JPH02189982A - Wavelength multiple discrimination type semiconductor photodetector - Google Patents

Abstract

PURPOSE:To discriminate a plurality of lights having different wavelengths and to photodetect them by forming the interval of second and fourth semiconductor layers in sufficient size to generate an optical coupling. CONSTITUTION:An N-type InP clad layer (first semiconductor layer) 2, a superlattice structure second semiconductor layer 3, a clad layer (third semiconductor layer) 4, a superlattice structure fourth semiconductor layer 5, and a N-type clad layer (fifth semiconductor layer) 6 are sequentially laminated on a board 1. In this case, parameters necessary in design include first the thickness lof second and fourth superlattice structure well layers of absorption end wavelength, and second the thickness (d) of a third semiconductor layer for efficiently coupling between waveguide layers. Thus, a distance L between diffused regions coincides with a completely bonding length determined according to the thickness (d) of the third semiconductor layer. Accordingly, 2-wavelength lights 13 are incident from the end face of the fourth semiconductor layer, the light is absorbed by the fourth semiconductor layer, and output as a current signal through a P-type side electrode 10. Thus, the wavelengths can be easily discriminated to be photodetected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor light-receiving device, and particularly relates to a wavelength multiplexing discrimination type semiconductor light-receiving device that is capable of discriminating and receiving a plurality of lights of different wavelengths. .

[Conventional technology]

Conventionally, optical communication has used a transmission method based on modulation of a single light beam. However, a wavelength multiplexing method using a plurality of lights of different wavelengths is attracting attention as a transmission method with higher density and higher speed. In this case, the light emitting element (semiconductor laser)
In addition to the light emitting diode (LED) or light emitting diode (LED>), the light receiving element also needs a function to discriminate wavelengths and identify each signal.

Currently, well-known semiconductor light-receiving elements for optical communications include, for example, PIN-type light-receiving elements with a light absorption layer of Ino, 53Ga, 47As, lattice-matched to a Si, Ge, or InP substrate. Electronics Letters (EIectron, LetL,) 1984. v
ol, 20°PP653-pρ654), avalanche multiplication type photodetector (for example, IEE Electron Device Letters
n Device LetL, ) 1986, vol. 7
．． P11257-258> etc. The PIN type photodetector is advantageous due to its low capacity and easy manufacturing process.
Avalanche multiplication type photodetectors are attracting attention because of their internal gain effect and high-speed response. In these light-receiving elements, when light having an energy larger than the pan 1-gap energy of the light absorption layer enters the light-receiving part,
The light is absorbed by optical absorption 71 to generate electrons and holes 7, and the carriers (electrons and holes) travel due to the electric field, thereby obtaining a current signal.

However, in such a structure, it is structurally difficult to realize the function of discriminating and receiving light of different wavelengths as long as one light receiving element is used. This is because with these structures, it is not easy to identify the generated current in wavelength units.

On the other hand, Larsson et al.
We proposed a wavelength multiplexing discrimination type semiconductor photodetector with a waveguide structure and a superlattice light absorption layer, and in order to confirm the functionality of wavelength discrimination in practice, we published Applied Physics Letters (Appl, phys, 1.etL, ) 1986 v
ol, 49pp233-235). FIG. 3 shows an element structure diagram of this wavelength multiplexing discrimination type semiconductor light receiving element. The laminated structure is an n-type GaAs substrate 3], an n-type Al on -J-
32 GaAs layers] type GaAs layer/n type A I GaA
Superlattice structure 33 consisting of s layer, p-type AlGaAs# 3
4 + p-type GaAs layer 35. Here, by implanting protons, regions other than the region 40.4] are made to have a high resistance, thereby obtaining a waveguide region 404]. Here electrode 37
By providing 38 and 39, the waveguides 40 and 4 of each
] It is possible to apply different voltages to the photocurrent and obtain the photocurrent number I. Further, the light 42 including two wavelengths is incident from the end face. Here, when light is absorbed in the optical waveguide, it is converted into a current signal, but whether the light is absorbed or guided is determined by the absorption edge energy of the waveguide layer. In other words, when light with energy greater than the absorption edge energy is incident (on the short wavelength side), it is absorbed,
If light with small energy is incident (on the long wavelength side), it will be guided. By the way, this structure is characterized by having a superlattice structure between the light absorption layer and the light waveguide layer.

In general, the absorption edge energy of superlattice structures differs from that of ordinary bulk materials. In other words, due to the quantum leveling of holes and electrons due to the superlattice structure, their absorption edge energy becomes larger than the original bulk absorption edge energy. This is shown in equation (1).

Here, e is the well layer thickness in the superlattice structure, E5 is the Huff 1-gap energy as a bulk, ml is the purchase price of electrons, and mp is the mass of holes. Furthermore, if we consider the case where an electric field is applied to the superlattice structure mentioned above, there is a phenomenon in which spatial separation of electrons and holes occurs in the Ip layer, and the absorption edge energy becomes smaller than the absorption edge energy in the absence of an electric field (5 tar
k effect). In particular, the dependence of the absorption edge energy on the electric field is relatively large, and wavelength discrimination near the absorption edge or the applied electric field can make this possible. Larson (A, I, arss
Specifically, different voltages are applied to the waveguide region 40.4], and due to the above-mentioned effect, the waveguide region 40 absorbs short wavelength light and guides long wavelength light, and the waveguide region 40. 41 to absorb long wavelength light. As a result, a semiconductor light-receiving element capable of distinguishing between two wavelengths is obtained.

