JPS63158881A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To remove an error by dark currents by a method wherein identical two semiconductor photodetectors are formed into one chip: one semiconductor photodetector is light-shielded but outputs only dark currents, and is input to the other semiconductor photodetector inputs optical signal. CONSTITUTION:Two P-type regions 20, 21 are shaped to an N-type semiconductor substrate 12. The P-type region 20 forms a semiconductor photodetector into which an optical signal is projected through a nonreflective film 5, but the P-type region 21 is light-shielded by a wiring layer 14 consisting of a substance having high reflectivity to beams. The semiconductor photodetector shaped by the P-type region 20 and a semiconductor photodetector formed by the P-type region 21 are shaped into one chip in the same size and structure, thus approximately equalizing the magnitude and temperature characteristics of the dark current components of both photodetectors. Accordingly, an output in which dark current components are cancelled is acquired at all times by taking the difference of two outputs on usage, and stable control is enabled without an error even when the intensity of incident beams is small or even when dark currents components change.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor light receiving device that receives an optical signal and outputs a current proportional to the intensity of the signal, and particularly relates to a semiconductor light receiving device that receives an optical signal and outputs a current proportional to the intensity of the signal. The present invention relates to a light receiving device that eliminates errors due to

[Conventional technology]

FIG. 3 shows an example of a conventional semiconductor light receiving device and its connection circuit. In FIG. 3, the semiconductor light-receiving element 11 is normally connected in series with a resistor 3t, and reverse biased by a power source 2.
The voltage generated across the resistor 3 when receiving optical input is utilized. That is, in FIG. 3, the semiconductor light receiving element 11 generates a current I proportional to the intensity of light input. Therefore, a voltage of V,=XA·R is generated in the resistor 3, and this voltage is used as a signal proportional to the light intensity.

[Problem that the invention seeks to solve]

The conventional semiconductor light-receiving element 11 described above generates a current IP proportional to the optical input as well as a dark current component independent of the optical input, so the actual output voltage Voutri, Vou, ==R(ID+I,): R-I, +R・I,:
VD+V.

In addition to the output (a) which is proportional to the light intensity, a constant voltage V
D is added constantly. At this time, optical input-output (■. u
t) Characteristics are shown in Figure @4.

Therefore, the output V. When using ut to control other circuits, if the intensity of the optical input is large and vP is sufficiently large compared to VD, VD can be ignored, and vout is almost proportional to the intensity of the optical input, so there is no problem. However, the intensity of the optical input is small, and ■
, is small, VD cannot be ignored, so Vout
has the disadvantage that it is not proportional to the optical input, making accurate control impossible. Also, Mel ■. Even if it can be adjusted to be controllable, the voltage will vary by 5V due to temperature changes, etc. The disadvantage is that if the value of changes, the control will go out of order.

[Means for solving problems]

In the semiconductor light receiving device of the present invention, two identical semiconductor light receiving elements are provided in one chip, one semiconductor light receiving element is shielded from light and only dark current is output, and the other semiconductor light receiving element is used for optical signals. is now entered.

〔Example〕

Next, the present invention will be explained using the drawings.

FIG. 1 shows an example of a semiconductor light receiving device and its connection circuit according to the present invention. In FIG. 1, a semiconductor light-receiving device 1 consists of a semiconductor light-receiving element 1a and a semiconductor light-receiving element 1b, which are made to have the same size and structure within one chip. Therefore, it is considered that the semiconductor light-receiving elements 1a and 1b have substantially the same characteristics, and in particular, the magnitude of their dark current components, temperature characteristics, etc. are also considered to be the same. The semiconductor light-receiving element 1a is configured to receive an optical signal 4 so as to output an et current in proportion to the light intensity, but the semiconductor light-receiving element 1b is shielded from light as shown by a dotted hatched area. Therefore, the current generated by the semiconductor light-receiving element Ia has a current component proportional to the input light intensity and a dark current component. However, the current generated by the semiconductor light-receiving element 1b is only a dark current component. When the connection as shown in Fig. 1 is made, the resistance value of the resistor 3a connected to the semiconductor light receiving element 1a is
The voltage generated at is R(I, +I,):ReI, +811 I,:VD+
VP, is connected to the semiconductor light receiving element 1b, and has a t resistance value R.
The voltage generated across the resistor 3b is 几.In=-Vn. Therefore, when the voltages generated across the resistors 3a and 3b are input to the subtraction circuit 5, the output of the subtraction circuit 5 is . ,
is Vout ” (Vn ” VP) VD = vP, the voltage component VD due to the dark current is erased and the output voltage V. ut is only the component vP that is proportional to the input light intensity.

The optical input-output (■.ut) ratio at this time is shown in FIG.

Note that on the upper side, resistors 3a and 3b are externally connected, but by forming these resistors on the same chip as semiconductor photodetectors 1a and lb, the resistance values of resistors 3a and 3b are the same, and the resistors In addition to making it possible to reduce the difference in voltage generated due to the difference in values, it also eliminates the labor required for externally attaching a resistor.
It is also possible to reduce the installation area.

FIG. 5 also shows an example of the device structure of the semiconductor light receiving element according to the invention. In FIG. 5, two P-type regions 20 and 21 are formed on the N-type semiconductor substrate 12. The P-type region 20 forms a semiconductor light-receiving element with a normal structure in which an optical signal is incident through the entire non-reflection film 5. However, the P-type region 21 is shielded from light by the wiring layer 14 formed of a material having a high reflectance to light (for example, mirror-like aluminum, gold, etc.).

a semiconductor light receiving element formed by the P-type region 20;
The semiconductor light-receiving elements formed in the P-type region 21 have the same size and structure within one chip, so their dark current component size and temperature characteristics are almost the same. has.

In addition, 13 is an insulating film, 17 is a cathode electrode, 22°23
is determined by the anode electrode.

FIG. 6 shows another embodiment of the semiconductor light-receiving device according to the present invention. This embodiment is similar to resistor 3 in the bonding example shown in FIG. The resistor 4 and subtraction circuit 5 are also formed on the same chip. By doing so, the resistance values of the resistors 3 and 4 are made the same, and it is possible to reduce the difference in voltage generated due to the difference in the resistance values, and it is also possible to achieve economic efficiency.

〔Effect of the invention〕

As is clear from the above explanation, in the semiconductor photodetector according to the present invention, by providing two semiconductor photodetectors having the same size and structure in one chip, dark current components can be reduced. are made equal, and one semiconductor photodetector is shielded from light by a material such as aluminum or gold that has a high reflectivity to output only dark current, and the other semiconductor photodetector is configured to output only a dark current. During use, by taking the difference between the two ways of output, an output with the dark current component canceled can always be obtained.

Therefore, only 9 outputs are always obtained, which are proportional to the intensity of the incident light.When controlling other circuits using the output, if the intensity of the incident light is low or due to temperature changes, dark current components This has the effect that stable control without error is possible even when the value changes.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention and an example of its connection;
Fig. 2 is a graph showing the optical input-output (■out) characteristics when using the semiconductor photodetector shown in Fig. 1, Fig. 3 is a circuit diagram showing a conventional semiconductor photodetector and its connection example, and Fig. 4 5 is a graph showing the optical input-output (■. ut) characteristics when using a conventional semiconductor light receiving device, FIG. 5 is an O cross-sectional view showing an example of the device structure of the light receiving element according to the present invention, and FIG. FIG. 3 is a circuit diagram showing another embodiment. DESCRIPTION OF SYMBOLS 1... Semiconductor light receiving device, la... Light receiving element into which light is input, 1b... Light receiving element shielded, 2... Power supply, 3, 3a , 3b...
Resistor, 4... Optical input, 5... Subtraction circuit. Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] Two identical semiconductor light-receiving elements are provided in one chip, one semiconductor light-receiving element is shielded from light and outputs only dark current, and the other semiconductor light-receiving element receives an optical signal. A semiconductor light receiving device characterized by: