JP2003133587A - Light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting diode of high luminance capable of improving light take-out efficiency. SOLUTION: The light emitting diode is composed by successively stacking a one-conductivity type semiconductor layer 2 and an opposite-conductivity type semiconductor layer 3 on one main surface of a single crystal substrate 1, attaching one electrode 4 on the opposite-conductivity type semiconductor layer 3 and attaching the other electrode 5 composed of metal on the other main surface of the single crystal substrate 1. On the other main surface of the single crystal substrate 1, a number of recesses 6 whose cross sectional shapes are roughly V-shaped are formed at the density of 400 pieces/mm<2> to 40,000 pieces/mm<2> , for instance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source for a printer,
The present invention relates to a light emitting diode used as a light emitting device such as a DVD recording light source, a remote control light source, an illumination light source, a traffic signal, a display, and an indicator.

[0002]

2. Description of the Related Art Conventionally, LEDs (Light Emitting Dio)
de) A light emitting diode is used as a light source for a printer such as an array head.

As such a conventional light emitting diode, for example, as shown in FIG. 2, an n-type semiconductor layer 12 and a p-type semiconductor layer 13 are provided on one main surface of a single crystal substrate 11 made of GaAs or the like.
And are sequentially grown epitaxially and p
While forming an n-junction, one electrode 14 is partially provided on the upper surface of the p-type semiconductor layer 13, and the single crystal substrate 1
There is known a structure in which the other electrode 15 is formed on the other main surface of 1, and electrons in the n-type semiconductor layer 12 and p-type semiconductor layer 13 in the n-type semiconductor layer 12 are applied by applying a predetermined power between the two electrodes. Holes and p
It functions as a light emitting diode by recombining near the n-junction, converting the energy generated by the coupling into light, and emitting the obtained light to the outside through the upper surface of the p-type semiconductor layer 13.

[0004]

However, when the conventional light emitting diode described above is caused to emit light, not all the light generated in the vicinity of the pn junction is emitted directly above the light emitting diode. Light is directed downward. Some of such light is reflected at the interface with the other electrode and is emitted obliquely from the upper surface of the light emitting diode, or is absorbed while repeating reflection inside, so that As a result, the brightness is lowered and it is impossible to obtain desired characteristics.

Therefore, in order to solve the above-mentioned drawback, a DBR (Distibuted Bragg) is provided between the single crystal substrate and the n-type semiconductor layer.
Interposing a multilayer film for light reflection called Reflector),
It has been proposed to improve the light extraction efficiency by reflecting light upward with this multilayer film.

However, the above-mentioned multilayer film is formed so that the reflectance of light incident perpendicularly to the film surface is optimized, and when the light emitting diode is made to emit light, The light that is obliquely incident is almost not reflected. Therefore, most of the light obliquely incident on the multilayer film is transmitted through the multilayer film, and there is a disadvantage that these transmitted lights cannot be used for improving the brightness.

The present invention has been devised in view of the above-mentioned drawbacks, and an object thereof is to provide a high-luminance light emitting diode capable of improving the light extraction efficiency.

[0008]

A light emitting diode according to the present invention comprises a single crystal substrate, a semiconductor layer of one conductivity type and a semiconductor layer of opposite conductivity type, which are sequentially laminated on one main surface of the single crystal substrate, and one layer of semiconductor layer on the opposite conductivity type. In the light emitting diode in which the other electrode made of metal is adhered to the other main surface of the single crystal substrate, the other main surface of the single crystal substrate has a large number of recesses having a substantially V-shaped cross section. , Is formed.

The light emitting diode of the present invention is characterized in that the wavelength of light generated near the interface between the one conductivity type semiconductor layer and the opposite conductivity type semiconductor layer is 850 nm to 950 nm.

Further, the light emitting diode of the present invention is characterized in that a part of the other electrode is filled in a concave portion of the other main surface of the single crystal substrate.

Furthermore, in the light emitting diode of the present invention, the plane orientation of the other main surface of the single crystal substrate matches the (100) plane,
Alternatively, it is characterized in that the (100) plane is tilted by X ° (0 <X ≦ 5).

Furthermore, in the light emitting diode of the present invention, the base angle θ of the recess is 60 ° to 80 °, and the opening width w is 5 μm to 5 °.
It is characterized by being set to 0 μm.

Still further, in the light emitting diode of the present invention, the recesses are formed on the other main surface of the single crystal substrate at 20 lines / mm to 200 lines / mm.
It is characterized in that it is formed in a stripe shape with a density of mm.

