JP2002222988A - LED array and LED head - Google Patents

Abstract

(57) Abstract: Provided is an LED array that uses a silicon substrate to obtain high light emission on the short wavelength side. SOLUTION: One-conductivity-type semiconductor layer 2 and opposite-conductivity-type semiconductor layer 3 are sequentially laminated for each light-emitting diode on a silicon semiconductor substrate 1, and individual electrodes 4 are connected to the opposite-conductivity-type semiconductor layer 3,
The common electrode 5 is formed on the back surface of the semiconductor substrate 1. The reverse conductivity type semiconductor layer 3 includes a light emitting layer 3a, a cladding layer 3b, and an ohmic contact layer 3c.
lxGa1-xAs / AlyGa1-yAs (x = 0.05-
0.35, y = 0.25 to 0.45).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED array, and more particularly, to an LED array used as an exposure light source for a photosensitive drum for a page printer. Also,
The present invention relates to an LED head having a plurality of LED arrays of the present invention arranged in a straight line.

[0002]

2. Description of the Related Art A conventional LED array will be described with reference to FIGS. Two types of LED arrays are presented, one LED array will be described with reference to FIGS. 6 and 7, and the other LED array will be described with reference to FIGS. 8 and 9.

First, one LED array will be described.
FIG. 6 is a cross-sectional view of the LED array, and FIG. 7 is a plan view thereof.

[0004] Reference numeral 11 denotes a long semiconductor substrate. On this semiconductor substrate 11, a semiconductor layer 12 of one conductivity type and a semiconductor layer 13 of opposite conductivity type are sequentially laminated for each light emitting diode.
An individual electrode 14 is connected to the opposite conductivity type semiconductor layer 13, and a common electrode 15 for a plurality of light emitting diodes is formed on the back surface of the semiconductor substrate 11. Reference numeral 16 denotes an insulating film made of a silicon nitride film or the like.

In such an LED array, the individual electrodes 1
Each light emitting diode is selectively caused to emit light by flowing a current between the light emitting diode 4 and the common electrode 15.

Next, the other LED array will be described with reference to FIGS. FIG. 8 is a cross-sectional view of this LED array, and FIG.
Is a plan view thereof.

Reference numeral 11 denotes a long semiconductor substrate. On the semiconductor substrate 11, a semiconductor layer 12 of one conductivity type and a semiconductor layer 13 of opposite conductivity type are sequentially laminated for each light emitting diode, and An individual electrode 14 is connected to the semiconductor layer 13.

The one-conductivity-type semiconductor layer 12 is formed wider than the opposite-conductivity-type semiconductor layer 13 so that an extended portion R, which is an exposed portion thereof, is disposed, and the common electrode 15 (15
a, 15b) are connected. Reference numeral 16 denotes an insulating film made of a silicon nitride film or the like.

[0009] Further, as shown in FIG.
(15a, 15b) are adjacent island-like semiconductor layers 12, 13
(Light emitting diodes) are connected and divided into two groups so as to belong to different groups, and adjacent island-shaped semiconductor layers 1
2 and 13 are connected to the same individual electrode 14.

In the LED array having such a configuration, each light emitting diode can be selectively made to emit light by selecting a combination of the individual electrode 14 and the common electrode 15 (15a, 15b) and flowing an electric current.

Regarding one LED array or the other LED array as described above, both are manufactured in large numbers at one time.

That is, many LED arrays are arranged and formed in a matrix on a common semiconductor substrate, and each LED array is cut into chips by a method such as dicing. The LED head is arranged on a mounting board and connected to an external circuit by wire bonding or the like.

According to this LED head, an optical lens is provided on a substrate on which an LED array chip is mounted, and an LED is provided.
The LED head may be assembled as a head. In this LED head, light emitted by the LED array is condensed by an optical lens on the mounting substrate and is imaged on a photosensitive drum.

[0014]

In recent years, demand for amorphous silicon photosensitive drums that do not require replacement of photosensitive drums has increased due to increased environmental awareness.

The amorphous silicon photosensitive drum has a light sensitivity peak on the short wavelength side as compared with the OPC drum, and a wavelength of about 685 nm is suitable.

However, when the light emitting layer of the above-mentioned LED array is constituted by a semiconductor layer made of aluminum gallium arsenide (AlGaAs), there is a problem that it is difficult to increase the light emitting efficiency at a short wavelength of around 685 nm.

To explain this point in detail, when the Al content ratio of the AlGaAs layer, which is the light emitting layer, is increased in order to shorten the light emitting wavelength, the non-light emitting component increases accordingly, and as a result, the light emission efficiency decreases. ing.

Generally, when the Al content ratio x of aluminum gallium arsenide (AlxGa1-xAs) exceeds 0.2, the indirect transition type non-radiative recombination component increases in the active layer. If it exceeds, the transition becomes an indirect transition type, and the band gap increase ratio with respect to the increase in the Al composition becomes smaller than that in the direct transition region.

Usually, in order to confine carriers in the light emitting layer, the cladding layer is formed using a material having a larger band gap than the light emitting layer. When the emission wavelength is around 685 nm, the cladding layer must indirectly transition inevitably. Therefore, the Al composition x is set to 0.6 or more in order to increase the band gap of the cladding layer.

The light emitting layer of the LED array is made of AlGaAs.
In the case where the semiconductor device is constituted by a semiconductor layer made of s, there are the following problems.

When a GaAs substrate is used as the semiconductor substrate, it is made of the same material as the film formed thereon, so that a relatively high optimum film forming temperature is set to improve the crystallinity of the film. be able to.

However, when the semiconductor substrate is a silicon substrate and a GaAs film or an AlGaAs film is formed on this substrate, the semiconductor substrate is 100 times thicker than that formed on a GaAs substrate.
By forming the film at a low temperature of about ° C., defects in crystallinity of the film due to a difference in thermal expansion coefficient between the film and the substrate are prevented.

However, in order to efficiently mix AlAs with GaAs, the film should be formed at a temperature higher than the optimum film formation temperature on the silicon substrate. At a relatively low temperature, such as near the temperature, a clad layer (AlGaAs layer) having an Al composition (x) of 0.6 or more as described above is formed. However, it is difficult to perform the mixed crystal of AlAs. It became worse, the luminous efficiency decreased, and the driving voltage increased.

Further, GaAs or AlG is formed on a silicon substrate.
When aAs is deposited, a tensile stress is inherent in the deposited film due to a difference in thermal expansion coefficient between the deposited film and the substrate. It shifts to a direction in which the band gap becomes smaller, that is, the emission wavelength becomes longer. Therefore, in the case where AlGaAs is used for the light emitting layer, a comparison between the case of forming a film on a silicon substrate and the case of forming a film on a GaAs substrate is as follows.
In order to obtain the same wavelength, it is necessary that the film formed on the silicon substrate has a higher Al composition than the film formed on the GaAs substrate. Therefore, the above-described effects are further increased, and adverse effects such as a decrease in luminous efficiency and an increase in drive voltage are increased.

Thus, it can be said that it is difficult to produce a high-efficiency LED array (LED head) having a wavelength corresponding to an amorphous silicon photosensitive drum using a silicon substrate because of the above-mentioned problems.

For reference, the present inventor measured the relationship between the Al composition of the cladding layer and the luminous intensity of an LED array having a 685 nm luminous wavelength using a silicon substrate. The results shown in FIG. 12 were obtained. FIG. 13 shows the result of measuring the relationship between the Al composition of the cladding layer and the driving voltage.

These measurement results were obtained at an LE of 600 dpi.
The evaluation was performed using an LED array used for a D printer, and the emission intensity and drive voltage at 10 mA.

As is clear from the results shown in FIGS. 12 and 13, when the Al composition ratio of the cladding layer is increased, the light emission intensity decreases and the driving voltage increases.
This is because a high quality AlG
This is because it is very difficult to form an aAs film, particularly when the Al composition is high.

On the other hand, in a semiconductor light emitting device such as an LED or a semiconductor laser, a semiconductor quantum well structure or a semiconductor superlattice structure is used for the purpose of improving luminous efficiency and shortening an emission wavelength.

The luminous body having the quantum well structure includes a barrier layer having a barrier effect and a well layer sandwiched between the barrier layers. The barrier layer is formed of a material having a larger band gap than the well layer.

In such a quantum well structure, a quantum level is generated in each of the conduction band and the valence band in the potential well portion, and the transition energy becomes larger than the band gap of the well layer, so that the quantum level becomes larger. In a semiconductor light emitting device such as an LED or a semiconductor laser having a light emitting layer having a well structure, the wavelength is shorter than the wavelength inherent in the material of the well layer.

Incidentally, a technique has been proposed in which the characteristics of a superlattice quantum well structure having a short wavelength are utilized in a semiconductor laser or the like (see JP-A-1-86584).

By the way, the one using an AlGaAs super lattice structure is generally used for increasing the luminance and shortening the wavelength of a red LED.
An As substrate.

