JPH02220478A - Photodetector - Google Patents

Abstract

PURPOSE:To unite this photodetector to other semiconductor element and to realize an output of a large electric current by a method wherein a light waveguide layer used to optically detect incident light is formed as one part of a collector layer between the collector layer and a base layer. CONSTITUTION:A light waveguide layer 3 used to optically detect incident-light is formed as one part of a collector layer 2 between the collector layer 2 and a base layer 4. When the light waveguide layer 3 used to detect the incident light is formed as a semiconductor layer, it can be easily formed collectively with other semiconductor elements and a forward bias is applied between an emitter and a base. In addition, since a potential barrier is lowered, a stream of electrons, on the side of the emitter, flowing to the side of a collector over a base region is increased; a large electric current can be caused to flow.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a photodetector, and more particularly to a photodetector configured as a waveguide hetero-bipolar phototransistor for receiving light and amplifying power, which is used in optical communications, optical information processing, etc. be. [Prior Art] A phototransistor is a semiconductor photodetector having a power amplification function. Here M, Konagai et al., J.
Appl, Phys, Vol. 48. No,
10, PP, 4389-4394, 1977, a phototransistor having a heterojunction will be described. FIG. 7 shows the cross-sectional structure of a heterojunction phototransistor.
collector [72,p”-base N which is GaAs
An emitter layer 74 of 73, n-Ala, 5Gao, and tAs is sequentially grown epitaxially, and an emitter [74] is formed on a part of the upper surface of the base layer 3 by etching as shown. After this, an emitter electrode 75 made of Au+Ge+Ni is used as an electrode for the emitter layer 74, and a base electrode 7 made of Au+Zn is used as an electrode for the base layer 73.
6. A collector electrode 77 made of Au ten-button is attached as an electrode of the n''-GaAs substrate 71. The incident light 78 enters from the emitter [74 side. A reflective coating was applied.The energy Ei of the incident light 78 is 1.4 (eV) < compared to the energy gap Eg of the emitter layer 74.
If the condition of Ei<Eg is satisfied, the incident light 78 is not absorbed by the emitter layer 74 and is absorbed by the base layer 73 and the collector layer 72.
It is absorbed by. FIG. 8 is a diagram showing the potential distribution of the phototransistor shown in FIG. 7. Incident light 78 absorbed as shown in FIG.
creates 71 electron-hole 72 pairs. Electrons 71 flow to the collector side, and holes 72 flow to the base side. The holes 72 cannot flow to the emitter side due to the potential barrier between the emitter and the base, and are captured in the base region. Therefore, a considerable amount of space charge is formed in the base region, and as a result of this space charge strengthening the forward bias between the emitter and the base, electrons 71 flow from the emitter side over the base region to the collector. That is, in a heterobibolar transistor, holes generated by light irradiation are captured in the base region, and light irradiation corresponds to minority carriers being injected into the base region. Therefore, due to the current multiplication effect of the transistor operation, a flow of carriers larger than the amount of electrons in the electron-hole pairs generated by the incident light can be obtained. [Problems to be Solved by the Invention] In the conventional example described above, since the light-receiving surface is set on the upper surface side of the emitter electrode, it is difficult to manufacture the light-receiving surface in an integrated manner with a semiconductor laser diode or a waveguide element. Another drawback is that the light-receiving surface requires anti-reflection coating. Furthermore, if the light-receiving area is increased in order to increase the light-receiving sensitivity or to extract a large current, there is a drawback that the response speed becomes slow. SUMMARY OF THE INVENTION An object of the present invention is to provide a photodetector that can be easily manufactured integrally with other semiconductor elements and can output a large current. [Means for Solving the Problems] The photodetector of the present invention is a photodetector configured as a hetero-bipolar photo"transistor that performs power amplification according to incident light, and includes An optical waveguide layer for receiving the incident light is formed as a part of the collector layer. This optical waveguide layer may have a superlattice structure, and the superlattice structure constituting the optical waveguide layer is The superlattice layer constituting the lattice structure may be composed of a plurality of laminated parts each having a different band gap, and may be arranged in order from the base layer side to the collector layer side in order of decreasing band gap. A non-doped superlattice layer may be provided between the base layer and the base layer, and the base layer may have a superlattice structure.

[Operation J] Since an optical waveguide layer that receives incident light is formed as a semiconductor layer constituting the hetero-bipolar phototransistor, it is easy to form it integrally with other semiconductor elements. Furthermore, electron-hole pairs are generated by the light incident on the optical waveguide layer, but these holes are captured in the base region.