Furthermore, in the light emitting diode of the present invention, the recesses are 400 / mm ² to 400 on the other main surface of the single crystal substrate.
It is characterized in that it is formed at a density of 00 pieces / mm ² .

According to the light emitting diode of the present invention, a large number of concave portions having a V-shaped cross section are formed on the surface (other main surface) opposite to the one main surface on which the pn junction is provided. Therefore, of the light generated near the pn junction when the light emitting diode emits light, most of the light traveling downward is well reflected on the inner surface of the recess, and most of these reflected light is transmitted through the upper surface of the light emitting diode. Can be released to the outside.
Therefore, the brightness of the light emitting diode is improved, and the light extraction efficiency can be significantly improved.

Further, according to the light emitting diode of the present invention, a part of the other electrode is filled in the recess of the other main surface of the single crystal substrate, and the other electrode is brought into close contact with the inner surface of the recess, whereby the other electrode As a result, a sufficiently large area can be secured to the single crystal substrate. Therefore, the other electrode can be firmly adhered to the other main surface of the single crystal substrate, and the electric resistance (wiring resistance) of the electrode can be suppressed to be small.
It is also possible to reduce the loss of power supplied to the light emitting diode.

Further, according to the light emitting diode of the present invention, the plane orientation of the other main surface of the single crystal substrate is made to coincide with the (100) plane, or the (100) plane is X ° (0 <X ≦ 5). By setting so as to incline only, it is possible to easily form the above-mentioned concave portion by conventionally well-known anisotropic etching or the like, and there is also an advantage that the productivity of the light emitting diode is kept high.

[0018]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a sectional view of a light emitting diode according to an embodiment of the present invention, in which 1 is a single crystal substrate,
2 is an n-type semiconductor layer as one conductivity type semiconductor layer, 3 is a p-type semiconductor layer as an opposite conductivity type semiconductor layer, 4 is one electrode,
Reference numeral 5 is the other electrode, and 6 is a recess provided in the single crystal substrate.

As the material of the single crystal substrate 1, for example, a compound semiconductor such as n-type GaAs is used, and the n-type semiconductor layer 2 and the p-type semiconductor layer 3 are formed on one main surface of the single crystal substrate 1.
One electrode 4 and the other electrode 5 are provided on the other main surface, and function as a support base material that supports these.

In addition, in the single crystal substrate 1, the plane orientation of the other principal plane matches the (100) plane, or the (100) plane is X °.
It is formed to be inclined by (0 <X ≦ 5), and the other main surface has, for example, 400 recesses 6 each having a substantially V-shaped cross section.
A large number are formed in a matrix or randomly at a density of mm ^{2 to} 40,000 / mm ² .

These V-shaped recesses 6 have a base angle θ of, for example, 60 ° to 80 ° and an opening width w of, for example, 5 μm to 5 μm.
It is set within the range of 0 μm, and a part of the other electrode 5 described later is filled therein, and has an action of reflecting the light irradiated to the inner surface of the recess upward (on the one main surface side of the single crystal substrate 1). Do

When such a single crystal substrate 1 is made of GaAs, the well-known vertical Bridgman method (V
GaAs ingot (lump) formed by the B method)
Is sliced to a specified thickness and the surface is ground to G
A plate made of aAs is formed, and conventionally well-known photo-etching is applied to the other main surface of the obtained plate, and a concave portion 6 having a V-shaped cross section is formed.
It is manufactured by forming a large number at a predetermined density.

In this case, the plane orientation of the other main surface of the single crystal substrate 1 coincides with the (100) plane, or the (100) plane is X-oriented.
Since it is set to be inclined by 0 (0 <X ≦ 5), the well-known anisotropic etching or the like is used to form the recess 6
By forming the above, the concave portion 6 can be formed extremely easily and highly accurately, and the productivity of the light emitting diode can be kept high.

If the opening width of the recess 6 is smaller than 5 μm, it becomes difficult to sufficiently reflect the light generated near the pn junction upward, and the opening width is 50 μm.
When it exceeds, the concave portion 6 becomes too deep, and the single crystal substrate 1 may be cracked due to vibration during transportation. Therefore, it is preferable to set the opening width of the recess 6 to 5 μm to 50 μm.

The n-type semiconductor layer 2 and the p-type semiconductor layer 3 which are sequentially provided on one main surface of the single crystal substrate 1 are both GaAs type compound semiconductors, specifically, GaA.
s, AlGaAs, InGaAs, In _X Al _Y Ga
_1-XY As and the like, these semiconductor layers 3,
4 is doped with impurities for generating carriers (electrons, holes) at a predetermined concentration.

For example, the n-type semiconductor layer 2 is made of Si (silicon).
There 2 × 10 ¹⁸ atoms / cm ³ to 5 at a density of × 10 ^{1 8} atoms / cm ^3, the p-type semiconductor layer 3 Zn (zinc) is 2 × 10 ¹⁸ atoms /
Each is doped at a density of cm ^{3 to} 5 × 10 ¹⁸ pieces / cm ³ , and a pn junction is formed between the semiconductor layers 2-3.

Therefore, when a predetermined electric power is applied between one electrode 4 and the other electrode 5 which will be described later, electrons in the n-type semiconductor layer 2 and holes in the p-type semiconductor layer 3 respectively. The light-emitting diode emits light by injecting and recombining these electrons and holes near the pn junction.

The n-type semiconductor layer 2 and the p-type semiconductor layer 3 described above are formed by, for example, the well-known MOCVD method (Metal Orga).
nic Chemical Vapor Deposition) method, etc.
It is formed by sequentially epitaxially growing a GaAs single crystal thin film such as GaAs on one main surface of the single crystal substrate 1, and the semiconductor layers 2 and 3 are simultaneously doped with a predetermined amount of impurities such as Si and Zn. . Further, in such a thin film forming process, trimethylgallium (TMG), trimethylaluminum (TMA), arsine (AsH3) and the like are used as raw materials.

One electrode 4 is partially provided on the upper surface of the p-type semiconductor layer 3 described above, and the other electrode 5 is provided on the other main surface of the single crystal substrate 1, and a part thereof is placed in the recess 6. It is deposited and formed in the filled state.

The electrodes 4 and 5 are respectively ohmic-connected to the p-type semiconductor layer 3 and the single crystal substrate 1, and the semiconductor layers 2 and 3 described above are connected to the semiconductor layers 2 and 3 through the electrodes 4 and 5, for example, at 100 A / A. When a current is applied at a current density of cm ² or more, electrons are injected into the n-type semiconductor layer 2 and holes are injected into the p-type semiconductor layer 3, and the two are recombined in the vicinity of the pn junction to form a light emitting diode. For example, a wavelength of 850 nm to 950 n
Generates m light (infrared rays).

At this time, a large number of concave portions 6 having a V-shaped cross section are formed on the other main surface of the single crystal substrate 1 as described above, and of the light generated in the vicinity of the pn junction, light directed downward. Since most of them are well reflected upward on the inner surface of the recess 6 (on the one main surface side of the single crystal substrate 1), most of these reflected lights should be emitted to the outside through the upper surface of the light emitting diode. And improve the brightness of the light emitting diode,
The light extraction efficiency can be significantly improved.

In this case, the other electrode 5 adhered to the other main surface of the single crystal substrate 1 is partially filled in the recess 6 and closely adhered to the inner surface of the recess, so that the other electrode 5 6
The adhesion area between the single crystal substrate 1 and the single crystal substrate 1 is sufficiently wide so that the other electrode 5 can be firmly adhered to the other main surface of the single crystal substrate 1 and It is also possible to suppress the electric resistance (wiring resistance) to be small and reduce the loss of the power supplied to the light emitting diode.

Such one electrode 4 and the other electrode 5
Is formed of, for example, a laminated body (thickness: 0.3 μm to 0.6 μm) having a three-layer structure in which Cr (chromium), AuGe (gold / germanium alloy), and Au (gold) are sequentially laminated. The material is deposited to have a predetermined thickness by conventionally known sputtering, vacuum evaporation, or the like, and finely processed by conventionally well-known photolithography, etching, or the like to form a predetermined pattern.

The present invention is not limited to the above-mentioned embodiments, and various changes and improvements can be made without departing from the gist of the present invention.

For example, in the above-mentioned embodiment, the single crystal substrate 1 is formed of n-type GaAs, but instead of this, the single crystal substrate 1 is GaP, GaN, InP, I.
It may be made of other compound semiconductor such as nAs.

Further, in the above-described embodiment, the recesses 6 are formed on the other main surface of the single crystal substrate 1 at 400 / mm ^{2 to} 40,000.
Although a large number are formed in a matrix or randomly at a density of pcs / mm ² , instead of this, the V-groove shaped recesses 6 have a density (pitch) of 20 pcs / mm to 200 pcs / mm.
It may be formed in a stripe shape.

Further, in the above-described embodiment, an active layer made of the same kind of compound semiconductor is interposed between the n-type semiconductor layer 2 and the p-type semiconductor layer 3, or the ohmic contact of the electrode 4 with respect to the p-type semiconductor layer 3 is performed. A contact layer made of a GaAs-based compound semiconductor may be interposed between the p-type semiconductor layer 3 and the electrode 4 for good connection.

Furthermore, in the above-mentioned embodiment, the MOCVD method is adopted to epitaxially grow the semiconductor layers 2 and 3 on the single crystal substrate 1, but other methods such as MBE (Molecular Beam Epitaxy) are used. The semiconductor layers 2 and 3 may be epitaxially grown on the single crystal substrate 1 by a method or the like.

Furthermore, in the above-described embodiment, the n-type semiconductor layer 2 is used as the one conductivity type semiconductor layer and the p-type semiconductor layer 3 is used as the opposite conductivity type semiconductor layer. A p-type semiconductor layer may be used as the type semiconductor layer and an n-type semiconductor layer may be used as the opposite conductivity type semiconductor layer.

Furthermore, it goes without saying that the surfaces of the n-type semiconductor layer 2, the p-type semiconductor layer 3, the electrodes 4 and the like may be covered with a transparent protective film made of silicon oxide or the like in the above-mentioned embodiments.

[0041]

According to the light emitting diode of the present invention, the pn
Since a large number of concave portions having a V-shaped cross section were formed on the surface (other main surface) opposite to the main surface of the single crystal substrate on which the junction was provided, when the light emitting diode was caused to emit light, the vicinity of the pn junction was observed. Of the light generated in (2), most of the light traveling downward is well reflected by the inner surface of the recess, and most of these reflected light can be emitted to the outside through the upper surface of the light emitting diode. Therefore, the brightness of the light emitting diode is improved, and the light extraction efficiency can be significantly improved.

Further, according to the light emitting diode of the present invention, a part of the other electrode is filled in the concave portion of the other main surface of the single crystal substrate, and the other electrode is brought into close contact with the inner surface of the concave portion, so that the other electrode As a result, a sufficiently large area can be secured to the single crystal substrate. Therefore, the other electrode can be firmly adhered to the other main surface of the single crystal substrate, and the electric resistance (wiring resistance) of the electrode can be suppressed to be small.
It is also possible to reduce the loss of power supplied to the light emitting diode.

Further, according to the light emitting diode of the present invention, the plane orientation of the other main surface of the single crystal substrate is made to coincide with the (100) plane, or the (100) plane is X ° (0 <X ≦ 5). By setting so as to incline only, it is possible to easily form the above-mentioned concave portion by conventionally well-known anisotropic etching or the like, and there is also an advantage that the productivity of the light emitting diode is kept high.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a light emitting diode according to an exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conventional light emitting diode.

[Explanation of symbols]

1 ... Single crystal substrate, 2 ... N-type semiconductor layer, 3 ...
p-type semiconductor layer, 4 ... one electrode, 5 ... other electrode, 6 ... recess

Claims (7)

[Claims] 1. A single-conductivity-type semiconductor layer and a reverse-conductivity-type semiconductor layer are sequentially stacked on one main surface of a single-crystal substrate, and one electrode is provided on the opposite-conductivity-type semiconductor layer to the other main surface of the single-crystal substrate. A light-emitting diode having a surface coated with another electrode made of a metal, wherein a large number of concave portions having a substantially V-shaped cross section are formed on the other main surface of the single crystal substrate. 2. The wavelength of light generated near the interface between the one conductivity type semiconductor layer and the opposite conductivity type semiconductor layer is 850 nm to 950 n.
The light emitting diode according to claim 1, wherein m is m. 3. The light emitting diode according to claim 1, wherein a part of the other electrode is filled in a recess in the other main surface of the single crystal substrate. 4. The plane orientation of the other main surface of the single crystal substrate is (1
00 or the (100) plane at X ° (0 <
The light emitting diode according to any one of claims 1 to 3, wherein the light emitting diode is set to be inclined by X ≤ 5). 5. The bottom angle θ of the substantially V-shaped recess is 60 ° to 80.
5. The light emitting diode according to claim 1, wherein the opening width w is set to 5 μm to 50 μm. 6. The number of the recesses on the other main surface of the single crystal substrate is 20 /
The light emitting diode according to any one of claims 1 to 5, wherein the light emitting diode is formed in a stripe shape with a density of mm to 200 lines / mm. 7. The method according to claim 1, wherein the concave portions are formed on the other main surface of the single crystal substrate at a density of 400 / mm ^{2 to} 40,000 / mm ^2. The light emitting diode described.