JP2844833B2 - Semiconductor light receiving element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor photodetector, and more particularly to an avalanche multiplication semiconductor photodetector excellent in low noise and high-speed response.

(Prior Art) Conventionally, an In _0.53 Ga _0.47 As layer lattice-matched on an InP substrate (hereinafter referred to as I) as a semiconductor light receiving element for optical communication in a band of 1 to 1.6 μm.
PIN-type semiconductor light-receiving device (Electron Letters (Eletron. Lett.) 1) with light absorption layer of nGaAs layer
984, 20 , pp653-pp654), avalanche multiplication type semiconductor photodetector (IEEE
Letters (IEEE. Electron Device Lett.) 1986,7, pp257
-258) is known. Above all, avalanche multiplication type semiconductor light receiving elements have been practically used for long-distance optical communication in that they have an internal gain effect and a high-speed response due to avalanche multiplication.

FIG. 4 shows a typical InGaAs-APD (an avalanche multiplication type semiconductor light receiving element is hereinafter abbreviated as APD). The operation principle of this APD will be described. Among the optical carriers generated in the InGaAs layer 4, hole carriers are injected into the InP avalanche multiplication layer 11 by an electric field. InP avalanche multiplication layer 1
A high electric field is applied to 1 and ionization collision occurs, leading to multiplication characteristics. In this case, it is known that noise and high-speed response characteristics which are important in device characteristics are controlled by a random ionization process of carriers in a multiplication process. Specifically, the ionization collision with a pure carrier occurs as the difference in the ionization rate between the electron and the hole in the multiplication layer InP layer becomes larger (when the ionization rates of the electron and the hole are α and β, respectively, α
When β / α> 1, electrons should be the main carrier that causes ionization collision when β / α> 1, and this is desirable in terms of device characteristics.

However, the ionization rate (β / α) is determined by material properties, and is at most about β / α2 in InP. This is significantly different from α / β20 of Si having low noise characteristics, and an innovative material technology is required to realize lower noise and faster response characteristics.

In contrast, F. Capasso et al. Applied a superlattice structure with large band discontinuity to the avalanche multiplication layer (Applied Physics Letters
I. Phys. Lett.), 40, pp. 38-40 (1982)) that the ionization rate ratio can be artificially controlled. For the optical communication wavelength band (1 to 1.6 μm), K. Brennan applied the InAlAs / InGaAs superlattice system as a multiplication layer, and the ionization rate α / β = 20 by the Monte Carlo method. Theoretically supposes that a degree can be obtained (IEEE.Trans.Electron Devices, E
D-33 , pp1502-1510 (1986)). An avalanche multiplication type photodetector using these superlattice structures is a conventional InGaAs-type photodetector.
APD is expected to be a device that far exceeds the characteristics of APD.

(Problems to be Solved by the Invention) As the above-mentioned superlattice APD, in particular, when it is limited to an optical communication in the 1 to 1.6 μm band, K.K. An InAlAs / InGaAs superlattice system proposed by K. Brennan is conceivable (the InAlAs layer has an In _0.52 Al _0.48 As composition in order to lattice match with the InP substrate. Hereinafter, it is abbreviated as an InAlAs layer). FIG. 3 shows the ionization process of electrons in the InAlAs / InGaAs rectangular superlattice structure proposed by Brennan. The electrons generated by light absorption travel through the superlattice multiplication layer, thereby taking in relatively large band discontinuity (ΔE _c 0.5 eV) in the conduction band as energy, and the ionization of electrons in the InGaAs well layer is likely to occur. . Therefore, the ionization rate (α /
β) is expected to increase.

However, the ionization threshold energy E _ie of the electrons in the InGaAs well layer is about 1 eV, and only one electron passes through one hetero to obtain at most 1 / 2ΔE _ie . Ideally, it is desirable to have a conduction band discontinuity of about ΔE _c E _ie, but in reality, the material is rate-determining at present.
Therefore, in order to improve device characteristics, a more effective structure is indispensable.

Accordingly, an object of the present invention is to solve these problems and to provide an avalanche multiplication type semiconductor light receiving element having low noise and high speed response.

(Means for Solving the Problems) A semiconductor light receiving element according to the present invention is a semiconductor light receiving element having at least an avalanche multiplication layer and a light absorption layer on a semiconductor substrate, wherein the avalanche multiplication layer has a superlattice structure. The lattice structure is based on a rectangular superlattice structure,
Further, each of the rectangular superlattice structures has a barrier layer region therein.
It is characterized by having a rectangular short-period superlattice structure comprising a well layer and a barrier layer thickness of 100 Å or less.

(Operation) The present invention has solved the problems left in the prior art by taking the above-described means. FIG. 2 is a view showing a band structure in the device of the present invention. Basically, in the rectangular superlattice (InAlAs / InGaAs) multiplication layer, a short-period rectangular superlattice structure (InAlAs / InGaAs) in which the well layer / barrier layer thickness is less than 100 mm in the InAlAs barrier layer region There is to make an area.