Electrons flow to the collector region. Holes captured in the base region do not flow to the emitter side due to the potential barrier between the emitter and base, resulting in the formation of a considerable space charge, and a forward bias is applied between the emitter and base. As a result, the potential barrier between the emitter and the base is lowered, so that the flow of electrons on the emitter side beyond the base region toward the collector side is increased, and a large current flows. [First Embodiment] FIG. 1 is a sectional view showing the structure of a first embodiment of the present invention. In the following semiconductor waveguides, in the case of n-type, rn-
J, p-type is rp-J, non-doped is "φ-",
rp"-J and rn-J are explained as indicating the difference in impurity concentration. Collector layers 2 and n of n--Alo, 5Gao, and tAs are formed on a substrate 1 of semi-insulating GaAs (SI-GaAs). - Form an optical waveguide N3 of Alo, zaGao, 76AS.Furthermore, sequentially form a base N4 of p"-GaAs, an emitter layer 5 of n-Ale, zaGao, tsAs, and a cap layer 6 of n"-GaAs. These layers are grown using liquid phase epitaxy (LPε method),
It is produced by a metal organic chemical vapor deposition method (MO-CVD method), a molecular beam epitaxial method (MBE method), or the like. Thereafter, the emitter layer and base layer are etched using a selective etching method to form electrodes on each. The emitter electrode 7 and collector electrode 9 have a three-layer structure of Au, Sn, and Au, and the base electrode 8 has a three-layer structure of Au, Zn, and Au, which are alloyed by heat treatment. The film thickness, impurity type, and concentration of each layer are as follows: Collector layer 2: 3 um Si 2 XIO"cm-'
Optical waveguide layer 3: 0.5gm St 2XlO”
cm-' base rgj4: 0.5μm Be
I XIO"cm-' Emitter N5: I Bm
Si 5X10"am-' Cap 46: D
, 5μm Si I XIO"cm-' emitter electrode 7 Au/Sn/Au = 100 people/100
Human collector electrode 9° / 2500 people Base electrode 8: Au/Zn/Au = 100 people/1
00 people / 2000 people. In this embodiment, as shown in FIG. 1, power amplification is performed using incident light 10 that enters the optical waveguide layer 3. Figure 2 (a) is a potential distribution diagram with bias conditions added on the A-A' cross section in Figure 1;
b) shows the electrons when light is incident in Fig. 2(a).
FIG. 3 is a potential distribution diagram schematically showing the movement of holes. Regarding the operation of this embodiment, Fig. 1 and Fig. 2 (a), (
This will be explained with reference to b). The bandgap of the guiding waveguide layer 3 at room temperature is Eg
341.72 eV, and the bandgap of the collector M2 is Egz41.80 eV. If the wavelength of 1G of incident light is 850 nm (nanometers), the energy of the incident light is Eg" 1.46 eV. That is, Eg<
Eg. Therefore, the optical waveguide layer 3 becomes transparent for the incident light . Furthermore, since Egs<Egg, the incident light lO is confined in the collector layer 2. As a result, the incident light 10 entering from the left end of the paper (see FIG. 1) travels from the waveguide region 11 at the left end of the paper toward the absorption region 12 at the right end. Second
In Figures (a) and (b), a power supply 21 provided between the emitter and collector applies a reverse bias between the base and collector. In Fig. 2(b), the incident light lO
is perpendicular to the plane of the paper and is guided from the front side to the back side. 1st
When the incident light lO that has been guided through the waveguide region reaches the absorption region I2, base 1'! The bandgap of 4 is ~1.4
Since it is eV, most of the energy is transferred to the base layer 4 side and absorbed. The absorbed incident light IO generates electron 205 and hole 206 pairs, where the hole 206 is captured in the base region and the electron 205 flows to the collector region. The holes 206 captured in the base region do not flow to the emitter side due to the potential barrier between the emitter and the base, and as a result, a considerable space charge is formed and a forward bias is applied between the emitter and the base. As a result, the potential barrier between the emitter and the base is lowered, thereby increasing the flow of electrons from the emitter side over the base region to the collector side. FIG. 3 is a sectional view showing the structure of a second embodiment of the present invention. Here, the emitter layer is n-Ale, 5GaO, ?