Using this GaAs substrate, a superlattice structure or the like is formed, or a red LED or an infrared LED is manufactured, thereby solving the problems of a difference in lattice constant and a difference in thermal expansion coefficient. And high quality AlGaAs layers and G
An aAs layer is formed.

However, on a silicon substrate, AlGa
In the technique of forming a superlattice structure of As, the difference in the thermal expansion coefficient between the deposited film and the substrate causes the emission wavelength to shift to a longer one, and as described above, the emission efficiency decreases and the driving voltage decreases. It has not yet been sufficiently studied due to its adverse effects such as a rise.

The present inventor has conducted intensive studies in view of the above description. As a result, by forming an AlGaAs superlattice structure on a silicon substrate, as the Al composition of the light emitting layer increases, the non-light emitting component increases, and Even if the efficiency tends to decrease, carriers can be efficiently confined in the light-emitting layer (well layer in the superlattice) by utilizing the quantum effect due to the superlattice structure. It has been found that controllable by the composition and thickness of the layer makes it possible to easily prevent and compensate for such a decrease in luminous efficiency, and as a result, the luminous efficiency can be improved particularly when the emission wavelength is short.

More specifically, in the prior art, a high-efficiency LED array (LED) having a wavelength corresponding to an amorphous silicon photosensitive drum on a silicon substrate is used.
Although it is difficult to manufacture a head, the present inventor has been keen to develop a technique for forming a light emitting layer having a super lattice structure on a silicon substrate and thereby improving the light emitting efficiency when the light emitting wavelength is short. As a result of repeated studies, it has been found that by specifying the atomic composition ratio of AlGaAs forming the light emitting layer, high efficiency can be achieved with a light emission wavelength corresponding to an amorphous silicon photosensitive drum on a silicon substrate.

Therefore, the present invention has been accomplished based on the above findings, and its object is to use a silicon substrate.
An object of the present invention is to provide an LED array that has obtained high light emission on the short wavelength side.

It is another object of the present invention to provide an LED head suitable for an amorphous silicon photosensitive drum using an LED array using a silicon substrate.

[0040]

According to the LED array of the present invention, a plurality of island-like semiconductor layers are sequentially arranged on a silicon substrate by sequentially stacking a semiconductor layer of one conductivity type, a semiconductor layer of the opposite conductivity type and one electrode. The other electrode is formed on the back surface of the silicon substrate, and the light emitting layer of the opposite conductivity type semiconductor layer is
lxGa1-xAs / AlyGa1-yAs (x = 0.05-
0.35, y = 0.15 to 0.4).

According to another LED array of the present invention, a plurality of island-shaped semiconductor layers are sequentially arranged on a silicon substrate by sequentially laminating a semiconductor layer of one conductivity type, a semiconductor layer of the opposite conductivity type and one electrode.
The other electrode is formed on the extending portion of the one conductivity type semiconductor layer, and the light emitting layer of the opposite conductivity type semiconductor layer is formed of AlxG
a1-xAs / AlyGa1-yAs (x = 0.05-0.3
5, y = 0.25 to 0.45).

The LED head according to the present invention is characterized in that a plurality of the LED arrays according to the present invention are arranged in a straight line.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The LED array of the present invention will be described with reference to FIGS. 1 and 2, and another LED array of the present invention will be described with reference to FIGS.

(Configuration of LED Array) First, FIGS. 1 and 2
Will be described. FIG. 1 is a cross-sectional view thereof, and FIG. 2 is a plan view thereof.

1 is a long silicon semiconductor substrate,
On this semiconductor substrate 1, for each light emitting diode, a one conductivity type semiconductor layer 2 and a reverse conductivity type semiconductor layer 3 are sequentially laminated,
The individual electrode 4 serving as the one electrode is connected to the opposite conductivity type semiconductor layer 3, and the common electrode 5 serving as the other electrode for a plurality of light emitting diodes is formed on the back surface of the semiconductor substrate 1. Reference numeral 6 denotes an insulating film made of a silicon nitride film or the like.

The semiconductor substrate 1 is composed of a single crystal semiconductor substrate of silicon (Si), and a substrate having the (100) plane turned off by 2 to 7 ° in the <011> direction is preferably used.

The one conductivity type semiconductor layer 2 is composed of a buffer layer 2a and an electron injection layer 2c. Buffer layer 2a has a thickness of 2 to 4 μm.
m, and the electron injection layer 2c has a thickness of 0.2 to
It is formed to a thickness of about 2.0 μm.

