Patent Description:
A configuration is known in which a bias voltage applied to an avalanche photodiode is controlled in order to provide stable light detection with respect to temperature (for example, Patent Literature <NUM>). In Patent Literature <NUM>, a voltage corresponding to the breakdown voltage of a temperature compensation diode is applied to the avalanche photodiode as a bias voltage. Hereinafter, in this specification, the "avalanche photodiode" will be referred to as an "APD".

Patent Literature <NUM> discloses a silicon photomultiplier (SiPM) device is provided with a SiPM matrix and a temperature compensation circuit fabricated on a substrate. The temperature compensation circuit can include a temperature sensor, a bias adjustment circuit and a current source. The bias adjustment circuit can adjust a bias voltage provided to the SiPM matrix in response to the signal from the temperature sensor in order to maintain a predefined overvoltage value at the SiPM matrix.

Patent Literature <NUM> discloses a system and method for calibrating optical components. The method may include accumulating data indicative of the variation of selected variables with temperature for a batch of sample optical components, over an operating temperature range; determining the values of the selected variables at a single temperature of at least one new optical component for installation within an optical sub-assembly; and estimating the values of the selected variables as a function of temperature over the operating temperature range for the at least one new optical component based on the accumulated data and the values determined at the single temperature.

Patent Literature <NUM> discloses a laser rangefinder comprises a transmitter controlled by sequence-controlled pulses emitted by a timer following actuation of a switch by an operator. The receiver of the rangefinder comprises an avalanche photodiode (APD) the sensitivity of which is controlled in a time-programmed manner by a bias voltage controller which receives timing pulses from the timer. The time-programmed control operates to render the APD insensitive to protect the receiver against optical element backscatter and atmospheric backscatter prior to rendering the APD sensitive to monitor return pulses from remote targets.

The gain of the APD is calculated from the amount of output charge when the APD detects photons. The gain of the APD changes according to the change in the bias voltage applied to the APD. Even if a constant bias voltage is applied to the APD, the gain of the APD changes as the ambient temperature changes. Therefore, maintaining the gain of the APD constant needs to change the bias voltage applied to the APD according to the ambient temperature.

When the difference voltage between the breakdown voltage of the APD and the bias voltage applied to the APD is controlled to be constant, the change in the gain of the APD is small even if the ambient temperature changes. Therefore, in order to obtain a desired gain in a stable manner with respect to temperature, it is considered to determine the difference voltage to obtain the desired gain. However, since the breakdown voltage of the APD also changes according to the ambient temperature, it has been difficult to determine the difference voltage to obtain the desired gain.

An object of one aspect of the present invention is to provide a determination method capable of easily determining a difference voltage to obtain a desired gain in the APD. An object of another aspect of the present invention is to provide a light detection device capable of easily obtaining a desired gain in the APD.

As a result of research, the inventors have newly found the following facts.

It is known that, assuming that a bias voltage applied to an APD is "Vr" and a gain of the APD to which the bias voltage is applied at a predetermined temperature is "M", the following Equation (<NUM>) is satisfied. [Equation <NUM>] <MAT>.

Through the research by the inventors, it has been clarified that "a" and "b" in Equation (<NUM>) have extremely low temperature dependence and can be used for temperature compensation for the gain. In this case, if data indicating a correlation between the bias voltage and the gain of the APD to which the bias voltage is applied is acquired at an arbitrary temperature, the above "a" and "b" can be obtained from Equation (<NUM>). Equation (<NUM>) indicates a regression line having "(<NUM>/M) × (dM/dVr)" as an objective variable and "M" as an explanatory variable, and "a" is the slope of the regression line and "b" is the intercept of the regression line.

In addition, the inventors of the present application have found that, once "a" and "b" are determined, a difference voltage between the breakdown voltage of the APD and the bias voltage applied to the APD at a desired gain can be obtained by the following Equation (<NUM>). "ΔV" in Equation (<NUM>) indicates the above difference voltage. [Equation <NUM>] <MAT>.

"ΔV" at the desired gain is derived by substituting "a" and "b" obtained from Equation (<NUM>) into "a" and "b" in Equation (<NUM>) and substituting the desired gain into "M" in the following Equation (<NUM>). That is, "ΔV" to obtain the desired gain is derived very easily without strictly considering the ambient temperature. For example, "ΔV" to obtain the desired gain is determined without considering the temperature characteristics of the breakdown voltage of the APD.

Once "ΔV" is determined, the bias voltage to obtain the desired gain can be controlled. For example, when the breakdown voltage of the temperature compensation diode is applied to the APD as a bias voltage, "ΔV" indicates a difference voltage between the breakdown voltage of the APD and the breakdown voltage of the temperature compensation diode. Therefore, "ΔV" to obtain the desired gain may be derived, and the impurity concentrations of the APD and the temperature compensation diode may be designed according to the derived "ΔV".

A determination method according to one aspect of the present invention is a determination method for determining a difference voltage between a breakdown voltage of an APD and a bias voltage applied to the APD in a light detection device including the APD and a temperature compensation unit. The temperature compensation unit is configured to provide temperature compensation for the gain of the APD by controlling the bias voltage based on the difference voltage. In this determination method, the bias voltage is "Vr", and the gain of the APD to which the bias voltage is applied is "M". In this case, the slope and intercept of the regression line having "(<NUM>/M) × (dM/dVr)", which is of data indicating the correlation between the bias voltage and the gain are obtained, as an objective variable and "M" as an explanatory variable. "ΔV" calculated by substituting the slope into "a" in the following Equation (<NUM>), substituting the intercept into "b" in the following Equation (<NUM>), and substituting a gain to be set in an avalanche photodiode of a light detection device into "Md" in the following Equation (<NUM>) is determined as the difference voltage. [Equation <NUM>] <MAT>.

In the one aspect described above, the slope and intercept of the regression line having "(<NUM>/M) × (dM/dVr)" as an objective variable and "M" as an explanatory variable are obtained. By substituting the obtained slope into "a" in Equation (<NUM>) and substituting the obtained intercept into "b" in Equation (<NUM>), the difference voltage to obtain the desired gain is determined. Therefore, the difference voltage to obtain the desired gain is determined very easily without strictly considering the ambient temperature.

In the one aspect described above, a plurality of "ΔV" calculated by substituting a plurality of different values as gains to be set in the APD into "Md" in Equation (<NUM>) may be determined as difference voltages corresponding to the plurality of values. In this case, the plurality of difference voltages corresponding to the plurality of values are determined very easily without strictly considering the ambient temperature.

A light detection device according to another aspect of the present invention includes an APD and a temperature compensation unit. The temperature compensation unit is configured to provide temperature compensation for the APD by controlling a bias voltage applied to the APD based on a difference voltage between a breakdown voltage of the APD and the bias voltage. The temperature compensation unit is configured to control the bias voltage so that the difference voltage becomes "ΔV". It is assumed that the bias voltage is "Vr" and a gain of the APD to which the bias voltage is applied is "M". "ΔV" is calculated for data indicating a correlation between the bias voltage and the gain by substituting a slope of a regression line having "(<NUM>/M) × (dM/dVr)" as an objective variable and "M" as an explanatory variable into "a" in following Equation (<NUM>), substituting an intercept of the regression line into "b" in the following Equation (<NUM>), and substituting a gain to be set in the APD into "Md" in the following Equation (<NUM>). [Equation <NUM>] <MAT>.

In another aspect described above, the temperature compensation unit is configured to control the bias voltage so that the difference voltage between the breakdown voltage of the APD and the bias voltage applied to the APD becomes "ΔV". "ΔV" is calculated by substituting the slope of the regression line having "(<NUM>/M) × (dM/dVr)" as an objective variable and "M" as an explanatory variable into "a" in Equation (<NUM>) and substituting the intercept into "b" in Equation (<NUM>). Therefore, a desired gain can be obtained very easily without strictly considering the ambient temperature.

In another aspect described above, the light detection device may further include a setting unit and a wiring unit. The setting unit may be configured to set the temperature compensation unit according to the gain to be set in the APD. The wiring unit may electrically connect the temperature compensation unit and the APD to each other. The temperature compensation unit may include a plurality of temperature compensation diodes. The plurality of temperature compensation diodes may have mutually different breakdown voltages. The wiring unit may be configured to apply a voltage corresponding to the breakdown voltage of each of the temperature compensation diodes to the APD as a bias voltage. The setting unit may be configured to set a temperature compensation diode to be used for controlling the bias voltage among the plurality of temperature compensation diodes so that "ΔV" calculated by substituting the gain to be set in the APD into "Md" in Equation (<NUM>) becomes the difference voltage. In this case, "ΔV" indicates a subtraction value obtained by subtracting the voltage corresponding to the breakdown voltage of the temperature compensation diode from the breakdown voltage of the APD. Therefore, it is possible to derive "ΔV" to obtain the desired gain and design the impurity concentrations of the APD and the temperature compensation diode so that the subtraction value becomes the derived "ΔV". A circuit may be designed so that the subtraction value becomes "ΔV". In the light detection device, a temperature compensation diode to be used for controlling the bias voltage among the plurality of temperature compensation diodes is set by the setting unit. Therefore, a gain desired according to the situation can be obtained very easily without strictly considering the ambient temperature. In other words, it is possible to easily switch a desired gain and obtain a desired gain in a stable manner with respect to temperature.

According to one aspect of the present invention, it is possible to provide a determination method capable of easily determining a difference voltage to obtain a desired gain in the APD. According to another aspect of the present invention, it is possible to provide a light detection device capable of easily obtaining a desired gain in the APD.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying diagrams. In addition, in the description, the same elements or elements having the same function are denoted by the same reference numerals, and repeated descriptions thereof will be omitted.

First, an outline of a light detection device according to the present embodiment will be described with reference to <FIG> is a block diagram of a light detection device. As illustrated in <FIG>, a light detection device <NUM> includes a detection operation unit <NUM>, a circuit unit <NUM>, and a power supply unit <NUM>.

The detection operation unit <NUM> includes a light receiving unit <NUM> and a temperature compensation unit <NUM>. The light receiving unit <NUM> includes at least one APD. In the present embodiment, the APD of the light receiving unit <NUM> is an avalanche photodiode arranged to operate in linear mode. The temperature compensation unit <NUM> is configured to provide temperature compensation for the gain in the APD of the light receiving unit <NUM>. The temperature compensation unit <NUM> is configured to control a bias voltage applied to the APD of the light receiving unit <NUM>. In the present embodiment, the temperature compensation unit <NUM> includes at least one temperature compensation diode.

The circuit unit <NUM> applies a voltage to the light receiving unit <NUM> and the temperature compensation unit <NUM> of the detection operation unit <NUM>. The circuit unit <NUM> is electrically connected to each electrode of the APD of the light receiving unit <NUM> and the temperature compensation diode of the temperature compensation unit <NUM>. In the present embodiment, the circuit unit <NUM> applies, to the APD of the light receiving unit <NUM>, a voltage which causes the temperature compensation diode included in the temperature compensation unit <NUM> to break down.

The power supply unit <NUM> generates an electromotive force for operating the detection operation unit <NUM>. The power supply unit <NUM> applies, through the circuit unit <NUM>, a potential to the APD of the light receiving unit <NUM> and the temperature compensation diode of the temperature compensation unit <NUM> in the detection operation unit <NUM>. The power supply unit <NUM> causes the temperature compensation diode included in the temperature compensation unit <NUM> to break down.

By applying a breakdown voltage to the temperature compensation diode of the temperature compensation unit <NUM>, a voltage corresponding to the breakdown voltage is applied to the APD of the light receiving unit <NUM> as a bias voltage. The temperature compensation diode and the APD have the same temperature characteristics with respect to the relationship between the gain and the bias voltage. In this case, when the ambient temperature changes, the breakdown voltage applied to the temperature compensation diode changes. Due to the change in the breakdown voltage applied to the temperature compensation diode, the bias voltage applied to the APD also changes according to the ambient temperature so that the gain of the APD is maintained. That is, the temperature compensation unit <NUM> provides temperature compensation for the gain in the APD of the light receiving unit <NUM>.

Next, an example of the physical configuration of the light detection device <NUM> will be described in more detail with reference to <FIG> is a schematic configuration diagram of a light detection device. The light detection device <NUM> includes a light detection unit <NUM>, an electromotive force generation unit <NUM>, a current limiting unit <NUM>, a bias voltage stabilization unit <NUM>, and a setting unit <NUM>. The light detection unit <NUM> includes the light receiving unit <NUM> and the temperature compensation unit <NUM> described above. The electromotive force generation unit <NUM> generates an electromotive force for operating the light detection unit <NUM>. The current limiting unit <NUM> limits a current flowing through the light detection unit <NUM>. The bias voltage stabilization unit <NUM> enables a current output equal to or greater than an upper limit value limited by the current limiting unit <NUM>. The setting unit <NUM> is configured to control the operation of the light detection unit <NUM>. A part of the light detection unit <NUM> is included in the detection operation unit <NUM>. A part of the light detection unit <NUM>, the bias voltage stabilization unit <NUM>, and the setting unit <NUM> are included in the circuit unit <NUM>. The electromotive force generation unit <NUM> and the current limiting unit <NUM> are included in the power supply unit <NUM>.

As illustrated in <FIG>, the light detection unit <NUM> includes, in addition to an APD <NUM> and the temperature compensation unit <NUM>, a wiring unit <NUM> for electrically connecting the temperature compensation unit <NUM> and the APD <NUM> to each other and a plurality of terminals <NUM>, <NUM>, <NUM>, and <NUM>. For example, the terminal <NUM> is a second terminal, and the plurality of terminals <NUM> are a plurality of first terminals. In this specification, "electrically connects" and "electrically connected" also include a configuration in which the path is temporarily cut by a switch or the like. In the present embodiment, the temperature compensation unit <NUM> includes three temperature compensation diodes <NUM>, <NUM>, and <NUM> as at least one temperature compensation diode described above. The temperature compensation unit <NUM> may include four or more temperature compensation diodes.

The APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> are included in the detection operation unit <NUM>. The wiring unit <NUM> and the plurality of terminals <NUM>, <NUM>, <NUM>, and <NUM> are included in the circuit unit <NUM>. The APD <NUM> includes a pair of electrodes 19a and 19b. Each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> includes a pair of electrodes 29a, 29b. For example, when the electrode 29a is a first electrode, the electrode 29b is a second electrode. For example, the temperature compensation diode <NUM> is a first temperature compensation diode, the temperature compensation diode <NUM> is a second temperature compensation diode, and the temperature compensation diode <NUM> is a third temperature compensation diode.

The temperature compensation diodes <NUM>, <NUM>, and <NUM> break down at mutually different voltages under the same ambient temperature. Hereinafter, a voltage applied to the corresponding temperature compensation diode when the temperature compensation diodes <NUM>, <NUM>, and <NUM> break down and a voltage applied to the APD <NUM> when the APD <NUM> breaks down are referred to as "breakdown voltages". In the following description, when comparing breakdown voltages, it is assumed that breakdown voltages at the same ambient temperature are compared with each other.

The plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM> have mutually different breakdown voltages. The temperature compensation diode <NUM> has a breakdown voltage higher than that of the temperature compensation diode <NUM>. The temperature compensation diode <NUM> has a breakdown voltage lower than that of the temperature compensation diode <NUM> and higher than that of the temperature compensation diode <NUM>. The temperature compensation diode <NUM> has a breakdown voltage lower than those of the temperature compensation diodes <NUM> and <NUM>. The breakdown voltages of the plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM> are lower than the breakdown voltage of the APD <NUM>.

The wiring unit <NUM> connects the electrode 19a of the APD <NUM>, the electrode 29a of the temperature compensation diode <NUM>, the electrode 29a of the temperature compensation diode <NUM>, and the electrode 29a of the temperature compensation diode <NUM> to both the terminal <NUM> and the terminal <NUM> in parallel with each other. The wiring unit <NUM> applies a voltage corresponding to the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> to the APD <NUM> as a bias voltage.

The terminal <NUM> is electrically connected to the electrode 19a of the APD <NUM>, the electrodes 29a of the temperature compensation diodes <NUM>, <NUM>, and <NUM>, and the current limiting unit <NUM> of the power supply unit <NUM>. The terminal <NUM> is electrically connected to the electrode 19a of the APD <NUM>, the electrodes 29a of the temperature compensation diodes <NUM>, <NUM>, and <NUM>, and the bias voltage stabilization unit <NUM>. The terminal <NUM> is electrically connected to the electrode 19b of the APD <NUM> and a signal reading circuit (not illustrated). The plurality of terminals <NUM> are electrically connected to the electrodes 29b of the temperature compensation diodes <NUM>, <NUM>, and <NUM> and the setting unit <NUM>. The respective terminals <NUM> are connected to the electrodes 29b of the temperature compensation diodes <NUM>, <NUM>, and <NUM> different from each other. In the present embodiment, the electrode 19a is the anode of the APD <NUM> and the electrode 19b is the cathode of the APD <NUM>. The electrode 29a is the anode of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>, and the electrode 29b is the cathode of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>.

The electromotive force generation unit <NUM> and the current limiting unit <NUM> serving as the power supply unit <NUM> apply a voltage to the light detection unit <NUM>. The electromotive force generation unit <NUM> and the current limiting unit <NUM> are electrically connected to the terminal <NUM>. In the present embodiment, the positive electrode of the electromotive force generation unit <NUM> is connected to a ground <NUM>, and the negative electrode of the electromotive force generation unit <NUM> is connected to the terminal <NUM> through the current limiting unit <NUM>.

The bias voltage stabilization unit <NUM> increases the upper limit value of the detection signal output from the APD <NUM>. The bias voltage stabilization unit <NUM> is connected to the light detection unit <NUM> and the electromotive force generation unit <NUM> in parallel with the current limiting unit <NUM>. The bias voltage stabilization unit <NUM> is, for example, a capacitor. In the present embodiment, one electrode of the capacitor is connected to the negative electrode of the electromotive force generation unit <NUM>, and the other electrode is connected to the terminal <NUM>. When a pulse signal output from the APD <NUM> due to incidence of light is detected, an output having a strength equal to or greater than the current value limited by the current limiting unit <NUM> is obtained according to the capacitance of the capacitor.

The setting unit <NUM> is configured to set the temperature compensation unit <NUM> according to the gain to be set in the APD <NUM>. The setting unit <NUM> is configured to select a temperature compensation diode to be operated among the plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM>. In other words, the setting unit <NUM> sets a temperature compensation diode to be used for controlling the bias voltage among the plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM>. The setting unit <NUM> sets a temperature compensation diode to be operated by controlling the current application states of the plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM>.

The setting unit <NUM> includes at least one switch <NUM>. At least one switch <NUM> is connected to a corresponding terminal <NUM>. In the present embodiment, the setting unit <NUM> includes two switches <NUM>. One switch <NUM> is electrically connected to the temperature compensation diode <NUM> through the corresponding terminal <NUM>. The other switch <NUM> is electrically connected to the temperature compensation diode <NUM> through the corresponding terminal <NUM>. The switches <NUM> is configured to switch between a state capable of electrically energizing corresponding temperature compensation diodes <NUM> and <NUM> and a state incapable of electrically energizing the corresponding temperature compensation diodes <NUM> and <NUM>. The setting unit <NUM> controls ON/OFF of the switch <NUM>.

In the present embodiment, the light detection unit <NUM> includes three terminals <NUM>. The three terminals <NUM> are connected to the temperature compensation diodes <NUM>, <NUM>, and <NUM>, respectively. The terminal <NUM> connected to the temperature compensation diode <NUM> is connected to a ground <NUM>. The terminal <NUM> connected to the temperature compensation diode <NUM> is connected to a ground <NUM> through the switch <NUM>. The terminal <NUM> connected to the temperature compensation diode <NUM> is connected to a ground <NUM> through the switch <NUM>. That is, only one terminal <NUM> is not connected to the switch <NUM>. The grounds <NUM>, <NUM>, <NUM> may be connected to each other. As a modification example of the present embodiment, the switches <NUM> may be connected to all the terminals <NUM>.

Next, the structure of the light detection unit <NUM> in the light detection device <NUM> will be described in detail with reference to <FIG> is a schematic cross-sectional view of a light detection unit. In <FIG>, only one of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is illustrated as the temperature compensation unit <NUM>. In the present embodiment, as illustrated in <FIG>, the light detection unit <NUM> is an optical member including a semiconductor substrate <NUM>. The semiconductor substrate <NUM> has main surfaces 50a and 50b facing each other. The APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> are formed on the semiconductor substrate <NUM> so as to be spaced apart from each other when viewed from a direction perpendicular to the main surface 50a. The APD <NUM> has a light incidence surface 51a on the main surface 50a side. The temperature compensation diodes <NUM>, <NUM>, and <NUM> are light-shielded APDs.

The semiconductor substrate <NUM> includes a semiconductor region <NUM> and semiconductor layers <NUM>, <NUM>, <NUM>, and <NUM>. Each of the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> includes the semiconductor region <NUM> and the semiconductor layers <NUM>, <NUM>, and <NUM>.

The semiconductor region <NUM> and the semiconductor layers <NUM>, <NUM>, and <NUM> are the first conductive type, and the semiconductor layer <NUM> is the second conductive type. Semiconductor impurities are added by, for example, a diffusion method or an ion implantation method. In the present embodiment, the first conductive type is P type and the second conductive type is N type. When the semiconductor substrate <NUM> is an Si-based substrate, a Group <NUM> element such as B is used as the P-type impurity, and a Group <NUM> element such as N, P, or As is used as the N-type impurity.

The semiconductor region <NUM> is located on the main surface 50a side of the semiconductor substrate <NUM>. The semiconductor region <NUM> forms a part of the main surface 50a. The semiconductor region <NUM> is, for example, P- type.

The semiconductor layer <NUM> forms a part of the main surface 50a. The semiconductor layer <NUM> is surrounded by the semiconductor region <NUM> so as to be in contact with the semiconductor region <NUM> when viewed from the direction perpendicular to the main surface 50a. The semiconductor layer <NUM> is, for example, N+ type. In the present embodiment, the semiconductor layer <NUM> forms a cathode in each of the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM>.

The semiconductor layer <NUM> is located between the semiconductor region <NUM> and the semiconductor layer <NUM>. In other words, the semiconductor layer <NUM> is in contact with the semiconductor layer <NUM> on the main surface 50a side and is in contact with the semiconductor region <NUM> on the main surface 50b side. The semiconductor layer <NUM> has a higher impurity concentration than the semiconductor region <NUM>. The semiconductor layer <NUM> is, for example, P type. In the present embodiment, the impurity concentration of the semiconductor layer <NUM> of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is higher than the impurity concentration of the semiconductor layer <NUM> of the APD <NUM>. The semiconductor layer <NUM> forms an avalanche region in each of the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM>.

The impurity concentration of the semiconductor layer <NUM> of the temperature compensation diode <NUM> is higher than the impurity concentration of the semiconductor layer <NUM> of the temperature compensation diode <NUM>. The impurity concentration of the semiconductor layer <NUM> of the temperature compensation diode <NUM> is higher than the impurity concentration of the semiconductor layer <NUM> of the temperature compensation diode <NUM>.

The semiconductor layer <NUM> forms a part of the main surface 50a. The semiconductor layer <NUM> is surrounded by the semiconductor region <NUM> so as to be in contact with the semiconductor region <NUM> when viewed from the direction perpendicular to the main surface 50a. In the present embodiment, the semiconductor layer <NUM> has a higher impurity concentration than the semiconductor region <NUM> and the semiconductor layer <NUM>. The semiconductor layer <NUM> is, for example, P+ type. The semiconductor layer <NUM> is connected to the semiconductor layer <NUM> at a portion that is not illustrated. The semiconductor layer <NUM> forms an anode of the light detection device <NUM>. The semiconductor layer <NUM> forms, for example, anodes of the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM>.

The semiconductor layer <NUM> is located closer to the main surface 50b of the semiconductor substrate <NUM> than the semiconductor region <NUM>. The semiconductor layer <NUM> forms the entire main surface 50b. The semiconductor layer <NUM> is in contact with the semiconductor region <NUM> on the main surface 50a side. In the present embodiment, the semiconductor layer <NUM> has a higher impurity concentration than the semiconductor region <NUM> and the semiconductor layer <NUM>. The semiconductor layer <NUM> is, for example, P+ type. The semiconductor layer <NUM> forms an anode of the light detection device <NUM>. The semiconductor layer <NUM> forms, for example, anodes of the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM>.

The light detection device <NUM> further includes an insulating film <NUM>, electrodes <NUM>, <NUM>, and <NUM>, a passivation film <NUM>, and an antireflection film <NUM> that are provided on the main surface 50a of the semiconductor substrate <NUM>. The insulating film <NUM> is stacked on the main surface 50a of the semiconductor substrate <NUM>. The insulating film <NUM> is, for example, a silicon oxide film. Each of the electrodes <NUM>, <NUM>, and <NUM> is disposed on the insulating film <NUM>. The passivation film <NUM> is stacked on the insulating film <NUM> and the electrodes <NUM>, <NUM>, and <NUM>. The antireflection film <NUM> is stacked on the main surface 50a of the semiconductor substrate <NUM>.

The electrode <NUM> penetrates the insulating film <NUM> to be connected to the semiconductor layer <NUM> of the APD <NUM>. A part of the electrode <NUM> is exposed from the passivation film <NUM> to form the terminal <NUM> of the APD <NUM>. The electrode <NUM> outputs a signal from the APD <NUM> at the terminal <NUM>.

The electrode <NUM> penetrates the insulating film <NUM> to be connected to the semiconductor layer <NUM> of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>. A part of the electrode <NUM> is exposed from the passivation film <NUM> to form the terminal <NUM> of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>.

The electrode <NUM> penetrates the insulating film <NUM> to be connected to the semiconductor layer <NUM>. That is, the electrode <NUM> is connected to the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM>. In other words, the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> are connected to the electrode <NUM> in parallel with each other. A part of the electrode <NUM> is exposed from the passivation film <NUM> to form, for example, the terminal <NUM>.

In the present embodiment, the terminal <NUM> is a pad electrode for the cathode of the APD <NUM>. The terminal <NUM> is a pad electrode for the cathode of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>. The terminal <NUM> is a pad electrode for the anode of each of the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM>.

The APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> are connected to the terminal <NUM> in parallel with each other. When a reverse bias is applied to the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM>, a positive voltage is applied to the pad electrode for the cathode, and a negative voltage is applied to the pad electrode for the anode.

The antireflection film <NUM> is stacked on the semiconductor layer <NUM> of the APD <NUM>. A part of the antireflection film <NUM> is exposed from the passivation film <NUM>. Therefore, light transmitted through the antireflection film <NUM> can enter the semiconductor layer <NUM> of the APD <NUM>. The semiconductor layer <NUM> of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is covered with the insulating film <NUM> and is shielded from light.

Next, the temperature compensation unit <NUM> will be described in more detail. Each of the APD and the temperature compensation diodes <NUM>, <NUM>, and <NUM> of the temperature compensation unit <NUM> have the same temperature characteristics with respect to the relationship between the gain and the bias voltage. In the light detection device <NUM>, a voltage corresponding to the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is applied to the APD <NUM> as a bias voltage.

The temperature compensation unit <NUM> is configured to control the bias voltage so that the difference voltage between the breakdown voltage of the APD <NUM> and the bias voltage applied to the APD <NUM> becomes constant. The difference voltage is determined as follows.

Assuming that the bias voltage applied to the APD is "Vr" and the gain of the APD to which the bias voltage is applied is "M", the following equation is satisfied. [Equation <NUM>] <MAT>.

"A" and "b" are constants. As can be seen from Equation (<NUM>), assuming that "(<NUM>/M) × (dM/dVr)" is an objective variable and "M" is an explanatory variable, for data indicating the relationship between the bias voltage and the gain in the APD, a regression line with a slope of "a" and an intercept of "b" is obtained. As illustrated in <FIG> and <FIG>, the slope "a" and the intercept "b" have extremely low temperature dependence. <FIG> is a graph of data indicating the relationship between the bias voltage applied to the APD and the gain of the APD to which the bias voltage is applied. In <FIG>, the horizontal axis indicates the gain of the APD, and the vertical axis indicates the value of "(<NUM>/M) × (dM/dVr)". A plurality of lines indicate data of mutually different ambient temperatures. Specifically, <FIG> illustrates data at eight ambient temperatures of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, -<NUM>, and -<NUM>. <FIG> is a graph illustrating the temperature dependence of the obtained slope "a" and intercept "b" of the regression line. In <FIG>, the horizontal axis indicates the ambient temperature, and the vertical axis indicates the values of "a" and "b". The solid line indicates the data of "a", and the broken line indicates the data of "b".

Assuming that the bias voltage applied to the APD is "Vr", the gain of the APD to which the bias voltage is applied is "M", and the breakdown voltage of the APD is "Vbr", the following equation is satisfied. [Equation <NUM>] <MAT>.

Here, "a" in Equations (<NUM>) and (<NUM>) indicates the same physical quantity. "b" in Equations (<NUM>) and (<NUM>) indicates the same physical quantity.

Therefore, by substituting "a" and "b" obtained from Equation (<NUM>) into "a" and "b" in Equation (<NUM>), the value of "(Vbr - Vr)" for the desired gain is uniquely calculated. "(Vbr - Vr)" is a subtraction value obtained by subtracting the bias voltage applied to the APD from the breakdown voltage of the APD. That is, "(Vbr - Vr)" corresponds to the difference voltage described above.

Assuming that the difference voltage is "ΔV", Equation (<NUM>) is expressed as Equation (<NUM>). [Equation <NUM>] <MAT>.

Therefore, by using Equation (<NUM>) in which the gain "M" of the APD in Equation (<NUM>) is set to a desired gain "Md", "ΔV" corresponding to the desired gain can be easily calculated. [Equation <NUM>] <MAT>.

Specifically, data indicating the relationship between the bias voltage applied to the APD and the gain of the APD to which the bias voltage is applied is acquired at an arbitrary temperature. In the acquired data, the slope of the regression line having "(<NUM>/M) × (dM/dVr)" as an objective variable and "M" as an explanatory variable is substituted into "a" in Equation (<NUM>), the intercept of the regression line is substituted into "b" in Equation (<NUM>), and the desired gain to be set in the APD <NUM> is substituted into "Md" in Equation (<NUM>). As a result, "ΔV" is calculated. The temperature compensation unit <NUM> controls the bias voltage applied to the APD <NUM> so that the difference voltage becomes the calculated "ΔV". Here, the acquired data indicating the relationship between the bias voltage and the gain does not have to be the data of the same APD as the APD <NUM> as long as the APD has the same material and structure as the APD <NUM>.

In the present embodiment, the difference voltage corresponds to a subtraction value obtained by subtracting a voltage corresponding to the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> in a breakdown state from the breakdown voltage of the APD <NUM>. In the temperature compensation unit <NUM>, a voltage corresponding to the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> placed in a breakdown state is applied to the APD <NUM> as a bias voltage.

In the present embodiment, the breakdown voltage of the APD <NUM> and the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> have mutually different values. By adjusting the impurity concentration of the semiconductor layer <NUM> of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> and the impurity concentration of the semiconductor layer <NUM> of the APD <NUM>, the difference voltage between the breakdown voltage of the APD <NUM> and the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is adjusted. As a modification example of the present embodiment, the difference voltage may be adjusted depending on the circuit configuration. The difference voltage may be adjusted by applying an external voltage to the terminal <NUM>. In the case of these modification examples, the breakdown voltage of the APD <NUM> and the breakdown voltages of the temperature compensation diodes <NUM>, <NUM>, and <NUM> may be equal to each other. The difference voltage may be adjusted by combining these plurality of methods.

In the present embodiment, the impurity concentration of the semiconductor layer <NUM> of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is higher than the impurity concentration of the semiconductor layer <NUM> of the APD <NUM>. As a result, the breakdown voltage of the APD <NUM> is higher than the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> by "ΔV". The three temperature compensation diodes <NUM>, <NUM>, and <NUM> have mutually different breakdown voltages. The three temperature compensation diodes <NUM>, <NUM>, and <NUM> are designed to obtain mutually different gains. "ΔV" is calculated for each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> according to Equation (<NUM>), and the impurity concentration of the semiconductor layer <NUM> of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is designed according to each calculated "ΔV". When calculating "ΔV" for each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>, the same value is substituted into "a". Similarly, when calculating "ΔV" for each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>, the same value is substituted into "b".

In the light detection device <NUM>, since a breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is applied, the breakdown voltage is applied to the APD <NUM> as a bias voltage. In the present embodiment, one of the breakdown voltages of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is applied to the APD <NUM> as a bias voltage. Which of the breakdown voltages of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is to be applied to the APD <NUM> as a bias voltage is controlled by the setting unit <NUM>.

Next, the operation of the light detection device according to the present embodiment will be described.

In the present embodiment, the terminal <NUM> is connected to the semiconductor layer <NUM> of the P+ type, and the semiconductor layer <NUM> is connected to the semiconductor layer <NUM> of the P+ type. Therefore, the anodes of the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, or <NUM> are connected to the terminal <NUM> in parallel with each other. As a result, a negative potential is applied to the anodes of the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> by the power supply unit <NUM>.

The circuit unit <NUM> causes one of the plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM> to break down. The setting unit <NUM> selects a temperature compensation diode to be operated among the plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM> using the switch <NUM>. The setting unit <NUM> selects a temperature compensation diode to apply a breakdown voltage to the APD <NUM> as a bias voltage, by switching ON/OFF of the switch <NUM>. The setting unit <NUM> selects a temperature compensation diode to be used for controlling the bias voltage, among the plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM>, so that "ΔV" calculated by substituting the gain to be set in the APD <NUM> into "Md" in Equation (<NUM>) becomes a difference voltage.

The breakdown voltage of the selected temperature compensation diode corresponds to a potential difference between the potential applied to the terminal <NUM> corresponding to the temperature compensation diode and the potential applied to the terminal <NUM>. Therefore, a potential corresponding to the breakdown voltage of the selected temperature compensation diode is applied to the anode of the APD <NUM>. As a result, a voltage corresponding to the breakdown voltage of the selected temperature compensation diode is applied to the APD <NUM> as a bias voltage.

In the present embodiment, when operating the temperature compensation diode <NUM>, the setting unit <NUM> sets all the temperature compensation diodes <NUM>, <NUM>, and <NUM> to the state capable of being electrically energized. That is, the setting unit <NUM> turns on all of the switches <NUM> connected to the plurality of terminals <NUM>. In this case, the temperature compensation diode <NUM> has a lowest breakdown voltage among the temperature compensation diodes <NUM>, <NUM>, and <NUM> set in the state capable of being electrically energized, so that the temperature compensation diode <NUM> operates. That is, the breakdown voltage of the temperature compensation diode <NUM> is applied to the APD <NUM> as a bias voltage.

When operating the temperature compensation diode <NUM>, the setting unit <NUM> sets the temperature compensation diodes <NUM> and <NUM> to the sate capable of being electrically energized, and sets the temperature compensation diode <NUM> to the state incapable of being electrically energized. In the present embodiment, the setting unit <NUM> turns on the switch <NUM> connected to the terminal <NUM> corresponding to the temperature compensation diode <NUM>, and turns off the switch <NUM> connected to the terminal <NUM> corresponding to the temperature compensation diode <NUM>. Since the switch <NUM> is not connected to the terminal <NUM> corresponding to the temperature compensation diode <NUM>, the temperature compensation diode <NUM> is in the state capable of being electrically energized. In this case, the temperature compensation diode <NUM> has a lowest breakdown voltage between the temperature compensation diodes <NUM> and <NUM> set in the state capable of being electrically energized, so that the temperature compensation diode <NUM> operates. That is, the breakdown voltage of the temperature compensation diode <NUM> is applied to the APD <NUM> as a bias voltage.

When operating the temperature compensation diode <NUM>, the setting unit <NUM> sets the temperature compensation diode <NUM> to the state capable of being electrically energized, and sets the temperature compensation diodes <NUM> and <NUM> to the state incapable of being electrically energized. In the present embodiment, the setting unit <NUM> turns off the switch <NUM> connected to the terminal <NUM> corresponding to the temperature compensation diodes <NUM> and <NUM>. Since the switch <NUM> is not connected to the terminal <NUM> corresponding to the temperature compensation diode <NUM>, the temperature compensation diode <NUM> is set in the state capable of being electrically energized. In this case, the temperature compensation diode <NUM> set in the state capable of being electrically energized operates. That is, the breakdown voltage of the temperature compensation diode <NUM> is applied to the APD <NUM> as a bias voltage.

According to the operation described above, the gain of the APD <NUM> is selected by the setting unit <NUM>. <FIG> is a graph illustrating the output characteristics of the APD <NUM> according to the setting by the setting unit <NUM>. In <FIG>, the vertical axis indicates the output voltage of the APD <NUM>, and the horizontal axis indicates time. Each piece of data <NUM>, <NUM>, and <NUM> indicates the output characteristics of the APD <NUM> when pulsed light with the strength equal to each other enters the APD <NUM>. The data <NUM> indicates the output characteristics of the APD <NUM> in a state in which the temperature compensation diode <NUM> is operating. The data <NUM> indicates the output characteristics of the APD <NUM> in a state in which the temperature compensation diode <NUM> is operating. The data <NUM> indicates the output characteristics of the APD <NUM> in a state in which the temperature compensation diode <NUM> is operating.

As illustrated in <FIG>, the output peak of the APD <NUM> in a state in which the temperature compensation diode <NUM> is operating is larger than the output peak of the APD <NUM> in a state in which the temperature compensation diode <NUM> is operating. The output peak of the APD <NUM> in a state in which the temperature compensation diode <NUM> is operating is larger than the output peak of the APD <NUM> in a state in which the temperature compensation diode <NUM> is operating. Thus, it has been confirmed that an operating temperature compensation diode <NUM>, <NUM>, <NUM> is switched by the setting unit <NUM>, so that the gain of the APD <NUM> is selected.

In the present embodiment, the setting unit <NUM> sets the temperature compensation diode <NUM> to a state capable of being electrically energized, regardless of whether or not the temperature compensation diode <NUM> is in a state capable of being electrically energized. In a state incapable of electrically energizing the temperature compensation diode <NUM>, the setting unit <NUM> switches, by the switch <NUM>, between a state capable of electrically energizing the temperature compensation diode <NUM> and a state incapable of electrically energizing the temperature compensation diode <NUM>. Hereinafter, a case where the temperature compensation diode <NUM> is selected as a temperature compensation diode to be operated by the setting unit <NUM> will be described as an example.

In the present embodiment, since a combination of the electromotive force generation unit <NUM> and the current limiting unit <NUM> is connected to the terminal <NUM>, the breakdown voltage of the selected temperature compensation diode <NUM> is applied to the terminal <NUM>. In the present embodiment, the output voltage of the electromotive force generation unit <NUM> is equal to or higher than the operating voltage of the APD <NUM>. In other words, the output voltage of the electromotive force generation unit <NUM> is equal to or higher than the upper limit of the temperature change of the breakdown voltage of each temperature compensation diode <NUM>, <NUM>, <NUM>. For example, the output voltage of the electromotive force generation unit <NUM> is <NUM> V or higher. The current limiting unit <NUM> is configured to include, for example, a current mirror circuit or a resistor.

The gain of the APD <NUM> can be arbitrarily set according to the breakdown voltage difference between the selected temperature compensation diode <NUM> and the APD <NUM>. When the gain of the APD <NUM> is set to an optimal multiplication factor Mopt having a high S/N ratio, the detection accuracy can be improved.

In the present embodiment, the anodes of the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> are integrally formed in the semiconductor layer <NUM>. For example, when the potential applied to the terminal <NUM> is <NUM> V and the breakdown voltage of the selected temperature compensation diode <NUM> is <NUM> V under an ambient temperature of <NUM>, a potential of -<NUM> V is applied to the anode of the APD <NUM>. Therefore, when the breakdown voltage of the APD <NUM> is <NUM> V under an ambient temperature of <NUM>, the APD <NUM> operates in a state in which the potential difference between the anode and the cathode is lower by <NUM> V than the breakdown voltage.

As described above, the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> have the same temperature characteristics with respect to the relationship between the gain and the bias voltage. Therefore, as long as the selected temperature compensation diode <NUM> is in a breakdown state, the APD <NUM> operates while maintaining the gain of a case in which a bias voltage lower by <NUM> V than the breakdown voltage is applied under an ambient temperature of <NUM>. In other words, in the light detection device <NUM>, a voltage that causes the selected temperature compensation diode <NUM> to break down is applied to the temperature compensation diode <NUM>, so that temperature compensation is provided for the gain of the APD <NUM>.

Next, the operational effects of the light detection devices in the above-described embodiment and modification examples will be described. Conventionally, when manufacturing a light detection device including an APD and a temperature compensation diode having the same temperature characteristics, it has been necessary to select and combine APDs having desired temperature characteristics with respect to the relationship between the gain and the bias voltage. For this reason, it has been difficult to reduce the cost. In this regard, in the light detection device <NUM>, the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> are independently formed on the same semiconductor substrate <NUM>. In this case, the temperature compensation diodes <NUM>, <NUM>, and <NUM> and the APD <NUM> having the same temperature characteristics over a wide temperature range with respect to the gain and the bias voltage are formed more easily and accurately than in a case where the temperature compensation diodes <NUM>, <NUM>, and <NUM> and the APD <NUM> are formed on mutually different semiconductor substrates. Therefore, temperature compensation for the gain of the APD <NUM> can be provided while suppressing the manufacturing cost.

The semiconductor substrate <NUM> includes the semiconductor region <NUM> of the first conductive type. Each of the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> includes the semiconductor layer <NUM> and the semiconductor layer <NUM>. In the semiconductor substrate <NUM>, the semiconductor layer <NUM> is a second conductive type. The semiconductor layer <NUM> is a first conductive type having a higher impurity concentration than the semiconductor region <NUM>. The semiconductor layer <NUM> is located between the semiconductor region <NUM> and the semiconductor layer <NUM>. As described above, the temperature compensation diodes <NUM>, <NUM>, and <NUM> have the same configuration as the APD <NUM>. Therefore, it is possible to easily form the temperature compensation diodes <NUM>, <NUM>, and <NUM> whose temperature characteristics with respect to the gain and the bias voltage are very similar to that of the APD <NUM>.

In the semiconductor substrate <NUM>, the impurity concentration in the semiconductor layer <NUM> of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is higher than the impurity concentration in the semiconductor layer <NUM> of the APD <NUM>. In this case, in the light detection device <NUM>, for example, the breakdown voltage of the APD <NUM> is higher than the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>. As a result, temperature compensation for the gain of the APD <NUM> arranged to operate in linear mode is provided.

In the light detection device <NUM>, the difference voltage to obtain the desired gain is determined by substituting the slope of the regression line having "(<NUM>/M) × (dM/dVr)" as an objective variable and "M" as an explanatory variable into "a" in Equation (<NUM>) and substituting the intercept of the regression line into "b" in Equation (<NUM>). Therefore, a desired gain can be obtained very easily without strictly considering the ambient temperature.

The temperature compensation unit <NUM> includes the temperature compensation diodes <NUM>, <NUM>, and <NUM>. The temperature compensation unit <NUM> applies a voltage corresponding to the breakdown voltage, which is applied to any one of the temperature compensation diodes <NUM>, <NUM>, and <NUM>, to the APD <NUM> as a bias voltage. For example, when the temperature compensation diode <NUM> is in a breakdown state, the difference voltage corresponds to a subtraction value obtained by subtracting a voltage corresponding to the breakdown voltage of the temperature compensation diode <NUM> from the breakdown voltage of the APD <NUM>. Therefore, it is possible to derive "ΔV" to obtain the desired gain and design the impurity concentrations of the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> so that the subtraction value becomes "ΔV". A circuit between the temperature compensation diodes <NUM>, <NUM>, and <NUM> and the APD <NUM> may be designed so that the subtraction value is "ΔV".

The light detection device <NUM> includes the setting unit <NUM> and the wiring unit <NUM>. The setting unit <NUM> sets the temperature compensation unit <NUM> according to the gain to be set in the APD <NUM>. The wiring unit <NUM> electrically connects the temperature compensation unit <NUM> and the APD <NUM> to each other. The plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM> have mutually different breakdown voltages. The wiring unit <NUM> applies, to the APD <NUM> as a bias voltage, a voltage corresponding to the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>. The setting unit <NUM> sets a temperature compensation diode to be used for controlling the bias voltage among the plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM> so that "ΔV" calculated by substituting the gain to be set in the APD <NUM> into "Md" in Equation (<NUM>) becomes a difference voltage. As a result, a temperature compensation diode to be used for controlling the bias voltage among the plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM> is set by the setting unit <NUM>. Therefore, a gain desired according to the situation can be obtained very easily without strictly considering the ambient temperature. In other words, it is possible to easily switch a desired gain and obtain the desired gain in a stable manner with respect to temperature.

The circuit unit <NUM> electrically connects the APD <NUM> and the temperature compensation diodes <NUM>, <NUM>, and <NUM> to the terminal <NUM> in parallel with each other. In this configuration, when any one of the plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM> is in a breakdown state, the breakdown voltage of the temperature compensation diode in the breakdown state is applied to the APD <NUM> as a bias voltage. As a result, the difference voltage between the breakdown voltage of the APD <NUM> and the bias voltage applied to the APD <NUM> is set, and the APD <NUM> has a gain corresponding to the difference voltage. Therefore, according to a temperature compensation diode that breaks down, a gain desired according to the situation can be obtained in a stable manner with respect to temperature in the APD <NUM>.

The circuit unit <NUM> includes at least one switch <NUM>. The switches <NUM> are electrically connected to the corresponding temperature compensation diodes <NUM> and <NUM>. The switches <NUM> switch between a state capable of electrically energizing the corresponding temperature compensation diodes <NUM> and <NUM> and a state incapable of electrically energizing the corresponding temperature compensation diodes <NUM> and <NUM>. The plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM> include the temperature compensation diode <NUM> and the temperature compensation diode <NUM>. The temperature compensation diode <NUM> has a higher breakdown voltage than the temperature compensation diode <NUM>. The switch <NUM> is electrically connected to the temperature compensation diode <NUM>. In this case, when the temperature compensation diode <NUM> is set to a state capable of being electrically energized by the switch <NUM>, the temperature compensation diode <NUM> preferentially breaks down even if the temperature compensation diode <NUM> is in a state capable of being electrically energized. In this manner, it is possible to switch a gain desired according to the situation in the APD <NUM> with simple control.

At least one switch <NUM> is connected to the corresponding terminal <NUM>. A high voltage is applied between the electrode 29a of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> and the APD <NUM>. Therefore, a control in a case where the switch <NUM> is electrically connected to the electrode 29b through the terminal <NUM> can be easier than that in a case where the switch <NUM> is disposed between the electrode 29a and the APD <NUM>.

The circuit unit <NUM> is configured to set the temperature compensation diode <NUM> into a state capable of being electrically energized regardless of whether or not to be capable of electrically energizing the temperature compensation diode <NUM>. In this case, even if the temperature compensation diode <NUM> is damaged or a local temperature change occurs in the vicinity where the temperature compensation diode <NUM> is disposed, the temperature compensation diode <NUM> breaks down. Therefore, the flow of a large current to the APD <NUM> is prevented, and the failure of the light detection device <NUM> is prevented.

The plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM> further include the temperature compensation diode <NUM>. The temperature compensation diode <NUM> has a breakdown voltage that is higher than the breakdown voltage of the temperature compensation diode <NUM> and lower than the breakdown voltage of the temperature compensation diode <NUM>. The switch <NUM> is electrically connected to the temperature compensation diode <NUM>. In a state incapable of electrically energizing the temperature compensation diode <NUM>, the circuit unit <NUM> is configured to switch by the switch <NUM> between a state capable of electrically energizing the temperature compensation diode <NUM> and a state incapable of electrically energizing the temperature compensation diode <NUM>. In this case, in a state capable of electrically energizing the temperature compensation diode <NUM>, the temperature compensation diode <NUM> breaks down. In a state incapable of electrically energizing the temperature compensation diode <NUM>, the temperature compensation diode <NUM> breaks down when the temperature compensation diode <NUM> is set in a state capable of being electrically energized. In a state incapable of electrically energizing the temperature compensation diode <NUM>, the temperature compensation diode <NUM> breaks down when the temperature compensation diode <NUM> is set in a state incapable of being electrically energized. In this manner, it is possible to switch a gain desired according to the situation in the APD <NUM> with simple control.

Next, an example of a method for manufacturing a light detection device will be described with reference to <FIG> is a flowchart illustrating a method for manufacturing the semiconductor substrate <NUM> in the light detection device <NUM>.

First, a semiconductor wafer is prepared (process S1). The semiconductor wafer is a substrate before being processed as the semiconductor substrate <NUM>, and has main surfaces 50a and 50b facing each other. The semiconductor wafer has a first conductive type semiconductor region corresponding to the semiconductor region <NUM>. The semiconductor region is provided on the main surface 50a side of the semiconductor wafer, and forms the entire main surface 50a. For example, the semiconductor region of the semiconductor wafer is P- type. In the present embodiment, the semiconductor layer <NUM> of the first conductive type, which has an impurity concentration higher than the semiconductor region of the semiconductor wafer, is formed in the semiconductor wafer by adding impurities from the main surface 50b side. For example, the semiconductor layer <NUM> is P+ type.

Subsequently, the difference voltage between the breakdown voltage of the APD <NUM> and the bias voltage applied to the APD <NUM> is determined. The determination method is as follows.

First, the slope and intercept of the regression line, which has "(<NUM>/M) × (dM/dVr)" as an objective variable and "M" as an explanatory variable in the data indicating the correlation between the bias voltage applied to the APD and the gain of the APD are obtained (process S2). Here, "Vr" is a bias voltage applied to the APD, and "M" is the gain of the APD to which the bias voltage is applied. The above data used in process S2 corresponds to a separate body having the same material and structure as the APD <NUM>.

Then, the difference voltage to obtain the desired gain is determined by using the result obtained in process S2 and Equation (<NUM>) (process S3). The above difference voltage corresponds to "ΔV" calculated by substituting the obtained slope into "a" in Equation (<NUM>), substituting the obtained intercept into "b" in Equation (<NUM>), and substituting the desired gain to be set in the APD <NUM> into "Md" in Equation (<NUM>). In the present embodiment, a plurality of values different from each other are determined as a gain to be set in the APD <NUM>, and a plurality of difference voltages described above are determined for these values. A plurality of "ΔV" calculated by substituting a plurality of values different from each other into "Md" in Equation (<NUM>) are determined as the difference voltages corresponding to the plurality of values.

Subsequently, as first ion implantation process (process S4), impurity ions are implanted to the main surface 50a side using an ion implantation method to add impurities, forming the second conductive type semiconductor layer <NUM> and the first conductive type semiconductor layers <NUM> and <NUM>. For example, the semiconductor layer <NUM> is N+ type, the semiconductor layer <NUM> is P type, and the semiconductor layer <NUM> is P+ type. In the present embodiment, the semiconductor layer <NUM> is formed by implanting second conductive type impurity ions into different portions spaced apart from each other in one ion implantation process. The semiconductor layer <NUM> is formed by implanting first conductive type impurity ions after the semiconductor layer <NUM> is formed. The semiconductor layer <NUM> may be formed by implanting first conductive type impurity ions before the semiconductor layer <NUM> is formed.

The semiconductor layers <NUM> and <NUM> are formed at locations overlapping each other when viewed from the direction perpendicular to the main surface 50a. The semiconductor layer <NUM> is formed by implanting first conductive type impurities at a location deeper than the semiconductor layer <NUM> when viewed from the main surface 50a side. The semiconductor layers <NUM> and <NUM> are formed at a plurality of portions spaced apart from each other when viewed from the direction perpendicular to the main surface 50a, in a region serving as one semiconductor substrate <NUM>. The plurality of portions include a portion where the APD <NUM> is disposed and a portion where each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is disposed. In the first ion implantation process, second conductive type impurities are added to each portion so that the impurity concentration of the semiconductor layer <NUM> is the same. Similarly, first conductive type impurities are added to each portion so that the impurity concentration of the semiconductor layer <NUM> is the same.

Subsequently, as second ion implantation process (process S5), impurities are further added only to the semiconductor layer <NUM> in some of the above-described plurality of portions by using an ion implantation method. In the present embodiment, the first conductive type impurities are further implanted into the semiconductor layer <NUM> only in a portion where each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is disposed. Accordingly, in the light detection device <NUM>, the impurity concentration in the semiconductor layer <NUM> of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is higher than the impurity concentration in the semiconductor layer <NUM> of the APD <NUM>. In this case, the light detection device <NUM> is configured such that the breakdown voltage of the APD <NUM> is higher than the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>.

The amount of the first conductive type impurities implanted into the semiconductor layer <NUM> of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> in processes S4 and S5 depends on the difference voltage determined in process S3. In the present embodiment, the amount of the first conductive type impurities implanted into the semiconductor layer <NUM> of the temperature compensation diode <NUM> is larger than the amount of the first conductive type impurities implanted into the semiconductor layer <NUM> of the temperature compensation diode <NUM>. Therefore, the breakdown voltage of the temperature compensation diode <NUM> is configured to be larger than the breakdown voltage of the temperature compensation diode <NUM>. The amount of the first conductive type impurities implanted into the semiconductor layer <NUM> of the temperature compensation diode <NUM> is larger than the amount of the first conductive type impurities implanted into the semiconductor layer <NUM> of the temperature compensation diode <NUM>. Therefore, the breakdown voltage of the temperature compensation diode <NUM> is configured to be larger than the breakdown voltage of the temperature compensation diode <NUM>.

In the second ion implantation process, the first conductive type impurities may be further implanted into the semiconductor layer <NUM> only in a portion where the APD <NUM> is disposed, not in a portion where each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is disposed. In this case, in the light detection device <NUM>, the impurity concentration in the semiconductor layer <NUM> of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> is lower than the impurity concentration in the semiconductor layer <NUM> of the APD <NUM>. In the light detection device <NUM> in this case, the breakdown voltage of the APD <NUM> is configured to be lower than the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>.

By the processes described above, the semiconductor substrate <NUM> of the light detection device <NUM> is formed. Processes S2 and S3 may be performed before process S1 or after process S4. In the present embodiment, the semiconductor layers <NUM>, <NUM>, and <NUM> are formed from the state in which the semiconductor layer <NUM> has already been formed. However, the semiconductor layer <NUM> may be formed after the semiconductor layers <NUM>, <NUM>, and <NUM> are formed.

In the manufacturing method described above, the semiconductor layer <NUM> and the semiconductor layer <NUM> are formed in each portion by implanting ions into a plurality of different portions. Thereafter, ions are further implanted into the semiconductor layer <NUM> in some of the portions. Therefore, the plurality of temperature compensation diodes <NUM>, <NUM>, and <NUM> and the APD <NUM> each of which is set to the desired breakdown voltage can be easily manufactured while having the same temperature characteristics with respect to the gain and the bias voltage. In this case, the gain of the APD <NUM> can be arbitrarily set according to the difference voltage between the breakdown voltage of each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> and the breakdown voltage of the APD <NUM>. Therefore, when each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> and the APD <NUM> is set to the desired breakdown voltage, the detection accuracy can be improved. For example, when the gain of the APD <NUM> is set to the optimal multiplication factor Mopt having a high S/N ratio according to the above difference voltage, the detection accuracy can be improved. Thus, in the manufacturing method described above, temperature compensation for the gain of the APD <NUM> is provided while suppressing the manufacturing cost, and the detection accuracy can be improved.

In the difference voltage determination method described above, the slope and intercept of the regression line, which has "(<NUM>/M) × (dM/dVr)" as an objective variable and "M" as an explanatory variable are obtained. By substituting the obtained slope into "a" in Equation (<NUM>) and substituting the obtained intercept into "b" in Equation (<NUM>), the difference voltage to obtain the desired gain is determined. Therefore, the difference voltage to obtain the desired gain is determined very easily without strictly considering the ambient temperature.

In the determination method described above, a plurality of "ΔV" calculated by each substituting a plurality of different values as gains to be set in the APD <NUM> into "Md" in Equation (<NUM>) are determined as difference voltages corresponding to the plurality of values. Therefore, the plurality of difference voltages corresponding to the plurality of values are determined very easily without strictly considering the ambient temperature.

While the embodiment of the present invention and the modification examples have been described above, the present invention is not necessarily limited to the embodiment and the modification examples described above, and various changes can be made.

In the present embodiment, the configuration in which the so-called reach-through type APD <NUM> is arranged to operate in linear mode has been described. The light detection device <NUM> may have a configuration in which the reverse type APD <NUM> is arranged to operate in linear mode.

In the present embodiment, the light detection device <NUM> including the electromotive force generation unit <NUM>, the current limiting unit <NUM>, the bias voltage stabilization unit <NUM>, and the setting unit <NUM> has been described. However, the light detection device according to the present embodiment may have a configuration in which at least one of the electromotive force generation unit <NUM>, the current limiting unit <NUM>, the bias voltage stabilization unit <NUM>, or the setting unit <NUM> is not included. In this case, an external device connected to the light detection device may function as the electromotive force generation unit <NUM>, the current limiting unit <NUM>, the bias voltage stabilization unit <NUM>, or the setting unit <NUM>. The light detection device <NUM> may include a signal reading circuit (not illustrated).

In the present embodiment, the configuration has been described in which the switch <NUM> is connected to the terminal <NUM> of the light detection unit <NUM> and the switch <NUM> is controlled by the setting unit <NUM>. However, the switch <NUM> may be disposed inside the light detection unit <NUM>.

In the present embodiment, the terminals <NUM>, <NUM>, <NUM>, and <NUM> have been described as pad electrodes. However, the terminals <NUM>, <NUM>, <NUM>, and <NUM> may be configured by the semiconductor in the semiconductor substrate <NUM>.

The switch <NUM> for switching the electrical connection between each of the temperature compensation diodes <NUM>, <NUM>, and <NUM> and the APD <NUM> may be disposed in the wiring unit <NUM>, and ON/OFF of the switch <NUM> in the wiring unit <NUM> may be controlled by the setting unit <NUM>. Also in this case, the setting unit <NUM> controls the bias voltage applied to the APD <NUM>. Since a high voltage is applied between the APD <NUM> and each of the temperature compensation diodes <NUM>, <NUM>, and <NUM>, the switch <NUM> connected to the terminal <NUM> is controlled more easily than in a case where the switch disposed in the wiring unit <NUM> is controlled.

The temperature compensation unit <NUM> may include a plurality of temperature compensation diodes having the same breakdown voltage. According to this configuration, even if a part of the temperature compensation diode is damaged or a local temperature change occurs in the vicinity where a part of the temperature compensation diode is disposed, the normal operation of the light detection device <NUM> can be realized.

Claim 1:
A determination method for determining a voltage for a light detection device (<NUM>) having an avalanche photodiode (<NUM>), comprising:
assuming that a bias voltage applied to the avalanche photodiode (<NUM>) is "Vr" and a gain of the avalanche photodiode to which the bias voltage is applied is "M", obtaining a slope and an intercept of a regression line having "(<NUM>/M) × (dM/dVr)" as an objective variable and "M" as an explanatory variable, the "(<NUM>/M) × (dM/dVr)" being of data indicating a correlation between the bias voltage and the gain; and
determining a difference voltage between a breakdown voltage of the avalanche photodiode and the bias voltage,
wherein the light detection device (<NUM>) includes a temperature compensation unit (<NUM>) configured to provide temperature compensation for the gain of the avalanche photodiode (<NUM>) based on the determined difference voltage, and
when determining the difference voltage, "ΔV" is determined as the difference voltage, the "ΔV" being calculated by substituting the slope into "a" in following Equation (<NUM>), substituting the intercept into "b" in the following Equation (<NUM>), and substituting a gain to be set in the avalanche photodiode into "Md" in the following Equation (<NUM>),
[Equation <NUM>] <MAT>