The emitter layer 35 is made of ^S, and the structure of the optical waveguide in the collector layer is an optical waveguide layer 31 having a superlattice structure. The rest of the structure is the same as the first embodiment, and the same numbers as in FIG. 1 are given. The configuration of the superlattice structure is n-Alo,
3Gao, 7A, 860 layers, and n-GaAs, 10 layers each with 50 layers each. The bandgap of this superlattice structure is Eg=1.72eV
Therefore, it has almost the same bandgap as n-Ale, x4Gao, and A3, but because the waveguide loss is small, the amount of attenuation in the waveguide is small, making the element
It has become possible to make it smaller than what is shown in the figure. Next, the superlattice structure of the leading waveguide 31 shown in FIG.
Laminated 25 layers of 15 GaAs layers, then n-Alo,
5Gao, 60 layers of tAs, and 30 layers of n-GaAs were stacked at 25N. In this case, the band gaps 1 and 7 of the optical waveguide layer 31 are
2 eV became 1.68 eV and 1.59 eV, the bandgap discontinuity at the base-collector interface was relaxed, and after light was incident, electrons more easily flowed from the emitter side to the collector side. Note that it is clear that the above effect will be further enhanced if the optical waveguide layer 31 has a larger number of band gaps and is arranged from the base layer to the collector layer in order of increasing band gap. FIG. 4 is a sectional view showing the structure of a third embodiment of the present invention. In this embodiment, φ- GaAs and φ-AIJa
A φ-superlattice layer 45 having a superlattice structure made of +-1IA8 is provided. The rest of the structure is the same as that of the first embodiment, and the same numbers as in FIG. 1 are given. To explain the manufacturing procedure, a collector layer 2 of n-Ale, 3Gao, and tAs, and an optical waveguide N3 of n-Ale, 14Gao, and ysA3 are formed on a 5l-GaAs substrate 1, and then a 6-GaAs layer and a collector layer 2 of n-Ale, 3Gao, and tAs are formed. *-A
10. A φ-superlattice layer 45 in which a4Gao and tsAs WI are laminated alternately, a base layer 4 made of p''-GaAs, an emitter layer 5 made of n-Alo, z4Gao, and tsAs, and a cap layer 6 made of n-GaAs are sequentially formed. Epitaxial growth was performed. After that, selective etching was performed up to the φ-superlattice layer 45 to obtain the shape shown in FIG. 4, and then an emitter electrode 7, a base electrode 8, and a collector electrode 9 were formed. FIG. 5(a) shows Figure 4B when bias conditions are added
FIG. 5(b) is a diagram showing the potential distribution in the -8′ cross section, and FIG. 5(b) is a diagram showing the potential distribution when light is incident on the state shown in FIG. 5(a). Next, the operation of this embodiment will be explained in FIGS. 4 and 5 (a).
) and (b). In FIG. 4, the incident light lO that enters from the left end of the element has most of its energy in the waveguide 3 in the waveguide region 11, and is guided to the right in FIG. Here, the difference from the first embodiment is that the incident light lO is
Since the light is not reflected at the interface between the absorption region 12 and the absorption region 12, the detection limit has become even higher. Further, when the bias applied to the absorption region 12 is removed, the incident light IO is not absorbed by the amplification region 12 and is further propagated to the right. On the other hand, as shown in FIG. 5(b), when light is incident on a bias-applied state, $-GaAs and 6- Alo, z4Gao, tsA
The band gap of the superlattice structure composed of the s-layer decreases due to the Stark effect, and the refractive index increases. As a result, the incident light 10 is absorbed by the φ-superlattice layer 45, and at the same time, the light confinement by the φ-superlattice layer 45 deteriorates, so that the light also transfers energy to the base layer 4, increasing absorption. . The incident light lO absorbed in the absorption region 12 consists of an electron 502-hole 501 pair and an electron 205-hole 2 pair.
The hole 501 flows to the base layer 4 due to the electric field, and the electron 205 flows to the collector side. This embodiment differs from the third embodiment in that the absorption energy in the φ-superlattice layer 45 is different from the third embodiment. Since the number of electron 502-hole 501 pairs generated increases, the length of the absorption region can be shortened. In addition, since the holes 501 are added to the holes 206 in the base layer,
The density of holes captured in the valence band of the base layer 4 increases, and as a result, more space charges are formed. This lowers the potential barrier between the emitter and base,
The number of electrons flowing from the emitter to the collector increases. FIG. 6 is a sectional view showing the structure of a fourth embodiment of the present invention. This example is based on p”-GaA of the third example shown in FIG.
