JP3187213B2 - Light emitting and receiving diode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting and receiving diode having both a light receiving function and a light emitting function.

[0002]

2. Description of the Related Art Conventionally, electrophotographic printing apparatuses have been used in copiers, printers and the like. In this manner, in the case of forming the selectively exposed electrostatic latent image of the photosensitive surface of the photosensitive drum, the emission using a semiconductor laser or a light emitting diode (L ight E mitting D iode, hereinafter LED) as an exposure light source Is exposed while on / off control is performed for each pixel. Alternatively, a fluorescent lamp or a cold-cathode tube is used as an exposure light source, and light from the exposure light source is irradiated on a photosensitive surface through a liquid crystal shutter to open and close the liquid crystal shutter in pixel units.

A printing apparatus using an LED as an exposure light source for forming an electrostatic latent image has an advantage that printing can be performed at a high speed and at a high resolution.
There is one disclosed in Japanese Patent No. 30154. In order to further reduce the cost and size of the device, a device using an LED as both an exposure light source for forming an electrostatic latent image and an image sensor for reading an image (hereinafter, an integrated printing and reading device) has been proposed. . An example of such an apparatus is disclosed in Japanese Patent Application Laid-Open No. 58-157252.

FIG. 7 is a perspective view of an essential part showing an example of the structure of an integrated printing / reading apparatus, and shows a state in which a document image to be recorded is read. In FIG. 1, reference numeral 10 denotes a wiring board, and reference numerals 12 and 14 denote an LED array and a control IC provided on the wiring board 10. A plurality of LEDs, for example, 64 LEDs are arranged and integrated in the arrangement direction A, and the LED array 12 is constituted by these. And a plurality of LED arrays 12
Are arranged in the arrangement direction A. Further, a control IC 14 is provided for each LED array 12, and the corresponding LED array 12 and control IC 14 are electrically connected.

Reference numeral 16 denotes a document positioned at a predetermined position on a transparent document mounting plate (not shown). Reference numerals 18 and 20 denote a converging lens array and an illumination light source provided between the document mounting plate and the LED array 12. Show. Arrangement of multiple converging lenses in direction A
And the lens is fixed to the holder 22, and the convergent lens array 18 is constituted by these. Further, a converging lens array 18
The LED array 12 and the LED array 12 are opposed to each other so that their optical axes coincide with each other, and illumination light sources 20 are provided on both sides of the converging lens array 18.

When reading an original image, an illumination light source 20 is used.
The light L1 from the light source is irradiated onto the document 16 and the reflected light L2 is incident on the LED array 12 via the converging lens array 18. The reflected light L2 has a light intensity corresponding to the density of the document 16 and forms a document image. On the other hand, when reflected light L2 is incident on the pn junction of the LED while a reverse voltage is applied, electrons or holes in an amount proportional to the intensity of the reflected light are excited and move in the depletion layer of the pn junction. As a result, a current flows through the pn junction. By detecting this current, the original image can be converted into an electric signal.

Reference numeral 24 denotes a light shielding plate provided between the illumination light source 20 and the LED array 12. The light shielding plate 24 is arranged so that light other than the light L2 from the converging lens array 18 does not enter the LED array 12.

In such an integrated printing / reading apparatus, the light L1 used for reading the original 16 has a wavelength of 380.
680 nm visible light, so the LED must receive visible light. Organic photosensitive drums, which are inexpensive to manufacture, are widely used as photosensitive drums. Since the organic photoconductor drum has high sensitivity to light having a wavelength of 660 to 780 nm, the emission wavelength of the LED is generally 660 to 780 nm.

FIGS. 8A and 8B are a plan view and a cross-sectional view schematically showing a main part of the LED array.
(B) shows a cross section taken along line VIIIB-VIIIB in FIG. 8 (A). The LED 26 electrically connects the n-layer 28 and the p-layer 30 forming a pn junction, the n-side electrode 32 and the p-side electrode 34 electrically connected to the n-layer 28 and the p-layer 30, and the n-layer 28 and the p-side electrode 34. And an interlayer insulating film 36 having a window 36a exposing the p-layer 30.

The LED 26 is manufactured, for example, as follows. First, the _{n-GaAs X} P _1-X wafer is prepared as n layer 28, laminating the interlayer insulating film 36 on the layer 28.
The interlayer insulating film 36 is a transparent film made of SiO, SiN or SiON. Thereafter, a window 36a is formed in the interlayer insulating film 36, and the n-layer 28 in the p-layer formation region is exposed through the window 36a.

Next, Zn is thermally diffused into the n-layer 28 through the window 36a by using a sealed tube method as an impurity introduction technique. A p layer 30 is formed in the Zn diffusion region. The interlayer insulating film 36 has a thickness or material that does not transmit Zn and acts as a diffusion mask. Zn diffuses not only in a direction perpendicular to the wafer surface but also in a direction parallel to the wafer surface. Therefore, the p layer 30 is formed not only in the region inside the window 36a but also below the interlayer insulating film 36 around the window 36a. If the depth from the wafer surface to the pn junction interface is referred to as the pn junction depth, the pn junction 3 having a large pn junction depth is formed in the region inside the window 36a.
8a are formed, and a pn junction 38b having a shallow pn junction depth is formed around the periphery of the window 36a. The pn junction depth of the deep pn junction 38a is generally controlled such that the maximum emission output intensity is obtained at the emission wavelength desired when using the LED. Here, control is performed so that the maximum light emission output intensity is obtained at a wavelength of 660 to 780 nm at which the light sensitivity of the organic photosensitive drum increases.

Next, a p-side electrode 34 is formed on the p-layer 30. Further, the n-side electrode 3 is provided on the opposite side of the n-layer 28 from the p-layer 30.
Form 2

[0013]

When the photoelectric conversion characteristics when the LED 26 is used as the light receiving element are experimentally examined, the following can be found. FIG. 9 shows the results of this experiment. In the same figure, VIIIB of FIG.
The sectional structure of the main part of the LED 26 taken along line -VIIIB is shown. The position X in the direction along the VIIIB-VIIIB line is shown on the horizontal axis of the experimental result, and the photoelectric conversion current generated when the scanning light is applied to the p-layer 30 at the position X is shown on the vertical axis. In the experiment, a scanning light having a sufficiently small spot size as compared with the p-layer 30 was irradiated from a direction perpendicular to the p-layer 30 using the LED 26 designed to emit light at a wavelength of 740 nm. Then, the wavelength of the scanning light is set to 550 and 740.
The scanning light was scanned along the line VIIIB-VIIIB for each wavelength, and the photoelectric conversion current at the position X was measured. The solid and dotted curves in the figure indicate the scanning light wavelengths of 550 and 7 respectively.
The experimental results when 40 nm are set are shown.

As can be understood from the drawing, the wavelength of the scanning light is set to a wavelength in a visible region suitable for reading an original image, for example, 550 nm.
In this case, the photoelectric conversion current is large at the shallow pn junction 38b and small at the deep pn junction 38a.
On the other hand, when the wavelength of the scanning light is set to a wavelength longer than the wavelength in the visible region, for example, 740 nm, the photoelectric conversion current becomes shallow pn.
It increases at both the junction 38b and the deep pn junction 38a.

The reason is considered as follows. That is, since the visible light has a short wavelength, it can reach only a relatively shallow region of the p-layer 30, and the amount of light reaching the deep pn junction 38a is extremely small. As a result, in the case of visible light, the amount of photoelectric conversion at the deep pn junction 38a decreases. On the other hand, light having a longer wavelength than visible light is
Deep pn junction 38
The amount of light reaching a is greater. As a result, in the case of light having a long wavelength, the amount of photoelectric conversion at the deep pn junction 38a increases.

As described above, the light receiving function of the LED 26 is performed by the shallow pn junction 38b, but in the conventional LED 26, the shallow pn junction 38b is formed only below the interlayer insulating film 36 around the window 36a. Moreover, a shallow pn junction 3
8b is formed linearly. Therefore, since the width of the shallow pn junction 38b is very small, it is difficult to increase the light receiving sensitivity.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a light emitting and receiving diode capable of increasing the light receiving sensitivity as compared with the conventional one.

[0018]

In order to achieve this object, a light-emitting / receiving diode according to the present invention comprises an n-GaAsP first semiconductor layer and a p-GaAsP second semiconductor layer forming a pn junction, and a second light-emitting diode. The thickness of the semiconductor layer is 0.3 to 2 μm
, And the impurity concentration of the second semiconductor layer is set to 5 × 10 ²⁰ to 10 ²³ cm ⁻³ .

[0019]

According to the present invention, the light receiving sensitivity of the light emitting and receiving diode is increased by the thickness of the second semiconductor layer, and the emission intensity of the light emitting and receiving diode is increased by the impurity concentration of the second semiconductor layer.

According to the present invention, the light receiving sensitivity to visible light can be increased by setting the thickness of the second semiconductor layer to 0.3 to 2 μm. In addition, by making the thickness of the second semiconductor layer substantially constant over substantially the entire surface, the area of the region having the light receiving function can be increased.

The impurity concentration of the second semiconductor layer is 5 × 10
With ²⁰ to 10 ²³ cm ^-3, the emission intensity of the light emitting and receiving diodes, can be a size suitable for practical use.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. The drawings are only schematically shown to the extent that the invention can be understood, and thus the invention is not limited to the illustrated examples.

FIG. 1 is a cross-sectional view of a main part schematically showing the configuration of the embodiment. The light emitting and receiving diode of this embodiment includes an n-GaAsP first semiconductor layer 40 forming a pn junction and a p-type semiconductor layer.
The GaAsP second semiconductor layer 42 is provided. The layer thickness D of the second semiconductor layer 42 is set to a substantially constant layer thickness in the range of 0.3 to 2 μm, and the second semiconductor layer 42 that spreads in a plane with the substantially constant layer thickness D is formed. The impurity concentration of the second semiconductor layer 42 is set to 10 ²⁰ to 10 ²³ cm ⁻³ .

In this embodiment, the first semiconductor layer 40 is n-
A GaAs _0.8 P _0.2 substrate, wherein the second semiconductor layer 42 is a p-GaAs layer formed by thermally diffusing impurities such as Zn on one substrate surface 40 a side of the first semiconductor layer 40.
_0.8 P _0.2 layer. Here, the layer thickness D of the second semiconductor layer 42 is a depth (pn junction depth) from one substrate surface 40a to the pn junction interface.

On one substrate surface 40a, an interlayer insulating film 44 and a p-side electrode 46 are sequentially provided. Interlayer insulating film 4
4 is an Al ₂ O ₃ film and the p-side electrode 46 is an Al electrode.
The interlayer insulating film 44 has a window 44 a exposing the second semiconductor layer 42.
And the p-side electrode 46 is electrically connected to the second semiconductor layer 42 through the window 44a. On the other substrate surface 40b of the first semiconductor layer 40, an n-side electrode 48 is provided. n-side electrode 4
8 is an alloy electrode made of Au, Ge and Ni.

A method for manufacturing the light emitting and receiving diode of this embodiment will be described with reference to an example. 2 and 3 are cross-sectional views of main parts showing main steps of this manufacturing method step by step, and show cross sections corresponding to FIG.

First, as the first semiconductor layer 40, for example, n-
A GaAs _0.8 P _0.2 substrate is prepared. GaAs _0.8 P
_0.2 is a material conventionally used when the emission wavelength of the light receiving and emitting diode is 740 nm. Then, an interlayer insulating film 44 is stacked on one substrate surface 40a of the first semiconductor layer 40 by using a thin film forming technique (FIG. 2A). The interlayer insulating film 44 has a material and / or thickness that does not transmit impurities diffused into the first semiconductor layer 40, and an Al ₂ O ₃ layer is stacked as the interlayer insulating film 44 by, for example, a sputtering method.

Next, a portion of the interlayer insulating film 44 is selectively removed using photolithography and etching techniques to form a window 44a in the interlayer insulating film 44 (FIG. 2B). The window 44a exposes the first semiconductor layer 40 in a region where the second semiconductor layer 42 is to be formed, and the interlayer insulating film 4 having the window 44a is provided.
4 is used as a mask for impurity diffusion.

Next, a diffusion control layer 50 is laminated on the interlayer insulating film 44 by using a thin film forming technique (FIG. 2C). The diffusion control layer 50 covers the first semiconductor layer 40 in a region corresponding to the window 44a. The diffusion control layer 50 is formed, for example, by plasma CVD.
Si laminated by (Chemical Vapor Deposition) method
The amount of impurities diffused into the first semiconductor layer 40, that is, the impurity concentration of the second semiconductor layer 42 is controlled by arbitrarily and suitably selecting the material and / or thickness of the diffusion control layer 50, which is the N layer.

Next, Zn as an impurity is diffused through the interlayer insulating film 44 and the diffusion control layer 50 into the first semiconductor layer 40 in a region corresponding to the window 44a.
Next, a p-GaAs _0.8 P _0.2 second semiconductor layer 42 is formed (FIG. 3A). Here, the second semiconductor layer 42 having a substantially constant layer thickness D and a planar spread is formed over substantially the entire area corresponding to the window 44a.

At the time of diffusion, the first semiconductor layer 40 is
The substrate is kept in an atmosphere containing Zn vapor while being heated. By appropriately and suitably selecting the heating temperature and the Zn vapor concentration in the atmosphere at this time, the diffusion depth of Zn, that is, the layer thickness D of the second semiconductor layer 42 is obtained. Control. The layer thickness D of the region mainly corresponding to the window 44a is controlled to be a substantially constant value within a range of 0.3 to 2 μm, for example, 1 μm. The impurity concentration of the second semiconductor layer 42 is controlled by the Zn vapor concentration and the material and / or thickness of the diffusion control layer 50 as described above. The impurity concentration of the second semiconductor layer 42 is set to 10 ²⁰ to 10
Control is performed to a certain value within the range of ²³ cm ^-3 , for example, 10 ²¹ cm ^-3 . The thickness D can also be controlled by the material and / or thickness of the diffusion control layer 50.

Next, the diffusion control layer 50 is selectively removed by using an etching technique to expose the interlayer insulating film 44.
For example, it is removed by wet etching using HF. Thereafter, an electrode material 52 is laminated on the interlayer insulating film 44 by a thin film forming technique (FIG. 3B). Electrode material 52
For example, Al is laminated by a sputtering method.

Next, the p-side electrode 46 is formed by processing the electrode material 52 into a predetermined shape using photolithography and etching techniques (FIG. 3C). Thereafter, an n-side electrode 48 is formed on the other substrate surface 40b of the first semiconductor layer 40 (FIG. 1), and the light emitting and receiving diode of this embodiment is completed. The light receiving and emitting diode is suitable for use in forming a diode array that is used both as an image sensor and an exposure light source of an electrophotographic system.

FIG. 4 shows GaAs _0.8 P versus incident light wavelength.
It is a figure showing signs of a change of an absorption coefficient of _0.2 . The horizontal axis of the figure shows the wavelength (μm) of light incident on GaAs _0.8 P _0.2 , and the vertical axis shows the absorption coefficient (cm ⁻¹ ) of GaAs _0.8 P _0.2
Is shown in logarithmic notation. Here, GaAs _0.8 which is generally used when manufacturing a light emitting diode having an emission wavelength of 740 nm is used.
_Pay attention to P _0.2 .

The light intensity I of the incident light that has traveled the distance x in GaAs _0.8 P _0.2 is 37% of the light intensity I ₀ at the time of incidence.
Assuming that the distance has attenuated to (I = (1 / e) · I ₀ ), the distance x at this time can be calculated using the absorption coefficient.

A wavelength around 550 nm (almost 500 to 600)
The absorption coefficient of GaAs _0.8 P _0.2 with respect to the incident light (in the range of nm) is about 1 × 10 ^{4 to} 3 × 10 ⁴ cm ⁻¹ (see FIG. 4). It is about 0.3 to 0.7 μm. In addition, the wavelength
The absorption coefficient of GaAs _0.8 P _0.2 with respect to incident light of 40 nm is about 1 × 10 ³ cm ⁻¹ (see FIG. 4). When the distance x in this case is calculated, the distance x is about 10 μm. As can be understood from these, 550 nm
Visible light in the vicinity can reach only a very shallow surface layer of GaAs _0.8 P _0.2 .

Therefore, in order to obtain a practically satisfactory light receiving sensitivity for visible light near 550 nm, the lower limit (I _MIN. ) Of the incident light intensity I at which photoelectric conversion can be performed is defined as I _MIN.
Considering (1 / e) · I ₀ as a rough guide, GaAs
_It is considered that the second semiconductor layer 42 should be formed so that the depletion layer exists at a depth within _0.3 to 0.7 μm from the _0.8 P _0.2 surface layer. Therefore, it is considered that the thickness D of the second semiconductor layer 42 should be approximately 0.3 to 0.7 μm.

On the other hand, the inventors of the present application set the Zn concentration of the second semiconductor layer at 10 ¹⁹ to 10 ²⁰ cm ^−3, which is the same as the conventional one, and set the layer thickness of the second semiconductor layer to 0.5, 1, 2 The light-receiving and light-emitting diodes were manufactured in the same manner as in the above-described embodiment, and an experiment was conducted to examine the light-receiving sensitivity of each of the light-receiving and light-emitting diodes. In the experimental example in which the thickness of the second semiconductor layer was 0.5 μm, a pn junction could not be formed, and thus the light receiving sensitivity could not be examined. This is because of the current impurity diffusion technology, the layer thickness is 0.5 μm.
This is because it is extremely difficult to form the following second semiconductor layer. Within the range in which a pn junction can be formed,
The light receiving sensitivity was best when the layer thickness of the second semiconductor layer was 1 μm. The light receiving sensitivity when the layer thickness of the second semiconductor layer was 2 μm was about ／ of the light receiving sensitivity when the layer thickness of the second semiconductor layer was 1 μm, which was practically satisfactory. When the thickness of the second semiconductor layer was 5 μm, a practically satisfactory light receiving sensitivity could not be obtained.

Considering the above, it can be considered that by setting the thickness D of the second semiconductor layer 42 to a value within the range of approximately 0.3 to 2 μm, it is possible to obtain practically satisfactory light receiving sensitivity. it can. In addition, since the second semiconductor layer 42 is formed in a planar shape with a substantially constant layer thickness D, the area of the region contributing to light reception becomes wider than before, so that the light reception sensitivity can be higher than before.

FIG. 5 is a diagram showing the relationship between the layer thickness D of the light emitting and receiving diode and the light emission intensity. The horizontal axis in the figure is the layer thickness D (μ
m) and the vertical axis indicate light emission intensity (unit: arbitrary). In the drawing, the thickness of the second semiconductor layer is variously changed, the Zn concentration of the second semiconductor layer is set to 10 ²⁰ and 10 ²¹ cm ^-3, and the light-emitting / receiving diode is manufactured in the same manner as in the above-described embodiment. Manufacture and emit light intensity of each light receiving and emitting diode (light output)
The result of having investigated is shown. Zn concentration of 10 ²⁰ and 10 ²¹ cm
Curves a and b show the relationship between the layer thickness D and the luminous intensity when ^-3 is set. The emission intensity when the Zn concentration is 10 ²⁰ cm ⁻³ is relatively expressed assuming that the maximum emission intensity in this case is 1, and the emission intensity when the Zn concentration is 10 ²¹ cm ⁻³ is the maximum in this case. It is relatively expressed assuming that the emission intensity is 1.

As can be understood from the curve a, when the Zn concentration is set to 10 ²⁰ cm ^-3 , the thickness of the second semiconductor layer is set to 6
The emission intensity becomes maximum when the thickness is set to 発 光 8 μm, and the emission intensity decreases as the pn junction depth becomes shallower or deeper. This is for the following reason.
That is, the layer thickness of the second semiconductor layer (p of the light emitting / receiving diode)
If the n-junction depth is small, electron-hole carriers contributing to light emission are more likely to be trapped in impurity levels or defect levels on the surface of the second semiconductor layer, thereby lowering light emission efficiency. Therefore, it is better to increase the thickness of the second semiconductor layer to some extent in order to increase the luminous efficiency. On the other hand, in the p-type second semiconductor layer, the absorption coefficient for the light of the emission wavelength increases, so that when the thickness of the second semiconductor layer is large, the light is absorbed by the second semiconductor layer while propagating through the second semiconductor layer. And therefore p
This is because the light absorption amount increases as the n-junction depth increases.

However, as can be understood from the curve b, when the Zn concentration is 10 ²¹ cm ⁻³ , the light emission intensity can be maximized when the thickness of the second semiconductor layer is 1 to 2 μm. Moreover, although the maximum light emission intensity in the curve b is lower than the maximum light emission intensity in the curve a, there is no problem in forming an electrostatic latent image on the photosensitive drum, and therefore, it is practically satisfactory. Thus, even if the thickness of the second semiconductor layer is reduced, it is considered that a light-emitting / receiving diode having an emission intensity that is practically satisfactory can be manufactured by increasing the Zn concentration of the second semiconductor layer.

FIG. 6 is a diagram for explaining the design conditions of the light emitting / receiving diode. The abscissa of the figure shows the Zn concentration (cm ⁻³ ) of the second semiconductor layer, and the ordinate shows the layer thickness (μm) of the second semiconductor layer in logarithmic representation. In the figure, the Zn concentration of the second semiconductor layer was changed stepwise, and the layer thickness of the second semiconductor layer at which the light emission intensity became maximum was experimentally examined at each step.
Then, a combination of the Zn concentration and the layer thickness of the second semiconductor layer at which the maximum emission intensity was obtained was obtained. A curve c is obtained by plotting and smoothing the values of this combination.

In designing the light emitting / receiving diode, particularly the second semiconductor layer, first, the thickness of the second semiconductor layer is set to a value in the range d of 0.3 to 2 μm in order to enhance the light receiving sensitivity. This range d is indicated by hatching in the figure. Next, let us consider a Zn concentration that maximizes the emission intensity in the range d.
As can be understood from the curve c, even if the layer thickness of the second semiconductor layer is reduced, the emission intensity can be maximized by increasing the Zn concentration. Within the range d, Zn
The emission intensity can be maximized by setting the concentration to approximately 5 × 10 ²⁰ cm ⁻³ or more. On the other hand, if the Zn concentration is too high, the semiconductor crystal will be seriously damaged. In order to suppress damage to the semiconductor crystal to a practically satisfactory level, it is desired that the Zn concentration be approximately 10 ²³ cm ⁻³ or less.

Therefore, the thickness of the second semiconductor layer is set to about 0.3
By setting the thickness to about 2 μm (about 0.3 μm or more and 2 μm or less), it is possible to obtain a light-receiving sensitivity suitable for practical use. In this case, the Zn concentration of the second semiconductor layer is set to 5 × 10 ²⁰ to 10
It is considered that the emission intensity suitable for practical use can be obtained by setting to ²³ cm ^-3 (approximately 5 × 10 ²⁰ cm ^-3 or more and 10 ²³ cm ^-3 or less).

The present invention is not limited only to the above-described embodiments, and accordingly, the shapes, arrangement positions, forming techniques, forming materials, numerical conditions, and others of the components can be arbitrarily and suitably changed.

For example, in the above-described embodiment, the case where GaAs _0.8 P _0.2 is used as the first and second semiconductor layers has been described, but the composition ratio X of GaAs _X P ₁ -X is set to a value other than 0.8. It is considered that the present invention can also be applied to such cases.

The second semiconductor layer may be formed by a technique other than the thermal diffusion technique of impurities, for example, a liquid phase epitaxial method. Zn as an impurity of the second semiconductor layer
Other than these may be used.

[0049]

As is apparent from the above description, according to the light emitting and receiving diode of the present invention, the light receiving sensitivity to visible light can be increased by setting the thickness of the second semiconductor layer to 0.3 to 2 μm. can do. In addition, by making the thickness of the second semiconductor layer substantially constant over substantially the entire surface, the area of the region having the light receiving function can be increased.

The impurity concentration of the second semiconductor layer is 5 × 10
With ²⁰ to 10 ²³ cm ^-3, the emission intensity of the light emitting and receiving diodes, can be a size suitable for practical use.

Therefore, it is possible to provide a light emitting / receiving diode having higher light receiving sensitivity than the conventional one and having a light emission intensity suitable for practical use.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing a configuration of a main part of an embodiment.

FIGS. 2A to 2C are cross-sectional views illustrating an example of a manufacturing process of the embodiment.

FIGS. 3A to 3C are cross-sectional views illustrating an example of a manufacturing process according to the embodiment.

FIG. 4 is a diagram showing the relationship between the wavelength of incident light and the absorption coefficient in GaAsP.

FIG. 5 is a diagram showing a relationship between a layer thickness of a second semiconductor layer and light emission intensity.

FIG. 6 is a diagram provided for describing design conditions of a light receiving and emitting diode.

FIG. 7 is a perspective view showing a configuration of a main part of the integrated printing / reading apparatus.

FIGS. 8A and 8B are a plan view and a cross-sectional view illustrating a configuration of a main part of an LED array.

FIG. 9 is a diagram showing photoelectric conversion characteristics of an LED having a conventional structure.

[Explanation of symbols]

 40: n-GaAsP first semiconductor layer 42: p-GaAsP second semiconductor layer

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01L 31/10 31/12 (56) References JP-A-57-78186 (JP, A) JP-A-57-30389 (JP, A) JP-A-55-86174 (JP, A) JP-A-55-98880 (JP, A) JP-A-49-16394 (JP, A) JP-A-50-3282 (JP, A) JP-A Sho 60 -110177 (JP, A) JP-A-58-107689 (JP, A) JP-A-58-157252 (JP, A) JP-A-64-35970 (JP, A) Technical report of IEICE 85 [194] (1985) p. 43-48 SSD85-98 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 33/00 B41J 2/44 B41J 2/45 B41J 2/455 H01L 31/10 H01L 31/12 JICST file (JOIS )

Claims (3)

(57) [Claims] 1. A light emitting and receiving diode comprising an n-GaAsP first semiconductor layer and a p-GaAsP second semiconductor layer forming a pn junction, wherein the layer thickness of the second semiconductor layer is in the range of 0.3 to 2 μm. almost constant layer thickness, the second 5 × 10 the impurity concentration of the semiconductor layer of the inner ²⁰ to 10 ²³ c
m- ³ . 2. The light emitting and receiving diode according to claim 1, wherein the impurity added to the second semiconductor layer is Zn. 3. The light emitting and receiving diode according to claim 1, wherein an impurity is added to the first semiconductor layer by thermal diffusion to form the second semiconductor layer.