JPS59182581A - Photo detecting semiconductor element - Google Patents

Abstract

PURPOSE:To perform wave length selective photo detection to a high sensitivity by a method wherein a photo absorption layer made of semiconductor having a forbidden band width narrower than that of the semiconductor constituting an emitter layer and wider than that of the semiconductor constituting a base layer is added to a hetero junction photo transistor. CONSTITUTION:When the light to be detected is incident from the side of the photo absorption layer 5, the light of a wave length shorter than that lambdag of the absorption end of said layer 5 is absorbed to said layer 5 and therefore not absorbed to either one of the emitter layer 4 and the base layer 3. On the other hand, when the wave length of the incident light is between the lambdag of the absorption layer 5 and the lambdag of the base layer 3, said light is absorbed to said layer 3 after penetration through the absorption layer 5 and the emitter layer 4. Thereby, the absorption in the base layer generates only with respect to the wave length lambdag of the photo absorption layer and that lambdag of the base layer, causing to show sensitivity, and accordingly a high emitter injection efficiency can be obtained regardless of the degree of wave length selectivity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to the structure of a novel photodetecting semiconductor element having wavelength selectivity, that is, having sensitivity only in a specific wavelength region.

Conventional Structures and Problems In recent years, with the development of the fields of optical communication and optical information processing, there has been an increasing demand for small, highly sensitive photodetecting elements.

In particular, in wavelength division multiplexing optical communication systems that simultaneously transmit light of different wavelengths, a photodetector element with steep wavelength selectivity is strongly desired. In addition, in fields such as remote sensing, there is a desire for a Zr element that selectively detects light in a specific wavelength range.

Conventionally, various photodiodes and phototransistors have been used as small, highly sensitive photodetecting elements. However, these elements have a property of being sensitive over a fairly wide wavelength range determined by the light absorption characteristics of the semiconductor moon phase used. Therefore, in order to obtain the aforementioned wavelength selectivity, it is necessary to place a spectroscopic device such as a spectrometer using a prism or a diffraction grating or an interference filter in front of the photodetector, which makes the device complicated. Moreover, it has disadvantages such as being large in size, causing light loss due to the spectrometer housing, and reducing the actual sensitivity. "Here, we will explain the structure and operating principle of a typical photodetector element that has been used in the past.

Figure 1 schematically shows the structure of a heterojunction phototransistor, which is known as a particularly highly sensitive photodetector element.
It is a front view. Further, FIG. 2 is a two-sided view corresponding to FIG. 1. In these figures, 1 is a semiconductor substrate, 2 is a collector layer, 3 is a base layer, 4 is an emitter layer, and 11 and 12 are electrodes. As in a normal transistor, the conductivity types of the base layer and other layers of the substrate are quite different. Note that the element is formed into a plateau shape by so-called mesa enching. Semiconductors have a forbidden band width specific to their materials, but in this case, the emitter layer 4 and the base layer 3 have different semiconductor attachments, so that the forbidden band width of the emitter layer 4 is equal to the forbidden band of the base layer 3. It is configured to be sufficiently wider than the width. Here, the light to be detected is made to enter from the emitter layer 4 side. Of the incident light, the light that passes through the emitter layer 4 and is absorbed by the base layer 3 generates charges in the base layer 3 and lowers the base potential. As a result, the collector current increases due to normal transistor action, and the device operates as a highly sensitive photodetecting element.

At this time, between the collector layer 2 and the emitter layer 4, a DC voltage in a direction that reverse biases the collector junction is applied to the electrode 1.
Needless to say, the voltage is applied via 1 and 12. By the way, emitter injection efficiency is a major factor that determines the amplification factor of a transistor. As mentioned above, if the forbidden band width of the emitter layer 4 is sufficiently larger than the forbidden band width of the base layer 3, the emitter injection efficiency becomes large, and a high amplification factor, that is, high sensitivity can be obtained.

Now, the wavelength dependence of sensitivity in this conventional element is as follows. Generally, the forbidden band width of a semiconductor is Eq
(Jf' position is electron volt), then λq=124
It has the property of absorbing light with a wavelength shorter than the absorption edge wavelength λq (unit: μm) given by /Eq. Therefore, in the device of this example, light having a wavelength shorter than λq of the emitter layer 4 is absorbed by the emitter layer and does not reach the base layer 3.

Also, light with a wavelength longer than λq of Bene) @3 is not absorbed by either the emitter layer or the base layer (Eq of Emintano is larger than E(J of the base layer, so
λq of the transmitter layer is on the shorter wavelength side than λq of the base layer. ). However, λq of emitter layer 4 and base layer 3
After the light with a wavelength between λq passes through the emitter layer 4,
It is absorbed by the base layer 3.

That is, this element exhibits sensitivity to light in the above wavelength range.

In such an element, in order to obtain a significant wavelength selectivity, it is considered that the λq of the emitter layer and the base layer should be made close to each other, that is, the Eq of the emitter layer and the base layer should be made close to each other. However, in that case, the emitter injection efficiency described above decreases, the amplification factor of the transistor decreases, and the sensitivity decreases.

By the way, the inventors have discovered that a photodetector element having high sensitivity and steep wavelength selection can be obtained by using a novel structure including a semiconductor light absorption layer.

Purpose of the Invention In view of the conventional problems as described above, the present invention provides a photodetecting semiconductor that exhibits arbitrary wavelength selectivity, particularly steep wavelength selectivity, and is highly sensitive, without using a spectroscopic device in conjunction with the present invention. The purpose is to provide devices.

Structure of the Invention The present invention is based on a conventional heterojunction phototransistor that uses a semiconductor having a forbidden band width narrower than that of a semiconductor constituting an emitter layer and wider than that of a semiconductor constituting a base layer. By adding a light absorption layer, a highly sensitive wave-selective photodetection semiconductor device can be realized.

DESCRIPTION OF EMBODIMENTS A specific embodiment of the present invention will be described using FIG. [n]. In the diagrams showing the element structure of each embodiment, the same reference numerals are used to refer to the same components in the conventional example and the actual examples.

FIG. 3 is a sectional view schematically showing the structure of a photodetecting semiconductor element in a first embodiment of the present invention.

Note that the two-view diagram is the same as that of FIG. 2, which is a top plan view of the conventional example, and will therefore be omitted. In FIG. 3, 1 is a semiconductor substrate, 2
3 is a base layer, 4 is an emitter layer, 5 is a light absorption layer, and 11.12 is an electric conductor. base layer 3
4. Part conductivity type and other layers and substrates? The difference between the L stones is the same as in the conventional example. However, the forbidden band width of the emitter layer is wider than that of the base layer, which is the same as in the conventional example.

In this embodiment, the light absorption M5 is made of a semiconductor having a forbidden band width narrower than the forbidden band width of the emitter layer 4 and wider than the forbidden band width of the base layer 3. As a result, the wavelength dependence of sensitivity in this example is as follows.

In this embodiment as well, the light to be detected is incident from the top surface of the element, that is, from the side of the light absorption layer 5. At this time, the absorption end plate length λq of the light absorption layer 5 (the definition of λq is based on the structure of the conventional example and its problems). (as explained in Section 4) is absorbed by the light absorption layer 5 and does not reach the emitter layer 4 and the base layer 3. Further, light having a wavelength longer than λq of the base layer 3 is not absorbed by any of the light absorbance 5, the emitter layer 4, and the base layer 3. This is because the forbidden band width Eq of the light absorption layer and the emitter layer is wider than the Eg of the base layer, and therefore λq of the light absorption layer and the emitter layer is on the shorter wavelength side than λq of the base layer.

On the other hand, when the wavelength of the incident light is between λq of the light absorption layer 5 and λq of the base layer 3, the incident light is absorbed by the base layer 3 after passing through the light absorption layer 6 and the emitter layer 4. Ru゛. This is because the ECI of the light absorption layer is smaller than the Eg of the emitter layer.
And since it is larger than Eq of the base layer, λq of the emitter layer is on the shorter wavelength side than λq of the light absorption layer, and λcr=- of the light absorption layer is on the shorter wavelength side than λq of the base layer. This is due to

As will be seen from Section 2, the element of this example has a light absorption of 1
The base layer absorbs only light having a wavelength between λq of the light and λq of the base layer, and exhibits sensitivity. That is, the sensitive wavelength range can be arbitrarily set depending on the forbidden band width Eq of the light absorption layer and the base layer. In particular, if the Eg of the light absorption layer and the base layer are made close to each other, a photodetection element with a narrow sensitivity wavelength range, that is, steep wavelength selectivity can be realized. In the case of this example, since Eg of the emitter layer is sufficiently larger than xg of the Beine book, a high emitter injection efficiency can be obtained regardless of the degree of wavelength selectivity, and a large amplification factor, that is, a high 1.8 degrees. can get.

FIG. 4 shows an example of the wavelength dependence of sensitivity (solid line) in the photodetector semiconductor element of this example in comparison with that of the comparative example (broken line). Sensitivity is expressed by the magnitude of collector current that corresponds to unit incident light amount.

In this case, the Eqs of the Bene layer, emitter layer, and light absorption layer are o, 99 eV, 1.35 eV, and 1.
01 electronic volume/Lt). When these are converted to absorption edge wavelength λq, each is approximately 1.25 μm10.9
2 μm and 1.23 μm. The thickness of each layer is 3 μm for the collector layer, 1 μm for the base layer, and 2 μm for the base layer.
m. As can be seen from FIG. 4, the half-width of the sensitivity-wavelength curve (solid line) of this device is extremely small, about 0.05 μm, and steep wavelength selectivity is obtained. Furthermore, the maximum sensitivity is extremely high at approximately 40 QA/W. The structure of the device of the comparative example is the same as that of the above example except that it does not include a light absorption layer. In this case, the device has a characteristic of 0.9 to 1.25 as shown by the broken line in FIG.
It can be seen that sensitivity is exhibited over a wide wavelength range of μm.

By the way, in principle, in order to obtain steep wavelength selectivity, it is considered that the closer the Eqs of the light absorption layer and the base layer are, the better, as described above. However, the inventors have discovered that if the difference in ECI is too small, the wavelength selectivity and sensitivity will be reduced. Figure 5 shows an element similar to the element whose characteristics are shown in Figure 4, but only the Eq of the light absorption layer is changed to 0.995 eV, and the Eq O difference between the light absorption layer and the base layer is made much smaller. This is the characteristic when In this case, it can be seen that the half-width is conversely large to about 0.07 μm, and the wavelength selectivity is reduced, and the sensitivity is also considerably reduced. This is because the thickness of the light absorption layers is finite, so the light absorption vector (wavelength dependence) of these layers is not ideal, and the absorption edge wavelength λq is τ1.
This is thought to be because it exhibits characteristics that change gradually over time. In other words, if the EqCλq) of the light absorption layer and the base layer are very close, there will be some absorption by the light absorption layer even in the e length between the two λq, and the light absorption of the base layer in this wavelength region will be It is thought that a situation occurs in which the wavelength becomes insufficient and the sensitivity in this wavelength range decreases, resulting in a relatively large width at half maximum. As a result of a detailed study of this point, we found that in order to obtain steep wavelength selectivity, the above-mentioned difference in xg should be adjusted to 1 to 3. It turned out that it was appropriate to set it as

Now, in the above explanation, E of the collector layer 2 in FIG.
I didn't mention g. In this example, Eq of the collector layer is considered to have no essential effect on the operation of the device. However, it has been experimentally found that when the Eq of the collector layer is made equal to the Eq of the base layer, the sensitivity becomes particularly high. This is because the light that was not absorbed by the base layer is absorbed in the collector layer and generates charges.
A portion of this charge is injected into the base layer due to the potential gradient existing at the bake-collector junction, contributing to an increase in collector current as well as light absorption in the base layer.
it is conceivable that. Therefore, it is desirable that the Eg of the collector j is a part of the xg of the base layer.

In this embodiment, the semiconductor substrate 1 and the collector layer 2 are separated, but a structure in which the semiconductor substrate also serves as the collector layer may be used without affecting the operation of the device.

Further, in this embodiment, the semiconductor substrate 1 and the collector layer 2 are continuous, but a buffer layer made of a semiconductor of the same conductivity type as both may be provided between them, which has no effect on the operation of the element. There is no.

In addition, during the explanation of this example, examples of the thickness of each layer were shown, but
These values are not necessarily limited to these values.

For the collector layer, emitter layer, and light absorption layer, 1 to 1
Appropriately, the thickness is about 0 μm, and for the base layer, about 0.1 to 2 μm.

FIG. 6 is a sectional view schematically showing the structure of a photodetecting semiconductor element in a second embodiment of the present invention.

In this embodiment, a light absorption layer 6, an emitter layer 4, a base layer 3, a collector Fit 27>1110 are formed on the semiconductor substrate 1.
The stacking order is reversed from that of the first embodiment. In this case, the light to be detected is made to enter from the semiconductor substrate 1 side. To avoid this, the electrode 11 on the substrate side is provided at the periphery so as not to block the incident light. Further, the forbidden band width of the semiconductor substrate 1 is equal to or wider than the forbidden band width of the light absorption layer 6. The other components are completely the same as in the first embodiment. The operation of this element is exactly the same as that of the first embodiment, and there is no difference in its characteristics.

FIG. 7 is a sectional view schematically showing the structure of a photodetecting semiconductor element in a third embodiment of the present invention.

In this embodiment, a light absorption layer 5, a collector layer 2, a base layer 3, and an emitter Iw 4 are laminated in this order on a semiconductor substrate 1. That is, this embodiment differs from the first and second embodiments in that the light absorption layer 5 is provided on the collector layer 2 side. In the case of this embodiment, since the light to be detected is incident from the semiconductor substrate 1 side, the mold rod 11 on the substrate side is the same as that of the second embodiment'.
Similarly, it is provided on the periphery. Furthermore, in this embodiment, the incident light must pass through the semiconductor substrate 1 and the collector layer 2 in addition to the light absorption layer 5 to reach the base layer 3, so the forbidden band width of the substrate and the collector layer is equal to the forbidden band width of the light absorption layer. It is made equal or larger so as not to interfere with the original operation of the element. The other components are exactly the same as those in the first embodiment, and their operation and characteristics are also the same.

FIG. 8 shows the fourth embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing the structure of a photodetecting semiconductor element in Example.

In this embodiment, an emitter layer 4, a base layer 3, a collector layer 2, and a light absorption layer 5 are sequentially laminated on a semiconductor substrate 1, and the structure has a structure in which the order of each layer is reversed in the third embodiment. ing. In the case of this embodiment, the light to be detected is incident from the top surface of the element, that is, from the absorption layer 5 side. The forbidden band width of the collector layer 2 is equal to or ih wider than the forbidden band lid of the light absorption layer 6, as in the case of the third embodiment. The components of the song are exactly the same as those in the first embodiment, and the operation and characteristics are also the same.

Note that in the third and fourth embodiments described above, it is also possible to use one layer as both the collector layer 12 and the light absorption layer 5, and in that case, there is no effect on the operation and characteristics of the element. .

Next, the semiconductor materials used in the above embodiments will be described. When manufacturing a photodetecting semiconductor device according to the present invention, it is necessary to sequentially stack semiconductor layers having different forbidden band widths. In such a case, in order to improve the crystallinity of each layer, it is essential to match the lattice constants of the substrate and the crystals of each layer with high precision. If these conditions are met,
The inventors have discovered that gallium-aluminum-arsenic semiconductors and indium-gallium-arsenic-phosphorus semiconductors are semiconductor materials whose characteristics are suitable for the photodetecting semiconductor element of the present invention.

The former (d) is a mixture of potassium arsenide (GaAs) and aluminum arsenide (AIAs,), where the content ratio of aluminum arsenic is X, Ga, -z AIX A
It is expressed as S (0≦x≦1). This system of crystals is
Regardless of the planting of X, the lattice constant is almost constant, while the forbidden band width is from 1.43 eV when
It changes significantly to 2.16 electron volts for X=1, which is very suitable for the device of the present invention.

The latter is a mixture of indium phosphorus (InP), indium arsenide (InAs), gallium phosphorus (Ga, P), and gallium arsenide (GaAs), and the content ratio of gallium to indium is x1 to the content of arsenic to phosphorus. In 1-x GaXAsyP + -y (0
";= -For example, if the values of X and y are chosen to approximately satisfy the relationship y=22X, then the lattice constant is
'! In the case of 20, it always matches the lattice constant of indium phosphorus. Also, at this time, the forbidden band width is x=o, 7
= 1·36 electrons 7+ (from root x==0.4
0.75 electron volts for the case 7.7 = 1 changes significantly, which is very suitable for the device of the present invention.

Furthermore, these semiconductor crystals can be easily formed by various mechanical growth methods.

Effects of the Invention As described above, the present invention provides a conventional heterojunction photovoltaic transistor with a forbidden band width narrower than the forbidden band width of the semiconductor constituting the emitter layer and wider than the forbidden band width of the semiconductor constituting the base layer. By adding a light absorption layer made of a semiconductor with a bandwidth, wavelength selectivity for any wavelength range, especially,
It has realized a highly sensitive photodetecting semiconductor element that exhibits steep wavelength selectivity, and has a powerful effect on conventional methods by providing a simple means of detecting light in a specific wavelength range without using a spectroscopic device. It is something that has.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of a conventional photodetection semiconductor device (heterojunction phototransinuta), FIG. 2 is a top view corresponding to FIG. 1, and FIG. 3 is a photodetection device according to the first embodiment of the present invention. FIG. 4 is a cross-sectional view showing the structure of a semiconductor device, and FIG. 4 is a characteristic curve showing an example of the wavelength dependence of the sensitivity of the photodetecting semiconductor device of the example of the present invention in comparison with that of a comparative example. Figure, 5th
The figure is a characteristic curve diagram showing an example of the wavelength dependence of sensitivity in a photodetecting semiconductor device according to an embodiment of the present invention. Third. FIG. 7 is a cross-sectional view showing the structure of a photodetecting semiconductor element according to a fourth example. DESCRIPTION OF SYMBOLS 1...Semiconductor substrate, 2...Collector layer, 3...Base layer, 4...Emitter layer, 5
......Light absorption layer, 11.12... Electrode. Name of agent: Patent attorney Toshio Nakao and one other person

Claims (9)

[Claims] (1) A heterojunction transistor having a structure in which a collector layer, a base layer, and an emitter layer made of a semiconductor having a forbidden band width wider than the forbidden band width of the semiconductor constituting the base layer are sequentially connected, A light absorption layer made of a semiconductor having a forbidden band width narrower than the forbidden band width of the semiconductor constituting the layer and wider than the forbidden band width of the semiconductor constituting the base layer is provided on the emitter layer side of the heterojunction transistor. A photodetecting semiconductor element characterized in that it is provided. (2) The difference in the forbidden band width of the semiconductor forming the base layer and the light absorption layer (71) is set to 1 inch to 3% of the forbidden band width of the semiconductor forming the base layer. A photodetecting semiconductor device according to claim 1, characterized in that: (3) Claim 1, characterized in that the base layer and the collector layer are made of semiconductors having the same forbidden band width.
2. The photodetector element according to item 2 or item 2. (4) The collector layer, the Vane layer, the emitter layer, and the light absorption layer are each made of a semiconductor whose main component is gallium arsenide, aluminum arsenide, or gallium/aluminum arsenide. Range 1
3. The photodetecting semiconductor device according to any one of items 1 to 3. (5) Collector layer, base layer, emitter layer, light'
Each of the H-layers contains indium phosphorus, indium arsenide,
Claims 1 to 3 are characterized in that the semiconductor is made of a semiconductor whose main component is gallium phosphorus, gallium arsenide, or a mixture of at least two of these. Photodetector semiconductor element. (6) A heterojunction transistor having a structure in which a collector layer, a base layer, and an emitter layer made of a semiconductor having a forbidden band width wider than the forbidden band width of the semiconductor constituting the base layer are successively connected, The forbidden band width of the semiconductor that makes up the collector layer. The forbidden band width of the semiconductor constituting the base layer is also made wider, and the forbidden band width of the semiconductor constituting the base layer is made equal to or narrower than the forbidden band width of the semiconductor constituting the collector layer. 1. A photodetecting semiconductor device, characterized in that a light absorption layer made of a semiconductor having a wide bandgap is provided on the collector layer side of the heterojunction transistor. (7) A patent characterized in that the difference in forbidden band width between the semiconductor constituting the base layer and the semiconductor constituting the light absorption layer is 1% to 3% of the forbidden band width of the semiconductor constituting the base layer. A photodetecting semiconductor device according to claim 6. (8) Gallium arsenide and aluminum arsenide for the collector layer, base layer, emitter layer, and light absorption layer, respectively. The photodetecting semiconductor device according to claim 6 or 7, characterized in that it is made of a semiconductor whose main component is either gallium or aluminum arsenide. (9) Collector layer, base layer, emitter layer, optical TF
Claims characterized in that each of the upper layers of the fl collection layer is made of a semiconductor mainly composed of indium phosphide, indium arsenide, gallium phosphide, gallium arsenide, or a mixture of at least two of these. Section 6 or Section 7
The photodetecting semiconductor device described in 2.