JPH0155586B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a composite optical semiconductor device comprising a semiconductor light emitting device and a semiconductor photodetecting device.

[Prior art and its problems]

Light emitting diode (hereinafter referred to as a light emitting diode) as a semiconductor light emitting device
Compared to semiconductor lasers, the output characteristics of LEDs (abbreviated as LEDs) have less temperature variation and better linearity, making them very easy to handle light sources except for problems with response and power level. However, when actually used in analog transmission, for example, it is necessary to further compensate for temperature characteristics and linearity.

Recently, this compensation method mainly uses a broadband optical/electrical negative feedback method (S56 National Institute of Electronics and Communication Engineers General Conference 2226), which simultaneously compensates for both temperature and linearity and has excellent stability. This method compensates for nonlinear distortion of the semiconductor light emitting device by detecting a portion of the optical output of the semiconductor light emitting device and feeding it back negatively to the semiconductor light emitting device drive circuit. In order to compensate for such nonlinear distortion, it is desirable to form a semiconductor light emitting element and a semiconductor photodetector element in an integrated manner.

Conventionally, a structure in which a semiconductor light emitting element and a semiconductor detection element are integrally formed has been devised as shown in FIG. 1, which is partially shown in cross section. i.e. for example LED
A light passing section 1-30 for passing the light output from the LED 1-10 to the outside is provided at approximately the center of one surface of the semiconductor light emitting device consisting of the LED 1-10.
For example, a photodiode (hereinafter abbreviated as PD)
Semiconductor photodetecting elements consisting of 1-20 are integrally formed in a layered manner.

The LED 1-10 is provided with a current confinement layer 1-12 made of, for example, N-type GaAs on a substrate 1-11 made of, for example, P-type GaAs.
A first composition layer 1-13 made of GaAlAs is formed. Further, a second composition layer 1-15 made of, for example, N-type GaAlAs is formed on the first composition layer 1-13 via an active layer 1-14 made of, for example, N-type GaAs or GaAlAs. It's summery.

Next, the PD1-20 is the N-type GaAlAs
For example, GaAlAs or GaAs
A P-type layer 1-22 made of, for example, P-type GaAs is formed through a low impurity concentration layer 1-21 made of P-i-N structure.
The N-type layer made of GaAlAs is shared with the second composition layer 1-15 of the LED 1-10. In addition,
One electrode 1-17 of LED1-10 is connected to LED1-10.
-10 and outside the light receiving part of PD1-20, and the other electrode 1-16 is an LED.
1-10. Also,
One electrode of PD1-20 is also used as one electrode 1-17 of LED1-10, and the other electrode 1
-23 is provided on one surface of the light receiving section of PD1-20.

In the above structure, the light output from the active layer 1-14 is detected by the PD 1-20, and is also partially outputted to the outside through the light passage section 1-30 and enters the optical fiber 1-40. do. Furthermore, the PD1
The -20 output is guided to an external electronic circuit and constitutes the broadband optical/electrical negative feedback described above.

However, such a structure has the following problems.

In order to implement a wideband optical/electrical negative feedback system, the optical output guided to the optical fiber 1-40 and the PD1-20
In terms of distortion compensation, it is a necessary condition for the optical outputs received by the optical system to have similar waveforms, but recent research has revealed that the above-mentioned structure does not result in similar waveforms. That is, since the double hetero layer consisting of the first composition layer 1-13 and the second composition layer 1-15, which is the path for the current that drives the LED 1-10, is a very thin layer, the LED 1-10 cannot be viewed microscopically. As shown in the equivalent circuit diagram shown in FIG. 2, the micro LEDs 2-21 in each part are connected via the spreading resistor 2-22. And LED1
The following situation occurs because the path of the current driving -10 is long.

First, when the current driving the LED 1-10 is small, the voltage drop caused by the spreading resistor 2-22 is small, so that the current flows uniformly through the active layer 1-14, emitting light uniformly. However, when the current driving LED1-10 is increased, the spreading resistance 2-2
2, the voltage drop is large and a sufficient voltage is not applied to the peripheral micro LEDs compared to the central micro LEDs, so the light output of the central micro LEDs is greater than the light output of the peripheral micro LEDs. The relationship between current and light output in this case is as shown in Figure 3, where the light output increases as the current increases in the small LED at the center, drawing a downwardly convex curve 3-1; depicts an inverse curve 3-2 that is symmetrical to this. That is,
In the conventional structure, the PD 1-20 receives the light output that passes through the light passage part 1-30 provided at the center of the LED 1-10 and enters the optical fiber 1-40, and the light around the LED 1-10. As the current value increases, the waveforms of the optical outputs of the optical outputs differ, making it impossible to achieve highly accurate broadband optical/electrical negative feedback.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned problems, and its purpose is to configure a semiconductor photodetection element that detects a light output having a waveform similar to the light output to the outside of a semiconductor light emitting element, An object of the present invention is to provide a composite optical semiconductor device capable of performing effective broadband optical/electrical negative feedback.

[Summary of the invention]

In this invention, a semiconductor light detecting element for detecting the light output of the semiconductor light emitting element is formed on a semiconductor light emitting element by dividing it into a plurality of parts, and the light output of the semiconductor light emitting element is separated between the plurality of light detecting parts. A composite optical semiconductor device is obtained in which a plurality of light passage portions for emitting light to the outside are formed by dividing each into a plurality of sections.

〔Effect of the invention〕

This invention constitutes a PD that can detect optical output with a waveform similar to the external optical output of an LED, compensates for nonlinear distortion of the LED, and performs an effective wide-band optical/electrical negative feedback complex. An optical semiconductor device can be obtained.

[Embodiments of the invention]

A first embodiment of the invention will be described with reference to FIG. 4, which partially shows a cross-sectional view.

That is, it has a P-N junction that forms a light emitting part,
For example, on one surface of a semiconductor light emitting element consisting of LED4-10, a plurality of photodetecting elements consisting of PD4-20, for example, which detect a part of the light output from LED4-10, are arranged concentrically in a plurality of annular configurations. There is. Also, each gap of PD4-20 is an optical fiber 1
-40 as an external light passage section 2-30.

For example, LED4-10 has an impurity concentration of 1×
10 ¹⁸ /cm ³ and a thickness of 100 to 200 μm on a substrate 4-11 made of P-type GaAs with an impurity concentration of 1, for example.
×10 ¹⁸ /cm ³ and a thickness of 4 to 5 μm, for example, through a current confinement layer 4-12 made of N-type GaAs with an impurity concentration of 1 × 10 ¹⁸ /cm ³ and a thickness of 4 to 5 μm. P
A first composition layer 4-13 of type Ga _1-x AlxAs (x=0.3 to 0.4) is formed. Further, on this first composition layer 4-13, for example, ^N -type GaAs ^or
Active layer 4- consisting of Ga _1-x Al _x As (x = 0.06 to 0.1)
For example, if the impurity concentration is 1×10 ¹⁸ /cm ³
Then, N-type Ga _1-x AlxAs (x=0.3 to
0.4), the second composition layer 4-15 is formed. Note that the current confinement layer 4-12
is formed in part to improve current concentration and obtain high luminous efficiency. Also, this LED
One electrode 4-17 of the substrate 4-10 is provided on a part of the upper surface of the second composition layer 4-15, and the other electrode 4-16 is provided on the lower surface of the substrate 4-11. There is. On the other hand, PD4-20 has on the N-type layer,
For example, through a low impurity concentration layer 4-21 made of GaAlAs with a thickness of 10 ^μm or GaAs with ^a thickness of 5 μm,
A P-type layer 4-22 made of GaAs is formed and P-i
-N structure. Note that the N-type layer at this time is shared with the second composition layer 4-15 of the LED 4-10. One electrode 4 of this PD4-20
-17 is provided on a part of the upper surface of the N-type layer 4-15 of the LED 4-10, and the other electrode 4-23
is provided on the upper surface of a diffusion layer 4-26 made of, for example, P ⁺ type GaAs, which is formed to obtain ohmic contact with a part of the P-type layer 4-22 of each PD 4-20.

PD4-2 having the above-mentioned multiple ring configuration
If the annular ring width is formed to be, for example, several micrometers, several tens of fine PDs can be constructed considering that the LED diameter is usually 200 to 300 micrometers, for example.

