JPS60195981A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To improve the frequency characteristic and to reduce the noise in a semiconductor photodetector having internal amplifying function by shortening a lifetime of holes generated by the incident light. CONSTITUTION:A semi-insulating GaAs substrate 11, N<-> type GaAs semiconductor layer (the first semiconductor layer) 12, an Al0.3Ga0.7As semiconductor layer (the second semiconductor layer) 13 of tunneling layer, an N<+> type GaAs semiconductor layer (the third semiconductor layer) 14 of contacting layer, and ohmic electrodes 15, 16 made of Au.Ge/Au are provided. The relationships of forbidden band width of the semiconductor layers are the layer 13> the layer 12, the layer 13> the layer 14. The boundary of the first and second semiconductor 12, 13 are in the lattice matched state, holes generated in the layer 12 are not trapped by the incident light, the lifetime of the holes is extremely short, and the pulse current corresponding to the incident light is less tailed.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an improvement in a semiconductor light receiving device that has an internal amplification function and is capable of low noise and high speed operation.

Prior Art and Problems Conventionally, as this type of semiconductor light receiving device, one having the configuration shown in FIG. 1 is known. In addition, this is MSM (met
aI semiconductor.

rmetal) diode.

In the figure, 1 is a semi-insulating GaAs substrate, 2 is an n- (or non-doped) type GaAs semiconductor layer, 3.4, 5.
Reference numeral 6 indicates a horizontal electrode, and reference numeral 7 indicates a depletion layer.

FIG. 2 shows an energy band diagram when a bias voltage is applied to the MSM diode shown in FIG. 1 and viewed along the dashed-dotted line in FIG. The same parts are indicated by the same symbols.

In the figure, 8 and 9 are natural oxide films, 10 is a trap,
e represents an electron and h represents a hole, respectively.

When light enters the GaAs semiconductor layer 2 of the MSM diode shown in FIGS. 1 and 2, an electron-hole pair is generated in the GaAs semiconductor layer 2 of i, and the electron e is Schottky 114fH,4fi I reach it, but hole h is blank. The electrons e are trapped at the interface between the tree electrode 3 and the GaAs semiconductor layer 2, and as a result of this action, electrons e are drawn in from the Schottky electrode 3 side, causing a tunnel current to flow.

Therefore, this MSM diode has an internal amplification function.

By the way, if the hole h among the electron-hole pairs generated as described above is trapped in the part shown by the arrow in Fig. 2, then there is no problem with the force j5,
When a hole h is trapped in a trap 9 that depends on the interface state, the life time of the hole h in that case is long, so it depends on the influence.

In this case, electrons e are injected for a long time.

That is, even after the incidence of light has stopped, the pulse current response to that light has a long tail, and the frequency characteristics deteriorate.

OBJECTS OF THE INVENTION The present invention attempts to improve frequency characteristics and reduce noise by making extremely simple modifications to the structure of a semiconductor photodetector having an internal amplification function.

Structure of the Invention: A semiconductor light-receiving device according to the present invention includes a first semiconductor layer with a low carrier concentration that absorbs light, an ohmic electrode formed on the first semiconductor layer, and a first semiconductor layer that absorbs light. a second semiconductor layer having a low carrier concentration, which is formed on the first semiconductor layer, has a forbidden band width wider than that of the first semiconductor layer, and has a thickness that allows carriers to tunnel; a third semiconductor layer formed on the semiconductor layer and having a high carrier concentration and having a bandgap narrower than the forbidden band width of the second semiconductor layer and having a carrier supply function;
The structure is characterized by comprising an ohmic electrode formed on a semiconductor layer.

The interface between the first semiconductor layer and the second semiconductor layer is in a lattice-matched state. Therefore, there is no trap depending on the interface state at the interface, and the first semiconductor layer is not affected by the incidence of light. Since the holes of the generated electron-hole pairs are no longer trapped, the lifetime of the holes is extremely short, resulting in good pulse current response and improved frequency characteristics.

Examples of the invention FIG. 3 is a cutaway side view of essential parts showing one embodiment of the present invention.

In the figure, 11 is a semi-insulating GaAs substrate, 12 is an n-
type (or non-doped) GaAs semiconductor layer (first semiconductor layer), and 13 is an AI tunneling layer. 1. G
a, , Am semiconductor ji (first semiconductor layer), 14 is an n+ type GaAs semiconductor layer (third semiconductor layer) which is a contact layer, 15 is, for example, gold-germanium/gold (Au-Ge
/Au), 16 is also the same <Au-
Ohmic electrode made of Ge/Au, hν is incident light, e
indicates an electron, and h indicates a hole.

In this embodiment, the GaAs semiconductor layer 12, which is the first semiconductor layer, has a thickness of, for example, about 3 [μm], and when doped, it has a thickness of about 1X10'' to 10'4 [1 arch].

AI, which is the second semiconductor layer. , 5Gao, IAs semiconductor layer 13 has a thickness of, for example, about 5O-100C, and is not doped as long as carriers can tunnel sufficiently.

The GaAs semiconductor layer 14, which is the third semiconductor layer, has a thickness of, for example, about 0.5 to 1 [μm], and an impurity concentration of 1
Make it about Xl0” (a1 bow).

The distance between the Alo, , Ga, , As semiconductor layer 13 and the ohmic electrode 16, therefore, the distance between the ohmic electrode 15 and the ohmic electrode 16 in plan view *zi is 1-1
0 (μm) (7) can be selected, and the radiation i! of Ohmink electrodes 15 and 16 can be selected within the range of (7). 2 and 13 are 1
It can be selected within the range of ~5 [μm].

