JPS6133266B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor light receiving element having an amplification function.

One of the typical semiconductor detectors for optical fiber transmission systems with an amplification function is the avalanche photodiode (hereinafter abbreviated as APD).
There is. Taking a planar Si-APD as an example, we will briefly explain its operating principle. FIG. 1 shows the structure in cross section. A p layer 2 was formed on the p ⁺ -Si substrate 1 by epitaxial growth, and phosphorus was diffused on its surface.
An n-type guard ring 5 is provided to form the n ⁺ layer 3 and prevent edge breakdown.
When a reverse bias is applied to the n ⁺ p junction by the n ⁺ layer side electrode 6 and the p ⁺ layer side electrode 7, an electric field distribution as shown in FIG. 2 is generated in the p layer 2. When light 4 enters from the n ⁺ layer 3 side, since the n ⁺ layer 3 is thin, the light 4 is hardly absorbed there and is absorbed by the p layer 2. If the energy of photon 4 is larger than the band gap Eg of the semiconductor (here Si), then p
Electron 8-hole 9 pairs are created in layer 2 (see Figure 3),
Electrons 8 and holes 9 are separated by the electric field, with electrons 8 traveling toward the n ⁺ side electrode and holes 9 traveling toward the p side electrode. The carriers, which are accelerated by the electric field and have high energy, collide in the avalanche region to ionize other bound electrons, and this phenomenon continues to increase in the form of an avalanche (see FIG. 4). It is usually used at a multiplication factor of several 10 to 100.

Another type of semiconductor detector with an amplification function is a phototransistor. Here we use heterostructure phototransistors (e.g., M.Konagai
et al., J.Appl.Phys., Vol.48, No.10, PP.4389−
4394, 1977), we will explain its operating principle.
FIG. 5 shows a cross-sectional structure of a heterostructure phototransistor. On the n ⁺ GaAs substrate 10, an n-type GaAs layer 11 (collector), a p-type GaAs layer 12 (base),
After sequential epitaxial growth of n-type Ga _1-x Al _x As layer 13 (emitter), n-type Ga _1-x Al _x As layer 13
(Emitsuta) partially by selective etching, p
Etch down to the GaAs layer 12 (base).
The electrode 14 to the n-type Ga _1-x Al _x As emitter 13 has
Au+Ge+Ni, electrode 1 to p-type GaAs base 12
5 is made of Au+Zn, and the electrode 16 to the n ⁺ GaAs substrate 10 is made of Au+Sn. Light 4 is n type
Ga _1-x Al _x As enters from the emitter 13 side. Figure 6
FIG. 5 shows the energy band structure of the np-nGa _1-x Al _x As/GaAs heterostructure phototransistor shown in FIG. A reverse bias is applied between the base and the collector, and a forward bias is applied between the emitter and the base. Let Ei be the energy of the incident photon, and let the energy gap of Ga _1-x Al _x As be
If the energy gap of Eg ₁ and GaAs is Eg ₂ , and the condition of Eg ₁ > Ei > Eg ₂ is satisfied, n-
The Ga _1-x Al _x As layer becomes a "window", and light passes through without being absorbed, and is absorbed by the p-GaAs layer (base), creating 8 electron-hole pairs there. Of these, electrons run down the potential barrier created between the two junctions and flow left and right. n-Ga _1-x Al _x As/p
A large barrier to holes is formed in the valence band of the −GaAs heterojunction, and holes are trapped in the base region, contrary to the case of electrons. This results in the formation of a significant space charge in this region, which strengthens the left forward bias and increases the flow of electrons across the barrier from left to right in the conduction band. This increased electron flow almost passes through the base layer, and the right n-
Flows into the GaAs region. In other words, the trapping of holes generated by light irradiation in the base region corresponds to the injection of minority carriers into the base region of a transistor. Therefore, due to the current multiplication effect of the transistor operation, it is possible to obtain a flow of carriers larger than the amount of electrons in the electron-hole pairs generated by the incident light.

As explained above, the APD is a light receiving element that uses only the avalanche effect, and is also a light receiving element that uses only phototransistor operation.

The conventional elements described above do not have sufficient gain in the used band, so they have the disadvantage that when used for relaying long-distance transmission, the relaying interval becomes short.

The present invention uses both the avalanche effect and transistor operation to provide a semiconductor photodetector having an amplification function with higher gain than an avalanche photodiode.

The present invention will be explained in detail below using the drawings.

FIG. 7 is a cross-sectional view showing the structure of an Al _x Ga _1-x As based semiconductor material as an embodiment of the present invention.
n ^- type GaAs collector layer 1 on n ⁺ type GaAs substrate 17
8, p ⁺ Al _x Ga _1-x As base layer 19, and n ⁺ type
After epitaxially growing the Al _y Ga _1-y As emitter layer 20 (where y≧x), p ⁺ Al _x Ga _1-x As
-n ^- To prevent edge breakdown at the GaAs junction, the periphery is etched into a mesa shape.
An ohmic electrode 21 is deposited on a part of the surface of the n ⁺ Al _y Ga _1-y As emitter layer 20, and an ohmic electrode 22 is deposited on the n ⁺ -GaAs substrate 17. When a voltage is applied between the electrodes 22 and 21 by the DC power supply 31 so that the n ⁺ GaAs substrate side electrode 22 is positive, the direction between the emitter and the base is forward, so the applied voltage is reversed between the base and collector. Acts as a bias voltage. Therefore, the light 4 is made to enter from the emitter 20 side. The energy of light 4 is transmitted to the collector material GaAs
of the base material is greater than the energy of the bandgap of
When the energy is smaller than the forbidden band width of Al _x Ga _1-x As, the light 4 passes through the emitter layer 20 and the base layer 19 and is absorbed by the collector layer 18 . Since y≧x, the forbidden band width of the emitter layer is even larger than that of the base layer 19. Figure 8 shows its energy band structure. A strong electric field as shown in Figure 2 is generated at the collector junction, and the electron 8-hole 9 pairs generated at the collector junction due to light absorption are separated by the electric field, and the hole 9 is separated from the base. Electron 8 again to the area
moves to the right n-side electrode. The carriers that are accelerated by the electric field and gain high energy are further multiplied in an avalanche style in the avalanche region. The multiplied holes flow into the base region. There is a large barrier to holes in the valence band between the emitter and base, and holes that flow into the base region are captured by the base region, where they form space charges and further strengthen the forward bias. It turns out. As a result, it increases the flow of electrons across the barrier and across the conduction band from left to right.

FIG. 9 shows an embodiment of the present invention using an In _1-x Ga _x As _y P _1-y based semiconductor material. Here, p-n-p
The only difference from FIG. 7 is that it is connected, and the operation is exactly the same as the embodiment shown in FIG. On the p ⁺ -InP substrate 25, a p ^- In _1-x Ga _x As _y P _1-y collector layer 26,
n ⁺ −In _1-x ′Ga _x ′As _y ′P _1-y ′Base layer 27, p ⁺ −
The emitter layer 28 of In _1-x ″Ga _x ″As _y ″P _1-y ″ is epitaxially grown in sequence. Here, the subscript is 0≦
It is within the range of x''<x'≦x≦0.47, 0≦y''<y'≦y≦1, and is a value that allows lattice matching with the InP substrate. In _1-x Ga _x As _y P _1-y capable of lattice matching with InP substrate
Among them, InP has the largest forbidden band width, and In ₀ . ₅₃ Ga ₀ . ₄₇ As has the smallest band width. FIG. 10 shows the band structure. Electrons are trapped in the base layer, which increases the forward bias and increases the flow of holes.

Note that in the above embodiment, the band width of the base-collector junction part 29 was a heterojunction with a stepped change, but the band width of the base-collector junction part 29 gradually narrowed as shown in FIG. Also good.
Further, the element structure may include a base electrode in addition to the emitter electrode and the collector electrode, as shown in FIG.

In addition, in the above embodiment, Ga _x Al _1-x As system,
Although we have described an example using the In _1-x Ga _x As _y P _1-y system, other combinations of compound semiconductors and mixed crystal semiconductors (e.g.
It is clear that the structure of the present invention can also be realized using the Ga _x Al _1-x As _y Sb _1-y system. Also,
It is also clear that any combination of n-p-n and p-n-p can be implemented.

As explained above, according to the present invention, p-n
In a -p or np-n junction, the forbidden band width of the emitter material is wider than or equal to the forbidden band width of the base material, the forbidden band width of the collector material is narrower than the forbidden band width of the base material, and the forbidden band width of the emitter material is narrower than the forbidden band width of the base material. When a reverse bias sufficient to cause avalanche multiplication is applied and a photon with an energy greater than the forbidden band width of the collector and smaller than the forbidden band width of the base is incident from the emitter side, the photon will be transferred between the emitter and the base. It is absorbed near the base-collector junction and in the collector, where it generates electron-hole pairs, which are multiplied by avalanche.
In addition, amplification by phototransistor action is added to enable a high-gain semiconductor light-receiving element, and its use as a light-receiving element in a long-distance optical fiber transmission system is extremely effective.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a Brehner-type Si-APD, Figure 2 is a characteristic diagram showing the electric field distribution when a reverse bias is applied to the element in Figure 1, and Figure 3 is a diagram showing the electric field distribution when a reverse bias is applied to the element in Figure 1. Energy band diagram showing the band structure of n ⁺ -p junction. Figure 4 is a schematic diagram for explaining avalanche multiplication. Figure 5 is n-Ga _1-x Al _x As/P-GaAs/n-
A cross-sectional view of a GaAs heterophototransistor. Figure 6 shows the forbidden band width of the emitter when a reverse bias is applied between the base and collector of the transistor in Figure 5.
Figure 7 is an energy band diagram showing the band structure when a photon with energy smaller than Eg ₁ and larger than the base forbidden band width Eg ₂ is incident from the emitter side.
FIG. 8 is a cross-sectional view of an embodiment of the present invention using an Al _x Ga _1-x As-based semiconductor material, and FIG. 8 shows a cross-sectional view of an embodiment of the present invention made of an Al x Ga 1-x As-based semiconductor material. Figure 9 is an energy band diagram showing the band structure when a photon with energy greater than the forbidden band width enters from the emitter side.
A cross-sectional view of an embodiment of the present invention using an In _1-x Ga _x As _y P _1-y based semiconductor material, FIG. 10 is an energy band diagram showing the band structure of the embodiment of FIG. 9, and FIG. 11 is an embodiment of the present invention. FIG. 3 is an energy band diagram showing a band structure explaining that the band width of the collector junction portion of FIG. 1...p ⁺ -Si substrate, 2...p-Si layer, 3...n ⁺
-Si layer, 4... Incident light, 5... Guard ring, 6
...n ⁺ layer side electrode, 7...p ⁺ layer side electrode, 8...electrons generated by light absorption, 9...holes generated by light absorption, 10...n ⁺ -GaAs substrate , 11...
n-GaAs layer (collector), 12... p-GaAs layer (base), 13... n-Ga _1-x Al _x As layer (emitter), 14... Ohmic electrode, 15... Ohmic electrode, 16... ... Ohmic electrode, 17...
n ⁺ -GaAs substrate, 18...n ^- -GaAs layer (collector), 19...p ⁺ -Al _x Ga _1-x As layer (base), 2
0...n ⁺ -Al _y Ga _1-y As layer (emitter), 21...
Ohmic electrode, 22... Ohmic electrode, 25
...p ⁺ -InP substrate, 26...p ^- -
In _1-x Ga _x As _y P _1-y layer (collector), 27...n ⁺ −
In _1-x ′Ga _x ′As _y ′P _1-y ′layer (base), 28...p ⁺ −
In _1-x ″Ga _x ″As _y ″P _1-y ″ layer (emitter), 29... Collector junction where the band width gradually narrows.

Claims (1)

[Claims] 1 The first compound semiconductor layer, the second compound semiconductor layer, and the third compound semiconductor layer are p-type and n-type, respectively.
and p-type compound semiconductor layers or n-type, p-type, and n-type compound semiconductor layers, and the forbidden band width of the first compound semiconductor layer is set to be wider than the forbidden band width of the third compound semiconductor layer. and lattice matching is achieved between the first, second and third compound semiconductor layers, and a reverse bias is applied between the second compound semiconductor layer and the third compound semiconductor layer. , the second compound semiconductor layer is larger than the forbidden band width of the third compound semiconductor layer.
When a photon having an energy smaller than the forbidden band width of the compound semiconductor layer is incident from the surface on the first compound semiconductor layer side, the inside of the third compound semiconductor layer, the second compound semiconductor layer, and the second compound semiconductor layer are The carriers generated by the photon absorption at the junction with the compound semiconductor layer of No. 3 are multiplied by avalanche, and the current is multiplied by transistor operation, so that the avalanche multiplication and the current multiplication operate in the same region. A semiconductor light-receiving element configured as follows.