JP2001068729A - Led array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve the variation of the illuminant intensities of respective light emitting devices caused by the variation of their sizes and resolve the difficulty of their electrical isolation from each other, by forming an oxidized AlGaAs layer on a buffer layer of each light emitting device. SOLUTION: An AlxGa1-xAs (0.9<=x<=1) layer 3 has its thickness of 50 to 5000 Å and exhibits its resisitivity not smaller than 1×105 Ωcm by its wet oxidation to make largely improvable the insulating quality of respective light emitting devices from each other. Also, since the respective light emitting devices are insulated electrically from each other by their wet-oxidized AlxGa1-xAs (0.9<=x<=1) layer 3 of 50 to 5000 Å in their thickness, the etching depth for isolating electrically the respective light emitting devices from each other can be made shallow to make reducible largely the variation of the sizes of the respective light emitting devices. As a result, the variation of the illuminant intensities of the respective light emitting devices are reduced largely to make improvable the manufacturing yield of an LED array and its printing quality when applying it to the exposure source of a printer, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an LED array, and more particularly to an LED array used as an exposure source in an electrophotographic process.
For ED arrays.

[0002]

2. Description of the Related Art GaAs and AlGaAs are formed on a silicon substrate.
s, InGaP, InGaAs, InGaAsP, Ga
Epitaxially growing a compound semiconductor such as AsP
The conventional manufacturing process and its structure when configuring an ED array are as follows.

First, a plan view of an LED array is shown in FIG.
FIG. 3A is a cross-sectional view taken along the line B-′B in FIG. In FIG. 3, 1 is a silicon substrate having a specific resistance of 1 × 10 ³ to 10 ⁴ Ωcm, 2 is a buffer layer made of a compound semiconductor having a first conductivity, and 4 is a buffer layer made of a compound semiconductor having a first conductivity. 5 is a light emitting layer made of a compound semiconductor having a second conductivity, 6 is an insulating layer made of SiO ₂ , SiN _x, etc., 7 is a light emitting layer 4 made of a compound semiconductor having a first conductivity. An individual electrode that is ohmic-connected to a portion thereof; 8 is a first common electrode that is ohmic-connected to a portion of a light emitting layer made of a compound semiconductor having a second conductivity; 9 is a compound semiconductor that has a second conductivity Is a second common electrode that is ohmic-connected to a part of the light emitting layer 5 made of.

Next, an example of a conventional method for manufacturing an LED array will be specifically described with reference to FIG. First, FIG.
As shown in FIG. 1, GaAs, AlGaAs, InGaP, InG
A buffer layer 2 made of a compound semiconductor such as aAs, InGaAsP, or GaAsP is grown by a normal two-step growth method so as to have as high a resistance as possible, and then has a carrier density of 1 × 10 ¹⁷ to 1 × 10 ¹⁸ atoms · cm. ^-3 n-type light-emitting layer 4 and a carrier density of 1 × 10 ¹⁷ to 1 ×
A substrate on which a p-type light emitting layer 5 of 10 ¹⁹ atoms · cm ⁻³ is grown is used.

Note that GaAs is further formed on the p-type light emitting layer 5.
s, InGaP, InGaAs, InGaAsP, or GaAsP as a carrier density of 1 × 10 ¹⁹ a
A p-type contact layer (not shown) of not less than toms · cm ⁻³ may be provided.

Thereafter, as shown in FIG. 4B, in order to form a light emitting portion, the other portions are subjected to ordinary photolithography, and then sulfuric acid (H ₂ SO ₄ ) and a hydrogen peroxide solution (H ₂ H ₂ O).
It is removed with an O ₂ ) -based mixed etchant. On this occasion,
In order to electrically separate the light emitting portions from each other, the silicon substrate 1 is etched with a mixed solution of ammonium fluoride (NH ₄ F) and aqueous hydrogen peroxide (H ₂ O ₂ ) in a range of 0.1 μm to 0.5 μm. This is because when the buffer layer 2 is epitaxially grown, As and P diffuse into the silicon substrate 1 and exhibit n-type conductivity, so that each light emitting portion is electrically separated including the buffer layer 2. It is necessary for

Next, as shown in FIG. 4C, in order to expose a part of the n-type light emitting layer 4, a part of the p-type light emitting layer 5 and the n-type light emitting layer 4 are etched by photolithography and etching. Remove some.

