JPH0719917B2 - Light emitting / light receiving integrated device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-emitting / light-receiving integrated device having the same structure and the same composition, one of which emits light and the other of which receives and detects reflected light. is there.

2. Description of the Related Art Conventionally, as a character or image reading detector for a facsimile or a copying machine, a method is known in which light is applied from the outside and the reflected light is read by a photodiode. A method using a light emitting diode as an external light source is also known. However, it is not possible to obtain a diode having the same structure and the same composition integrated on the same substrate and which can be used for both light emission and light reception and which shows excellent characteristics. This is for the following reason.

The structure of a conventional light emitting element (light emitting diode) is shown in FIG.
The structure of a conventional light receiving element (avalanche photodiode) is shown in FIG. First, in FIG. 4, 10 is an n-type alxGAl
-XAs (x = 0.03), 11 is n + type AlxGal-xAs, 12 is p +
Types AlxGal-xAs, 13 and 14 are ohmic electrodes. When the ohmic electrode 14 is positively biased and the ohmic electrode 13 is negatively biased, the injected electrons and holes are recombined at the pn junction interface to emit light.

Next, in FIG. 5, 15 is p + type AlxGal-xAs, 16 is P
Type AlxGal-xAs, 17 is n + type AlxGal-xAs, and 18 and 19 are electrodes. When the electrode 18 is biased to be negative and the electrode 19 is biased to be positive so that light is incident from the end face, the light just causes p-type AlxGal.
The charges excited at the interface between -xAs16 and n + -type AlxGal-xAs17 cause the p region of p-type AlxGal-xAs16 to change to p + -type AlxGal-xAs15.
In the course of traveling toward the ground, it is multiplied by the avalanche effect, and is collected in the electrode 18 through the p + type AlxGal-xAs15 and flows as a current.

In the light emitting diode of the embodiment shown in FIG. 4, the composition of AlxGal-xAs is x = 0.03, and the emission wavelength at this time is Al.
Corresponding to the energy band gap of xGal-xAs,
It becomes 0.8um. On the other hand, in the avalanche photodiode of the embodiment of FIG. 5, if the composition of AlxGal-xAs is x = 0.03 as in the case of the light emitting diode, AlxGal-xAs
It corresponds to the energy band gap of xAs and becomes a photodiode with a sensitivity of about 0.8um.

However, if the light emitted from this light emitting diode is received by this avalanche photodiode, almost no sensitivity is obtained. This is for the following reason.

The energy bandgap of AlxGal-xAs at x = 0.03 is 1.4614 eV at room temperature, and the corresponding light wavelength is
It is 0.848um. Therefore, light having a shorter wavelength than this is excited, but the emission center wavelength of the actual light emitting diode of the conventional example is only slightly shorter than this. This is because light having a too short wavelength is absorbed before it reaches the outside of the crystal from the light emitting portion.
On the other hand, in the case of the conventional avalanche photodiode, the center of sensitivity is on the wavelength side considerably shorter than 0.848 μm. This is because the number of electrons that can be excited by light at the very limit of the energy band gap is small.

For the above reasons, even if a conventional light emitting diode and avalanche photodiode having the same composition (same energy band gap) are integrated on the same substrate and the reflected light of the light emitted by the light emitting diode is received by the avalanche photodiode, Since the center of the wavelength is on the longer wavelength side than the center of the received light wavelength, a sufficient number of electron-hole pairs cannot be formed, and thus sufficient sensitivity cannot be obtained.

Problems to be Solved by the Invention In such a conventional method, it was not possible to integrate devices having the same structure and the same composition and use one of them for light emission and the other for receiving the reflected light. For this reason, there is a problem in that there are restrictions in application, and if the structures and compositions are not the same, it is necessary to perform separate manufacturing processes for the light emitting unit and the light receiving unit, which complicates the manufacturing process.

The present invention has been made in view of the above points, and has the same structure and the same composition, but sufficient sensitivity can be obtained even when any one is used for light emission and the other is used for receiving the reflected light.
The present invention relates to a light-emitting and light-receiving integrated device, which is extremely advantageous in application and in which the manufacturing process does not need to be changed between the light-emitting portion and the light-receiving portion, which makes the manufacturing process extremely simple.

Means for Solving the Problems In order to solve the above problems, the present invention provides an energy band gap on the side close to the p-type region at the junction of the p-type (p + -type) region and the n-type (n + -type) region. , A plurality of elements having a structure smaller than the energy band gap on the side closer to the n-type region are integrated on the same substrate, light emission is performed on the side closer to the n-type region of the junction, and the reflected light is detected. By performing this on the side closer to the p-type region of the junction, it is possible to detect emitted light and reflected light with high sensitivity and with the same structure and composition.

Action The present invention has the same structure and composition due to the above structure,
It is easy to integrate and any element may be used for light emission and light reception.

Embodiment FIG. 1 is a structural diagram of an embodiment of the present invention. In the figure, 1 is an n-type GaAs substrate, 2 is an n-type AlxGal-xAs layer, 3 is a junction, 4 is a p-type AlyGal-yAs layer (x> y), and 5 and 6 are ohmic electrodes. The p-type AlyGal-yAs4 has an acceptor concentration of 1 · 10 ¹⁹ , and the n-type AlxGal-xAs2 has a donor concentration of 5 · 10 ¹⁶ . In this embodiment, x = 0.03, y
= 0.01, and the Al concentration of the joint 3 was gradually changed from 0.03 to 0.01.

The thickness of the n-type GaAs substrate 1 was 400 μm, the thickness of the n-type layer 2 was 2 μm, the junction 3 was 2 μm, and the p-type layer 4 was 1 μm.

Next, the manufacturing method of the element will be described. On the n-type GaAs substrate, n-type AlxGal-xAs layer 2, by molecular beam epitaxy,
Each layer of the junction 3 and the p-type AlyGal-yAs layer (x> y) 4 was grown to a predetermined thickness. If molecular beam epitaxy is used, it is easy to continuously change the Al concentration in the region of the junction 3.

Next, the operation of the device of this example will be described. In FIG. 1, the electrode 6A is positively biased, the electrode 5A is negatively biased, the electrode 6B is negatively biased, and the electrode 5B is positively biased. In that case, the light emitting unit 8
Light emission occurs in the area of, and the light hits and is reflected by the object of the reflective object 7. Of the reflected light, the light that reaches the light receiving portion 9 is absorbed here and flows as a current between the electrodes 5B and 6B.
By detecting this current, the surface state of the reflection target 7 can be detected.

Energy band diagrams of the device of this example are shown in FIGS. 2 and 3. Figure 2 is an energy band diagram of the light emitting part.
The p-type semiconductor layer 4 is biased positively and the n-type semiconductor layer 2 is biased negatively. AlyGal-yAs of the p-type semiconductor layer 4 (y = 0.01)
The energy band gap of AlxGal-xAs (x = 0.03) of the n-type semiconductor layer 2 is larger than that of the n-type semiconductor layer 2. In addition, the energy band gap changes slowly at the junction.

In this case, electrons are injected from the 2 side and holes are injected from the 4 side. Since the acceptor concentration in the p-type region is as large as 1 · 10 ¹⁹ and the donor concentration in the n-type region is as small as 5 · 10 ¹⁶ ,
Recombination is dominated by the lesser carriers, the electrons, and occurs on the injection side. Therefore, the emission wavelength at this time is a wavelength corresponding to the energy band gap on the side close to the n-type region of the junction 3.

On the other hand, the energy band in the case of receiving light is as shown in FIG. In this case, the p-type semiconductor layer 4 is negatively biased and the n-type semiconductor layer 2 is positively biased. When the light hits here, electron hole pairs are formed. The generated electrons and holes drift in the junction 3 and cause avalanche breakdown under a high electric field to multiply the electrons and holes, respectively. In the case of the present embodiment, since the electron activation rate is higher than the hole activation rate, the sensitivity is almost lost due to the electron avalanche breakdown. In order to cause the avalanche breakdown, it is necessary to travel a sufficient distance for accelerating the electrons. Therefore, in the case of FIG. 3, the electrons excited near the p-type semiconductor layer 4 in the junction are It works most effectively. By the way, the energy band gap of this portion is smaller than the energy band gap of the light emitting portion shown in FIG. That is, the wavelength contributing to the avalanche breakdown is a wavelength corresponding to the semiconductor energy band gap of the p-type semiconductor layer 4.