The relationship between the forbidden band widths of the GaAs semiconductor layer 12 which is the first semiconductor layer and the A16.2Qao semiconductor layer which is the second semiconductor layer, and the GaAs semiconductor layer 14 which is the third semiconductor layer is as follows. It is as follows.

Ad, , Ga0. , As semiconductor layer 13 > GaAs semiconductor layer 12 , Alo, s Gao, y As semiconductor J113 > Ga
As semiconductor layer 14 FIG. 4 is an energy band diagram when a bias voltage is applied to the embodiment described in FIG. 3, and the same parts as those described in relation to FIG. 3 are indicated by the same symbols. .

In this embodiment, electron-hole pairs are generated by the light hν entering the GaAs semiconductor layer 12, and the electron e reaches the ohmic electrode 16, but the hole hv
is trapped at the interface between the GaAs semiconductor layer 12 and the Alo, Gao, and As semiconductor layer 13, and due to the presence of the hole h there, the electron e from the 7caAs semi-uniform layer 14 becomes AI. ,,Ga,... Since they tunnel through the As semiconductor layer 13 and are drawn into the GaAs semiconductor layer 12, so-called optically excited carriers are amplified.

In this embodiment, Qaf where the hole h is trapped is
i, s semiconductor layer 12 and A16. z The interface with the Ga6.7 As semiconductor layer 13 is lattice matched, and there are no traps depending on the interface state, so the life time of holes h trapped there is short, so that the incident light hν The pulse current corresponding to the current tail is less likely to tail, and the frequency characteristics are therefore improved.

FIG. 5 shows a cutaway side view of a main part of another embodiment of the present invention.

In the figure, 21 is InP substrate, 22 is Ino, 5aG
ao, 47 As semiconductor layer, 23 InP semiconductor layer, 24
is I no, ssG a 11.4? A 8 semiconductor layer, 25 and 26 indicate ohmic electrodes, respectively.

This embodiment differs only in the semiconductor material, but the carrier concentration, the thickness of the epitaxially grown semiconductor layer, etc. are the same as the embodiment shown in FIG.

FIG. 6 is a plan view of a main part illustrating an electrode configuration for achieving good coupling efficiency between the semiconductor light receiving device of the present invention and an optical fiber.

In the figure, reference numerals 31 and 32 represent electrodes having comb-shaped portion numbers, and reference numeral 33 represents an optical fiber.

Effects of the Invention In the semiconductor light receiving device of the present invention, the first semiconductor layer having a low concentration of light, which absorbs light, and the ohmic electrode formed on the first semiconductor layer are similar to the first semiconductor layer. a second semiconductor layer with a low carrier concentration, which is formed on the semiconductor layer and has a forbidden band width wider than that of the first semiconductor layer and has a thickness that allows carriers to tunnel;
a third semiconductor layer formed on the semiconductor layer with a high carrier concentration and having a forbidden band width narrower than that of the second semiconductor layer and having a carrier supply function; The structure is characterized in that it includes an ohmic electrode formed on the ohmic electrode.

Since such a configuration is adopted, among the carrier pairs generated when light enters the first semiconductor layer,
One carrier immediately reaches the ohmic electrode formed on the tenth semiconductor layer, and the other carrier is trapped at the interface between the first semiconductor layer and the second semiconductor layer. Depending on the presence of the other carrier, one carrier tunnels from the third semiconductor layer through the second semiconductor layer and is injected into the first semiconductor layer. In this process, the interface between the first semiconductor layer and the second semiconductor layer is lattice matched,
Since there are no traps caused by the interface state,
The life time of the other trapped carriers is extremely short, so there is no possibility that the presence of the other carriers will impede the current flowing through the first semiconductor layer and respond to the incident light. The frequency characteristics of the pulse current are extremely good. In addition, to manufacture such a semiconductor light receiving device, it is possible to sufficiently manufacture the semiconductor light receiving device using current technology, and there is no process that requires special technology.

[Brief explanation of the drawing]

FIG. 1 is a cutaway side view of the main part of the conventional example, FIG. 2 is an energy band diagram of the conventional example shown in FIG. 1, and FIG. 3 is a cutaway side view of the main part of an embodiment of the present invention. FIG. 4 is an energy band diagram in the embodiment shown in FIG. 3, FIG. 5 is a cutaway side view of main parts of another embodiment of the present invention, and FIG. 6 is coupled with an optical fiber. 1 and 2 respectively represent a plan view of a main part of an embodiment of the invention with a particularly advantageous electrode pattern; In the figure, 11 is a semi-insulating GaAs substrate, 12 is an n-
type (or non-doped) GaAs semiconductor layer, 13 is A
lo, s Gao, 7 As semiconductor layer, 14 is n+ type G
In the aAs semiconductor layer, 15 and 16 are ohmic electrodes, e is an electron, h is a hole, and hv is incident light. Patent Applicant Fujitsu Ltd. Representative Patent Attorney Shoji Aitani Representative Patent Attorney Hiroshi Watanabe - Figure 1 Figure 3 Figure 4 Figure 6 Figure 1

Claims (1)

[Claims] a first semiconductor layer with a low carrier concentration that absorbs light; an ohmic electrode formed on the first semiconductor layer; and an ohmic electrode formed on the first semiconductor layer and in the first semiconductor layer. a second semiconductor layer with a low carrier concentration that is wider than the forbidden band width and has a thickness that allows carriers to tunnel;
A third semiconductor layer having a high carrier concentration and having a forbidden band width narrower than the forbidden band width of the semiconductor layer of the semiconductor layer and having a carrier supply function, and an ohmic electrode formed on the third semiconductor layer. ``Semiconductor photodetector device'' characterized by: