upper cladding layer 20 is made of p-In _0.5 Al having a thickness of 1.0 μm.
_The intermediate semiconductor layer 22 is made of Ga _0.3 Al _0.7 As with a thickness of 0.1 to 3.0 μm, and the ohmic contact layer 24 is made of 0.1 μm.
It is made of p-GaAs having a thickness of 01 to 0.03 μm. The current blocking layer 26 is made of n-In _0.5 Al _0.5 P having a thickness of about 0.01 to 0.2 μm and a diameter of about 110 μm, and the transparent conductive film 28 is made of indium. It is composed of tin oxide.

The electrode pad 30 and the thin line electrode 32 are formed by laminating Au having a thickness of 1.2 μm on AuGe having a thickness of 0.2 μm so that Au is the uppermost surface of the semiconductor light emitting device.
It is composed of a composite film of a single metal and alloy of uGe / Au. The AuGe film is formed by using the Au transparent conductive film 28.
This is because the bonding strength of AuGe to the transparent conductive film is stronger than the bonding strength to Au, and the bonding strength of the electrode pad 30 and the fine wire electrode 32 is improved through the AuGe film. However, the electrode pad 30 and the thin line electrode 32 may be formed by directly forming Au on the transparent conductive film 28 without using the AuGe film. Further, Ti may be used instead of Au.

The electrode pad 30 has a circular shape with a diameter of about 100 μm, and is slightly smaller than the current blocking layer 26. The line width of the fine wire electrode 32 is set to 25 μm or less, and preferably in the range of about 1 to 20 μm. The reason for setting the line width to this range is that if the line width is too narrow, there is a possibility that disconnection or an increase in sheet resistance may be caused by the influence of foreign matter during the preparation of the fine line electrode 32. On the other hand, if the line width is too wide, the area where the light is extracted on the light emitting surface, that is, the area of the opening 38 is reduced, and the light extraction efficiency is reduced. The electrode 40 is made of AuGe having a thickness of 0.2 μm.

Next, a method for manufacturing the above-described semiconductor light emitting device will be described. A buffer layer 12, a reflection layer 14, a lower cladding layer 16, an active layer 18, an upper cladding layer 20, an intermediate semiconductor layer 22, an ohmic contact layer 24, and a current blocking layer 26 are formed on a semiconductor substrate 10 by CVD (Chemical Vap).
or Deposition) method. Thereafter, the current block layer 26 is masked in a circular shape with a photoresist and etched with hot phosphoric acid or hot sulfuric acid. By this etching, the unblocked portion of the current block layer 26 is removed up to the ohmic contact layer 24. As a result, the current block layer 26 is formed in a circular shape. Then, the photoresist is removed, washed with water, and dried.

Next, the semiconductor substrate 10 having undergone the above-described steps is
Indium, tin and oxide are converted to DC in a mixed gas atmosphere of argon and oxygen in a C magnetron sputtering device.
The transparent conductive film 28 is formed by forming about 2400 angstroms by magnetron sputtering. During DC magnetron sputtering, the temperature of the semiconductor substrate 10 is 1
The temperature is maintained at 50 to 200 ° C., and the mixture ratio of argon and oxygen is 100: 1, and the pressure of the mixed gas is about 1 × 10
⁻³ torr.

The electrode pad 30 and the thin line electrode 32 are formed by sequentially depositing AuGe and Au by vacuum deposition.
It is formed by patterning. Thereafter, the semiconductor substrate 10 is mirror-polished to about 150 μm,
0 is formed on the lower surface of the semiconductor substrate 10 by a vacuum evaporation method.

Next, the semiconductor substrate 10 having undergone the above steps is heated at about 350 to 450 ° C. in an inert gas atmosphere such as argon.
The heat treatment is performed in the temperature range described above. The semiconductor light emitting device thus formed is subjected to a scribing device, and a lattice-shaped cut is formed on the lower surface of the semiconductor substrate 10 with a diamond needle. Further, by breaking the semiconductor substrate 10 with a breaking device, each semiconductor light emitting element is separated and formed into an element.

Next, the operation of the semiconductor light emitting device in this embodiment will be described. When a positive voltage is applied to the electrode pad 30 and a negative voltage is applied to the electrode 40, the electrode pad 3
The current injected from 0 is directly injected from the electrode pad 30 into the transparent conductive film 28. In addition, the current injection into the transparent conductive film 28 is also performed from a path passing from the electrode pad 30 to the thin wire electrode 32. For this reason, the current distribution in the transparent conductive film 28 is more uniform than when current is injected only from the electrode pads 30. The sheet resistivity of the thin wire electrode 32 made of metal is lower than the sheet resistivity of the transparent conductive film 28.
This is a factor that leads to an improvement in the uniformity of the current distribution in the transparent conductive film 28 even if the line width or the area of the thin wire electrode 32 is relatively small. Further, the arrangement of the grid electrode 36 along the vicinity of the end of the transparent conductive film 28 serving as the light emitting surface contributes to the improvement of the uniformity of the current distribution near the outer periphery of the transparent conductive film 28. When the current distribution in the transparent conductive film 28 becomes uniform, the current is uniformly injected into the entire active layer 18. By increasing the size of the radial electrodes 34 and the grid electrodes 36 in accordance with the area of the active layer 18, current can be uniformly injected into the entire active layer 18 regardless of the area of the active layer 18. become. The light emitted from the active layer 18 is emitted from the opening 3 of the fine linear electrode 32.
8 to the outside of the semiconductor light emitting device.

The following effects are produced by making the current density distribution uniform throughout the active layer 18.

(1) The distribution of the light emission intensity over the entire area of the active layer 18 can be made uniform. As a result, the light intensity distribution in the near-field image is made uniform. It will be described later that the uniformity of the light intensity distribution in the near-field image is experimentally supported. By making the distribution of the light emission intensity in the active layer 18 uniform, light emission can be efficiently performed in the entire active layer 18.

(2) Even when the current of the semiconductor light emitting element is increased, the saturation of the light emission intensity hardly occurs. That is, if the current density distribution in the active layer 18 is non-uniform, the light emission intensity is saturated at a location where the current density is high, whereas if the current density distribution in the active layer 18 is uniform, Since a portion having a large current density does not occur, saturation of light emission intensity does not easily occur. As a result, the saturation point of the light output moves to the high current side in the current-light output characteristics. It will be described later that the fact that the saturation point of the light output moves to the high current side is experimentally confirmed.

(3) Due to the presence of the thin wire electrode 32, current is injected into the transparent conductive film 28 over a wider area. That is, the area where the ohmic contact is made on the upper surface of the transparent conductive film 28 substantially increases. As a result, the resistance of the semiconductor light emitting element when a voltage is applied in the forward direction decreases. The reduction in the resistance of the semiconductor light emitting device also means that the value of Vf decreases. It will be described later that the decrease in the resistance value when the forward voltage is applied is experimentally confirmed.

Next, experimental data on the characteristics of the semiconductor light emitting device according to the present embodiment will be shown in comparison with the conventional data. Here, as a comparative example, a semiconductor light emitting element having the same element structure as that of the semiconductor light emitting element according to the present embodiment except that the thin wire electrode 32 is excluded is used. FIG. 4 is a graph comparing the intensity distribution of a near-field image in the present embodiment with a comparative example. The horizontal axis of the graph of FIG. 4 is a line A passing through the center O of the upper surface of each semiconductor light emitting element and reaching the ends A and A ′ of the light emitting surface.
It represents the distance along -A '. The vertical axis of the graph in FIG. 4 relatively represents the intensity of the near-field image. In the graph of FIG. 4, the solid line and the dotted line show the distribution of the light intensity of the near-field image for the present embodiment and the comparative example, respectively.

As shown in the graph of FIG. 4, in the comparative example, the near-field image intensity gradually decreases toward both ends A and A 'of the light emitting surface. , The near-field image intensity is kept constant up to the vicinity of both ends A and A ′. Note that the near-field image intensity is substantially zero near the center of the light emitting surface due to the influence of the electrode pad 30 and the current blocking layer 26. Since the electrode pad 30 is made of a metal material that blocks light, light emission from the electrode pad 30 is limited.