The buffer layer 2a is formed of gallium arsenide or the like, and the electron injection layer 2b is formed of aluminum gallium arsenide (A
lxGa1-xAs) or the like.

The buffer layer 2a is formed by adding one conductivity type semiconductor impurity such as silicon to 1 × 10 ¹⁶ to 10 ¹⁷ atoms (atoms).
/ Cm ³ , and the electron injection layer 2b contains one conductivity type semiconductor impurity such as silicon at 1 × 10 ¹⁶ to 10 ¹⁹ atoms (at.
oms) / cm ³ . In addition, the electron injection layer 2c
The composition of Al is about x = 0.4 to 0.7.

The opposite conductivity type semiconductor layer 3 includes a light emitting layer 3a, a cladding layer 3b, and an ohmic contact layer 3c.

The light emitting layer 3a is made of AlxGa1-xAs / AlyGa
It is a superlattice structure composed of 1-yAs.

The composition of the AlxGa1-xAs layer serving as the well layer is set to x = 0.05 to 0.35. In addition, A serving as a barrier layer
The composition of the lyGa1-yAs layer is set to y = 0.25 to 0.45.

The thickness of the AlxGa1-xAs layer serving as the well layer is preferably in the range of 20 to 100 °, and the AlxGa1-xAs layer serving as the barrier layer is preferably formed of AlxGa1-xAs.
The thickness of the yGa1-yAs layer may be, for example, about 100 °, and more preferably, 50 to 200 °.

The number of each of the well layer and the barrier layer is preferably 1 to 10 layers. In order to set the emission wavelength in the well layer to be around 685 nm, the x value of the Al composition and the film thickness are set as conventionally known.

Regarding this optimum film thickness, Kronich
It is derived from quantum mechanical theory such as the Penny model. When the Al composition is determined for the well layer, the film thickness is necessarily determined.

The barrier layer may have any thickness as long as the tunnel effect can be maintained so that the quantum well effect can be obtained.
It is good to set it to about 00 °.

The second cladding layer 3b is made of gallium arsenide or the like and preferably has a thickness of about 0.2 to 1 μm.

The ohmic contact layer 3c is made of gallium arsenide or the like, and preferably has a thickness of about 0.01 to 0.1 μm.

The second cladding layer 3b is made of zinc (Zn) or the like.
1 × 10 ¹⁶-10¹⁸atom
s / cm^Three The second ohmic contact layer
3c is 1 × 10 of a reverse conductivity type semiconductor impurity such as zinc.¹⁹~
10²⁰atoms / cm^Three Content.

The second cladding layer 3b is made of aluminum gallium arsenide (AlxGa1-xA) similarly to the electron injection layer 2b.
s) and the like. The composition of this Al is x = 0.4-
It is good to form with about 0.7. Note that the Al composition does not need to match between both the second cladding layer 3b and the electron injection layer 2b.

The insulating film 6 is made of silicon nitride or the like and has a thickness of about 3000 to 5000 °. The individual electrode 4 and the common electrode 5 are made of gold / chrome (Au / AuGe / C
r) etc., and is formed to a thickness of about 1 μm.

As shown in FIG. 2, the LED head according to the present invention has island-shaped semiconductor layers 2 and 3 composed of a semiconductor layer 2 of one conductivity type and a semiconductor layer 3 of the opposite conductivity type arranged on a substrate 1 in a line. By selecting the electrode 4 and passing a current, it is used as an exposure light source for a photosensitive drum for a page printer.

(Configuration of Another LED Array) The LED array shown in FIGS. 3 and 4 will be described. FIG. 3 is a cross-sectional view thereof, and FIG. 4 is a plan view thereof.

Reference numeral 1 denotes a long silicon semiconductor substrate;
On the semiconductor substrate 1, one-conductivity-type semiconductor layer 2 and reverse-conductivity-type semiconductor layer 3 are sequentially laminated for each light-emitting diode, and an individual electrode 4 is connected to the reverse-conductivity-type semiconductor layer 3 and provided. .

The one-conductivity-type semiconductor layer 2 is formed wider than the opposite-conductivity-type semiconductor layer 3 so that an extended portion R which is an exposed portion thereof is provided, and the common electrode 5 (5a) is formed on the extended portion R. 5b)
Are connected. Reference numeral 6 denotes an insulating film made of a silicon nitride film or the like.

As shown in FIG. 4, the common electrode 5 (5
a, 5b) are connected and divided into two groups so that the adjacent island-shaped semiconductor layers 2 and 3 (light-emitting diodes) belong to different groups, and the adjacent island-shaped semiconductor layers 2 and 3 have the same individual electrode. 4 is connected.

In the LED array having such a configuration, by selecting a combination of the individual electrode 4 and the common electrode 5 (5a, 5b) and flowing an electric current, each light emitting diode can selectively emit light.

The substrate 1 is made of a single crystal semiconductor substrate of silicon (Si), and the (100) plane is set to 2-7 in the <011> direction.
A substrate that has been turned off is preferably used.

The one conductivity type semiconductor layer 2 includes a buffer layer 2a,
It comprises an ohmic contact layer 2b and an electron injection layer 2c.

The buffer layer 2a has a thickness of about 2 to 4 μm, and the ohmic contact layer 2b has a thickness of 0.1 to 1.
The electron injection layer 2c is formed to a thickness of about 0 μm.
It is formed to a thickness of about 2.0 μm.

The buffer layer 2a and the ohmic contact layer 2b are formed of gallium arsenide, and the electron injection layer 2c is formed of aluminum gallium arsenide (AlxGa1-xAs).

The ohmic contact layer 2 b is made of one conductivity type semiconductor impurity such as silicon at 1 × 10 ¹⁶ to 10 ¹⁷ ato.
ms / cm ³ , and the electron injection layer 2 c contains one conductivity type semiconductor impurity such as silicon at 1 × 10 ¹⁶ to 10 ^{19 at}
It contains about ms / cm ³ .

The buffer layer 2a is provided to prevent misfit dislocation due to mismatch of the lattice constant between the substrate 1 and the semiconductor layer.
It does not have to be contained. The composition of Al in the electron injection layer 2c is about x = 0.4 to 0.7.

The opposite conductivity type semiconductor layer 3 includes a light emitting layer 3a, a cladding layer 3b, and an ohmic contact layer 3c.

The light emitting layer 3a is made of AlxGa1-xAs / AlyGa
A 1-yAs superlattice structure with A
The composition of the lxGa1-xAs layer is x = 0.05-0.35, and the composition of the AlyGa1-yAs layer serving as the barrier layer is y.
= 0.25 to 0.45.

The thickness of the Al.sub.x Ga.sub.1-x As layer serving as the well layer is preferably in the range of 25 to 100.degree.
The thickness of the yGa1-yAs layer may be, for example, about 100.degree., more preferably in the range of 50 to 200.degree., and the number of each of the well layer and the barrier layer is 1 to 10
It may be a layer.

In order to set the emission wavelength to be around 685 nm in the well layer, the x value of the Al composition and the film thickness are set as is well known. This optimum film thickness is derived from a quantum mechanical theory such as the Kronig-Penny model.

The barrier layer may have any thickness as long as the tunnel effect can be maintained so that the quantum well effect can be obtained.
It is good to make it about 00 °.

The second cladding layer 3b has a thickness of 0.2 to 1
The thickness of the ohmic contact layer 3 is about 3 μm.
c is formed to a thickness of about 0.01 to 0.1 μm. The second ohmic contact layer 3c is made of gallium arsenide or the like.

The second cladding layer 3b is made of zinc (Zn) or the like.
1 × 10 ¹⁶-10¹⁸atom
s / cm^Three The second ohmic contact layer
3c is 1 × 10 of a reverse conductivity type semiconductor impurity such as zinc.¹⁹~
10²⁰atoms / cm^Three Content.

The second cladding layer 3b is made of aluminum gallium arsenide (AlxGa1-xA) similarly to the electron injection layer 2b.
s) and the like. The Al composition of the second cladding layer 3b is formed with x = about 0.4 to 0.7.

The insulating films 6a and 6b are made of silicon nitride or the like and have a thickness of about 3000 to 5000 °. The individual electrode 4 and the common electrode 5 are made of gold / chrome (Au / Au).
Ge / Cr) or the like, and is formed to a thickness of about 1 μm.

According to the LED array having such a configuration, FIG.
As shown in FIG. 2, the island-shaped semiconductor layers 2 and 3 composed of the one-conductivity-type semiconductor layer 2 and the opposite-conductivity-type semiconductor layer 3 are arranged in a row on the substrate 1, and the same individual Electrode 4
Are connected in two groups so that the lower one conductivity type semiconductor layer 2 connected to the same individual electrode 4 is connected to a different common electrode 5. By selecting the individual electrode 4 and the common electrode 5 and passing an electric current, it is used as a light source for exposure of a photosensitive drum for a page printer.