With this configuration, PD4-20
Since the light passing portions 4-30 and 4-30 are arranged alternately at intervals of several μm, the PD on the upper surface of the LED 4-10
4-20 can be considered to be uniformly formed in terms of spatial arrangement. Note that there is no need to particularly consider the problem of spreading resistance caused by providing a plurality of PDs. This is because the length of the current path within the second composition layer 4-15 for a plurality of PDs such as PD 4-20 is shorter than the length of the current path of LED 4-10. The increase in spreading resistance due to the long current path of LED4-10 and the unevenness of the light output as a monitor light due to this are
Compensation is made by detecting with PD.

Therefore, the problem of dissimilarity between the waveform of the optical output to the outside and the waveform of the optical output to the PD, which is caused by uneven voltage drops at various parts when viewing the LED 4-10 microscopically, is greatly reduced. be able to. Furthermore, by making the areas of the light passing section 4-30 and PD 4-20 variable, the light output to the outside of the optical fiber 1-40 and
The optical output detected by PD4-20 can be freely set.

In the first embodiment described above, the PD4-20 is arranged concentrically in a plurality of annular configurations, but even if this shape is a polygon such as a triangle or a quadrilateral or an ellipse, a plurality of PD4-20s can be provided concentrically and spaced. It is clear that it is sufficient if they are formed evenly in terms of arrangement.

Next, a second embodiment of the invention will be described with reference to FIG.

In the first embodiment described above, the PD 4-20 and the light passing section 4-30 are formed concentrically and alternately in a plurality of annular shapes, but in this second embodiment,
A plurality of circular PDs 5-20 are evenly distributed and formed on one surface of 4-10 in the form of islands.

Here, the composition, impurity concentration, etc. of LED4-10 and PD5-20 are the same as in the first embodiment.
That is, PD5-20 on one surface of LED4-10
The light passing section 5-30, which is the part that does not form the
PD5-20 can be considered to be equally spaced in the same way as in the first embodiment.

Therefore, the external light output of LED4-10 and PD
The optical output to the optical fiber 1-40 can be obtained as a substantially similar waveform, and the optical output to the optical fiber 1-40 and
The optical output detected by PD4-20 can be freely set.

In addition, in the second embodiment described above, the circular PD5-
Although a plurality of 20 are formed, it is clear that the shape may be a polygon such as a triangle or a quadrangle, or an ellipse as long as a plurality of the shapes are evenly distributed.

[Brief explanation of drawings]

Figure 1 is a perspective view showing a part of a conventional example in which an LED and PD are integrally formed, Figure 2 is an equivalent circuit diagram of the conventional example shown in Figure 1, and Figure 3 is an LED drive current. FIG. 4 is a perspective view showing a cross section of a part of a composite optical semiconductor device showing a first embodiment of the invention, and FIG. 5 shows a second embodiment of the invention. FIG. 2 is a perspective view showing a part of the composite optical semiconductor device in cross section. 1-40...Optical fiber, 2-21...Minute
LED, 2-22... Spreading resistor, 4-10...
LED, 4-11...Substrate, 4-12...Current confinement layer, 4-13...First composition layer, 4-14...
Active layer, 4-15... Second composition layer, 4-16...
...LED electrode, 4-17...LED and PD electrode, 4-20, 5-20...PD, 4-21...
Low impurity concentration layer, 4-22...P type layer, 4-23
...PD electrode, 4-30, 5-30...light passage section.

Claims (1)

[Scope of Claims] 1. A semiconductor light-emitting device comprising a semiconductor light-emitting device and a plurality of semiconductor photo-detecting devices integrally formed in a layer on one surface of the semiconductor light-emitting device, wherein a portion of the light output from the semiconductor light-emitting device is is detected by the plurality of semiconductor photodetecting elements, and another part of the light output from the semiconductor light emitting element is taken out to the outside via a light passing section formed between the plurality of semiconductor photodetecting elements. A composite optical semiconductor device characterized by: 2. The composite optical semiconductor device according to claim 1, wherein the plurality of semiconductor photodetecting devices are formed concentrically with each other on one surface of the semiconductor light emitting device. 3. The composite optical semiconductor device according to claim 1, wherein the plurality of photodetecting elements are formed in an island shape on one surface of the semiconductor light emitting device.