FIG. 5 is a graph comparing current-light output characteristics of this embodiment and a comparative example. The horizontal axis of the graph in FIG. 5 is the forward injection current, and the vertical axis represents the light output. The solid line in the graph of FIG. 5 indicates the current-light output characteristic of the present embodiment, and the dotted line indicates the current-light output characteristic of the comparative example. As shown in FIG. 5, in this embodiment, the saturation of the light output occurs on the high current side as compared with the comparative example. That is, the saturation point of the light output has shifted to a much higher current side than the comparative example.
As a result, in the present embodiment, by increasing the current to be injected, it is possible to obtain a higher intensity light output than in the comparative example.

FIG. 6 is a graph comparing the current-voltage characteristics of this embodiment and the comparative example. The horizontal axis of the graph in FIG. 6 is the forward current, and the vertical axis is the forward voltage. The solid line in the graph of FIG. 6 indicates the current-voltage characteristic of the present embodiment, and the dotted line indicates the current-voltage characteristic of the comparative example. As shown in FIG. 6, when the same forward current is applied to the present embodiment and the comparative example, the present embodiment has a lower voltage. That is, when a voltage is applied in the forward direction, the semiconductor light emitting element has a lower resistance in this embodiment than in the comparative example.

As described above, according to the present embodiment, the thin wire electrode 32 composed of the radial electrode 34 connected to the electrode pad 30 and the grid electrode 36 connected to the radial electrode is disposed on the transparent conductive film 28. Thereby, the distribution of the current density injected into the transparent conductive film 28 from the electrode pad 30 is made uniform.

As a result, the distribution of the current density injected into the active layer 18 is made uniform, and the intensity distribution of the near-field image is made uniform. Further, even when the light emitting area is increased, the light emitting output can be increased without lowering the light emitting efficiency. Further, the saturation point of the light output moves to the high current side, so that a light output with higher intensity can be obtained as compared with the related art. In addition, the fine wire electrode 32
, The current injection from the electrode pad 30 is performed substantially over a large area including the thin wire electrode 32, and the forward resistance of the semiconductor light emitting device can be reduced. Further, the efficiency of heat radiation of the semiconductor light emitting element and the reliability are improved.

[Second Embodiment] A second embodiment of the present invention will be described. This embodiment corresponds to a modification of the first embodiment. FIG. 7 is a diagram showing a plane of the semiconductor light emitting device according to the second embodiment of the present invention viewed from the light emitting surface side. As shown in FIG. 7, a circular electrode pad 30 is formed on the transparent conductive film 28.
And a thin wire electrode 42 connected to the wire. The thin wire electrode 42 is composed of a radial electrode 44 formed of a thin wire extending radially from the center of the electrode pad 30 in all directions, and a concentric circumferential electrode 46 formed of two concentric thin wires having the same center as the electrode pad 30. It is configured. The radial electrodes 44 are connected to the electrode pads 30, and the radial electrodes 44 are connected to concentric circumferential electrodes 46. The thin wire electrode 44 has a portion where the radial electrode 44 and the concentric circumferential electrode 46 do not exist, that is, an opening 48 for transmitting light. This embodiment is the same as the first embodiment except that the grid electrode 36 of the first embodiment is replaced by a concentric circumferential electrode 46. The fine wire electrode 42 constitutes the low resistance electrode in the present embodiment.

In the present embodiment, similarly to the first embodiment, the current is uniformly injected into the transparent conductive film 28 due to the presence of the fine wire electrode 42. As a result, the distribution of the current density injected into the active layer 18 is made uniform, and an effect similar to that of the first embodiment is produced.

That is, the distribution of the current density injected into the active layer 18 is made uniform, and the intensity distribution of the near-field image is made uniform. Further, when the light emitting area is increased, the light emitting output can be increased without lowering the light emitting efficiency. Further, the saturation point of the light output moves to the high current side, so that a light output with higher intensity can be obtained as compared with the related art. In addition, the forward resistance of the semiconductor light emitting device can be reduced. Further, the efficiency of heat radiation of the semiconductor light emitting element and the improvement of reliability are brought about.

The present invention is not limited to the above embodiment, but can be variously modified. The shape of the fine wire electrode is not limited to the combination of the radial electrode and the circumferential electrode as in the first embodiment or the combination of the radial electrode and the concentric circumferential electrode as in the second embodiment. For example, the radial electrodes are not directed in eight directions, but in any direction, for example, 10 directions.
It is also possible to have a shape that radiates in the directions, 16 directions, and it is also possible to constitute a curve instead of a straight line. The grid electrode and the concentric circumferential electrode may be formed in an arbitrary grid such as a rectangle, or may be formed in an elliptical circumference. Further, the width of the thin line is not necessarily required to be uniform in the thin line electrode, and the thin line electrode does not need to be formed of the thin line. In short, it is only necessary that the electrode having the opening is connected to the electrode pad 30 so that a uniform current can be injected into the transparent conductive film.

[0037]

As described above, according to the semiconductor light emitting device of the present invention, an electrode pad is provided on a transparent conductive film, and a thin wire connected to the electrode pad and extending to near the end on the transparent conductive film. Since the electrodes are formed, the distribution of the current density injected into the transparent conductive film can be made uniform, and the distribution of the current density injected into the light emitting layer can be made uniform.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a semiconductor light emitting device according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing the semiconductor light emitting device according to the first embodiment of the present invention.

FIG. 3 is a plan view showing the semiconductor light emitting device according to the first embodiment of the present invention.

FIG. 4 is a graph showing an intensity distribution of a near-field image of the semiconductor light emitting device according to the first embodiment of the present invention in comparison with a comparative example.

FIG. 5 is a graph showing current-light intensity characteristics of the semiconductor light emitting device according to the first embodiment of the present invention in comparison with a comparative example.

FIG. 6 is a graph showing current-voltage characteristics of the semiconductor light emitting device according to the first embodiment of the present invention in comparison with a comparative example.

FIG. 7 is a plan view illustrating a semiconductor light emitting device according to a second embodiment of the present invention.

FIG. 8 is a sectional view showing a conventional semiconductor light emitting device.

FIG. 9 is a plan view showing a conventional semiconductor light emitting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Semiconductor substrate 12 Buffer layer 14 Reflection layer 16 Lower cladding layer 18 Active layer 20 Upper cladding layer 22 Intermediate semiconductor layer 24 Ohmic contact layer 26 Current block layer 28 Transparent conductive film 30 Electrode pad 32 Fine wire electrode 34 Radial electrode 36 Grid electrode 38 Opening 40 Electrode 42 Fine wire electrode 44 Radial electrode 46 Concentric circumferential electrode 48 Opening

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F041 AA05 AA21 AA33 CA34 CA35 CA36 CA53 CA64 CA82 CA83 CA88 CA92 CA93 CA94

Claims (6)

[Claims] 1. A semiconductor light emitting device having a light emitting layer formed between a semiconductor substrate and a transparent conductive film, wherein: an electrode pad provided on the transparent conductive film; A thin line electrode which is connected to the electrode pad and formed up to near the end on the transparent conductive film. 2. The apparatus according to claim 1, wherein said electrode pad is provided near a central portion of said transparent conductive film.
3. The semiconductor light emitting device according to item 1. 3. The thin wire electrode includes: a radial electrode extending radially from the electrode pad; and a grid electrode formed along each side of the transparent conductive film and connected to the radial electrode. The semiconductor light emitting device according to claim 2, wherein: 4. The thin wire electrode includes: a radial electrode extending radially from the electrode pad; and a concentric circumferential electrode formed concentrically with the electrode pad and connected to the radial electrode. The semiconductor light-emitting device according to claim 2. 5. The semiconductor light emitting device according to claim 1, wherein a line width of said thin wire electrode is 25 μm or less. 6. The semiconductor light emitting device according to claim 1, wherein said electrode pad and said fine wire electrode are made of a metal material.