The base layer 4 which is p-Gao, yAlo, sAs
A superlattice layer 66 is formed by alternately laminating layers of .phi.-GaAs and .phi.-GaAs. The rest of the structure is the same as that of the fifth embodiment, and the same numbers as in FIG. 4 are given. In the fourth embodiment, p''-GaA is used as the base layer 4.
s was used. If the base layer 4 is made thinner, the response speed becomes faster, but there is a drawback that the base resistance becomes higher and the overall response speed becomes slower. Furthermore, there is also a drawback that Be, which is a dopant on the φ-supersuperlattice layer, is diffused. In order to solve this problem, in this embodiment,
By forming the base layer 4 as the above-mentioned superlattice layer 66, it was possible to suppress an increase in base resistivity. This is because, in the case of this example, the holes move in φ-GaAs, which has a higher mobility than p''-GaAs. Therefore, the response speed was shortened. In each of the above examples, , AlxGa+-mAs system has been described, but other combinations of compound semiconductors and mixed crystal semiconductors (for example, Int-xGaJsyP+-y system, (
The structure of the present invention can also be realized by AIXGal-jyln+-yP system). Also, n-p-n, p
-n-p Any combination can be implemented. Also,
Since absorption is used, the electric field between the emitter and base is turned on. By turning it off, it is also possible to create a device as a waveguide optical switch that does not take out the absorbed current. Furthermore, since the effects produced by each embodiment are independent, the embodiments may be combined. [Effects of the Invention] Since the present invention is configured as described above, it has the following effects. The device according to claim 1 has the advantage that it can be easily manufactured integrally with other semiconductor devices and can output a large current. According to the second aspect, since the amount of attenuation in the optical waveguide layer is reduced, there is an effect that the device can be miniaturized. In the third aspect of the present invention, the discontinuity at the base-collector interface is relaxed, and electrons can more easily flow from the emitter side to the collector side, so that a large current can be output more easily. In the fourth aspect, since electron-hole pairs are also formed between the base layer and the collector layer, a large current can be easily obtained and the photodetector can be made smaller. There is. According to the fifth aspect of the present invention, the base layer can be made thinner and the resistivity of the base layer can be kept low, so that the response speed of the element can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of the first embodiment of the present invention, FIG. 2(a) is a potential distribution diagram in a state where a bias condition is applied in the AA' cross section of FIG. 1, FIG. 2(b) is a potential distribution diagram when light is incident on the state shown in FIG. 2(a), and FIGS. 3 and 4 are respectively the second and third embodiments of the present invention. A cross-sectional view showing the structure of FIG. 5(a) is
Figure 4 is a potential distribution diagram when a bias condition is applied in the B-B' cross section. Figure 5 (b) is a potential distribution diagram when light is incident on the object in the state shown in Figure 5 (a). 6 is a sectional view showing the structure of the fourth embodiment of the present invention, FIG. 7 is a sectional view showing the structure of the conventional example, and FIG. 8 is a potential distribution showing the operation of the one shown in FIG. 7. It is a diagram. 1...Substrate, 2...Collector layer, 3.31...Optical waveguide layer, 4...Base layer, 5.35 ...Emitter layer, 6...Cap layer, 7...Emitter electrode, 8...Base electrode, 9... ...Collector tm, 10...Incoming light, 11... Waveguide region, 12... Absorption region, 21... ...power supply, 45.......phi-lattice layer, 66... superlattice layer, 205, 502... electron, 206, 501... hole.

Claims (1)

[Claims] 1. In a photodetector configured as a hetero-bipolar phototransistor that performs power amplification according to incident light, an optical waveguide layer for receiving the incident light is provided between the collector layer and the base layer. A photodetector characterized in that a collector layer is formed as a part of a collector layer. 2. The photodetector according to claim 1, wherein the optical waveguide layer has a superlattice structure. 3. In the photodetector according to claim 2, the superlattice layer constituting the superlattice structure is composed of a plurality of laminated parts each having a different band gap, from the base layer side to the collector layer side in descending order of band gap. A photodetector characterized in that the photodetector is disposed in a. 4. The photodetector according to claim 1, 2 or 3, wherein a non-doped superlattice layer is provided between the base layer and the collector layer. 5. The photodetector according to claim 1, 2, 3 or 4, wherein the base layer has a superlattice structure.