JPH01146375A - Method of evaluating semiconductor photodetector - Google Patents

Abstract

PURPOSE:To evaluate linearity of output characteristics of a semiconductor photodetector in the form of a wafer or chip for decreasing manufacturing cost, by obtaining output characteristics of photoelectric current in relation to intensity of incident light to the photodetector from dependency of capacitance on bias voltages and dependency of series resistance on bias voltages and then evaluating linearity thereof. CONSTITUTION:Output characteristics of photoelectric current in relation to intensity of incident light to a semiconductor photodetector are obtained from dependency of capacitance on bias voltage and dependency of series resistance on bias voltage, and linearity of the output characteristics of the semiconductor photodetector thus obtained is evaluated. More particularly, a prober 26 is brought into contact with a p-electrode of one chip in a wafer 21, and a bias voltage is applied between the prober 26 and a substrate stage 22, so that dependency of capacitance on the bias voltage is measured by adding signal current modulated at a frequency of 1MHz and an amplitude voltage of 10mV. The dependency thus obtained is processed by a computer 24 and recorded in a plotter 25. A photodetector presenting little capacitance at a reverse voltage of 1V is found to have good linearity. A photodetector presenting large capacitance is found to have poor linearity.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for evaluating the output characteristics of a semiconductor photodetector, the purpose is to evaluate the linearity of the output characteristics in a wafer or chip state and reduce manufacturing costs. The linearity of the output characteristic of the semiconductor photodetector is evaluated by determining the output characteristic of the photocurrent with respect to the incident light intensity from the bias voltage dependence of the capacitance or the bias voltage dependence of the series resistance. Features.

[Industrial application field]

The present invention relates to a method for evaluating the output characteristics of a semiconductor light receiving element.

Recently, optical fiber communication has been put into practical use, and it is expected to improve the quality and reduce the cost of the -layer of semiconductor light-receiving elements (photodiodes) used in optical fiber communication.

[Conventional technology]

Many semiconductor light-receiving elements (photodiodes) made of silicon, germanium, compound semiconductors, etc. are used, and for example, an InGaAs-based light-receiving element is known as a semiconductor light-receiving element with high light reception efficiency for light wavelengths in the 1.3 μm band. It is being FIG. 4 shows a cross-sectional view of the PTN type InGaAs photodetector, where l in the figure is an n-InP substrate and 2 is an n-InP substrate.
-InP buffer layer, 3 is n-1nGaAs light absorption layer, 4 is n-1nP chip Fa layer.

5 is a p-light receiving region, 6 is a p-electrode, and 7 is an n-electrode. When a reverse bias voltage is applied between the electrodes and light is incident on the p-light receiving layer 5, light is generated in the n-rnGaAs light absorption layer 3. This structure is such that electrons and holes are excited, a photocurrent flows through the pn junction, and its output is detected.

Now, one of the important characteristics of the above-mentioned light receiving element is the linearity of the optical output (linearity; 1
There is a FIG. 5 is a diagram showing the conventional linearity measurement method. In the figure, 11 is a light receiving element, 12 is a temperature controller, 13 is a light emitting element, 14 is an attenuator, 15 is an optical fiber, and 16 is an output meter. It is. For example, assuming that the light receiving element is used at a low temperature, the temperature of the temperature controller 12 is set to -40°C, and the light from the light emitting element 13 is passed through the attenuator 14 and the optical fiber 15 to the light receiving element 11. Let light enter. Then, the current output of the light receiving element 11 with respect to the light energy from the light emitting element 13 can be obtained. Note that current output is generally expressed in power as the product of photocurrent and bias voltage.

The light energy of the light emitting element 13 is switched by the attenuator 14 to change the amount of light incident on the light receiving element 11, and the output characteristics obtained by plotting the current output (watts) of the light receiving element 11 against the incident light power (watts) are shown in the sixth graph. Shown in the figure. In Fig. 6, when the current output increases in proportion to the incident light power, it is said that the linearity is good, and the curve I shown by the solid line indicates a light receiving element (good product) with good linearity, and the dotted line shows it. The curve ■ is a light-receiving element (defective product) with poor linearity due to low incident light power. It should be noted that conventionally, since it takes a lot of man-hours to detect a curve as shown in FIG. 6, a method of measuring three predetermined points on the curve is usually adopted. In addition, the linearity also changes depending on the temperature of the light receiving element 11, and the higher the temperature, the better the linearity becomes, which is why the light receiving element 11 is housed in the temperature controller 12.

[Problem that the invention seeks to solve]

By the way, in the conventional measurement method shown in FIG. 4, the light-receiving element 11 to be measured is a completed product assembled into a package, so if the linearity is measured and the product is found to be defective, the assembled completed product must be discarded. If this happens, assembly man-hours will be wasted, and manufacturing costs will increase accordingly.

Therefore, the present invention proposes an evaluation method aimed at solving these problems, evaluating linearity in a wafer or chip state, and reducing manufacturing costs.

[Means for solving problems]

The purpose is to obtain the output characteristics of the photocurrent with respect to the incident light intensity of the semiconductor photodetector from the bias voltage dependence of the capacitance or the bias voltage dependence of the series resistance, and to evaluate the linearity of the output characteristics of the semiconductor photodetector. This is achieved by the method for evaluating semiconductor light receiving elements.

[For production]

That is, in the present invention, the relationship between capacitance and bias voltage or the relationship between series resistance and bias voltage is measured to evaluate the output characteristic linearity of a semiconductor light receiving element. The capacitance and series resistance of the semiconductor photodetector are related to the expansion of the depletion layer in the heterobarrier, and it is assumed that this is also related to the linearity of the output characteristics, and the linearity of the output characteristics is evaluated by detecting these. It is.

〔Example〕

Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a method for measuring the bias voltage dependence of capacitance or the bias voltage dependence of series resistance according to the present invention, in which 21 is a UUNI A-122 substrate stage, 23 is an LCR meter, and 24 is a computer. , 25
is a block. Then, the prober 26 is brought into contact with the p-electrode W of one chip (element) within the wafer 25, and between the prober 26 and the substrate stage 22 (which is in contact with the n-electrode on the back surface of the wafer). Apply bias voltage.

Then, the bias voltage dependence of the capacitance measured by adding a signal current modulated at a frequency IMH2 and an amplitude voltage of 10 mV is processed by the computer 24, and the plotter 2
Record in 5. Figures 2(a) and 2(b) illustrate the measurement results of the bias voltage dependence of the capacitance. Figure 2(a) shows a photodetector with poor linearity, and Figure 2(b) shows a photodetector with good linearity. This is an example of a light receiving element. Second
From the figure, the capacitance (
PF), the capacitance of the light receiving element with poor linearity in FIG. 2(a) is 101.89PF, 105.06PF, 118. ?
! 6PF, 115.09PF.

The capacitance of the photodetector with good linearity in Fig. 2 (bl) is 42.15PF, 44.12PF, 41.74PF.
, 44.62PF, 44.66PF.

Therefore, in the above example, if the capacitance at a reverse bias voltage of 1■ is detected, the light receiving element with small capacitance has good linearity, the light receiving element with large capacitance has poor linearity, and the output characteristic has linearity (linearity). It is possible to evaluate the

Note that whether the linearity is good or bad is detected by a conventional measuring method on the assembled finished product after the above-mentioned measurement.

Next, to explain the bias voltage dependence of series resistance measured under similar measurement conditions, Figure 3 (a), (
3(b) shows the measurement results of the bias voltage dependence of the series resistance, FIG. 3(a) shows an example of a light receiving element with good linearity, and FIG. 3(b) shows an example of a light receiving element with poor linearity. From Fig. 3, the value of the series resistance (Ω) at the forward bias voltage (V) is expressed as , for a photodetector with good linearity, and , for a photodetector with poor linearity.
There is clearly a significant difference, with light receiving elements with large series resistance having poor linearity, and light receiving elements having low series resistance having good linearity.

Therefore, according to the present invention, it is possible to evaluate the linearity of output characteristics in the state of a wafer at room temperature without using a temperature controller. It can only be assembled into a finished product, reducing manufacturing costs.

Note that although the above is an example in which evaluation is performed in the state of a wafer, it goes without saying that evaluation can be performed in the same manner even after cutting into chips.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the linearity of output characteristics can be evaluated in the state of a wafer or chip, which has a significant effect on reducing manufacturing costs.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the measurement method according to the present invention, Figure 2 (
al, (bl is a diagram showing the bias voltage dependence of capacitance, Figure 3 (al, (bl is a diagram showing the bias voltage dependency of series resistance), Figure 4 is a cross-sectional view of an InGaAs photodetector, and Figure 5 is Figure 6 is a diagram showing the conventional measurement method, and Figure 6 is a diagram showing the output characteristics of the light receiving element. In the figure, 21 is a wafer, 22 is a substrate stage, 23 is an LCR meter, 24 is a computer, 25 is a plotter, and 26 is a Showing the prober.
t: rz diagram Figure 3 1nGαc5fjlK I J /1111 +'m V
IJ figure 4 is shown in the image 5.

Claims (1)

[Claims] The output characteristics of the photocurrent with respect to the incident light intensity of the semiconductor photodetector are expressed as the bias voltage dependence of the capacitance, or
A method for evaluating a semiconductor light-receiving device, characterized in that the linearity of the output characteristic of the semiconductor light-receiving device is evaluated based on the bias voltage dependence of the series resistance.