As shown in this figure, when the electrons generated by light absorption travel through the present superlattice multiplication layer, the electrons feel the conduction band discontinuity (ΔE _c ) of the superlattice structure as a valley and effectively reduce ΔE _c . It is clear, as Brennan points out, that gaining energy and making it easier to reach ionization. In the present invention, even when electrons travel through the InAlAs barrier layer, the conduction band discontinuity is effectively reduced in order to experience a short-period superlattice region in which each of the well layer and the barrier layer thickness is 100 ° or less. Experience more. Therefore, it becomes possible for electrons to acquire energy more efficiently.

In this case, the layer thickness of the short-period superlattice structure is determined for the following reasons. In other words, regarding the well layer thickness, it is necessary to form a sufficiently large quantum level in order to alleviate the trap development of electrons, and for this purpose, it is important that the quantum level is 100 ° or less. The thickness of the barrier layer is limited to 100 ° or less, which is also easy for tunnel ring running or hot carrier formation in order to alleviate the trapping phenomenon. Here, the energy that the electron actually obtains by experiencing one hetero in the short-period superlattice structure region is (ΔE _c −E _{1, e} ). E _{1, e} is the first quantum level of the conduction band.

As described above, in this structure, by intentionally creating a short-period superlattice structure in the barrier layer region in the superlattice multiplication layer, it is possible to increase the number of electron hetero experiences and obtain large energy Becomes This enables selective ionization of electrons, and achieves device characteristics that surpass the prior art. Specifically, low noise and high speed response characteristics are realized by increasing the ionization rate.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a structural sectional view of an avalanche multiplication type light receiving element formed according to an embodiment of the present invention. The structure of this embodiment is such that an n-type InP buffer layer 2, an n-type rectangular superlattice avalanche multiplication layer 3, an n-type InGa
An As light absorbing layer 4 and an n-type InP window layer 5 are sequentially laminated. Here, the rectangular superlattice avalanche multiplication layer 3 is according to the present invention, and in a rectangular superlattice structure composed of a 500Å well layer and an 875Å barrier layer, 25Å in some regions in the barrier layer.
It has a basic superlattice structure (10 periods) in which a 5-period rectangular short-period superlattice structure composed of a well layer and a 50 ° barrier layer is interposed. Thereafter, ap ⁺ region 6 is formed by a diffusion method, and further, a passivation film 7 and electrodes 8 and 9 are formed to obtain an element structure.

Here, a light carrier is generated by absorbing light in the InGaAs light absorbing layer 4. Among them, only electrons are in the superlattice multiplication layer 3
And a multiplication phenomenon occurs according to the above-described action. In this embodiment, since the well layer thickness of the structure of the short-period superlattice is 25 °, the first quantum level energy on the conduction band side is formed (ΔE _c / 2) eV above the conduction band bottom.

In the device according to the above embodiment, the electric field intensity required for multiplication is 50 times larger than that of the device having the conventional rectangular superlattice structure multiplication layer (well layer 500Å, barrier layer 500Å, 10 periods).
It has been experimentally confirmed that it is reduced by about kV / cm. This is because the short-period superlattice structure according to the present invention allows the electrons to gain more energy during traveling. It indicates the facts. Further, it has been confirmed that the ionization ratio (α / β) and the high-speed response have been improved.

In this embodiment, the light absorption layer and the avalanche multiplication layer are different layers. However, the present invention can be effectively operated and effective even when the avalanche multiplication layer is formed in the light absorption layer.

The element structure according to the present invention is basically sufficient for the growth technique of the rectangular superlattice structure, and can be easily manufactured by MOCVD, MBE, or the like.

(Effects of the Invention) As described above, the avalanche multiplication type light-receiving element obtained by the present invention can reduce the multiplied electric field intensity by using a short-period rectangular superlattice in the superlattice avalanche layer. Improvement of the conversion ratio and device characteristics excellent in high-speed response are achieved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a superlattice avalanche multiplication type light receiving element according to an embodiment of the present invention. FIG. 2 is a diagram showing a band structure of a superlattice avalanche multiplication type light receiving element of the present invention. Third
The figure shows the band structure of a conventional superlattice avalanche multiplication photodetector by K. Brennan.
FIG. 4 is a cross-sectional view of a conventional InGaAs avalanche multiplication type light receiving element. 1 .... n-type InP substrate, 2 .... n-type InP buffer layer, 3 ....
n-type rectangular superlattice avalanche multiplication layer, 4 ... n-type InGa
As light absorption layer, 5: n-type InP window layer, 6: p ⁺ diffusion region, 7: passivation film (SiN film), 8: p
Side ohmic electrode, 9 ... n-side ohmic electrode, 10 ...
Incident light, 11 ... n-type InP avalanche multiplication layer, 12 ... n
Type InP cap layer, 13 ... p ⁺ diffusion region, 14 ... p ^- diffusion region.

Claims (1)

(57) [Claims] 1. A semiconductor light receiving device having at least an avalanche multiplication layer and a light absorption layer on a semiconductor substrate, wherein the avalanche multiplication layer has a superlattice structure, and the superlattice structure basically has a rectangular superlattice structure. And a rectangular short-period superlattice structure having a well layer and a barrier layer thickness of 100 Å or less in the barrier layer region of the rectangular superlattice structure.