JP2851771B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device,
In particular, the present invention relates to a semiconductor light emitting device used for an LED print head or the like.

[0002]

2. Description of the Related Art As shown in FIG. 1, a conventional semiconductor light emitting device has a structure in which silicon nitride (SiN) is formed on an n-type GaAs substrate 1.
_x ), a diffusion mask 2 made of silicon oxide (SiO ₂ ) or the like is provided, and zinc (Zn) is diffused into the n-type GaAs substrate 1 at the same pitch at a depth of 10 to 50 μm from the opening of the diffusion mask 2. Thus, the semiconductor light emitting device is formed by forming the p-type region 3 having p-type conductivity. Note that ohmic electrodes 4 and 5 are formed on the back surface of the n-type GaAs substrate 1 and the p-type region 3 respectively.

When a semiconductor light emitting device is formed using such an n-type GaAs substrate 1, the absolute value of the electron diffusion length varies depending on the defect density and carrier density in the GaAs substrate 1, but the etch pit density ( EPD) is 10 ³ or more
In the case of a crystal of about 10 ⁴ / cm ² , the thickness is 10 to 50 μm, which is about one digit larger than that of holes. for that reason,
Most of the semiconductor light emitting device having the structure as shown in FIG. 1 emits light in the p-type region 3.

The emission spectrum of a semiconductor light emitting device in which Zn is diffused at the same pitch into an n-type GaAs substrate 1 to form a p-type region 3 has a peak emission wavelength of 91 as shown in FIG.
0 to 960 nm.

On the other hand, when light having an intensity I _O is incident on a substance having an absorption coefficient α, the light intensity I at a distance t is given by the following equation (1).
It is represented by I = I _o exp (−αt) Equation 1

[0006]

As shown in FIG. 4, by the way, as shown in FIG.
The absorption coefficient α of the n-type GaAs crystal at a wavelength of 6 eV or less is 10 cm ^-1 or less. FIG. 4 is a diagram showing the absorption coefficient of an n-type GaAs crystal doped with impurities at a high concentration at 25 ° C., wherein the vertical axis represents the absorption coefficient α and the horizontal axis represents the energy E. From equation 1, n of 300 μm thickness
74% or more of the light having a wavelength of 90 nm or more emitted from the p-type region 3 with respect to the n-type GaAs substrate 1 reaches the back surface of the n-type GaAs substrate 1 and is reflected by the back surface. Reflectance 100
%, 55% or more of the light generated in the p-type region 3 is again n-type GaAs, as shown in FIG.
Light appears on the front surface side of the substrate 1 and leaks between the p-type region 3 and the adjacent p-type region 3 ′ and also from the adjacent p-type region 3 ′.
Light leaking from between the p-type region 3 and the adjacent p-type region 3 ′ becomes light emission blur, and light leaking from the adjacent p-type region 3 ′ becomes leak light emission. Such light emission bleeding and leakage light emission significantly reduce print quality when used in an electrophotographic process as a print head.

As a countermeasure against light emission bleeding, Japanese Patent Laid-Open Publication No.
No. 79 proposes to form a bleeding barrier layer 6 made of a polyimide thin film on a diffusion mask 2 such as silicon nitride or silicon dioxide. Further, Japanese Patent Laid-Open No.
Japanese Patent Publication No. 184880 proposes that the diffusion mask 2 is formed of aluminum oxide (Al ₂ O ₃ ) and is also used as a bleeding blocking layer. Further, Japanese Unexamined Patent Publication No.
In the publication, it is proposed to form a bleeding barrier layer having an insulator / metal / insulator structure.

All of these measures against light emission bleeding complicate the manufacturing process of the semiconductor light emitting device, except that the thin film of aluminum oxide is also used as the diffusion mask 2. In addition, all of these countermeasures are applied to one p-type region 3
Only by preventing light emission bleeding from the periphery, it is not possible to prevent light reflected from the back surface of the n-type GaAs substrate 1 from leaking from the adjacent p-type region 3 ′. There was a problem of deteriorating the quality.

[0009]

SUMMARY OF THE INVENTION A semiconductor light emitting device according to the present invention has been invented in view of such problems of the prior art, and is characterized by n-type GaAs.
In a semiconductor light emitting device in which a p-type region is provided in a substrate and an electrode is provided in the n-type GaAs substrate and the p-type region,
When the thickness of the aAs substrate is 250 μm or more and the maximum emission intensity of the emission spectrum is I _O , I _O /
The point is that the p-type region is formed by diffusing Zn so that the longest wavelength end λm of the two portions is 910 nm or less.

[0010]

With the above construction, it is possible to prevent bleeding of light at the periphery of the p-type region and leakage of light from the adjacent p-type region, thereby significantly improving the printing quality of the electrophotographic process. . Further, an inexpensive semiconductor light emitting device having a high production yield can be provided without complicating the production process. Further, according to the present invention, since a direct transition type GaAs having high quantum efficiency can be used as a light emitting region, a semiconductor light emitting element array having a high light emitting intensity and a high speed printer can be supplied.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The sectional structure of the semiconductor light emitting device according to the present invention is the same as the semiconductor light emitting device shown in FIG. That is, silicon nitride (SiN _x ) is formed on the n-type GaAs substrate 1.
Mask 2 made of silicon or silicon oxide (SiO ₂ )
Is formed, and zinc (Zn) is diffused at the same pitch to a depth of 10 to 50 μm in the n-type GaAs substrate 1 in which the diffusion mask 2 is opened, thereby forming a p-type region 3 having p-type conductivity. To form a semiconductor light emitting device. Note that n-type G
Ohmic electrodes 4 and 5 are formed on the back surface of the aAs substrate 1 and on the p-type region 3 respectively.

In the semiconductor light emitting device according to the present invention, the n-type G
The thickness of the aAs substrate 1 is 250 μm or more. That is, when the thickness of the n-type GaAs substrate 1 is less than 250 μm, light emission bleeding or leakage light emission occurs, thereby deteriorating the printing quality of the electrophotographic process. The thickness of the n-type GaAs substrate 1 is 25
When the thickness is 0 μm or more, the light emitted from the p-type region 3 becomes n-type G
It was confirmed that the light was absorbed as much as possible before reaching the rear surface of the aAs substrate 1, and no light emission bleeding or leakage light emission was observed. Further, it was confirmed that printing by the electrophotographic process did not impair the quality. That is, when the thickness of the substrate 1 is 250 μm, the reciprocating optical path when the light reflected on the back surface comes out to the front surface is 50 μm.
0 μm = 0.05 cm. 910 nm or more (1.3
(6 eV or less), since the absorption coefficient of the GaAs substrate is 10 cm ⁻¹ , the reflectance of the back surface is 10
In the case of 0%, about 60% of light is emitted to the surface side. When the thickness is smaller than 250 μm, light is further emitted to the surface side. Therefore, in order to prevent more than 60% of the light from being emitted to the surface, the thickness is set to 250 μm or more.

The diffusion mask 2 has good adhesion to the n-type GaAs substrate 1 such as silicon nitride or silicon oxide, and prevents the transmission of Zn during the diffusion of Zn and the diffusion mask HF or the like during the formation of the mask. Any window can be opened.

The energy gap of the p-type region 3, which is a light emitting region, changes according to the following equation 2 depending on the hole concentration. Eg (p-GaAs) = 1.424-1.6 × 10 ⁻⁸ P _O ^1/3 (eV) Equation 2 Hole Concentration P _O cm ^{−3 From} this, p-type region 3 If Zn is excessively diffused in order to form, the hole concentration increases, the energy gap decreases, and the emission wavelength increases. When the emission wavelength becomes longer, the light is more easily transmitted through the n-type GaAs substrate 1. Therefore, in the present invention, in order to increase the absorption coefficient α of the n-type GaAs substrate with respect to the emission spectrum, the energy gap of the p region 3 is made as close as possible to 1.424 (eV) without increasing the hole concentration, and the LED emission is increased. The wavelength of 910 nm or more in the spectrum (the wavelength at which the absorption coefficient α in the n-type GaAs crystal becomes 10 (cm ⁻¹ ) or less) is reduced as much as possible. That is, as shown in FIG. 2, when the peak intensity of the emission spectrum is I _o , the Zn doping concentration in the p-type region 3 is determined so that the longest wavelength end λm of the I _O / 2 portion is 910 nm or less. . In the spectrum of FIG. 2, the light of 910 nm or more is 40% or less,
Considering that about 60% of light having a thickness of 910 nm or more emerges from the surface when a substrate having a thickness of 250 μm is used, 40% × 60% = 24%, and 24% in the semiconductor light emitting device according to the present invention. Light will come out on the surface,
This value has no problem in the electrophotographic process. Zinc is obtained by thermal diffusion or ion implantation.
The GaAs substrate 1 is diffused from the surface to the inside. Therefore, it attaches a concentration gradient from the surface to the depth direction, for example, if caused to diffuse Zn from the surface to about 10 ¹⁸ cm ^-3 at the position of 10 to 20 [mu] m, when the peak intensity of the emission spectrum of the I _o, I _O The emission spectrum has a longest wavelength end λm of / 2 nm or less at 910 nm or less. In addition, as a diffusion source of Zn,
ZnAs ₂ or Zn / Ga / As can be used. The diffusion time and temperature are not particularly specified.
The diffusion density of is 91 when the wavelength λm in the LED emission spectrum is 91.
The diffusion conditions are set so as to be 0 nm or less.

The electrode 4 formed on the back side of the n-type GaAs substrate 1 is made of Cr, GeAu, Au, etc.
It is formed to a thickness of about. The electrode 5 formed in the p-type region 3 is made of Cr, Zn, Au, Al, Ti, or the like.
It is formed to a thickness of about 00 nm. Further, in order to reduce the wiring resistance, Al, Au, etc.
It may be formed in a thickness of about 00 nm to 10 μm.

[0016]

As described above, according to the semiconductor light emitting device of the present invention, the thickness of the n-type GaAs substrate is set to 250 μm or more, and the maximum emission intensity of the emission spectrum is set to I _O.
, The longest wavelength end λm of the I _O / 2 portion is 910
Since Zn is diffused into the n-type GaAs substrate to form a p-type region so as to be not more than nm, light emission bleeding and leakage light emission can be prevented. Thus, the printing quality of the electrophotographic process can be significantly improved. When the maximum emission intensity of the emission spectrum is I _O , I _O /
Since Zn is diffused into an n-type GaAs substrate to form a p-type region so that the longest wavelength end λm of the two portions is 910 nm or less, the manufacturing process is not complicated,
An inexpensive semiconductor light emitting device having a high production yield can be provided. When a single crystal thin film of AlGaAs, GaAsP, InAlGaP, or the like is used, the wavelength can be shortened from 870 nm. In the invention, a direct transition type GaAs having high quantum efficiency is used.
Can be used as a light emitting region, so that the light emitting intensity is high and a semiconductor light emitting element array for a high-speed printer can be supplied.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross section of a semiconductor light emitting device according to the present invention.

FIG. 2 is a diagram showing an emission spectrum of the semiconductor light emitting device according to the present invention.

FIG. 3 is a diagram showing an emission spectrum of a conventional semiconductor light emitting device.

FIG. 4 is a diagram showing an absorption coefficient of an n-type GaAs crystal.

FIG. 5 is a diagram showing light emission bleeding and leakage light emission in a conventional semiconductor light emitting element.

[Explanation of symbols]

1 ... n-type GaAs substrate, 2 ... diffusion mask, 3 ...
..P-type region, 4 ... electrodes, 5 ... electrodes

Claims (1)

(57) [Claims] 1. A semiconductor light emitting device having a p-type region provided on an n-type GaAs substrate and electrodes provided on the n-type GaAs substrate and the p-type region, wherein the n-type GaAs substrate has a thickness of 250.
μm or more, and when the maximum emission intensity of the emission spectrum is I _O , Zn is diffused so that the longest wavelength end λm of the I _O / 2 portion is 910 nm or less, and the p-type region is formed. A semiconductor light emitting device characterized by the above-mentioned.