By dividing the common electrode 5 into two groups as described above, the number of pads of the common electrode is reduced by half, thereby reducing the number of wire bonding in mounting the LED array chip. In the present embodiment, the image is divided into two groups. However, the number of divisions is not limited to two, and may be divided into three or more. Also in this configuration, the individual electrodes and the divided common electrodes are selected so that the individual luminous bodies emit light independently.

(Method of Manufacturing LED Array) Next, a method of manufacturing the above-described LED array will be described.

First, a semiconductor layer 2 of one conductivity type and a semiconductor layer 3 of opposite conductivity type are sequentially laminated on a single crystal substrate 1 by MOCVD or the like.

When these semiconductor layers 2 and 3 are formed,
The substrate temperature is set to 400 to 500 ° C. and 200 to 200
After forming an amorphous gallium arsenide film to a thickness of 0 °, the substrate temperature is increased to 700 to 900 ° C. to form semiconductor layers 2 and 3 having a desired thickness.

In this case, TMG ((C
H_Three )_Three Ga), TEG ((C_Two H _Five )_Three Ga), Al
Shin (AsH_Three ), TMA ((CH_Three )_Three Al), TE
A ((C_Two H_Five )_Three Al) is used to control the conductivity type.
As a gas for controlling, silane (SiH_Four ), Sele
Hydrogen hydride (H_Two Se), TMZ ((CH_Three )_Three Zn)
H is used as the carrier gas._TwoEtc. are used
It is.

Next, semiconductor layers 2 and 3 are patterned in an island shape so that adjacent elements are electrically separated from each other. This etching is performed by wet etching using a sulfuric acid-hydrogen peroxide-based etchant, dry etching using CCl ₂ F ₂ gas, or the like.

After that, in the LED array shown in FIGS. 3 and 4, etching is performed so as to expose a part of one end of the one conductivity type semiconductor layer 2. This etching is also performed by wet etching using a sulfuric acid / hydrogen peroxide based etchant, dry etching using CCl ₂ F ₂ gas, or the like.

Next, a silane gas is formed by a plasma CVD method.
(SiH_Four ) And ammonia gas (NH _Three ) Using nitridation
An insulating film made of silicon is formed and patterned.
Then, chromium and gold are formed by vapor deposition or sputtering.
And patterning.

Thus, according to the LED array of the present invention,
The light emitting layer 3a is made of AlxGa1-xAs / AlyGa1-yAs (x
= 0.05 to 0.3, y = 0.15 to 0.4), it is possible to obtain high light emission on the short wavelength side near 685 nm, and particularly to the amorphous silicon photoreceptor. An LED head suitable for the drum was obtained.

The point that the luminous efficiency is improved in this way is that when the double hetero structure is used, the wavelength is due to the band gap of the luminescent layer. Need to be larger,
As described above, the Al composition must be further increased on the silicon substrate due to the stress generated in the film formation.
However, with the superlattice structure as described above, the emission wavelength can be controlled by the composition and thickness of the emission layer,
Therefore, it was not necessary to increase the Al composition, and as a result, the decrease in the emission intensity due to the increase in the Al composition ratio was eliminated.

(LED Head) Next, the LED head of the present invention will be described. This LED head has a plurality of LED arrays of the present invention arranged in a straight line, and the configuration thereof is conventionally known.

Since high light emission can be obtained on the short wavelength side near 685 nm, it is particularly suitable for an LED head suitable for an amorphous silicon photosensitive drum.

The inventor of the present invention has proposed that 700 nm or less, preferably 6 nm or less.
It is considered to be useful for LED heads having an emission wavelength of 90 nm or less.

[0097]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present inventor has proposed an LE having the configuration shown in FIGS.
The D array was manufactured by the above-mentioned manufacturing method.

The buffer layer 2a and the electron injection layer 2c of the one conductivity type semiconductor layer 2 are as follows.

The buffer layer 2a was formed of a gallium arsenide layer having a thickness of 2 μm, and the electron injection layer 2c was formed of an aluminum gallium arsenide layer (Al _0.6 Ga _0.4 As) having a thickness of 0.7 μm. Both the buffer layer 2a and the electron injection layer 2c contained silicon as one conductivity type semiconductor impurity.

As for the reverse conductivity type semiconductor layer 3, the well layer of the light emitting layer 3a is made of Al _0.15 Ga _0.85 As,
Of thickness. Further, the barrier layer was made of Al _0.35 Ga _0.65 As, and its thickness was set to 100 °. All were non-doped.

The cladding layer 3b has a thickness of 0.4 μm.
Aluminum gallium arsenide (Al _0.6Ga_0.4As)
And the ohmic contact layer 3c is 0.01 μm
And formed with gallium arsenide.

Both the second cladding layer 3b and the ohmic contact layer 3c contained zinc (Zn) as a semiconductor impurity of the opposite conductivity type. The LED array thus obtained is referred to as Example 1.

Further, Example 2 was manufactured in which the structure of the light emitting layer 3a was changed and the other structures were completely the same.

That is, the light emitting layer 3a has a well layer of Al.
The thickness was _0.2 Ga _0.8 As and the thickness was 40 °. Further, the barrier layer is made of Al _0.4 Ga _0.6 As and has a thickness of 100 mm.
I made it. All were non-doped.

Then, these Examples 1 and 2 were converted to 600 dp.
i was configured as an LED array for an LED printer.

According to this LED array, about 20 × 20
μm light emitting diodes are arranged at a pitch of 42.3 μm, and 128 LED elements are used as one LED array chip.

Then, these LEDs were individually lit, and the characteristics were evaluated using their average values.

When the emission intensities in Examples 1 and 2 were measured, the results shown in FIG. 5 were obtained.

As comparative examples, in the LED arrays shown in FIGS. 6 and 7, and the LED arrays shown in FIGS. This comparative example is shown in FIG.
Indicates that there is no superlattice. Note that both LED arrays have the same characteristics.

The horizontal axis of the figure is the current flowing through the LED.
The vertical axis is the emission intensity.

As is clear from the results, Example 1,
The LED array No. 2 obtained a significantly higher light emission intensity than the comparative example.

The emission wavelength of Example 1 was 680 n
m, and the emission wavelength of Example 2 is 689 nm. Further, conventionally, it is 685 nm.

Next, the present inventor measured the relationship between the Al composition ratio in the well layer of the light emitting layer and the light emission intensity in the LED array of Example 1, and the result shown in FIG. 10 was obtained.

The light emission intensity was obtained by preparing and evaluating a 600 dpi LED array, and is the light emission intensity when a current of 10 mA flows.

The barrier layer has an Al composition ratio of 0.4 and a thickness of 1
The wavelength was set to 00 °, and the film thickness was changed in accordance with the Al composition ratio of the well layer so that the wavelength was within the range of 680 nm to 690 nm.

As is clear from the figure, the Al composition ratio of the well layer is 0.05 to 0.35, preferably 0.15 to 0.35.
At 25, the light emission intensity is significantly increased.

The inventor of the present invention has made it impossible to increase the Al composition of the cladding layer because the film is formed on the silicon substrate. It is considered that the luminous efficiency decreases when the value is increased.

Further, when the Al composition ratio is reduced to less than 0.05, it is necessary to reduce the film thickness to about several tens of millimeters in order to make the wavelength 685 nm. However, as a result, it is considered that the light emission intensity is reduced.

The present inventor measured the relationship between the Al composition ratio and the luminous intensity in the well layer of the luminous layer in Example 2. The results shown in FIG. 10 were repeatedly obtained. Confirmed by experiments.

Next, the present inventor measured the relationship between the Al composition ratio in the barrier layer of the light emitting layer and the light emission intensity in the LED array of Example 1, and obtained the result shown in FIG.

This light emission intensity was obtained by preparing and evaluating an LED array of 600 dpi, and is the light emission intensity when a current of 10 mA flows.

The Al composition ratio of the well layer is set to 0.15, the thickness of the barrier layer is set to 100 °, and the film thickness is changed according to the Al composition ratio of the barrier layer so that the wavelength is 680 nm or more.
It was designed to be within the range of 690 nm.

As is apparent from the results shown in FIG. 11, the Al composition ratio of the barrier layer is set to be larger than the Al composition of the well layer, and is more preferably 0.25 to 0.45, preferably 0.30 to 0.45.
It is good to set to 0.40.

The point that the Al composition ratio of the barrier layer is made larger than the Al composition of the well layer must be confined to the well layer, so that the band gap of the barrier layer is made larger than that of the well layer.

As described above, the upper limit of the Al composition ratio is defined when the Al composition ratio of the barrier layer exceeds 0.45.
As described above, the adverse effect caused by forming a film on the silicon substrate becomes remarkable, and the light emission intensity decreases.

Further, the inventor of the present invention provided AlxG as a light emitting layer on both the silicon substrate and the GaAs substrate.
In the LED array provided with the super lattice structure of a1-xAs / AlyGa1-yAs, the superiority between the two was examined, and the results shown in Table 14 were obtained.

The LED arrays using the silicon substrate are the first and second embodiments, and the LED array using the GaAs substrate
In the ED array, only the substrate was changed,
Other configurations are the same as those of the first and second embodiments. Note that substantially the same result was obtained between Example 1 and Example 2.

The emission intensity was measured and evaluated.
To do this, a 600 dpi LED array was created and a current of 10 mA was passed.

FIG. 14 shows the Al composition ratio of the well layer,
These are experimental data that measure the relationship with the film thickness and define their preferred ranges.

That is, as shown in FIG.
When the l composition ratio exceeds 0.20, the emission intensity tends to decrease.
The emission intensity increases as the values increase to 0, 0.15, and 0.20. Within these composition ratio ranges, the optimum film thicknesses are determined.

As is evident from the results, when the film is formed on the silicon substrate, the thickness of the well layer may be reduced as compared with the film formed on the GaAs substrate.

According to experiments repeatedly conducted by the present inventor, it has been found that even if the thickness of the well layer is reduced, if the thickness is less than 25 °, it becomes difficult to control the thickness and the reproducibility is poor. Therefore, the thickness is preferably set to 25 ° or more.

[0133]

As described above, according to the LED array of the present invention, a plurality of island-shaped semiconductor layers formed by sequentially laminating a semiconductor layer of one conductivity type, a semiconductor layer of opposite conductivity type and one electrode on a silicon substrate are provided. The light emitting layer of the opposite conductivity type semiconductor layer is AlxG
a1-xAs / AlyGa1-yAs (x = 0.05-0.3
5, y = 0.15 to 0.4) makes it possible to obtain high light emission on the short wavelength side near 700 nm or less, and particularly to an LED suitable for an amorphous silicon photosensitive drum. The head is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an LED array of the present invention.

FIG. 2 is a schematic plan view of the LED array of the present invention.

FIG. 3 is a schematic sectional view of another LED array of the present invention.

FIG. 4 is a schematic plan view of another LED array of the present invention.

FIG. 5 is a diagram showing a relationship between a current value and light emission intensity in the LED array.

FIG. 6 is a schematic sectional view of a conventional LED array.

FIG. 7 is a schematic plan view of a conventional LED array.

FIG. 8 is a schematic sectional view of another conventional LED array.

FIG. 9 is a schematic plan view of another conventional LED array.

FIG. 10 is a diagram showing the relationship between the Al composition ratio of the well layer of the light emitting layer and the light emission intensity according to the LED array of the present invention.

FIG. 11 is a diagram showing the relationship between the Al composition ratio of the barrier layer of the light emitting layer and the light emission intensity according to the LED array of the present invention.

FIG. 12 shows a clad layer Al according to a conventional LED array.
FIG. 3 is a diagram illustrating a relationship between a composition ratio and emission intensity.

FIG. 13 shows a clad layer Al according to a conventional LED array.
FIG. 3 is a diagram illustrating a relationship between a composition ratio and a driving voltage.

FIG. 14 is a diagram showing a relationship between an Al composition ratio and a film thickness of a well layer of a light emitting layer according to the LED array.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Silicon semiconductor substrate 2 ... One conductivity type semiconductor layer 2a ... Buffer layer 2b ... Electron injection layer 2c ... Electron injection layer 3 ... Reverse conductivity type semiconductor layer 3a ... Light emitting layer 3b ... Cladding layer 3c ... Ohmic contact layer 4 ... Individual electrode 5: Common electrode 6: Insulating film

Claims (3)

[Claims] 1. A plurality of island-shaped semiconductor layers, which are formed by sequentially laminating a semiconductor layer of one conductivity type, a semiconductor layer of opposite conductivity type and one electrode on a silicon substrate, and forming the other electrode on the back surface of the silicon substrate. The light emitting layer of the opposite conductivity type semiconductor layer is formed of AlxGa1-xAs / AlyGa1-yA.
s (x = 0.05 to 0.35, y = 0.25 to 0.4
LED having a superlattice structure comprising 5)
array. 2. A method according to claim 1, wherein a plurality of island-shaped semiconductor layers are sequentially formed on the silicon substrate by sequentially laminating one conductivity type semiconductor layer, the opposite conductivity type semiconductor layer, and one electrode. An LED array having the other electrode formed thereon, wherein the light emitting layer of the opposite conductivity type semiconductor layer is formed of AlxGa1-xAs / AlyG.
a1-yAs (x = 0.05-0.35, y = 0.25
0.45) An LED array having a superlattice structure comprising: 3. An LED head comprising a plurality of LED arrays according to claim 1 or 2 arranged in a straight line.