JPH0745863A - Semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To prevent easily deterioration since the current does not flow in concectration by increasing the utilization efficiency of diffusion light at a light emitting region since current spreads within a light emitting layer. CONSTITUTION:A light emitting layer 6b consisting of a p-type semiconductor thin film and an electron injection layer 6a which is constituted by an n-type semiconductor thin film where p-n junction is injected into the light emitting layer 6b are provided. The carrier density of the electron injection layer 6a is smaller than that of the light emitting layer 6b. Therefore, the resistance of the electron injection layer 6a becomes larger than that of the light emitting layer 6b, thus the current spreads within the light emitting layer 6b and hence preventing flowing in concentration.

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,
For example, it is used as a light source for exposing a photosensitive drum of a page printer.

[0002]

2. Description of the Related Art The semiconductor light emitting device shown in FIGS.
A substrate 101 made of silicon (Si), gallium arsenide (GaAs) or the like and a mesa-shaped LED 102 are provided. The LED 102 includes a buffer layer 103 made of a semiconductor thin film bonded to one main surface of the substrate 101, an electron injection layer 104 made of an n-type semiconductor thin film bonded to the buffer layer 103, and an electron injection layer. It is composed of a light emitting layer 105 formed of a p-type semiconductor thin film that makes a pn junction with the layer 104, and a contact layer 106 formed of a p ⁺ type semiconductor thin film that makes a junction with the light emitting layer 105. A non-translucent anode electrode 107 is connected to the contact layer 106, and a cathode electrode 108 is connected to the other main surface of the substrate 101. Both electrodes 10
By applying a forward bias through 7, 108, electrons recombine with holes and emit light. This emitted light is taken out from the side to which the anode electrode 107 is connected and used.

[0003]

When the emitted light is taken out from the side to which the non-translucent anode electrode 107 is connected as in the above structure, the emitted light is blocked by the electrode 107, so that the emitted light is sufficiently emitted to the outside. I can't take it out. This is because the current i concentrates and flows right below the anode electrode 107 as shown by the broken line in the figure. In particular,
L composed by arranging a plurality of LEDs on a substrate
In the case of a semiconductor light emitting device including an ED array, the size of each LED is very small, for example, the chip width W is about 50 μm, and the width w of the anode electrode 107 is about 20 μm, while the size of the anode electrode 107 The distance d to the pn junction is only about 1 to 2 μm, so
It is difficult for the current to spread in the light emitting layer 105, and the light utilization efficiency becomes low. Furthermore, since the current flows partially concentratedly, there is a problem that the light emission deterioration progresses rapidly in that part and the life is shortened.

It is an object of the present invention to provide a semiconductor light emitting device which can solve the above technical problems.

[0005]

A semiconductor light emitting device according to the present invention comprises a light emitting layer formed of a p-type semiconductor thin film, and an electron injection layer formed of an n-type semiconductor thin film that makes a pn junction with the light emitting layer. And the carrier density of the electron injection layer is smaller than the carrier density of the light emitting layer.

[0006]

According to the structure of the present invention, since the electron injection layer has a smaller carrier density than that of the light emitting layer, the resistance of the electron injection layer becomes larger than the resistance of the light emitting layer. It is prevented from spreading inside and flowing partially concentrated.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor light emitting device according to a first embodiment of the present invention shown in FIG. 1 comprises a silicon substrate 1 and a mesa-shaped LED 2, and the LEDs 2 are arranged in rows on one main surface side of the silicon substrate 1. It is one of those formed. The LED
2 is manufactured by, for example, the MOCVD (metal organic vapor phase epitaxy) apparatus 20 shown in FIG. That MOCV
The D device 20 includes a quartz reactor 21 and Al (CH ₃ ) pipe-connected to the reactor 21 via a valve 22.
A source 29 of _3, a source 30 of Ga (CH _{3) 3,}
AsH ₃ supply source 31 and Zn (CH ₃ ) ₂ supply source 3
2, a supply source 33 of SiH ₄ , and trimethylindium
(In (CH ₅ ) ₃ ) source 34, H ₂ source 35 used as a carrier gas, H ₂ purifier 36, and high-frequency coil used to heat the inside of the reactor 21. 37, a support 38 that supports the silicon substrate 1 inside the reactor 21, and a treatment device 39 for the exhaust gas from the reactor 21.

In order to form the LED 2 by the MOCVD apparatus 20, first, the semiconductor crystal forming the buffer layer 3 is epitaxially grown on the one main surface 1a of the substrate 1. The buffer layer 3 is subjected to, for example, a cycle in which the temperature of the growth layer of GaAs is raised and lowered a plurality of times to apply thermal stress, or indium gallium arsenide (InGaAs).
And a GaAs growth layer are alternately and repeatedly grown a plurality of times to form a strained superlattice layer and reduce dislocations.

Next, an electron injection layer 6a made of an n-type semiconductor thin film is formed on the buffer layer 3, and a light emitting layer 6b made of a p-type semiconductor thin film is formed on the electron injection layer 6a. To do. The electron injection layer 6a and the light emitting layer 6b
Is, for example, aluminum gallium arsenide (AlGaA).
s) It can be formed by epitaxially growing a crystal. At this time, the carrier density of the electron injection layer 6a is made lower than that of the light emitting layer 6b. The carrier density of the electron injection layer 6a has the effect of the present invention that the current is expanded to reduce the deterioration of light emission, so that the light emitting layer 6b is formed.
The carrier density is less than 1/10 and the upper limit is 1 × 10 ¹⁶ c
It is preferably m ^-3 . When the carrier density of the electron injection layer 6a is smaller than 1 × 10 ¹⁵ cm ⁻³ and smaller than 1/10000 of the light emitting layer 6b, the resistance becomes excessive and the voltage during light emission is 10 mA per LED. The lower limit is 1 × 10 ¹⁵ c, because it exceeds 2 V when a current is passed.
It is good to set it to m / ^-3 and 1/10000 of the light emitting layer. In order to control the carrier density, the light emitting layer 6b is doped with an acceptor, and the electron injection layer 6a is a non-doped layer. That is, AsH ₃ , Ga (CH ₃ ) ₃ and Al
When (CH ₃ ) ₃ is supplied to the reactor 21 to grow an AlGaAs crystal, Zn (C 3
Zn is doped by supplying H ₃ ) ₂ to the reactor 21. Further, when the electron injection layer 6a is formed, if a normal n-type semiconductor thin film is to be formed, SiH ₄ gas is supplied to the reactor to dope Si. An n-type semiconductor thin film is formed by controlling the carrier density of 6a. That is, Ga (C
_{H 3) 3, Al (CH} 3) Si traces present in _3,
An impurity such as S gives an n-type semiconductor. Also, G
a a _{(CH 3) 3, Al (} CH 3) in ₃ carbon (C) by compensating as acceptors, can control the carrier density. For example, the emission wavelength is 700 nm
Al _X Ga _1-X As to form a red LED
, The carrier density of the light emitting layer 6b is 1 × 10 ¹⁶ cm ^{−3 when} Zn is an acceptor.
The carrier density of the electron injection layer 6a can be controlled in the range of about 2 × 10 ¹⁹ cm ⁻³ , and is 1 × 1 when the non-doped layer is used.
It can be 0 ¹⁷ cm ^-3 or less. The carrier density of the electron injection layer 6a can be controlled within a range of about 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ¹⁷ cm ⁻³ when Si is a donor when x = 0.4.

By making the band gap of the electron injection layer 6a larger than the band gap of the light emitting layer 6b, holes in the light emitting layer 6b become positive when the forward bias is applied.
It is preferable to prevent diffusion to the a side and increase the hole density of the light emitting layer 6b to increase the light emission efficiency. The light emitting layer 6b is made of Al _a Ga _1-a As, and the electron injection layer 6a is made of A _a Ga _{1 -a} As.
When configuring a l _b Ga _1-b As is, b> With a, the band gap of the electron injection layer 6a emitting layer 6b
Is larger than the band gap of. The composition of the light emitting layer 6b is preferably 0 <a <0.4. This is because in the case of Al _a Ga _1-a As, when a exceeds about 0.45, the direct transition type semiconductor changes to the indirect transition type semiconductor, so that the luminous efficiency decreases as the value of a increases, and it becomes practical. This is because the upper limit of a that can be provided is about 0.4.

Onto the light emitting layer 6b is joined a contact layer 6c composed of a p ⁺ type semiconductor thin film in which an acceptor is highly doped, and each semiconductor thin film 3, 6a, 6 is formed.
b and 6c are covered with a passivation film 7 after being etched into a mesa shape, and a non-translucent anode electrode 8a is bonded to the contact layer 6c and the substrate 1
The cathode electrode 8b is connected to the other main surface 1b.

According to the above structure, even if the carrier density of the electron injection layer 6a is set to 1/10 or less of the carrier density of the light emitting layer 6b, the light emitting layer 6b and the electron injection layer 6a form a pn junction. By applying a forward bias through 8a and 8b, the electrons diffused from the electron injection layer 6a to the light emitting layer 6b are recombined with the holes to emit light. At this time, since the electron injection layer 6a has a smaller carrier density than the light emitting layer 6b, the resistance thereof becomes larger than the resistance of the light emitting layer 6b, and as shown by a broken line arrow in FIG. It is possible to prevent the spread and the partial concentrated flow. This makes it possible to increase the light use efficiency even when the emitted light is taken out from the side to which the anode electrode 107 is connected.
It is possible to prevent premature deterioration due to a partial flow of current.

When the carrier density of the electron injecting layer 6a is reduced and the number of electrons injected into the light emitting layer 6b is insufficient and the required light emission intensity cannot be obtained, the semiconductor according to the second embodiment of FIG. Like a light emitting device, an auxiliary electron injection layer 6d composed of an n-type semiconductor thin film is formed so as to sandwich the electron injection layer 6a with the light emitting layer 6b, and the auxiliary electron injection layer 6d is formed.
It is preferable to make the carrier density of the electron injection layer 6a higher than the carrier density of the electron injection layer 6a and set the thickness of the electron injection layer 6a to 1 μm or less in order to make the diffusion length of the electrons or less. 4 (1) is
An energy band diagram when a forward bias is applied in the second embodiment is shown, and (2) of FIG. 4 shows an energy band diagram when no bias is applied in the second embodiment, and
_c is the minimum conduction band energy, and E _Fn is the n-type semiconductor layer 6
The Fermi levels of a and 6d, E _Fp the Fermi level of the light emitting layer 6b, and E _v the maximum valence band energy. In order to confine the holes h of the light emitting layer 6b in the light emitting layer 6b, the band gap E _ga of the electron injection layer 6a is made larger than the band gap E _gb of the light emitting layer 6b. By injecting electrons e from the auxiliary electron injection layer 6d into the light emitting layer 6b as indicated by an arrow J in the figure, sufficient emission intensity can be obtained even if the injection of the electrons e in the electron injection layer 6a is insufficient. You can The band gap E _gc of the auxiliary electron injection layer 6d is not particularly limited and may be smaller than the band gap E _{gb of} the light emitting layer 6b. For example, when the light emitting layer 6b and the electron injection layer 6a are made of AlGaAs, The auxiliary electron injection layer 6d may be made of GaAs. In order to control the carrier density of the auxiliary electron injection layer 6d, when the semiconductor thin film forming the electron injection layer 6a is grown, Si
H ₄ gas is supplied to the reactor to dope Si as a donor. Others are the same as the above-mentioned embodiment, and the same portions are denoted by the same reference numerals.

The light emitting layer 6b of the semiconductor light emitting device according to the third embodiment of the present invention shown in FIG. 5 is composed of an electron confining layer 6b 'and a light emitting layer 6b ", and the electron confining layer 6b'.
Is Al _0.40 Ga _0.60 As and has a carrier density of 5 × 1.
0 ¹⁷ cm ^-3 , and the light emitting layer 6b ″ is made of Al _0.35 Ga _0.65 A
s and has a carrier density of 5 × 10 ¹⁷ cm ⁻³ , and the electron injection layer 6 a has a thickness of 1.0 μm and a carrier density of 5 ×.
10 ¹⁵ cm ^-3 of Al _0.40 Ga _0.60 As, the auxiliary electron injection layer 6d is GaAs, and the carrier density is 5 × 1.
It is 0 ¹⁶ cm ^-3 . Others are the same as those in the second embodiment, and the same parts are designated by the same reference numerals.

FIG. 6 shows the relationship between the light emission position and the light emission intensity when the light emission is taken out from the side to which the anode electrode 8a of the semiconductor light emitting device of the third embodiment is connected. The width W of the LED 2 is 50 μm, the width w of the anode electrode 8a is 15 μm, the length Q of the LED 2 is 60 μm, and the length q of the anode electrode 8a is 4 μm.
It was set to 0 μm, and the relationship between the emission position in the width direction and the emission intensity was shown. Further, FIG. 7 shows that the carrier density of the electron injection layer is 1 ×.
The semiconductor light emitting device according to the comparative example having the same structure as that of the semiconductor light emitting device of the third embodiment except for 10 ¹⁷ cm ⁻³ shows the relationship between the light emitting position and the light emitting intensity. By comparing FIG. 6 and FIG. 7, it can be confirmed that according to the present invention, since the light emitting region is expanded, the light utilization efficiency can be increased. FIG. 8 shows the results of measuring the relationship between the energization time and the emission intensity in the semiconductor light emitting devices according to the third example and the comparative example with respect to five samples. It can be confirmed that the light emission intensity does not decrease for a long time and the early deterioration can be prevented because the light does not flow concentratedly in the air.

The present invention is not limited to the above embodiment. For example, the semiconductor that constitutes the LED is Al _X Ga _1-X
The carrier density of the electron injection layer is not limited to As and may be made of other semiconductor such as GaAs _X P _1-X.
^It is good to set it to ¹⁵ cm ⁻³ to 1 × 10 ¹⁶ cm ⁻³ . Further, the electron injection layer 6a may be doped with impurities such as Si instead of being a non-doped layer, but it is 1 × 10 ¹⁵ cm ⁻³ to 1 × 10 ¹⁶ cm.
^In the low carrier density range of about ^-3 , it is advantageous to use a non-doped layer for controlling the carrier density.

[0017]

According to the semiconductor light emitting device of the present invention, it is possible to spread the current in the light emitting layer and increase the light utilization efficiency.
Since the current does not flow partially concentratedly, it is possible to prevent early deterioration.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a semiconductor light emitting device according to a first embodiment of the invention.

FIG. 2 is a MOCV for forming a semiconductor thin film according to an embodiment of the present invention.
The figure which shows the structure of D device

FIG. 3 is a diagram showing a sectional configuration of a semiconductor light emitting device according to a second embodiment of the present invention.

FIG. 4 is an energy band diagram of a semiconductor light emitting device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a cross-sectional structure of a semiconductor light emitting device of a third embodiment of the present invention.

FIG. 6 is a diagram showing light emission characteristics of a semiconductor light emitting device according to a third embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between a light emission intensity and a light emitting position of a semiconductor light emitting device of a comparative example.

FIG. 8 is a graph showing the relationship between the emission intensity and the energization time of the semiconductor light emitting device of the third embodiment of the present invention and the comparative example.

FIG. 9 is a diagram showing a sectional configuration of a conventional semiconductor light emitting device.

FIG. 10 is a diagram showing a planar configuration of a conventional semiconductor light emitting device.

[Explanation of symbols]

 6a Electron injection layer 6b Light emitting layer

Claims (1)

[Claims] 1. A light emitting layer formed of a p-type semiconductor thin film, and an electron injection layer formed of an n-type semiconductor thin film that makes a pn junction with the light emitting layer, and the carrier density of the electron injection layer is light emission. A semiconductor light emitting device being made smaller than the carrier density of the layer.