Next, as shown in FIG. 4D, an insulating layer 6 made of SiO ₂ , SiN _x or the like is formed by plasma CVD or sputtering.

Next, as shown in FIG. 4E, the individual electrode 7, the first common electrode 8, and the second common electrode 9 are formed by photolithography and etching using an HF-based etchant.
Windows 6 ′ and 6 ″ for bringing the n-type light-emitting layer 4 and the p-type light-emitting layer 5 into ohmic contact are formed next to FIG.
As shown in FIG. 5, a laminated film of Cr / Au is formed by a vacuum deposition method, and an individual electrode 7, a first common electrode 8, and a second common electrode 9 are formed by photolithography and a lift-off method.

Thereafter, the individual electrodes 7, the first common electrode 8, and the second common electrode 9 are annealed in a hydrogen gas or nitrogen gas atmosphere at a temperature of about 250 to 450 ° C. for about 2 to 20 minutes. The layer 4 and the p-type light-emitting layer 5 were brought into ohmic contact to form an LED array.

[0011]

However, in the LED array formed on the silicon substrate 1 as in the above-mentioned prior art, as shown in FIG. All the compound semiconductor layers 2, 3, and 4 and the silicon substrate 1 except for the light emitting section are 0.1 μm to 0.5 μm.
Etching had to be performed, and the variation in the size of the luminous body was large. As a result, the luminous intensity of each luminous body varies greatly, and the production yield of the device and the printing quality when applied to an electrophotographic printer or the like are reduced. That is, when the size of the light emitting body varies, the PN junction also varies. Since the light emission intensity is proportional to the area of the PN junction of the light emitting portion, when the area decreases, the area where electrons and holes contributing to light emission recombine decreases.

Also, GaAs, AlGaAs, InGa
Since P has substantially the same lattice constant as germanium, the dislocation density can be reduced to 1/10 or less as compared with the case where P is epitaxially grown on the silicon substrate 1.
The emission intensity of the LED can be improved several times or more. However, since the specific resistance of the germanium substrate is 100 Ωcm or less, there is a problem that each light emitting unit cannot be electrically separated.

The present invention has been made in view of such problems of the prior art, and has solved the problem of variations in emission intensity due to variations in the size of the luminous bodies and the difficulty of electrical isolation of each luminous portion. An object is to provide an LED array.

[0014]

According to a first aspect of the present invention, there is provided an LED array having a buffer layer made of a compound semiconductor and a light emitting layer provided on a semiconductor single crystal substrate. An oxidized Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1) layer is provided on the buffer layer.

In the above LED array, the oxidized Al
_x Ga _1-x As (0.9 ≦ x ≦ 1) layer is 50 ° to 500
It is desirable to have a thickness of 0 °.

In the above-mentioned LED array, it is desirable that the semiconductor single crystal substrate is made of silicon or germanium.

[0017]

Embodiments of the present invention will be described below.
FIG. 1B is a plan view of the LED array according to the present invention, and FIG. 1A is a cross-sectional view taken along line A-′A of FIG. 1B. FIG.
In (a), 1 is a semiconductor single crystal substrate, 2 is a buffer layer, 3 is an Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1) layer,
Denotes an n-type light emitting layer, 5 denotes a p-type light emitting layer, 6 denotes an insulating layer, 7 denotes an individual electrode, 8 denotes a first common electrode, and 9 denotes a second common electrode.

The semiconductor substrate 1 is made of silicon, germanium or the like. Silicon is desirable in terms of mass productivity, and germanium is desirable in terms of matching lattice constant with the compound semiconductor layer.

The buffer layer 2 is made of GaAs, AlGaAs
s, InGaP, InGaAs, InGaAsP, Ga
It is made of a compound semiconductor such as AsP and has a thickness of 0.2 to 2 μm. It is grown to have as high a resistance as possible, such as 1 × 10 ⁴ Ωcm or more.

The Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1) layer 3 has a thickness of 50 ° to 5000 ° and exhibits a specific resistance of 1 × 10 ⁵ Ωcm or more due to wet oxidation described later; It is possible to greatly improve the insulation between the light-emitting members. In addition, each light emitting element is wet-oxidized at 50 ° to 5 °.
Al _x Ga _1-x As (0.9 ≦ x ≦ 1) layer 3 of 000 °
Therefore, the depth of the etching for electrically isolating the light emitters can be reduced, and the variation in the size of the light emitters can be greatly improved. The n-type light emitting layer 4 is made of GaAs, AlGaAs, InGaP, InGa
It is made of a compound semiconductor such as As, InGaAsP, or GaAsP, and has a thickness of about 0.2 to 5 μm. This n
The type light emitting layer 4 has a size of 5 × 10 ¹⁶ to 1 × 10 ¹⁸ atoms · c.
It has an electron density of about m ^-3 . Note that the carrier density, film thickness, and composition are appropriately selected depending on the desired light emission intensity and light emission wavelength of the LED.

The p-type light emitting layer 5 is made of GaAs, AlGaAs,
InGaP, InGaAs, InGaAsP, GaAs
It is made of a compound semiconductor such as P and has a thickness of about 0.2 to 5 μm. The p-type light emitting layer 5 has a size of 5 × 10 ¹⁶ to 1 ×
It has an electron density of about 10 ¹⁹ atoms · cm ⁻³ . Note that the carrier density, film thickness, and composition are appropriately selected depending on the desired light emission intensity and light emission wavelength of the LED.

If necessary, a p-type contact layer having a carrier density of 5 × 10 ¹⁷ to 2 × 10 ¹⁹ atoms · cm ^-3 is formed on the p-type light emitting layer 5 in order to reduce the ohmic resistance. 100-2000Å showing conductivity of
GaAs, InGaP, InGaAs having a thickness of about
A compound semiconductor layer such as s, InGaAsP, or GaAsP may be provided. The insulating layer 6 is made of SiO ₂ , SiN _x or the like.

The n-type light emitting layer 4 is provided with an individual electrode 7 connected thereto, and the p-type light emitting layer 5 is provided with a first common electrode 8 and a second common electrode 9 connected thereto. As described above, when the individual electrode 7 and the common electrodes 8 and 9 are formed on the same side of the single crystal semiconductor substrate 1 on which the light emitting layers 4 and 5 are formed, connection with an external circuit becomes easy. Further, by providing a plurality of common electrodes 8 and 9, the number of individual electrodes 7 can be reduced.

Next, a method for manufacturing the LED array will be described. As shown in FIG. 2A, MOCVD or MBE
The buffer layer 2 is formed to a thickness of 0.2 to 2 μm on the silicon substrate 1 by a normal two-stage growth method.

Next, Al _x Ga _{1 -x of} 50 to 5000 °
After growing the As (0.9 ≦ x ≦ 1) layer 3, the n-type light-emitting layer 4 and the p-type light-emitting layer 5 are formed to a thickness of 0.2 to 5 μm.

If necessary, a p-type conductive compound semiconductor layer (not shown) serving as a contact layer may be
Å2000 may be grown.

Then, as shown in FIG. 2B, in order to form a light emitting portion, the other portions are subjected to ordinary photolithography, and then sulfuric acid (H ₂ SO ₄ ) and a hydrogen peroxide solution (H ₂
It is removed with an O ₂ ) -based mixed etchant. On this occasion,
For wet oxidation to be described later, Al _x G
Etching is performed until the a _1-x As (0.9 ≦ x ≦ 1) layer 3 ′ is completely removed.

Thereafter, as shown in FIG.
Wet oxidation of the Al _x Ga _1-x As (0.9 ≦ x ≦ 1) layer 3 at 5000 ° is performed. First, the sample shown in FIG. 2B is placed in a quartz tube heating furnace. Then, the ultrapure water in a thermostat at about 90 ° C. is bubbled with nitrogen at a rate of 1 to 10 liters / min to supply the vapor of the ultrapure water into the quartz tube and heated to 400 to 500 ° C. By oxidizing for a time, Al _x Ga _{1 -x} As (0.
9 ≦ x ≦ 1) The oxide layer 3 of the layer 3 ′ is obtained. The time and temperature required for the oxidation are Al _x Ga _{1 -x} As (0.9 ≦ x ≦
1) It depends on the thickness of the layer 3 ', the Al composition x, and the size of the light emitting body.

In FIG. 1B, the size of the luminous body is defined and L ₁
+ L ₂ is 30 μm, and W is 20 μm. In this case, A
If the thickness of the lAs layer 3 is 100 °, 400 ° C., 30 ° C.
Oxidation of the AlAs layer 3 is completed by a minute wet oxidation.
Further, when the thickness of the Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1) layer 3 is less than 50 ° or when the Al composition x is less than 0.9, the oxidation time becomes long and the practical use becomes difficult. Not. Al _x G
a _1-x As (0.9 ≦ x ≦ 1) layer 3 has a thickness of 5000 °
In the case of exceeding, the crystallinity of the light emitting layers 4 and 5 thereon is deteriorated, and the light emission intensity of the LED is significantly reduced.

Next, as shown in FIG. 2D, in order to expose a part of the n-type light-emitting layer 4, a part of the p-type light-emitting layer 5 and the n-type light-emitting layer 4 are etched by photolithography and etching. Remove some.

Next, as shown in FIG. 2E, an insulating layer 6 made of SiO ₂ , SiN _x or the like is formed by plasma CVD or sputtering.

Next, as shown in FIG. 2 (f), the individual electrode 7, the first common electrode 8, the second common electrode 9 and the n-type light emitting layer 4, p and p are formed by photolithography and etching with an HF-based etchant. Next, as shown in FIG. 2 (g), a Cr / Au laminated film is formed by vacuum evaporation to form windows 6 ′ and 6 ″ for the mold light emitting layer 5 to make ohmic contact. The individual electrode 7, the first common electrode 8, and the second common electrode 9 are formed by a lift-off method.

Thereafter, annealing is performed at about 250 to 450 ° C. for about 2 to 20 minutes in an atmosphere of hydrogen gas or nitrogen gas, so that the individual electrode 7, the first common electrode 8, the second common electrode 9,
Type light-emitting layer 4 and p-type light-emitting layer 5 are brought into ohmic contact, LE
Form a D array.

[0034]

As described above, in the LED array of the present invention, each light emitting element is formed of Al _x Ga _{1 -x} As (0.9 ≦ x ≦
1) Since the oxide film of the layer can be electrically insulated from the semiconductor single crystal substrate, the depth of the separation etching of the light emitting portion can be reduced, and the variation in the size of the light emitter can be greatly reduced. As a result, the variation in the luminous intensity of each luminous body is greatly improved, and the production yield of the LED array and the printing quality when applied to an exposure source such as a printer can be improved.

Further, in the LED array of the present invention, a large-diameter silicon substrate or a germanium substrate of 4 inches or more having excellent mechanical strength can be used as a semiconductor single crystal substrate, and GaAs, AlGaAs, InGaP, InG
Since an LED array can be formed by epitaxially growing a compound semiconductor such as aAs, InGaAsP, or GaAsP, a reduction in manufacturing yield due to cracks in the substrate can be significantly improved.

[Brief description of the drawings]

FIG. 1A is a sectional view of an LED array according to the present invention,
(B) is a plan view of the LED array of the present invention.

FIG. 2 is a sectional view showing a manufacturing process of the LED array of the present invention.

FIG. 3A is a cross-sectional view of a conventional LED array.
(B) is a plan view of a conventional LED array.

FIG. 4 is a cross-sectional view showing a manufacturing process of a conventional LED array.

[Explanation of symbols]

1 semiconductor single crystal substrate, 2 buffer layer, 3
_{ Al _x Ga _1-x As (0.9 ≦ x ≦ 1) layer, 4}
{N-type light-emitting layer, 5p-type light-emitting layer, 6} insulating layer,
7 ‥‥‥ individual electrode, 8 ‥‥‥ first common electrode, 9 ‥‥‥
Second common electrode

Continued on the front page (72) Inventor Shigeo Aono 3-5 Koikadai, Seika-cho, Soraku-gun, Kyoto F-term in Central Research Laboratory, Kyocera Corporation 2C162 AE05 AE21 AE28 AE47 FA04 FA17 FA23 5F041 AA05 CA33 CA35 CA36 CA37 CA38 CA39 CA77 CB23 FF13

Claims (4)

[Claims] 1. An LED array having a buffer layer made of a compound semiconductor and a light emitting layer provided on a semiconductor single crystal substrate, wherein an oxidized Al _x Ga _{1 -x} As is formed on the buffer layer.
LED provided with (0.9 ≦ x ≦ 1) layer
array. 2. The oxidized Al _x Ga _{1 -x} As (0.
The LED array according to claim 1, wherein 9 ≦ x ≦ 1) the layer has a thickness of 50 ° to 5000 °. 3. The LED array according to claim 1, wherein said semiconductor single crystal substrate is silicon. 4. The LED array according to claim 1, wherein the semiconductor single crystal substrate is made of germanium.