[Problems to be Solved by the Invention] The wavelength-discriminating semiconductor light-receiving device described above by Larsson et al. has the following problems.

First, it is not easy to form a high-resistance region by proton implantation, which causes electrical cross-hakes between waveguide regions. In addition, it is expected that defects will be introduced by implantation, which is fatal for optical communication technology that requires high reliability.

Second, the optical coupling in the coupling region between the waveguide regions 40 and 41 is insufficient, which causes coupling loss of the guided light. Here, in order to reduce the coupling loss, it is possible to shorten the distance between the couplings, but this causes the electrical crosstalk mentioned above.

Third, the Stark effect at the same superlattice size (5tar
Due to wavelength discrimination based on the difference in absorption edge wavelength due to the K effect, or due to the basic principle, at most 300 wavelength ranges are discriminated. For practical use, it is desirable to discriminate a wider range of wavelengths.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and provide a multi-wavelength discrimination type conductor light receiving element that can discriminate and receive light having a plurality of different wavelengths.

[Means to solve the problem]

The wavelength multiplexing discrimination type semiconductor light-receiving device of the present invention has a wavelength division multiplexing discrimination type semiconductor light receiving element having a wavelength division multiplexing discrimination type semiconductor light receiving element. Second. Third. 4th. It has a structure in which fifth semiconductor layers are stacked, and the second and fourth semiconductor layers are the first and fourth semiconductor layers. Third. The fifth semiconductor layer has a superlattice structure that has a higher effective refractive index and a lower cap energy than the second semiconductor layer, and has a superlattice structure that also serves as light absorption and a leading wave.
It is characterized by having a spacing of 100 mm or a height sufficient to create an optical cup link.

[Effect]

The present invention has solved the problems of the prior art by taking the above-mentioned measures.

FIG. 2 illustrates the basic structure of the present invention.

The first layer is placed on the semiconductor substrate -1-. Second. Third. 4th. laminating a fifth semiconductor layer and then forming ID type regions 25 and 26;
A voltage can be applied to each region via electrodes 27, 28, 29.

Here's the second one. The fourth semiconductor j- is formed from a superlattice structure, and since the well layer thickness e of the second semiconductor layer and the fourth semiconductor layer are different, the absorption edge wavelengths are different based on the above-mentioned equation (]). .

Now, let each absorption edge wavelength be λ1. Let it be λ2.

In such a structure, light 30 consisting of two wavelengths (wavelengths -λ and λ12) is incident from the end face of the fourth semiconductor layer. Here, λ 1. 〈 λ 1 〈 λ 1□ 〈 λ 2
...(If the relationship 2> is satisfied, the deviation is λ11 wavelength light is absorbed in the fourth semiconductor layer depleted by voltage application and extracted from the electrode 27 as a current signal. Also, λ
Since the 12-wavelength light is longer than the absorption edge wavelength of the fourth semiconductor layer, it is not absorbed and is guided. Here, the third semiconductor layer 23
When the thickness d is small, optical coupling occurs between the fourth semiconductor layer and the second semiconductor layer. This is the same effect as a directional coupler, and in this case, by optimizing the thickness d and the length from the input end face to the end of the p-type region 26,
% coupling occurs. Due to such an effect, the light having the wavelength λI2 is guided into the second semiconductor layer 21, absorbed, and extracted from the electrode 28 as a current signal.

Note that the thickness d and length can be determined by a commonly used directional coupler design method, so details of the method for determining d and I- will be omitted.

Although it is possible to discriminate between two wavelengths based on the following two principles, by applying this structure, compared to the conventional technology,
It has the following advantages.

First, it is preferable in terms of device reliability because it is essentially unnecessary to form a high resistance region by proton injection.

Second, due to the effect of the directional coupler, it is possible to achieve close to 100% coupling between the two waveguides by optimizing the design, and this solves the problem of coupling loss, which is a problem in Larsson et al. It's advantageous.

Third, the structure proposed by Larsson et al.
There is no doubt that the wavelength range of about 0 can be discriminated, but in this structure, the well layer thickness in the superlattice structure is calculated based on equation (1)! By changing the wavelength, it is possible to discriminate wavelengths in a wide range of wavelength ranges.

The above-mentioned effects make it possible to solve the problems of the prior art and obtain a wavelength-discriminating semiconductor light-receiving element with desirable characteristics.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a diagram of a wavelength multiplexing discrimination type semiconductor light-receiving element formed according to an embodiment of the present invention. In this example, InP is used for the 1-1.6 μm wavelength band useful for optical communication.
An InGaAsP system that is lattice-matched to the substrate is used.

n-type InP substrate], an n-type 1nP cladding layer (first semiconductor layer) 2, a second semiconductor layer with a superlattice structure which is an optical waveguide/absorption layer (the barrier layer is an InP layer, the well layer is Or In
053Ga0.47AS layer)3. n-type 1nP cladding layer (third semiconductor N)4. Furthermore, a fourth semiconductor layer with a superlattice structure which is an optical waveguide/absorption layer (barrier layer, qnP layer, well layer is In (,, 53ca0, 47As layer) 5.n type n+
'A cladding layer (fifth semiconductor layer) 6 is laminated using a vapor growth technique or the like. In this case, the first necessary design parameter is the well layer thickness a of the second and fourth superlattice structures, which is related to the absorption edge wavelength. The second factor is the thickness d of the third semiconductor layer in order to efficiently generate a cup link between the waveguide layers. Generally, the thinner d is, the smaller the complete bond length can be, which is advantageous in terms of device size. In this example, the second
The thickness of each of the fourth semiconductor layers was 1.5 μm, and the thickness d of the third semiconductor layer was 075 μm. The complete bond length in this case is 1
It was 70 μm. After stacking such a Jvj structure, p-type regions 8 and 9 are formed by Zn diffusion, and then a Si3N4 insulating film 7. n-side electrode 10.11. n-side electrode 1
form 2. In this case, the distance between the diffusion regions shown in Japan does not match the complete bond length determined by the third semiconductor layer thickness d.

In this example, for example, 1.171 m and 1.3 μm
The purpose is to discriminate between two wavelengths of light. In this case, the second
By setting the well layer thickness r of the semiconductor layer to 75 layers and the well layer thickness of the fourth semiconductor layer to 250 layers, it can be seen from equation (1) that the absorption edge wavelengths of each are lj8 μrn and 1.11 μm, respectively. .

In this structure, two wavelength light (11μm, 1.371m)
By making the light 13 incident on the end face of the fourth semiconductor layer, the 1.1 μl 1 light is absorbed by the 4!1' conductor layer and taken out as a current signal via the n-side electrode 10, as described in the operation section. On the other hand, the 1.3 μnl light is guided without being absorbed, is guided and absorbed by the second semiconductor layer due to coupling, and is taken out as a current signal via the p-side electrode]1.

Based on the above operations, two-wavelength light is discriminated.

In this example, InGaAsP is used as a material in the wavelength range of 1 to 1.6 μm, which is useful for optical communications, but this is different from other materials such as A, which is useful for wavelengths below 1 μm.
Needless to say, the structure is sufficiently applicable to lGaAs.

〔Effect of the invention〕

As explained above, the wavelength multiplexing discrimination type semiconductor light receiving device obtained by the present invention utilizes the fact that the superlattice structure, which is the optical waveguide absorption layer, shifts the absorption edge wavelength to 1 depending on the well layer thickness, and further improves the directionality. By combining the efficient coupling action of the coupler, it becomes possible to absorb light of different wavelengths in each optical waveguide layer and extract it as a photocurrent signal. This makes it possible to easily discriminate wavelengths and receive light in wavelength multiplexed optical communication.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a wavelength multiplexing discrimination type semiconductor light-receiving element that can discriminate between two wavelengths of light, which is an embodiment of the present invention, FIG. 2 is a diagram showing the basic principle of the present invention, and FIG. The figure does not show a conventional wavelength multiplexing discrimination type semiconductor light-receiving device implemented by Larsson et al. 1...rl type 1nP substrate, 2...n type TnP cladding layer, 3.=n type 1nP/n type InO, 53Ga,
478S superlattice structure, 4... n-type 1nP cladding layer,
5...n-type 1nP/n-type 1no, 5qGa0.478S superlattice structure, 6...n-type InP cladding layer, 7...
・Si3N4 insulating film, 8...p type region 1.9...p
Mold region, 10... n-side electrode 1.11... n-side electrode,
12. N-side electrode, 13. Incident light consisting of two wavelengths, 20
...first semiconductor layer, 21...second semiconductor layer (superlattice structure), 22...third semiconductor layer, 23...fourth semiconductor layer (
superlattice structure), 24... fifth semiconductor layer, 25... 1
) type region, 26...p type region, 27... electrode, 28
...electrode, 2...electrode, 31...n-type GaAs
Substrate, 32...n-type AlGaAs cladding layer, 3 B
-n-type GaAs/n-type AlGa superlattice structure group, 34
...n-type AlGaAs cladding layer, 35...p-type G
aAs layer, 36... Proton injection region, 37... Electrode, 38... Electrode, 39... Electrode, 40... Waveguide region, 41... Waveguide region, 42... 2 wavelengths The incident light consists of Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] It has a structure in which first, second, third, fourth, and fifth semiconductor layers are sequentially laminated on a semiconductor substrate, and the second and fourth semiconductor layers are the same as the first, third, and fifth semiconductor layers. The third semiconductor layer has a superlattice structure that has a higher effective refractive index and a lower band gap energy than the third semiconductor layer and serves as both optical absorption and optical waveguide, and optical coupling occurs between the second and fourth semiconductor layers. What is claimed is: 1. A wavelength multiplexing discrimination type semiconductor light-receiving element characterized by having a size sufficient for