As described in the description of the conventional example, in the case of receiving light, since it has a center on the shorter wavelength side than the corresponding energy band gap, it is very weak for light emitted from the semiconductor of the same energy band gap. Although it has only sensitivity, if the energy bandgap of the light receiving part is smaller than the energy bandgap of the light emitting part as in the present embodiment, light emitted from a part with a slightly larger energy bandgap In contrast, it is possible to have a good sensitivity.

As a result of actually emitting light and receiving the reflected light using the device of this example, very good sensitivity was exhibited.

In this example, the light emitting element and the light receiving element had the same structure, and a large number of elements could be easily integrated.

Although AlxGal-xAs and GaAs are used in this embodiment, if another material such as InGaAs, InGaAsP, or GaAsP III-V compound semiconductor material is used, the energy band gap can be easily changed by changing the composition. From this, it is apparent that the same formation as this embodiment and the same effect can be obtained.

As described above, according to the present invention, the p-type region, the n-type region,
The energy band gap of the junction on the side in contact with the n-type region is the energy band gap of the junction on the side in contact with the p-type region. When the pn junction is forward-biased, light is emitted to the center of the junction on the side in contact with the n-type region, and when the pn junction is reverse-biased, it is generated at the junction on the side in contact with the p-type region. A plurality of pn junction elements that generate a photocurrent centered on a pair of electrons and holes are provided in the same substrate, and at least any one element emits light, and at least another one element emits light. It has good sensitivity by being used for receiving and detecting the light emitted from the light emitting element and reflected, and with the same configuration, it can also emit light by simply changing the electrical bias conditions regardless of the location of the element. It can also be used for light, so it is not necessary to change the manufacturing process between the light emitting part and the light receiving part, and by controlling the voltage applied to each element from the outside according to the application, it can be used at any place among multiple elements. The present invention provides a light-emitting and light-receiving integrated device having an effect of being extremely advantageous from the viewpoint of application that any number of the devices can be used for light emission or light reception.

[Brief description of drawings]

FIG. 1 is a structural diagram of the device of this embodiment, FIG. 2 is an energy band diagram of a light emitting portion of this embodiment, FIG. 3 is an energy band diagram of a light receiving portion of the device of this embodiment, and FIG. 5 is a structural diagram of the light emitting diode of FIG. 5, and FIG. 5 is a structural diagram of a conventional avalanche photodiode. 1 ... n-type substrate, 2 ... n-type semiconductor layer, 3 ... junction,
4 ... p-type semiconductor layer, 5 ... electrode, 6 ... electrode, 7 ...
Reflecting object, 8 ... Light emitting part, 9 ... Light receiving part.

Claims (2)

[Claims] 1. A light-emitting element and a light-receiving element having the same structure, a plurality of the light-emitting elements and the light-receiving element being in the same substrate, wherein the light-emitting element receives and detects the light emitted from and reflected by the light-emitting element. A light-receiving integrated device, wherein both the light-emitting device and the light-receiving device are a p-type region made of a compound semiconductor, an n-type region made of a compound semiconductor having a bandgap larger than that of the p-type region, and the p-type region and the n-type region. The p-type region and the n-type region are made of a mixed crystal compound semiconductor that is located between the p-type region and the n-type region, and the energy band gap on the side in contact with the n-type region is p-type due to the difference in composition. And a junction that is larger than the energy band gap on the side in contact with the region, and the light emitting element is formed in a predetermined region of the laminated structure. The p-type region and the n-type region when forward biased, emits mainly side in contact with the n-type region of the joint, further wherein the receiving element is in a predetermined area of the laminated structure,
When the p-type region and the n-type region are formed in the vicinity of the light-emitting element and reverse biased, the electron-hole pair generated on the side of the junction contacting the p-type region serves as a photocurrent. A light-emitting / light-receiving integrated device characterized in that 2. The light emitting / receiving integrated device according to claim 1, wherein the acceptor concentration of the p-type region is higher than the donor concentration of the n-type region.