JPS63278281A - Light detector - Google Patents

Abstract

PURPOSE:To make the integration easy by a method wherein a waveguide is formed collectively at a light detector and the light is made easily incident so that the efficiency to couple with an optical fiber can be enhanced and that the light can be made incident from a cleavage face. CONSTITUTION:This detector is constituted in such a way that semiinsulating compound semiconductor waveguide layers, e.g., semiinsulating AlGaAs light waveguide layers 12A, and compound semiconductor light-absorption layers whose conductivity type is an i-type or a type close to the i-type, e.g. n-type GaAs light-absorption layers 12B, are laminated alternately. If the light L is incident in a state that a reverse bias voltage from a power supply E is impressed between a region 14 and a region 15, an electron and hole pair is generated in the light-absorption layers 12B. In the light waveguide layers 12A, the light which is incident from an oblique direction advances while it is reflected between the light- absorption layers 12B whose refractive index is small as compared with that of the light waveguide layers 12A; it generates the electron and hole pair when it enters the light- absorption layers 12B. The light is hardly detected at a tapered part 16A from the electron and hole pair generated in this manner. Because a distance from the p-type impurity diffusion region 14 to the n-type impurity diffusion region 15 is short at a straight part 16B, an electric field is sufficiently high and the electron and hole pair is separated; the light is then detected.

Description

Detailed Description of the Invention [Summary] The present invention provides a photodetector in which an optical waveguide layer and an optical absorption layer are alternately laminated to form an optical waveguide layer and an absorption layer. By forming an impurity diffusion region of one conductivity type and an impurity diffusion region of the opposite conductivity type in the layer, a funnel-shaped impurity non-diffusion region extending from one cleavage plane to the other cleavage plane is defined,
By concentrating the incident light at the tapered part of the funnel-shaped impurity non-diffusion region, and by making the condensed light enter the straight part for optical detection, the optical fiber This improves the optical coupling efficiency with the optical fiber, and also enables high-speed optical detection, that is, detection of high-speed optical pulses.

[Industrial application field]

The present invention relates to a photodetector with good optical coupling efficiency and a configuration suitable for integration.

[Conventional technology]

Conventionally, a pin photodiode, an avalanche photodiode ((
avalanche photo di.

de:APD) and the like are known.

FIG. 5 shows a cutaway side view of a main part of a conventional PIN photodiode.

In the figure, 1 is an n-type A6GaAs layer, 2 is an i-type GaA layer
s layer, 3 is an n-type A6GaAs layer, 3A is a p-type region, 4 is an insulating film made of silicon dioxide (SiOz), 5 is a p-side electrode, 6 is an n-side electrode, 7 is a power source, and L is an incoming light are shown respectively. Incidentally, the thickness of the n-type Aj2GaAs layer 1 is 2 [μm], and the thickness of the i-type GaAs layer 2 is 3 to 4 (
, cam), the thickness of the n-type AβGaAs layer 3 is 1 [μ
m] Toshishita. Note that, depending on the structure, there are some that allow light to enter from the back surface.

In this pin photodiode, when a reverse bias voltage is applied as shown in the figure and light is incident, the light is absorbed in the depleted i-type GaAs layer 2 and electrons and positive Hole pairs are generated, electrons flow into the p-type region 3A, and holes flow into the n-type AffGaAs layer 1, so that a so-called photocurrent flows and light is detected.

[Problem that the invention seeks to solve]

By the way, when light is incident on the pin photodiode shown in Figure 5, it is common to use an optical fiber as the optical transmission path, but the wavelength λ of the light to be handled is 0.8.
When expressed as [μm], the core diameter of the optical fiber is 6 [μm] to 10 [μm] for a single mode.

In addition, in order to increase the speed of the pin photodiode, it is necessary to reduce the capacitance to an extremely low value (~0.01 (pF)).
The receiving diameter must also be as small as 6 to 10 μm.

Therefore, for such a pin photodiode,
It is difficult to make light enter with high coupling efficiency. Lenses have also been used to focus the light, but it is difficult to maintain high precision alignment between the pin photodiode and the lens, and integration is difficult, and the direction in which the light is incident is If it is limited to the side or back side, integration becomes even more difficult.

The present invention improves coupling efficiency with an optical fiber by integrally forming a waveguide in a photodetector to facilitate light entry, and also allows light entry from a cleavage plane. Try to facilitate integration.

[Means for solving problems]

In the photodetector of the present invention, a semi-insulating compound semiconductor optical waveguide layer (for example, the semi-insulating Aj2GaAs optical waveguide layer 12A) and a compound semiconductor optical absorption layer whose conductivity type is i-type or close to i-type (
For example, an optical waveguide and absorption layer (for example, an optical waveguide and absorption layer 12) formed by alternately laminating n-type GaAs light absorption layers 12B) and one cleavage plane when the optical waveguide and absorption layer is viewed from the surface. A tapered portion (for example, the tapered portion 16A) that gradually becomes narrower toward the other cleavage plane, and a straight portion (for example, the straight portion 16A) that continues with the tapered portion and extends with a constant width.
B) One conductivity type impurity diffusion region (for example, p
type impurity diffusion region 14) and an opposite conductivity type impurity diffusion region (for example, n-type impurity diffusion region 15) formed on the outside of the other one.

[Effect]

By adopting the above means, the optical waveguide/absorption layer and the optical fiber can be coupled with high optical coupling efficiency, and the light efficiently focused at the Taber part is reliably focused on the narrow straight part. The light is incident on the cleavage plane, surface, and can be detected at high speed.
Since it can be placed on either back side, it is advantageous for integration.

〔Example〕

FIG. 1 shows a cutaway perspective view of essential parts of an embodiment of the present invention. Note that electrodes and the like are omitted in the figure for the sake of clarity.

In the figure, 11 is semi-insulating A7! GaAs haphazard layer, 12 is a multi-quantum well (multi-quantum well)
we I I: MQW) optical waveguide and absorption layer, 13
14 is a p-type impurity diffusion region, 15 is an n-type impurity diffusion region, 16A is a tapered portion of the impurity non-diffusion region, 16B is a straight portion of the impurity non-diffusion region, and 17 is a semi-insulating A#GaAs camp layer. The width of the straight portion, E indicates the power supply, and L indicates the incident light.

FIG. 2 is an enlarged and detailed cutaway front view of the main parts of the optical waveguide and absorption layer 12, and the same symbols as those used in FIG. 1 indicate the same parts or have the same meanings. shall be.

In the figure, 12A indicates a semi-insulating Aj2GaAs optical waveguide layer, and 12B indicates an n-type GaAs optical absorption layer. Note that since the impurity concentration in the n-type GaAs light absorption layer 12B is extremely low, it can essentially be called i-type.

Examples of main data of each part in this embodiment are as follows.

(1) Thickness of the optical waveguide layer 11: 3 to 4 [μm] (2) Thickness of the optical waveguide and absorption layer 12: 2 to 6 [μm] (3) Thickness of the optical waveguide layer 12A: 0.01 to 0.2 [μm] (4) Thickness of light absorption layer 12B: 0.01 to 0.2 [μm] Impurity concentration: I x 10” (cn+-”) or less (5) Thickness of cap layer 13: 1 .5Cμm] (6) Impurity for n-type impurity diffusion region 14: Zn Diffusion means: thermal diffusion (7) Impurity j G for n-type impurity diffusion region 15
a A 5i for s system Cd for InP system Diffusion means: Thermal diffusion (8) Width 17:3Cμm for straight portion 16B] As can be seen from the figure below, the optical waveguide and absorption layer I2 is similar to the optical waveguide layer 12A. and light absorbing layers 12B are alternately laminated, and when a reverse bias voltage is applied from a power source E between the n-type impurity diffusion region 14 and the n-type impurity diffusion region 15, as shown in FIG. When light is incident as shown in FIG. When the light propagates through the light absorption layer 12B, which has a lower refractive index than the light guide layer 12A while being reflected, and enters the light absorption layer 12B, it generates electron-hole pairs as described above. In addition, since the n-type impurity diffusion region 14 and the n-type impurity diffusion region 15 are polycrystalline and have a low refractive index, they have a lateral confinement effect on the light incident on the optical waveguide and absorption layer 12. Moreover, of course, since confinement in the vertical direction is also performed, the light is condensed at the tapered portion 16A and reaches the straight portion 16B.

The electron/genuine tag pair generated as described above has a long distance between the n-type impurity diffusion region 14 and the n-type impurity diffusion region 15 in the tapered portion 16A, and the electric field there is larger than that in the straight portion 16B. Since the light beams are small, many of them are recombined, and therefore, almost no optical detection is performed in the tapered portion 16A. However, in the straight portion 16B, the distance between the n-type impurity diffusion region 14 and the n-type impurity diffusion region 15 is extremely short, about 3 [μm], so the electric field is sufficiently high (
Therefore, the electron-hole pairs are separated, and the electrons flow into the n-type impurity diffusion region 14 and the holes flow into the n-type impurity diffusion region 15, and the p-type impurity diffusion region 14 and the n-type impurity A photocurrent flows between the diffusion region 15 and light detection.

FIG. 3 is a further enlarged and detailed cutaway front view of a part of the optical waveguide and absorption layer 12, and the same symbols as those used in FIGS. 1 and 2 refer to the same parts. or have the same meaning.

In the figure, h indicates a genuine bill, and e indicates an electron.

As can be seen from the figure, n-type impurity diffusion region 14, n (i
) type GaAs light absorption layer 12B, n type impurity diffusion region 15
each constitutes a pin photodiode in one layer,
It has a structure in which many of them are laminated. Then, the holes h generated in the light absorption layer 12B in the straight portion 16B are
The pair of electrons e is separated, and the electron e is transferred to the n-type impurity diffusion region 1.
4, the holes flow into the n-type impurity diffusion region X5. As already explained, the straight portion 16
In B, since the distance traveled by the carrier is extremely short, even high-speed optical pulses can be easily detected.

FIG. 4 is a cutaway perspective view of essential parts for explaining another embodiment of the present invention, and the same symbols as those used in FIGS. 1 to 3 indicate the same parts or have the same meanings. Shall have.

This embodiment differs from the embodiments described with reference to FIGS. 1 to 3 in that, as shown, a groove 18 is formed to separate the tapered portion 16A and the straight portion 16B.

With this configuration, the area of the electrode region related to the straight portion 16B becomes small, and therefore the capacitance becomes small, which is advantageous in terms of speeding up. Further, during operation, if a bias voltage is also applied to the electrode region related to the tapered portion 16A side, the optical waveguide effect and the light focusing effect in the tapered portion 16A are further improved.

In any of the embodiments described above, the thickness of the optical waveguide and absorption layer 12 can be selected to be about 2 to 6 μm.

Similarly, in both embodiments, light is incident from the cleavage plane on the tapered portion 16A side of the pin photodiode, but the distance between the optical waveguide layers 12A, and therefore the thickness of the optical absorption layer 12B Since the wavelength of the incident light is approximately equal to or lower than the wavelength of the incident light, it is possible to make the incident light not only by the above-mentioned means but also from the front surface or back surface of the tapered portion 16A side.

〔Effect of the invention〕

In the photodetector according to the present invention, optical waveguide and absorption layers are formed by alternately stacking optical waveguide layers and optical absorption layers, and one conductivity type impurity diffusion region is formed in the waveguide layer and the absorption layer. By forming an impurity diffusion region of opposite conductivity type, a funnel-shaped impurity non-diffusion region is defined from one cleavage plane to the other cleavage plane. Light is focused, and the focused light is made incident on the same straight portion for optical detection.

By adopting this configuration, the optical waveguide/absorption layer and the optical fiber can be coupled with high optical coupling efficiency, and the light that is efficiently focused at the tapered part is reliably focused on the narrow straight part. Since the light is incident on the cleavage plane, it operates as a photodetector with an extremely small capacity, and high-speed light detection is possible.Also, since the light can be incident on the cleavage plane, the front surface, or the back surface, integration is possible. It is advantageous when doing so.

[Brief explanation of drawings]

FIG. 1 is a cut-away oblique view of the main part of an embodiment of the present invention, FIG. 2 is a cut-away front view of the main part showing the optical waveguide and absorption layer 12 in enlarged detail, and FIG. 3 is a cut-away front view of the main part showing the optical waveguide and absorption layer 12 in detail. FIG. 4 is a cut-away front view of the main part showing another embodiment of the present invention in detail, and FIG. 5 is a cut-away front view of the main part of the conventional example. Each represents a side view. In the figure, 11 is semi-insulating AβGaAsβGaAs.
The buffer is a multi-quantum well.
well: MQW) optical waveguide and absorption layer, 13 is a semi-insulating A#GaAs camp layer, 14 is a p-type impurity diffusion region, 15 is an n-type impurity diffusion region, 16A is a tapered portion of the impurity non-diffusion region, 16B is a The straight portion of the impurity non-diffusion region, 17 is the width of the straight portion, E is the power source, and L is the incident light. Patent Applicant: Fujitsu Ltd. Representative Patent Attorney Akira Aitani Representative Patent Attorney Hiroshi Watanabe - Cutaway front view of essential parts of the embodiment Figure 2 r1 Cutaway front view of essential parts of optical special wave and absorption layer Figure 3

Claims (1)

[Scope of Claims] An optical waveguide and absorption layer constituted by alternately laminating a semi-insulating compound semiconductor optical waveguide layer and a compound semiconductor optical absorption layer whose conductivity type is i-type or close to i-type, and the optical waveguide. In order to define a pattern consisting of a tapered part whose width gradually becomes narrower from one cleavage plane to the other cleavage plane when looking at the absorbing layer from the surface, and a straight part which continues with the tapered part and extends with a constant width, A photodetector comprising an impurity diffusion region of one conductivity type formed on one side of a pattern and an impurity diffusion region of an opposite conductivity type formed on the other side of the pattern.