JP2005303268A - Light detecting element and method of controlling light detecting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light detecting element capable of preventing saturation caused by external light and extracting a component corresponding to a signal light to improve the dynamic range of the signal light. <P>SOLUTION: A element forming layer 22 has a well region 31 on a principal surface side and a surface electrode 25 is provided on the principal surface through an insulation layer 24. An electron holding region 32 is provided within the well region 31, and within the electron holding region 32 there is provided a positive-hole holding region 33. In addition, a control electrode 26 is provided at the site corresponding to the positive-hole holding region 33 in the principal surface of the element forming layer 22 through the insulation layer 24. The element forming layer 22 creates electrons and positive holes responding to irradiation of light and in accordance with the control of the voltages applied to the surface electrode 25 and control electrode 26, operates to select the state of storing electrons in the electron holding region 32 and holding positive holes in the positive-hole holding region 33 and the state of recombining the electrons and positive holes. Electrons remaining after the recombination are taken out as a light-reception output. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light detection element and a method for controlling the light detection element.

  Conventionally, various types of light detection elements such as photodiodes, phototransistors, and CCD image sensors are known. These light detection elements are a photoelectric sensor that detects the presence or absence of an object by a change in received light intensity, and a light transmission medium. It is widely used for various applications such as optical communication, a distance sensor that optically measures using a triangulation method, a phase difference between light transmission and reception, and an image sensor of a video camera or a digital camera.

  By the way, among these applications, a light detection element is used together with a light source, and when used in an environment in which ambient light such as natural light is incident (such as a photoelectric sensor for monitoring an intruder or an optical remote control device). Optical communication, distance sensors used for autofocus cameras and robot eyes, image sensors used with light sources to obtain distance images, etc.) and ambient light in addition to light emitted from the light sources. Therefore, the received light intensity increases as compared with the case where only the light emitted from the light source is received. On the other hand, in this type of light detection element, although the amount of carriers (electrons or holes) corresponding to the amount of received light is generated inside the element, the number of carriers generated with respect to the amount of received light is limited, and the amount of received light is limited. If it increases, the number of carriers generated gradually saturates. Therefore, when the signal light including the target information in the above-described application is received by the light detection element together with the environmental light, the dynamic range of the light detection element is reduced by the amount of the environmental light, which is larger than the signal light. There arises a problem that the output cannot be obtained.

  In addition, if the signal light and the ambient light are mixed, there is a possibility that the ambient light and the signal light cannot be distinguished when the ambient light varies. As a technique for distinguishing between ambient light and signal light, it is considered to use an optical filter that passes only a specific wavelength used for signal light. However, in the case of ambient light having a spectrum component over a wide range such as sunlight. Even through an optical filter, the influence of ambient light cannot be sufficiently removed.

As a technique for separating the signal light and the ambient light, it is considered to separate a component corresponding to the ambient light and a component corresponding to the signal light from the output of the light detection element. For example, it is considered that the light source output is intermittently turned on, and the difference between the light reception output between the light source turn-on period and the light source turn-off period is obtained to reduce the component with respect to the environmental light (see, for example, Patent Document 1). ). In other words, in a short time interval that does not change the ambient light, light is received by subtracting the received light output during the extinguishing period including only the component corresponding to the ambient light from the received light output during the lighting period including the ambient light and signal light components. Since the difference in output is obtained, it is possible to significantly increase the proportion of the component corresponding to the signal light by suppressing the component corresponding to the ambient light.
JP 2001-337166 A (paragraph 0029-0035)

  By the way, the technique described in Patent Document 1 described above separates the component corresponding to the signal light and the component corresponding to the ambient light with respect to the light reception output of the light detection element, and an external circuit is provided for the light detection element. Since the difference between the received light outputs is obtained, there is a problem that it becomes impossible to extract the component corresponding to the signal light when the light detection element is saturated. That is, in the presence of ambient light, the problem that the dynamic range of the light detection element with respect to the signal light becomes small and a large output cannot be obtained with respect to the signal light is still solved using the technique described in Patent Document 1. Not.

  This will be described in more detail. In general, since the limit of detection accuracy of the light detection element is determined by shot noise accompanying photoelectric conversion, it is necessary to increase the number of carriers generated by light irradiation in order to reduce the influence of shot noise. The number of carriers generated by the light detection element increases as the received light intensity increases and the light reception time increases (that is, the amount of received light increases) in the range where the light detection element is not saturated. Alternatively, the influence of shot noise can be reduced by increasing the light receiving time of the light detection element. However, as described above, in the presence of ambient light, the dynamic range of the light detection element decreases, so even if the amount of light emitted from the light source is increased or the light reception time of the light detection element is increased, the SN ratio is sufficiently large. I can't take it.

  Further, in Patent Document 1, an image sensor made up of a CCD sensor or a MOS sensor is used as a light detection element, and two light reception outputs for taking a difference must be once taken out from the image sensor. Must be read at least twice. That is, it takes two screens (two frames) of reading time until a result is obtained, resulting in a problem that the response speed is lowered accordingly.

  The present invention has been made in view of the above-mentioned reasons, and an object of the present invention is to prevent the saturation due to ambient light without providing an external circuit and extract a component corresponding to the signal light. It is an object to provide a photodetection element and a method for controlling the photodetection element that do not cause a decrease in response speed even when an image pickup element is configured by arranging a large number.

  According to a first aspect of the present invention, a light-sensitive portion made of a semiconductor capable of receiving light emitted from a light source and generating a number of holes and electrons corresponding to the amount of light received, and a control for discrimination are provided. A carrier discriminating portion for separating a target carrier that is one of holes and electrons generated in the photosensitive portion by controlling a voltage applied to the electrode and a non-target carrier that is the other; and a control electrode for coupling A recombination unit that recombines the target carrier generated in the photosensitive unit during the light source lighting period and the non-target carrier generated in the photosensitive unit during the light source extinguishing period at a predetermined timing by controlling the voltage applied to the coupling control electrode. And an output unit for taking out the target carrier remaining after recombination in the recombination unit is configured as one semiconductor device.

  According to this configuration, the target carrier generated by the photosensitive unit during the light source lighting period and the non-target carrier generated by the photosensitive unit during the light source extinguishing period are recombined by the recombination unit and remain after recombination. The target carrier corresponding to the ambient light component can be removed from the target carrier corresponding to the signal light component received by the photosensitive portion, and the ambient light component can be removed from the target carrier remaining after recombination. It can be removed greatly. As a result, the ambient light component of the target carrier delivered from the recombination unit to the output unit can be reduced, and saturation of the output unit due to the ambient light component can be prevented. In addition, since the above-described function is realized in one semiconductor device, the saturation of the semiconductor device itself does not occur as compared with the case where the ambient light component is removed from the signal extracted from the semiconductor device. The dynamic range for light (signal light) can be greatly improved. In addition, since a recombination unit is provided in the light detection element and the target carrier corresponding to the difference between the received light amounts in two different periods is used as the light reception output, when the image pickup element is configured by arranging a large number, It is possible to provide a light detection element that does not need to read out the screen and does not have a decrease in response speed.

  According to a second aspect of the present invention, in the first aspect of the invention, the carrier discriminating unit generates the number of target carriers generated during the lighting period and involved in the recombination in the recombination part during the extinguishing period. The number of non-target carriers involved in recombination is adjusted so as to be larger.

  According to this configuration, the relationship between the number of target carriers generated by the photosensitive unit and the number of non-target carriers is adjusted by the carrier discriminating unit. It becomes easy to remove the generated ambient light component.

  According to a third aspect of the invention, in the first or second aspect of the invention, the target carrier generated in the photosensitive portion is accumulated and held until recombination, and the non-purpose generated in the photosensitive portion. A non-purpose carrier holding unit that accumulates carriers and holds them until recombination is added, and the recombination unit includes a target carrier held by the target carrier holding unit and a non-purpose carrier held by the non-purpose carrier holding unit. It is characterized by recombining.

  According to this configuration, the target carrier and the non-target carrier are held by the target carrier holding unit and the non-purpose carrier holding unit, respectively, and are held by the target carrier and the non-purpose carrier holding unit held by the target carrier holding unit. Since the non-target carrier is recombined in the recombination section, the target carrier and the non-target carrier can be separately held until the recombination timing, and the target carriers generated in two different periods are respectively stored. And the non-target carrier can be separated and held so as not to recombine.

  According to a fourth aspect of the present invention, in the third aspect of the invention, the carrier discriminating section includes a switch element that discards the target carrier held in the target carrier holding section.

  According to this configuration, since the target carrier generated in one of the extinguishing period and the lighting period can be discarded, only the non-target carrier generated in the one period is retained, and recombination The difference in the number of the target carrier and the non-target carrier when recombining in the part can be increased. As a result, a relatively large number of target carriers can be taken out after recombination while the turn-off period and the turn-on period are relatively short, and the sensitivity can be increased.

  According to a fifth aspect of the present invention, in any of the first to fourth aspects of the present invention, an output unit for integrating the target carrier remaining after the recombination at the recombination unit is added.

  According to this configuration, even when the number of target carriers taken out from the recombination unit corresponding to one lighting period and one light-off period is small, the output is performed by integrating the target carriers in the output unit. The number of target carriers can be made relatively large.

  According to a sixth aspect of the present invention, in the third aspect of the invention, a first conductivity type element forming layer formed on a main surface of a semiconductor substrate and a second conductivity type provided on the main surface side of the element forming layer. A well electrode, a surface electrode facing at least the well region through an insulating layer on the main surface of the element formation layer and transmitting light, and the target carrier holding provided on the main surface side of the element formation layer in the well region A first holding region of the second conductivity type to be a part, a second holding region of the first conductivity type to be provided on the main surface side of the element forming layer in the first holding region and the non-target carrier holding part, and an element A control electrode which is opposed to an insulating layer in a portion corresponding to the second holding region in the main surface of the formation layer, and which is used as both the discrimination control electrode and the coupling control electrode, and is capable of transmitting light; The photosensitive portion is in the element forming layer. Te generates electrons and holes, which comprises using at least one of said first holding region and the second holding region as a recombination unit.

  According to this configuration, the configuration of claim 3 can be realized using a semiconductor device having a relatively simple structure. In particular, since at least one of the first holding region and the second holding region is also used as a recombination portion, the size can be reduced.

  According to a seventh aspect of the invention, there is provided the second conductivity type according to the sixth aspect of the invention, wherein the second carrier type is formed adjacent to the well region on the main surface side of the element forming layer and can discard the target carrier from the target carrier holding portion. And a drain electrode to which a voltage is applied so as to discard target carriers from the first holding region to the drain region.

  According to this configuration, since the target carrier generated in one of the lighting period and the extinguishing period can be discarded in the drain region, the non-purpose carrier holding unit generates the non-purpose generated in the one period. Only carriers are held, and the difference in the number of target carriers and non-target carriers to be recombined can be increased. As a result, it is possible to take out a relatively large number of target carriers after recombination while relatively shortening the lighting period and the extinguishing period, and the sensitivity can be increased.

  According to an eighth aspect of the present invention, in the third aspect of the invention, a first conductivity type element forming layer formed on a main surface of a substrate made of a semiconductor, and the target carrier holding portion provided on the main surface side of the element forming layer. A second conductivity type well region, a surface electrode at least on the main surface of the element forming layer that faces the well region through an insulating layer and transmits light, and in the well region on the main surface side of the element forming layer A first conductive type holding region provided as the non-purpose carrier holding portion, and an electrode opposed to the main surface of the element forming layer through a portion of the holding region corresponding to a part of the holding region via an insulating layer; A control electrode that can be used as both the control electrode for coupling and the control electrode for coupling, and is capable of transmitting light. The photosensitive portion generates electrons and holes in the element formation layer, and serves as the recombination portion in the well region. Small inside and outside holding area It characterized by using one and also.

  According to this configuration, the configuration of claim 3 can be realized using a semiconductor device having a relatively simple structure. In particular, since at least one of the inside and outside of the holding region is also used as a recombination portion in the well region, the size can be reduced.

  In the invention of claim 9, in the invention of claim 3, the element formation layer of the second conductivity type formed on the main surface of the substrate made of the semiconductor of the second conductivity type via the intermediate layer of the first conductivity type, A second conductivity type well region that is provided on the main surface side of the element formation layer and serves as the target carrier holding portion, and a surface that allows light to pass through the main surface of the element formation layer through at least the well region via an insulating layer Corresponding to the electrode, the first conductivity type holding region provided on the main surface side of the element forming layer in the well region and serving as the non-purpose carrier holding portion, and a part of the holding region of the main surface of the element forming layer And a control electrode that is used as the discrimination control electrode and the coupling control electrode and is capable of transmitting light. Generate holes, and Which comprises using at least one of the inside and outside of the holding region in the well region Te.

  According to this configuration, the configuration of claim 3 can be realized using a semiconductor device having a relatively simple structure. In particular, since at least one of the inside and outside of the holding region is also used as a recombination portion in the well region, the size can be reduced. Further, since the well region and the element formation layer are formed of a semiconductor of the same conductivity type, the well region and the element formation layer can function as a photosensitive portion that generates target carriers and non-target carriers up to a deep portion of the element formation layer, and Since the substrate and the intermediate layer of the conductivity type different from the element formation layer are provided between the element formation layer, the target carrier and the non-target carrier can be easily discriminated by adjusting the potential between the substrate and the intermediate layer. can do.

  According to a tenth aspect of the present invention, in the sixth to ninth aspects of the invention, the well region has a depth that does not reach the substrate in the element formation layer, and the well region and the element formation layer are formed at the bottom of the well region. A buried layer is formed to increase the potential barrier between the first and second electrodes.

  According to this configuration, by providing the buried layer at the bottom of the well region, it is possible to prevent the target carrier from leaking from the well region to the substrate, and in the output portion as compared with the case where no buried layer is provided. The number of target carriers to be delivered increases.

  The invention according to claim 11 is the method of controlling the photodetecting element according to claim 3, wherein the target carrier is accumulated in the target carrier holding unit during the lighting period, the non-target carrier is discarded, and the non-target carrier is discarded during the extinguishing period. The non-target carrier is integrated in the non-target carrier holding portion, and the voltage applied to the discrimination control electrode is controlled so that the target carrier is discarded.

  According to this method, since the target carriers are accumulated during the lighting period and the non-target carriers are accumulated during the non-lighting period, ideally, after the target carrier and the non-target carrier are recombined, the lighting period and the non-lighting period are ideal. The number of target carriers corresponding to the difference in the amount of received light with respect to the period remains, and an output with a greatly reduced ambient light component can be obtained.

  The invention of claim 12 is a method for controlling a photodetecting element according to any one of claims 6 to 10, wherein the target carrier is held in the target carrier holding part and the non-target carrier holding part. After applying a voltage for holding the non-target carrier to the control electrode, the voltage applied to the control electrode is changed, and the target carrier held by the target carrier holding part and the non-purpose held by the non-purpose carrier holding part It is characterized by recombining by moving at least one of the carriers.

  A thirteenth aspect of the invention is a method of controlling a light detection element according to the eighth or ninth aspect, wherein the target carrier holding part holds the target carrier and the non-target carrier holding part holds the non-target carrier. After the voltage to be applied to the control electrode is changed, the voltage applied to the control electrode is changed a plurality of times, whereby the target carrier is reciprocated in and out of the holding region in the well region and the non-target carrier is The target carrier and the non-target carrier are recombined by reciprocating between a part facing the control electrode and a part facing the control electrode in the holding region.

  According to this method, the target carrier is reciprocated inside and outside the holding region in the well region, and the non-target carrier is reciprocated between the portion facing the control electrode and the non-facing portion in the holding region. The target carrier and the non-target carrier can be recombined at a portion facing the control electrode in the region. Here, the non-target carriers trapped at the interface potential of the holding region recombine with the target carriers, and even if the target carriers are introduced into the holding region only once, all the non-target carriers can be extinguished. Since it is impossible, the movement of the target carrier and the non-target carrier is repeated several times. In addition, the component corresponding to the signal light can be extracted by applying the voltage to the control electrode and the relatively simple voltage control for controlling the potential of the applied voltage. Since the carrier only reciprocates, current does not flow to the outside and power consumption is reduced.

  The invention according to claim 14 is a method for controlling a photodetecting element according to claim 8 or claim 9, wherein non-target carriers are accumulated in the holding region and the target carriers are discarded during the turn-off period, and the lighting period. Is characterized in that the voltage applied to the surface electrode, the control electrode and the substrate is controlled so that the target carrier is accumulated in the holding region and the non-target carrier is discarded.

  According to this method, since the target carriers are accumulated during the lighting period and the non-target carriers are accumulated during the non-lighting period, ideally, after the target carrier and the non-target carrier are recombined, the lighting period and the non-lighting period are ideal. The number of target carriers corresponding to the difference in the amount of received light with respect to the period remains, and an output with a greatly reduced ambient light component can be obtained.

  In the invention of claim 15, in the invention of claim 14, each voltage applied to the surface electrode and the control electrode in the state in which the target carriers are accumulated in the lighting period and in the state in which the non-target carriers are accumulated in the extinguishing period. In a state where the polarity and the polarity of the voltage applied to the substrate are opposite to each other and the target carrier and the non-target carrier are recombined in at least one of the lighting period and the extinguishing period, the polarity of the voltage applied to the control electrode is Inversion is performed a plurality of times, and target carriers remaining in the well region after recombination are taken out.

  According to this method, the target carrier and the non-target carrier can be individually accumulated in the holding area in the lighting period and the non-lighting period, respectively, and the target carrier and the non-target carrier are taken in and out of the holding area, The target carrier and the non-target carrier can be recombined mainly in the holding region. Furthermore, the recombination probability between the target carrier and the non-target carrier can be increased by repeatedly putting the target carrier and the non-target carrier into and out of the holding region a plurality of times.

  The light detection element of the present invention separates a target carrier that is one of holes and electrons generated in the photosensitive portion and a non-target carrier that is the other, and separates the carrier from the photosensitive portion during the lighting period of the light source. The target carrier generated in step 1 and the non-target carrier generated in the photosensitive portion during the light-off period of the light source are recombined in the recombination unit, and the target carrier remaining after the recombination is taken out to the outside. If the period for separating the target carrier and the non-target carrier is appropriately controlled, the number of target carriers remaining after recombination can be made to correspond to the difference in received light amount between the lighting period and the extinguishing period. As a result, it is possible to significantly remove the component corresponding to the ambient light from the target carrier remaining after the recombination, and it is possible to prevent saturation due to the component corresponding to the ambient light. As a result, there is an advantage that the ambient light component of the target carrier delivered from the recombination unit to the output unit can be reduced and saturation of the output unit due to the ambient light component can be prevented. In addition, since the above-described function is realized in one semiconductor device, the saturation of the semiconductor device itself does not occur as compared with the case where the ambient light component is removed from the signal extracted from the semiconductor device. There is an advantage that the dynamic range for the light (signal light) can be greatly improved. In addition, since a recombination part is provided in the light detection element and the target carrier corresponding to the difference in the amount of light received between the lighting period and the light-off period is used as the light reception output, imaging is performed when an image sensor is configured by arranging a large number. There is an advantage that it is not necessary to read out two screens from the element, and it is possible to provide a photodetection element that does not have a decrease in response speed.

(Embodiment 1)
FIG. 4 shows an example in which a device that performs distance measurement using the light detection element 1 of the present embodiment is configured. This apparatus projects light from the light source 2 onto a target space including the object 3 whose distance is to be measured, and receives light from the target space including light reflected by the target 3 by the light detection element 1. A light receiving output reflecting the amount of reflected light from the object 3 is obtained from the light detecting element 1. As a technique for measuring the distance to the object 3 with this kind of configuration, a technique for measuring the time of flight of light until light projected from the light source 2 to the object space is received by the light detection element 1 is known. ing.

  That is, the intensity of light projected from the light source 2 to the target space is modulated with a modulation signal having an appropriate waveform such as a sine wave, and the light received by the light detection element 1 and the light projected from the light source 2 are A technique for obtaining a phase difference of a waveform of a modulation signal and converting the phase difference into a distance is known. As the light source 2, a light emitting diode or a semiconductor laser is mainly used.

  The intensity modulation of the light projected from the light source 2 to the target space is performed by a modulation signal that is a sine wave having a constant modulation frequency (for example, 20 MHz) output from the timing control unit 10. In addition, a period in which light is projected from the light source 2 to the target space and a period in which light is not projected are alternately provided, and the light modulated by the modulation signal is multiplied by a modulation period (reciprocal of the modulation frequency) (for example, 10000). Times) and a period during which light is not projected from the light source 2. A period during which light is projected into the target space is referred to as a light-on period of the light source 2, and a period during which light is not projected is referred to as a light-off period of the light source 2. That is, the light source 2 emits light intermittently.

  The light that enters the light detection element 1 during the light-off period of the light source 2 is only ambient light that does not include the light projected from the light source 2 into the target space, and the light that enters the light detection element 1 during the light-up period of the light source 2 is the light source. 2 is the total of the signal light including the light projected to the target space and the ambient light. Since the intensity of light projected from the light source 2 to the target space during the lighting period is modulated, the light incident on the light detection element 1 during the lighting period fluctuates microscopically. That is, light whose intensity is modulated at a high frequency is projected intermittently, and the period during which light is projected is the lighting period. Therefore, the light received by the photodetecting element 1 is mainly ambient light during the extinguishing period, and is mainly a combination of environmental light and signal light during the lighting period. Therefore, by subtracting the amount of light received during the light-off period from the amount of light received during the lighting period by the light detection element 1, it is theoretically possible to remove the component of ambient light and extract only the component of signal light.

  The light reception output output from the light detection element 1 is given to a distance calculation unit (not shown), and the distance calculation unit uses the light reception output extracted from the light detection element 1 at a plurality of timings to change the intensity of light emitted from the light source 2. The time of flight of light is obtained from the phase difference between this waveform and the waveform of the intensity change of the light received by the light detection element 1, and the distance from the flight time to the object 3 is obtained.

  If only one photodetecting element 1 is used alone, the distance is detected only for an object 3 existing in a specific direction when viewed from the photodetecting element 1, and a plurality of photodetecting elements 1 are arranged to form an image sensor. If the light receiving optical system is arranged in front of the image pickup device and the direction of viewing the target space from the image pickup device through the light receiving optical system is associated with the position of each light detection device 1, the distance in each direction is included in the pixel value. A distance image can be generated. For example, an image pickup device is provided in which the photodetecting elements 1 are arranged on the lattice points of a planar lattice made up of rectangular unit lattices, and an output unit 16 for taking out the received light output of the photodetecting device 1 is provided. Can be used to generate a distance image. In the case of configuring an image sensor, a configuration in which a CCD is used for the output unit 16 and the output unit 16 is also used by the plurality of light detection elements 1 can be employed.

  As will be described later, the number of electrons and holes corresponding to the amount of received light are generated in the light detection element 1, but in this embodiment, of the electrons and holes, the electrons are treated as target carriers, and the holes are not intended. Treat as a career. The output value of the light receiving output of the photodetecting element 1 corresponds to the number of electrons that are target carriers.

  As shown in FIG. 1, the photodetecting element 1 is formed with a p-type (second conductivity type) element laminated on the main surface of a substrate 21 made of an n-type (first conductivity type) semiconductor (for example, silicon). Layer 22 is provided. The element formation layer 22 includes a first layer 22a that contacts the substrate 21 and a second layer 22b that faces the substrate 21 with the first layer 22a interposed therebetween, and the second layer 22b is part of the first layer 22a. An n-type buried layer 23 is formed at a portion in contact with the. The thickness dimension of the first layer 22a is set to 5 μm, for example. A surface electrode 25 is opposed to the main surface of the element formation layer 22 via an insulating layer 24 which is an oxide layer (for example, a silicon oxide layer). In the insulating layer 24, a control electrode 26 and a gate electrode 27 that are separated from the main surface of the element forming layer 22 are embedded in different portions along the surface of the element forming layer 22. That is, the control electrode 26 and the gate electrode 27 are opposed to the element formation layer 22 through a part of the insulating layer 24. The surface electrode 25 and the control electrode 26 can transmit light.

A well region 31 is formed in a portion corresponding to the buried layer 23 in the second layer 22 b of the element formation layer 22. The well region 31 is an n ^{− type} region having a thickness substantially equal to that of the second layer 22 b of the element formation layer 22, and an n type electron holding region (first region) is formed on the main surface side of the element formation layer 22 in the well region 31. Holding region) 32 is formed. A p ^{+ -type} hole holding region (second holding region) 33 is formed in the electron holding region 32 on the main surface side of the element formation layer 22. The above-described control electrode 26 is disposed so as to face the hole holding region 33.

  An n-type drain region 34 a is formed on one side of the well region 31 on the main surface side of the element formation layer 22, and an n-type drain region 34 b is formed on the other side. Drain electrodes 35a and 35b are ohmically connected to the surfaces of the drain regions 34a and 34b, respectively. The drain regions 34a and 34b extend on a straight line in a direction perpendicular to the plane of FIG. 1, and the drain region 34a is provided closer to the well region 31 than the drain region 34b.

  An n-type charge transfer region 36 extending along the drain region 34b is formed between the well region 31 and the drain region 34b along the main surface of the element formation layer 22, and the gate electrode 27 described above is formed in the well region. 31 and the charge transfer region 36 are provided so as to correspond to each other. Between the well region 31 and the charge transfer region 36, a gate portion of a MOS structure is formed. A light shielding film 37 that blocks light is formed on the surface of the surface electrode 25 at portions corresponding to the gate electrode 27, the charge transfer region 36, and the drain region 34b.

  As described above, since the surface electrode 25 is provided on the substrate 21 and the element formation layer 22 via the insulating layer 24, the portion having the structure of the MIS device and not provided with the light-shielding film 37 It functions as a photosensitive portion 11 (see FIG. 4) that generates electrons and holes by irradiation. Here, the potential of the element formation layer 22 is set as a ground potential, and a constant voltage higher than the ground potential (hereinafter, a voltage higher than the ground potential is referred to as “positive voltage”) is applied to the substrate 21. Keep it. If electrons and holes generated by light irradiation are left untreated, they recombine and disappear in a relatively short time. Therefore, in order to separate and accumulate electrons and holes corresponding to the amount of received light, Applies a positive voltage, and a voltage lower than the ground potential (hereinafter referred to as a negative voltage) is applied to the control electrode 26 in advance.

  By setting the voltage of each part as described above, the potential for electrons (black circles) and holes (white circles) becomes as shown in FIG. In FIG. 2B, the left curve indicates the potential energy of the holes, the right curve indicates the potential energy of the electrons, the holes have a higher potential on the left side, and the electrons have a higher potential on the right side. That is, holes generated in the vicinity of the well region 31 (including the electron holding region 32 and the hole holding region 33) are mainly accumulated in the hole holding region 33, and electrons are mainly accumulated in the electron holding region 32. The number of electrons accumulated in the electron holding region 32 and the number of holes accumulated in the hole holding region 33 reflect the amount of light irradiated (that is, the amount of received light), and are integrated when the amount of received light increases. The number of electrons and holes also increases. Further, since a positive voltage is applied to the substrate 21 and the element formation layer 22 is at the ground potential, a reverse bias is generated between the substrate 21 and the element formation layer 22, and the substrate 21 and the element formation layer 22 are generated. Electrons and holes disappear in a short time due to disposal and recombination.

  Next, the operation will be described separately for the lighting period and the extinguishing period. During the extinguishing period, a positive voltage is applied to the surface electrode 25 and a negative voltage is applied to the control electrode 26. When light enters the light detection element 1, electrons generated in the photosensitive portion 11 are accumulated in the electron holding region 32 and holes are accumulated in the hole holding region 33. Thereafter, as shown in FIG. 3, when a positive voltage is applied to the drain electrode 35a, electrons (black circles) accumulated in the electron holding region 32 move to the drain region 34a. That is, while the positive voltage is applied to the surface electrode 25 during the extinguishing period and the negative voltage is applied to the control electrode 26, the drain electrode is switched from the extinguishing period to the lighting period (immediately before the lighting period). When a positive voltage is applied to 35a, holes generated during the extinguishing period are left in the hole holding region 33, and electrons generated during the extinguishing period are moved to the drain region 34a to empty the electron holding region 32. it can. Note that, when a negative voltage is applied to the surface electrode 25 when a positive voltage is applied to the drain electrode 35a, electrons can be quickly moved to the drain region 34a.

  On the other hand, during the lighting period, a positive voltage is applied to the surface electrode 25 and a negative voltage is applied to the control electrode 26 as in the extinguishing period. Electrons generated by the photosensitive portion 11 when light enters the light detection element 1 are held in the electron holding region 32, and holes are held in the hole holding region 33. In this state, the hole holding region 33 includes not only holes generated during the lighting period but also holes generated during the extinguishing period, while electrons in the electron holding region 32 are drained before the lighting period. Therefore, only the electrons generated during the lighting period are ideally included. At this time, since a negative voltage is applied to the control electrode 26, the electron holding region 32 has a low potential (potential well) with respect to electrons as shown in FIG. The region 33 has a low potential (potential well) with respect to holes, and electrons and holes are held separately in an electron holding region 32 and a hole holding region 33 without recombination.

  As is clear from the above description, by applying an appropriate voltage to the control electrode 26, the electrons and holes generated in the photosensitive portion 11 are distributed and integrated into the electron holding region 32 and the hole holding region 33. can do. That is, the control electrode 26, the electron holding region 32, and the hole holding region 33 function as the carrier discriminating unit 12 (see FIG. 4) that separates electrons and holes, and the control electrode 26 functions as a discriminating control electrode. It will be.

  Next, when a positive voltage is applied to the control electrode 26, the potential difference between the electron holding region 32 and the hole holding region 33 is reduced (potential barrier is lowered), and the positive voltage pushed out from the hole holding region 33 is increased. The holes recombine with electrons in the well region 31 (mainly the electron holding region 32). The recombination conditions include not only the voltage applied to the control electrode 26 to control the potential for electrons and holes, but also the time for applying the voltage, as well as the formation of the well region 31 and the hole holding region 33. The impurity concentration of the semiconductor is also involved. That is, since the voltage applied to the control electrode 26 is controlled to recombine electrons and holes, the control electrode 26 functions as a coupling electrode. In addition, since recombination of electrons and holes is performed in the well region 31, the well region 31 functions as the recombination portion 15 (see FIG. 4). In the recombination of electrons and holes, not only the holes pushed from the hole holding region 33 to the electron holding region 32 are recombined in the electron holding region 32 but also moved from the electron holding region 32 to the hole holding region 33. The generated electrons are also bonded to the holes trapped near the interface of the hole holding region 33.

  When recombining the holes in the hole holding region 33 and the electrons in the electron holding region 32, if the number of electrons is adjusted to be larger than the number of holes, the holes disappear after the recombination. Electrons remain. Since the remaining electrons are those generated in the well region 31 during the lighting period, if the electrons are extracted, the number of charges (signal charges) proportional to the signal light from which the influence of ambient light has been removed is extracted. Therefore, after a positive voltage is applied to the control electrode 26 to recombine electrons and holes, a residual voltage is accumulated in the electron holding region 32 by applying a negative voltage to the control electrode 26, and this electron Is taken out as a signal charge.

  That is, if a positive voltage is applied to the gate electrode 27 while electrons are held in the electron holding region 32, a channel is formed in the element formation layer 22 between the well region 31 and the charge transfer region 36, and this channel is passed through. Electrons move from the electron holding region 32 to the charge transfer region 36. The electrons transferred to the charge transfer region 36 are transferred using a well-known technique used for taking out charges in a CCD image sensor or the like, and taken out to the outside.

  The above operations will be briefly summarized. The timing controller 10 controls the timing of applying a voltage to the surface electrode 25, the control electrode 26, the gate electrode 27, the drain electrode 34b, and the drain electrode 35b described above. First, in the extinguishing period in which only light from the light source does not enter from the light source, a positive voltage is applied to the surface electrode 25 and a negative voltage is applied to the control electrode 26. When light is incident, electrons and holes are generated by photoexcitation in the substrate 21, element formation region 22, buried layer 23, well region 31, and hole holding region 33. Next, when a positive voltage is applied to the drain electrode 35a in a state where electrons are held in the electron holding region 32 and holes are held in the hole holding region 33 in the extinguishing period, the positive voltage generated in the extinguishing period is generated. The holes remain in the hole holding region 33, and electrons generated during the extinguishing period move to the drain region 34a and the electron holding region 32 becomes empty.

  Next, in the lighting period in which light from the light source is incident, a positive voltage is applied to the surface electrode 25 and a negative voltage is applied to the control electrode 26 as in the extinguishing period. Also in this case, when light is incident, electrons and holes are generated by photoexcitation in the substrate 21, element formation region 22, buried layer 23, well region 31, and hole holding region 33. In the lighting period, the hole holding region 33 includes not only holes generated in the lighting period but also holes generated in the extinguishing period, and the electron holding region 32 includes only electrons generated in the lighting period. Retained.

  After that, when a positive voltage is applied to the control electrode 26, the potential difference between the electron holding region 32 and the hole holding region 33 is reduced, and holes move from the hole holding region 33 to the electron holding region 32, and electrons and Rejoin. When a positive voltage is applied to the gate electrode 27 in a state where electrons are held in the electron holding region 32, the electron holding region 32 is separated from the electron holding region 32 through a channel formed in the element formation layer 22 between the well region 31 and the charge transfer region 36. Electrons move to the charge transfer region 36. The electrons transferred to the charge transfer region 36 are transferred through the charge transfer region 36 and taken out to the outside.

  Below, the structural example of the ranging apparatus using the photodetection element 1 mentioned above is shown, and the function of each part of the photodetection element 1 is expressed as shown in FIG. In FIG. 4, the photosensitive portion 11 is a region that generates electrons and holes by light irradiation, and includes a substrate 21, an element formation layer 22 (including a well region 31), an insulating layer 24, and a surface electrode 25. Corresponds to the part with the device structure. However, as described above, the electrons and holes in the substrate 21 and the element formation layer 22 disappear rapidly, so that the electrons and holes generated mainly in the well region 31 are electrons and holes generated in the photosensitive portion 11. It corresponds to.

  After the number ratio of electrons and holes generated in the photosensitive unit 11 is adjusted in the carrier discriminating unit 12, the holes are accumulated in the hole holding unit 13 and the electrons are accumulated in the electron holding unit 14. In this embodiment, since electrons are the target carriers and holes are the non-target carriers, the hole holding unit 13 is the non-purpose carrier holding unit and the electron holding unit 14 is the target carrier holding unit. In the light detection element 1, the hole holding region 33 corresponds to the hole holding unit 13, and the electron holding region 32 corresponds to the electron holding unit 14.

  The carrier discriminating unit 12 discriminates electrons and holes so that holes are accumulated in the hole holding unit 13 and electrons are accumulated in the electron holding unit 14. It has a function of determining the ratio between the number of electrons and the number of electrons accumulated in the electron holding unit 14, and for example, the number ratio of holes that are non-target carriers to electrons that are target carriers is 1: 2. Adjust to. The number ratio depends on the element structure (arrangement, shape, size, impurity concentration of the electron holding region 32 and hole holding region 33) and the difference in mobility between electrons and holes, and is applied to the control electrode 26. Depending on the polarity of the voltage, it is possible to discriminate between electrons and holes such that holes are accumulated in the hole holding unit 13 and electrons are accumulated in the electron holding unit 14. Further, the number ratio can be changed by changing the voltage applied to the surface electrode 25 and the control electrode 26. That is, if the height of the potential barrier and the depth of the potential well are controlled by the magnitude of the voltage applied to the surface electrode 25 and the control electrode 26, the number of holes accumulated in the hole holding unit 13 and the electron accumulation unit 14 are controlled. The number of electrons accumulated can be controlled.

  In addition, the number of electrons accumulated in the electron holding unit 14 can be adjusted by discarding the electrons from the electron holding unit 14. That is, by mixing the electrons accumulated in the electron holding unit 14 in the extinguishing period to the discarding unit 18 including the drain region 34a before the lighting period, mixing with the electrons accumulated in the electron holding unit 14 in the lighting period is performed. Can be prevented. The timing at which electrons are discarded from the electron holding unit 14 to the discarding unit 18 is controlled by the timing at which the switch element 17 realized by the drain electrode 35a is turned on. That is, by applying a positive voltage to the drain electrode 35 a, the switch element 17 can be turned on to discard the electrons from the electron holding unit 14. Thus, by discarding the electrons held during the extinguishing period to the discarding unit 18 via the switch element 17, the electrons generated only by the ambient light are discarded and remain after recombination with holes. The influence of ambient light on electrons can be reduced.

  The holes accumulated in the hole holding unit 13 and the electrons accumulated in the electron holding unit 14 are recombined in the recombination unit 15. The recombination unit 15 includes an electron holding region 32, a hole holding region 33, and a control electrode 26, and the recombination timing is controlled by the timing at which a positive voltage is applied to the control electrode 26. Before the recombination, most of the electrons held in the electron holding unit 14 are generated during the lighting period, so that the electrons remain after the recombination unit 15 recombines the electrons and holes. By doing so, it is possible to increase the proportion of the remaining electrons occupied by the component corresponding to the signal light as compared with the case where recombination is not performed. After recombination at the recombination unit 15, electrons remain in the electron holding unit 14 (electron holding region 32), so that the electrons remaining in the electron holding unit 14 are output by the gate electrode 27 and the charge transfer region 36. Take out to the outside through the part 16. Timings of operations of the carrier discriminating unit 12, the recombination unit 15, the output unit 16, and the switch element 17 are controlled by a timing control unit 10 that controls lighting and extinction of the light source 2. That is, the operation timings of the carrier discriminating unit 12, the recombination unit 15, the output unit 16, and the switch element 17 are controlled to synchronize with the lighting and extinguishing of the light source 2.

  In order to leave electrons after recombining electrons (target carriers) and holes (non-target carriers) in the recombination unit 15, as described above, the electrons are held in the electron holding unit 14 before recombination. It is necessary that the number of electrons is larger than the number of holes held in the hole holding unit 13, and in order to satisfy this condition, electrons accumulated in the electron holding unit 14 in the carrier discriminating unit 12 are required. It is necessary to increase the number of holes to be accumulated in the hole holding unit 13. Further, in order to remove components corresponding to ambient light from electrons taken out from the recombination unit 15, the number of electrons accumulated in the electron holding unit 14 and the number of holes accumulated in the hole holding unit 13 in the carrier discriminating unit 12. It is desirable to associate the ratio with the number with the ratio between the turn-off period and the turn-on period.

These conditions are examined below. Now, the extinguishing period is t1, the lighting period is t2, the intensity of the signal light is Ia, the intensity of the ambient light is Ib, the number of holes extracted from the carrier discriminating unit 12 is k times the number of electrons, and the photosensitive unit 11 is intensified. If the number of electrons passed from the carrier discriminating unit 12 to the electron holding unit 14 when α light is received for the time t is αIt, the number of electrons accumulated in the electron holding unit 14 during the lighting period is , Α (Ia + Ib) t2, and the number of holes accumulated in the hole holding unit 13 during the extinguishing period and the lighting period is kα {Ibt1 + (Ia + Ib) t2}. The number N of can be expressed as follows.
N = α (Ia + Ib) t2−kα {Ibt1 + (Ia + Ib) t2}
However, as an ideal condition, the electrons held in the electron holding unit 14 during the extinguishing period are all discarded in the discarding unit 18 and all the holes in the hole holding unit 13 are recombined with the electrons in the electron holding unit 14. Is assumed. From the condition that the number N of electrons must be positive, k <1 is obtained.

  Further, when the above equation is arranged into terms of the intensity Ia of the signal light and the intensity Ib of the environmental light, and a condition for setting the intensity Ib of the environmental light to 0 is obtained, t1 = {(1-k) / k} t2. If the ratio between the turn-off period t1 and the turn-on period t2 is adjusted according to the number ratio k of holes to electrons taken out from the carrier discriminating unit 12, the component corresponding to the ambient light is removed and the signal light is supported. It is possible to extract only the components that do. For example, if the extinguishing period t1 and the lighting period t2 are set to 1: 1, k = 0.5, and the number of electrons in the carrier discriminating unit 12 is set to twice the number of holes. It becomes possible to remove only the component corresponding to the signal light by removing the component corresponding to the ambient light. That is, under this condition, as shown in FIG. 5, the number of electrons E (t21) generated by ambient light in the lighting period t2 is the same as the number of holes H (t1) generated by ambient light in the turn-off period t1. Since it coincides with the total number of holes H (t21) generated by ambient light in the period, both are canceled by recombination, and the number of electrons E (t22) generated by signal light in the lighting period t2 is Since the number of holes H (t22) generated by the signal light in the lighting period is double, after recombination, only half the number of electrons E (t22) generated by the signal light in the lighting period t2 Will remain. As a result, after recombination, only the component corresponding to the signal light remains among the electrons that are the target carriers.

  Next, the effect of providing the discard unit 18 is verified. Now, the intensity of the signal light is Ia, the intensity of the ambient light is Ib, and the charge amount of the electrons held in the electron holding unit 14 is Qa, and the charge amount of the holes held in the hole holding unit 13 is When Qb is assumed, the relationship of Qa = A · Qb (A is a proportionality constant) is assumed to be satisfied. Here, Qa = β · Ia and Qb = β · Ib (β is a proportional constant). In addition, it is assumed that the length of the extinguishing period is equal to the length of the lighting period, and the intensity of the ambient light does not change between the focused extinguishing period and the lighting period.

  In addition, the switch element 17 is turned on at the timing when the light source 2 emits light and the lighting period in which the light source 2 emits light, and the electrons are discarded from the electron holding unit 14, and the switch element 17 is turned off in the lighting period. Assume that electrons are accumulated in the electron holding unit 14. By such an operation, the electrons held in the electron holding unit 14 during the extinguishing period are discarded until the transition to the lighting period (preferably immediately before), and the electrons held during the extinguishing period and the electrons held during the lighting period. And are prevented from mixing. When shifting from the lighting period to the extinguishing period, the electrons held in the lighting period and the electrons held in the extinguishing period may be mixed, so that the switch element 17 may be kept off.

  When the discard unit 18 is not provided, the charge amounts of the target carrier and the non-target carrier held during the extinguishing period are A · β · Ib and β · Ib, respectively, and are accumulated in the electron holding unit 14 during the lighting period. The charge amounts of the electrons and the holes accumulated in the hole holding unit 13 are A · β (Ia + Ib) and β (Ia + Ib), respectively. β (Ia + 2Ib) −β (Ia + 2Ib). When focusing on the intensities Ia and Ib, β {(A−1) Ia + (2A−2) Ib} is obtained.

  On the other hand, when the discarding unit 18 is provided, the holes are only held in the hole holding unit 13 immediately before the start of the lighting period, and the charge amount is β · Ib, and the electrons are held during the lighting period. Since the charge amounts of electrons and holes accumulated in the portion 14 are A · β (Ia + Ib) and β (Ia + Ib), respectively, the charge amount of electrons remaining after recombination is A · β (Ia + Ib) −. β (Ia + 2Ib). When focusing on the intensities Ia and Ib, β {(A−1) Ia + (A−2) Ib} is obtained.

  As described above, the provision of the discard unit 18 has a smaller coefficient with respect to ambient light by A · β, and thus it can be understood that the influence of the ambient light can be reduced as compared with the case where the discard unit 18 is not provided. If A = 2, the amount of charge remaining after recombination is β (Ia + 2Ib) when the discard unit 18 is not provided, whereas it remains after recombination when the discard unit 18 is provided. The amount of charge becomes β · Ia. That is, under the condition of A = 2, by providing the discard unit 18, electrons that are not affected by ambient light can be extracted. Here, A = 2 corresponds to the case where the number ratio k in the carrier discriminating unit 12 described above is 0.5 when the extinguishing period and the lighting period are 1: 1.

  By the way, in order to take out the electrons corresponding to the signal light in the recombination unit 15, it is necessary to assume that the intensity of the ambient light does not substantially vary between the turn-off period and the turn-on period. It is required to switch between the period and the lighting period within a time that does not cause a change in the intensity of the ambient light. On the other hand, the amount of time in which the intensity of ambient light does not change is relatively short, so the number of electrons and holes generated is small, and charge transfer is performed when the turn-off period and the turn-on period are provided once. The number of electrons transferred to the region 36 is significantly smaller than the number of electrons including a component corresponding to ambient light during the lighting period. Further, when the intensity of the ambient light is high, the light irradiation time (light-out period and lighting period) must be shortened so that the electron holding region 32 and the hole holding region 33 are not saturated. There is a possibility that the number of remaining electrons will be reduced later, and the S / N ratio may be lowered due to the influence of shot noise.

  In order to increase the signal charge, the charge transferred to the charge transfer region 36 is not immediately taken out, but a plurality of times of electrons in the turn-off period and the lighting period may be accumulated (integrated) in the charge transfer region 36. In other words, the recombination is performed after the light-off period and the light-on period, and a series of operations of transferring and holding the electrons to the charge transfer region 36 is repeated a plurality of times, thereby holding the electrons for a plurality of times in the charge transfer region 36. Is desirable. As described above, the electrons are held in the charge transfer region 36 by repeating the turn-off period and the turn-on period, recombination, and transfer a plurality of times, so that the components generated by the ambient light are substantially removed, and only the electrons corresponding to the signal light. Can be integrated. That is, when the intensity of incident light is large and the electron holding region 32 and the hole holding region 33 may be saturated by long-time exposure, the time per turn-off period and lighting period is shortened, and the number of integrations is reduced. By increasing (the number of repetitions), it is possible to extract a relatively large signal charge, and it is possible to prevent a decrease in the SN ratio due to the influence of shot noise.

  In this operation, the intensity of ambient light may change during the period in which electrons are accumulated in the charge transfer region 36 by repeating the turn-off period and the turn-on period a plurality of times. If there is no substantial change in the intensity of ambient light during each turn-off period and turn-on period for generating holes and holes, the fluctuations in the ambient light are offset when recombined. Even if the period and the lighting period are alternately repeated a plurality of times, the change in the intensity of the ambient light does not affect the output.

  In the present embodiment, the example in which the control electrode 26 is provided in the portion facing the hole holding region 33 formed inside the electron holding region 32 has been shown, but the portion facing the electron holding region 32 as shown in FIG. A control electrode 26 may be provided on the front panel. That is, the control electrode 26 may be disposed so as to surround the hole holding region 33 on the surface of the electron holding region 32. Using this configuration, when electrons are accumulated in the electron holding region 32 and holes are accumulated in the hole holding region 33, a positive voltage is applied to the control electrode 26 to recombine the electrons and holes. In this case, a negative voltage is applied to the control electrode 26.

  In the present embodiment, an example is shown in which the voltage applied to the control electrode 26 is controlled in order to lower the potential barrier between the electron holding region 32 and the hole holding region 33 during recombination. The potential barrier for electrons between the electron holding region 32 and the hole holding region 33 can be lowered by controlling the voltage applied to the substrate 21 by the timing control unit 10 instead of controlling the voltage applied to the substrate 21. . In this way, if the electrons and holes are recombined by controlling the voltage applied to the substrate 21 to control the height of the potential barrier, the electron holding region 32 can also be used as the recombination portion 15. In addition, the state of holding electrons and holes and the state of recombination can be selected simply by controlling the voltage applied to the substrate 21, and control is easy.

  Although an example in which the hole holding region 33 is formed inside the electron holding region 32 has been shown, the configuration in which the electron holding region 33 is formed inside the hole holding region 33 even when electrons are used as the target carrier. Can be adopted. In addition, although an example in which recombination of electrons and holes is performed in the electron holding region 32 that holds electrons that are target carriers is shown, electrons and positive holes are positively transferred in the hole holding region 33 that holds holes that are non-target carriers. It can also be configured to recombine with the holes.

  By the way, if the voltage applied to the surface electrode 25 is sufficiently high during the lighting period of the light source 2, the electron holding region 32 becomes a potential barrier against holes generated in the deep part of the substrate 21. It is possible to prevent the generated holes from accumulating in the hole holding region 33. That is, not only the control electrode 26 but also the surface electrode 25 can be used as the carrier discriminating unit 12, and a part of electrons generated during the lighting period is prevented from disappearing due to recombination with holes generated during the lighting period. be able to.

  Further, since electrons generated during the extinguishing period are discarded in the drain region 34a, only the electrons generated during the lighting period are held in the electron holding area 32, while holes generated during the lighting period are electrons in the electron holding area 32. Therefore, only holes generated during the extinguishing period are used for recombination. This substantially means that the holes H (t1) generated corresponding to the environmental light during the extinguishing period and the electrons (E (t21) + E (t22) generated corresponding to the environmental light and the signal light during the lighting period. )) Is recombined, and the ratio of the number of holes and electrons generated in the photosensitive portion 11 is 1: 1, so that H (t1) = H (t21) Only the electrons (t22) corresponding to the signal light can remain.

  By the way, in order to measure the distance to the object 3 using the distance measuring device, the intensity change of the light projected from the light source 2 to the object space is used. The phase difference between the modulation signal that modulates the light projected from the light source 2 into the target space and the modulation component included in the light received by the light detection element 1 is obtained. A procedure for obtaining the phase difference between the modulation signal and the modulation component included in the light received by the light detection element 1 when the modulation signal is a sine wave will be described below.

  FIG. 7A shows a change in the intensity of light from the light source 2, and FIG. 7B shows a change in the intensity of light received by the light detection element 1. In order to obtain the phase difference ψ shown in FIG. 7, a technique using the amount of light received by the photodetecting element 1 obtained at timings corresponding to a plurality of phases synchronized with the modulation signal and a plurality of timings not synchronized with the modulation signal are obtained. There is a technique that uses the amount of light received by the photodetecting element 1 to be used.

  First, a technique using the amount of received light obtained at the timing synchronized with the modulation signal will be described. Here, a section of 180 degrees is set for every 90 degrees of the phase of the modulation signal, and the received light amount is obtained for each section. That is, the received light amount is obtained for each of four sections in which the phase of the modulation signal is 0 to 180 degrees, 90 to 270 degrees, 180 to 360 degrees, and 270 to 90 degrees. The amount of light received in each section corresponds to the area of the figure indicated by the hatched portion in FIGS. Now, it is assumed that the amount of received light in each section is represented by A0 to A3, the maximum value of the received light intensity is Ab, the received light intensity is represented by Ad, and the phase difference is ψ.

  Here, g (θ) = (Ab−Ad) sin θ + (Ad + Ab) / 2 is set with the intensity of light incident on the light detection element 1 as a function of the phase θ (see FIG. 7B). In this case, the received light amounts A0 to A3 in the sections in which the phase of the modulation signal is 0 to 180 degrees, 90 to 270 degrees, 180 to 360 degrees, and 270 to 90 degrees are indicated by diagonal lines in FIGS. Since it corresponds to the area, each can be expressed by a definite integral as shown in the following equation.

However, the phase θ is a function of time t, θ = ωt (ω = 2πf; f is a modulation frequency), ψ is a phase difference of light transmission and reception (the unit of ψ is radians, and the distance L [m] to the object 3 , If light velocity c [m / s], L = ψ · c / 2ω), Ab is the maximum value of the intensity of light received by the light detection element 1, and Ad is the intensity of light received by the light detection element 1. Ad is equivalent to the intensity of light corresponding to the ambient light received by the light detection element 1. In the following formula, the values on both sides of the comma in square brackets mean the interval of integration.
A0 = ∫g (θ) dθ [−ψ, 180 ° −ψ]
A1 = ∫g (θ) dθ [90 ° −ψ, 270 ° −ψ]
A2 = ∫g (θ) dθ [180 ° −ψ, 360 ° −ψ]
A3 = ∫g (θ) dθ [270 ° −ψ, 90 ° −ψ]
If Aa = Ab−Ad and Ac = (Ab + Ad) / 2, then the received light amounts A0 to A3 are expressed by the following equations.
A0 = −2 Aa · cos ψ + Ac · π
A1 = -2 Aa · sinψ + Ac · π
A2 = 2Aa · cos ψ + Ac · π
A3 = 2Aa · sinψ + Ac · π
Since (A1-A3) / (A0-A2) is obtained from these relationships, tanψ is obtained, and therefore the phase difference ψ can be expressed by the following equation.
ψ = tan ⁻¹ (A1−A3) / (A0−A2) (1)
That is, when the waveform of the modulation signal is a sine wave, the phase difference ψ can be obtained by the above equation, and the distance to the object 3 can be obtained. In order to obtain an output corresponding to the received light amount A0 to A3 using the light detecting element 1 described in the present embodiment, one of the received light amounts A0 to A3 is taken out for each lighting period. That is, the target carriers corresponding to any of the received light amounts A0 to A3 are accumulated at a timing synchronized with the modulation signal in each lighting period. Therefore, it is necessary to repeat the lighting period and the extinguishing period four times.

  In order to distinguish the electrons and holes generated in the photosensitive portion 11 in the period corresponding to each light receiving amount A0 to A3 from the electrons and holes in the other period, light is emitted only in the period corresponding to each light receiving amount A0 to A3. It is necessary to control the sensitivity so that the sensitivity of the detection element 1 is increased and the sensitivity is decreased during other periods.

  In order to control the sensitivity, a plurality of surface electrodes 25 are arranged in a direction perpendicular to the paper surface, and a voltage pattern applied to the surface electrode 25 by combining a plurality of (preferably three or more) surface electrodes 25 as a set. Control. If the voltage applied to each surface electrode 25 is controlled, the depth of the potential well formed in the well region 31 at the portion facing the surface electrode 25 can be controlled. Therefore, a voltage pattern for applying a voltage for forming a deep potential well in a part of the set of surface electrodes 25 and a deep potential well formed in the entire set of surface electrodes 25 are formed. If the voltage pattern for applying the voltage to be switched is switched, the light receiving area is substantially changed, and the sensitivity can be changed by this control.

  Next, a technique for obtaining the phase difference ψ using the received light amount obtained asynchronously with the turning on and off of the light source 2 will be briefly described. In this technology, when a signal having a frequency different from the modulation frequency is caused to interfere with a signal corresponding to a change in the amount of received light (when mixed), a beat signal whose amplitude changes at a frequency corresponding to the frequency difference between the two can be obtained. We are using. The envelope of the beat signal contains the phase difference ψ, and the phase difference ψ can be obtained by extracting the received light amount corresponding to the envelope with a different phase of the envelope. For example, the amount of received light is obtained by integrating four intervals where the phase of the envelope is 0 to 180 degrees, 90 to 270 degrees, 180 to 360 degrees, and 270 to 90 degrees, and the respective received light amounts are A0 ′, A1 ′, and A2. If ′, A3 ′, the phase difference ψ can be obtained simply by replacing A0, A1, A2, A3 in the equation (1) with A0 ′, A1 ′, A2 ′, A3 ′.

  In order to obtain a beat signal, the voltage applied to the surface electrode 25 is controlled by a local oscillation signal having a frequency different from that of the modulation signal, and the function of the mixing circuit is controlled by the hole holding unit 13, the electron holding unit 14, and the recombination unit. 15 is realized. In short, by holding and recombining electrons and holes using a local oscillation signal having a frequency different from the modulation frequency of the modulation signal, the amount of electrons remaining after recombination becomes an amount corresponding to the amplitude of the beat signal. Thus, it is possible to obtain a light receiving output corresponding to the amplitude of the beat signal without using a mixing circuit.

(Embodiment 2)
In the first embodiment, the example in which the distance measuring device that measures the distance to the object 3 using the light detection element 1 is described has been described. However, the embodiment described below can also be used in the distance measuring device. is there. However, since the operation when used as a distance measuring device is the same as that of the first embodiment, an example in which the target carrier corresponding to the signal light is extracted based on the difference in the amount of light received between the extinguishing period and the lighting period will be described as an example. . In the first embodiment, holes that are non-target carriers of electrons and holes generated in the photosensitive portion 11 throughout the light-off period and the lighting period are changed to electrons that are target carriers generated in the photosensitive portion 11 during the lighting period. The configuration is adopted in which the target carrier corresponding to the signal light is taken out by recombining with. That is, only the non-target carrier is used as the carrier generated during the light-off period, but both the target carrier and the non-target carrier are used as the carrier generated during the light-up period.

  In this embodiment, the number ratio of carriers held in the hole holding unit 13 and the electron holding unit 14 is adjusted by holding only non-target carriers in the light-off period and holding only target carriers in the lighting period. Is unnecessary.

  FIG. 8 shows a principle diagram of this embodiment. In the illustrated example, a first photosensitive portion 11a having a structure suitable for extracting holes and a second photosensitive portion 11b having a structure suitable for extracting electrons are provided. Such photosensitive portions 11a and 11b can be realized by a structure in which the conductivity type of the semiconductor is replaced as long as the structure is a pn junction type or pin type photodiode. In addition, the MIS structure can be realized by changing the conductivity type of the semiconductor and setting the polarities of the voltages applied to the gates to opposite polarities.

  The holes generated in the first photosensitive portion 11a are held in the hole holding portion 13 via the gate portion 38a, and the electrons generated in the second photosensitive portion 11b are held in the electron holding portion 14 via the gate portion 38b. Retained. The timing for holding holes in the hole holding unit 13 via the gate portion 38a is different from the timing for holding electrons in the electron holding portion 14 via the gate portion 38b. If the expression that the gate portions 38a and 38b are open is used at these timings, the timing control portion 10 controls the gate portions 38a and 38b to open alternatively. The gate portions 38a and 38b of this type can be realized by the same MOS structure as that of the gate electrode 27 described in the first embodiment, and the timing controller 10 controls the applied voltages to control the gate portions 38a and 38b. It can be opened alternatively. As in the first embodiment, the holes held in the hole holding unit 13 and the electrons held in the electron holding unit 14 are recombined in the recombination unit 15, and carriers remaining after the recombination are output as target carriers. It is taken out through the part 16.

  In this embodiment, compared with the first embodiment, the switch element 17 and the discarding unit 18 are unnecessary, and two photosensitive units 11a and 11b are provided, and two gates corresponding to the photosensitive units 11a and 11b are provided. The parts 38a and 38b are added. That is, the number of holes accumulated in the hole holding unit 13 and the number of electrons accumulated in the electron holding unit 14 are adjusted by the hole holding unit 13, the electron holding unit 14, and the gate units 38a and 38b. . Therefore, in the present embodiment, the gate portions 38a and 38b separate electrons and holes and adjust the number of holes accumulated in the hole holding portion 13 and the number of electrons accumulated in the electron holding portion 14. Functions as a carrier discrimination unit. It is not essential to provide two photosensitive portions 11a and 11b. One photosensitive portion generates electrons and holes, and the hole holding portion 13 accumulates only holes from the photosensitive portion, thereby providing electrons. The gate portions 38a and 38b may be controlled so that only electrons from the photosensitive portion are accumulated in the holding portion 14. That is, the hole holding unit 13 and the electron holding unit 14 may share the photosensitive unit.

  Now, the operation will be described for the case where electrons are the target carrier as in the first embodiment. Since only the ambient light is incident on the first and second photosensitive portions 11a and 11b during the extinguishing period and it is not necessary to hold the target carrier, the gate 38a is opened and the gate 38b is closed. The holes generated in the first photosensitive portion 11 a are held in the hole holding portion 13. On the other hand, the electrons generated in the second photosensitive portion 11b are held in the electron holding portion 14 by closing the gate 38a and opening the gate 38b during the lighting period. That is, the timing control unit 10 opens and closes the gates 38 a and 38 b so as to synchronize with the light emission of the light source 2. The electrons held in the electron holding unit 14 by this operation correspond to the light amount obtained by adding the ambient light and the signal light. Here, it is assumed that the extinguishing period and the lighting period are set to 1: 1, and if the extinguishing period and the lighting period are set to a time that does not change the amount of ambient light, After the electrons and holes are recombined in the coupling portion 15, only the electrons that are the target carriers remain, and the number of electrons reflects the amount of signal light.

  In the configuration of the first embodiment, the photosensitive portion 11, the hole holding portion 13, and the electron holding portion 14 share a part of the structure (the well region 31 including the electron holding region 32 and the hole holding region 33 is , Which are shared by the photosensitive portion 11, the hole holding portion 13 and the electron holding portion 14), and the holes and electrons generated in a plurality of turn-off periods and lighting periods are transferred to the hole holding portion 13 and the electron holding portion 14. If the carrier for a plurality of times of the turn-off period and the turn-on period is held, carrier recombination is performed after one turn-off period and one turn-on period, and after recombination Must be accumulated (integrated) in the output unit 16.

  On the other hand, in the configuration of the present embodiment, gate portions 38a and 38b are provided between the first and second photosensitive portions 11a and 11b and the hole holding portion 13 and the electron holding portion 14, and the photosensitive portion 11a. , 11b and the hole holding part 13 and the electron holding part 14 are independent of each other, so that holes and electrons can be integrated before recombination of carriers. Is repeated a plurality of times, and holes and electrons are held in the hole holding part 13 and the electron holding part 14, respectively, and then recombination in the recombination part 15 can be performed.

  In the configuration of the first embodiment, the non-target carrier generated in the lighting period has a component corresponding to the signal light, and this component recombines with the target carrier, so that the component corresponding to the signal light in the target carrier. As a result, the number of target carriers with respect to the amount of signal light is reduced, and as a result, the sensitivity to signal light is slightly lowered. On the other hand, in this embodiment, the target carrier generated in the lighting period and the non-target carrier generated in the lighting period are recombined, so the lighting period and the lighting period can be set to 1: 1. For example, the target carrier generated corresponding to the signal light is not lost by recombination, and the sensitivity to the signal light is higher than that of the configuration of the first embodiment. Other configurations and operations are the same as those of the first embodiment. In each embodiment described above, the target carrier is an electron and the non-target carrier is a hole. However, the target carrier can be a hole and the non-target carrier can be an electron.

(Embodiment 3)
In the light detection element 1 described in the first embodiment, the target carrier generated during the extinguishing period of the light source 2 is discarded by the switch element 17 and the discarding unit 18, and the target carrier generated during the extinguishing period is generated during the lighting period. Although not mixed with the target carrier, this embodiment omits the switch element 17 and the discarding unit 18. In the first embodiment, holes pushed out from the hole holding region 33 are recombined with electrons in the well region 31. In this embodiment, however, the electron holding region 32 is not provided and the holes are extracted from the well region 31. By drawing the electrons into the holding region 33, the electrons are recombined with the holes.

In the photodetector 1 of the present embodiment, as shown in FIG. 9, a p-type element formation layer 22 is formed on the main surface of a substrate 21 made of a p ⁻ -type (first conductivity type) semiconductor (for example, silicon). They are stacked. A surface electrode 25 is provided on the main surface of the element formation layer 22 via an insulating layer 24 which is an oxide layer (for example, a silicon oxide layer). In the insulating layer 24, a control electrode 26 and a gate electrode 27 that are separated from the main surface of the element forming layer 22 are embedded in different portions along the surface of the element forming layer 22. The surface electrode 25 and the control electrode 26 can transmit light. Further, a charge transfer region 36 is also provided as in the first embodiment.

  An n-type well region 31 is formed in the element formation layer 22, and a p-type hole holding functioning as the hole holding unit 13 is formed on the main surface side of the element formation layer 22 and surrounded by the well region 31. Region 33 is formed. That is, the hole holding region 33 is a holding region that accumulates and holds holes that are non-target carriers. The control electrode 26 has a smaller area than the hole holding region 33 in plan view, and the entire control electrode 26 faces a part of the hole holding region 33. In the hole holding region 33, the region facing the control electrode 26 becomes an integrated coupling region 33 a that functions as the electron holding unit 14 and the recombination unit 15 that accumulate electrons, and the hole holding region 33 other than the integrated coupling region 33 a. The region becomes a evacuation region 33b for evacuating holes temporarily. The well region 31 and the hole holding region 33 can be irradiated with light, and when irradiated with light, electrons and holes are generated by photoexcitation. A positive voltage (5V in the illustrated example) is constantly applied to the surface electrode 25, and a negative voltage (-3V in the illustrated example) is applied to the control electrode 26 so that holes can be retained in the hole retaining region 33 during light irradiation. Apply. Therefore, as shown in FIG. 10, holes generated in the vicinity of the hole holding region 33 by light irradiation are held in the hole holding region 33, and electrons generated in the vicinity of the well region 31 are in the well region 31. Retained.

  Depending on the relationship between the thickness and area of the hole holding region 33, the area of the well region 31, and the voltage applied to the control electrode 26, the number of electrons at the time of recombination can be made larger than the number of holes. Since the element structure is determined by design, the number of electrons held in the well region 31 and holes held in the hole holding region 33 is adjusted by the voltage applied to the control electrode 26. It functions as the carrier discriminator 12. Further, since most of the electrons held in the well region 31 and the holes held in the hole holding region 33 are generated in the well region 31 and the hole holding region 33, the well region 31 and the hole holding region 33 The region 33 functions as the photosensitive portion 11.

  In the configuration of the present embodiment, the number of electrons held in the well region 31 before the recombination is corrected by appropriately adjusting the extinction period, the lighting period, and the voltage applied to the control electrode 26 of the light source 2. The number of holes held in the hole holding region 33 can be increased. In the present embodiment, the electrons generated during the extinguishing period are not discarded, but the electrons generated during the lighting period of the light source 2 are regenerated as holes equal to or more than the number of electrons generated during the extinguishing period of the light source 2. It is possible to satisfy the condition that the number of electrons that are combined and recombined is greater than the number of holes. In short, it is possible to remove the ambient light component while allowing the electrons to remain after recombination. The state of FIG. 10 shows a state in which electrons and holes are held in the well region 31 and the hole holding region 33 so as to satisfy the above conditions after the turn-off period and the turn-on period, respectively.

In this embodiment, in order to recombine electrons and holes, in this embodiment, a negative voltage (−3 V in the illustrated example) is applied to the control electrode 26 as shown in FIG. 10, and a positive voltage (see FIG. 11). In the example shown, the state of applying +3 V) is repeated a plurality of times. The period required for recombination is sufficiently shorter than the extinguishing period and the lighting period. For example, the polarity of the voltage to be applied is changed several times with a period of about 2 × 10 ⁻⁸ s. When a positive voltage is applied to the control electrode 26, holes move from the integrated coupling region 33a to the save region 33b, and electrons move from the well region 31 to the integrated coupling region 33a. At this time, some of the holes are trapped at the interface potential with the insulating layer 24, and the trapped holes disappear by recombination with electrons. However, some of the holes move in the p-type hole holding region 33 and remain in the evacuation region 33b. The purpose of recombination is to eliminate the holes, so the holes saved in the saving region 33b must also be eliminated. Therefore, a negative voltage is again applied to the control electrode 26, and the holes saved in the save area 33b are drawn into the integrated coupling area 33a. At this time, electrons move to the well region 31 which is mainly n-type.

  By repeating the above operation a plurality of times, holes in the hole holding region 33 can be eliminated by recombination. Further, since some of the electrons remain even when the holes disappear, applying a positive voltage to the control electrode 26 pulls in the electrons remaining in the integrated coupling region 33a and applies a positive voltage to the gate electrode 27. Thus, electrons can be transferred from the integrated coupling region 33a to the charge transfer region 36. Other configurations and operations are the same as those of the first embodiment.

  By the way, as described above, after recombination, electrons are transferred from the integrated coupling region 33a to the charge transfer region 36, and between the integrated coupling region 33a and the charge lighting region 36 as in the configuration shown in FIG. If the p-type save region 33b exists in the first electrode, there is a problem that electrons cannot be moved unless a relatively high voltage is applied to the gate electrode 27. Therefore, as shown in FIG. 12, it is desirable not to provide the evacuation region 33b in the portion of the hole holding region 33 that faces the charge transfer region 36. In the configuration example of FIG. 12, the save area 33b is U-shaped in plan view.

Further, in the above-described example, the impurity concentration in the integrated coupling region 33a and the save region 33b is constant, but in order to increase the mobility of holes between the integrated bond region 33a and the save region 33b, the save region For 33b, it is desirable to increase the impurity concentration. That is, when the integrated coupling region 33a is p-type, it is desirable that the save region 33b be p ^{+ type} . Further, instead of using the p ^{+ -type} save area 33b, as shown in FIG. 13, a save control electrode 28 facing the save area 33b is provided around the control electrode 26, and the integrated coupling area 33a, the save area 33b, When the holes are moved between the holes, the mobility of the holes may be increased by controlling the potential of the evacuation region 33b with respect to the holes. Further, in the configuration shown in FIG. 13, the charge transfer region 36 is transferred from the integrated coupling region 33a while preventing the holes from flowing out to the well region 31 so that the escape region 33b surrounds the entire circumference of the integrated coupling region 33a. When the electrons are moved, it is possible to increase the electron mobility by lowering the potential for the electrons in the save area 33b. Other configurations and operations are the same as those of the first embodiment.

(Embodiment 4)
In the present embodiment, as shown in FIG. 14, a p-type hole holding region (corresponding to the holding region of claims 8 and 9) 33 functioning as the hole holding portion 13 is formed in the n-type well region 31. ing. This configuration is the same as that of the third embodiment. However, in Embodiment 3, the p-type element forming layer 22 is laminated on the main surface of the p ⁻ -type substrate 21, whereas in the present embodiment, the substrate 21 and the element forming layer 22 are n-type, and the substrate A configuration in which a p-type intermediate layer 29 is provided between the element 21 and the element formation layer 22 is employed. The intermediate layer 29 is kept at the ground potential. Further, the impurity concentration of the save region 33b is made higher than that of the integrated coupling region 33a facing the control electrode 26 in the hole holding region 33, and the save region 33b is p ⁺ while the integrated bond region 33a is p-type. It is shaped.

  Further, in the third embodiment, the gate electrode 27 is disposed at a corresponding portion between the well region 31 and the charge transfer region 36. However, in this embodiment, the gate electrode 27 is not provided, and the well region 31 and the charge transfer region are provided. 36, and the voltage applied to the transfer electrode 39 provided via the insulating layer 24 with respect to the charge transfer region 36 is changed to transfer electrons from the well region 31 to the charge transfer region 36. The configuration is adopted. A plurality of transfer electrodes 39 are arranged in a direction perpendicular to the plane of FIG. 14, and two transfer electrodes 39 correspond to one well region 31. That is, the transfer electrode 39 for forming a potential well for receiving electrons from the well region 31 and the transfer electrode 39 for forming a potential well for transferring electrons from the potential well are associated with one well region 31. ing. This type of configuration is the same as that of a vertical transfer register in an IT (interline transfer) type CCD image sensor. The transfer electrode 39 is electrically separated from the surface electrode 25. The charge transfer region 36 is covered with a light shielding film 37.

  In the third embodiment, the number of electrons and the number of holes at the time of recombination are adjusted according to the relationship between the thickness and area of the hole holding region 33, the area of the well region 31, and the voltage applied to the control electrode 26. Yes. On the other hand, in the present embodiment, recombination is performed by controlling the voltage applied to the substrate 21 in addition to the thickness and area of the hole holding region 33, the area of the well region 31, and the voltage applied to the control electrode 26. Adjust the number ratio of electrons and holes.

  The operation will be described below. A positive voltage and a negative voltage can be applied to the substrate 21, the surface electrode 25, and the control electrode 26, respectively, and a positive voltage and a negative voltage in two steps of high and low can be applied to the transfer electrode 39. Three types of voltages, voltage, can be applied. Hereinafter, the two levels of positive voltages are distinguished and referred to as “high positive voltage” and “low positive voltage”. Note that the negative voltage applied to the transfer electrode 39 is a voltage used for transferring electrons, and is not involved in the operation described below.

  First, as an initial state, holes in the well region 31 disappear due to recombination with electrons, electrons in the well region 31 are transferred to the charge transfer region 36, and electrons in other regions are discarded through the substrate 21 or regenerated. Assume that the state has disappeared due to the bond. That is, the initial state is a state in which only electrons and holes in a thermal equilibrium state exist in the substrate 21, the element formation layer 22 (including the well region 31), and the intermediate layer 29. Such an initial state can be realized by providing the drain regions 34 a and 34 b shown in the first embodiment and discarding electrons and holes using the drain regions 34 a and 34 b and the substrate 21.

The above-described initial state is a state that is set after electrons are transferred from the well region 31 to the charge transfer region 36, and the timing control unit 10 controls the light source 2 and the like so that a light extinction period is reached after the initial state. In the extinguishing period, a low positive voltage is applied to the transfer electrode 39 adjacent to the well region 31 so that electrons and holes do not move from the well region 31 to the charge transfer region 36. Further, a negative voltage is applied to the surface electrode 25 and the control electrode 26, and a positive voltage is applied to the substrate 21 (first state). In the first state, only ambient light is irradiated, and among the electrons and holes generated in the substrate 21, the element formation layer 22 (including the well region 31), and the intermediate layer 29, the electrons are discarded through the substrate 21. The holes move toward the surface electrode 25. Here, since the hole holding region 33 is p-type or p ^{+ -type} , holes are mainly accumulated in the hole holding region 33. That is, the number of holes corresponding to the extinguishing period is accumulated in the hole holding region 33.

  Thereafter, during the lighting period, a positive voltage is applied to the surface electrode 25 and the control electrode 26, and a negative voltage is applied to the substrate 21 (second state). In the second state, most of the holes accumulated in the hole holding region 33 gather in the evacuation region 33b, and some of the holes are trapped by the interface potential of the integrated coupling region 33a and remain in the integrated coupling region 33a. . Of the electrons and holes generated in the substrate 21, the element formation layer 22 (including the well region 31), and the intermediate layer 29, the electrons move toward the surface electrode 25, and the holes are discarded through the substrate 21. The Due to the difference in conductivity types of the hole holding region 33, the well region 31 excluding the hole holding region 33, and the element formation layer 22 excluding the well region 31, the potential for electrons is the well region 31 excluding the hole holding region 33. Therefore, the number of electrons corresponding to the ambient light and the signal light is mainly accumulated in the well region 31. Some electrons recombine with holes remaining in the integrated coupling region 33a.

  When a time sufficient to complete recombination of holes and electrons remaining in the integrated coupling region 33a has elapsed (electrons have a significantly higher mobility than holes, this time is very short). While maintaining a state in which a positive voltage is applied to the electrode 25 and a negative voltage is applied to the substrate 21, only the polarity of the voltage applied to the control electrode 26 is inverted to a negative voltage (third state). In the third state, new holes are not accumulated in the hole holding region 33, and electrons corresponding to the ambient light and the signal light are accumulated in the well region 31. Further, in the third state, holes in the hole holding region 33 gather in the integrated coupling region 33a, and electrons gather in the well region 31 in a range excluding the hole holding region 33.

In a third state, when a time enough for holes to gather in the integrated coupling region 33a elapses (the hole holding region 33 is p-type or p ^{+ -type} and has a short distance, so the holes move in a relatively short time). Only the voltage applied to the control electrode 26 is changed to a positive voltage. That is, switching from the third state to the second state again. As described above, in the second state, the holes trapped at the interface potential of the integrated coupling region 33a and some electrons recombine. Thereafter, the second state and the third state are repeated alternately. The number of repetitions is repeated as many times as necessary so that the holes remaining in the hole holding region 33 are almost eliminated (about 2 to 3 times). When the holes in the hole holding region 33 almost disappear, the voltage applied to the surface electrode 25 from the third state is changed to a negative voltage, and a high positive voltage is applied to the transfer electrode 39 (fourth state). The high positive voltage is set so that electrons in the well region 31 move to the charge transfer region 36. The fourth state differs from the third state only in the voltage applied to the transfer electrode 39.

  In other words, in the fourth state, the electrons remaining in the well region 31 are components in which at least a part of the components of the ambient light are reduced from the components of the ambient light and the signal light. To the charge transfer region 36. After the fourth state, the light source 2 is turned off, a negative voltage is applied to the surface electrode 25 and the control electrode 26, and a state in which a positive voltage is applied to the substrate 21, that is, the first state is restored. Table 1 shows the voltage relationship of each part from the first state to the fourth state. Only the first state is in the extinguishing period, and transitions from (second state → third state) × n → fourth state in the lighting period (× n means repeating a plurality of times). Accordingly, in order to make the number of holes accumulated in the hole holding region 33 during the extinguishing period substantially coincide with the number corresponding to the ambient light component of the electrons accumulated in the well region 31 during the lighting period, It is necessary to adjust the length of the period and the lighting period and adjust the voltage applied to each part. In addition, an operation for returning to the initial state may be necessary between the lighting period and the extinguishing period.

  As described above, in this embodiment, the number of electrons and holes to be recombined is adjusted by controlling the voltage applied to the substrate 21 in addition to the voltage applied to the surface electrode 25 and the control electrode 26. Therefore, the number of electrons and holes can be easily adjusted.

  If the distance measuring device is configured in the same manner as in the first embodiment using the light detection element 1 having the configuration described in the present embodiment, it is necessary to control the sensitivity in order to obtain the received light amounts A0 to A3. As described in the first embodiment, the technology for controlling the sensitivity controls a voltage pattern applied to a set of surface electrodes 25 by combining a plurality of surface electrodes 25 arranged in a direction orthogonal to the paper surface. Such sensitivity control is performed while electrons are accumulated in the second state. For example, in order to integrate electrons corresponding to the received light amount A0, the modulation signal is used so that the sensitivity becomes high during the period corresponding to the received light amount A0 and low sensitivity during the period corresponding to the received light amounts A1 to A3. The voltage pattern applied to the surface electrode 25 is controlled at the timing of synchronization. After repeating the high sensitivity state and the low sensitivity state a plurality of times in the second state, the second state is entered to move to the third state to recombine electrons and holes, and to promote recombination. And the third state are repeated a plurality of times. While the second state and the third state are repeated for recombination, sensitivity control in the second state is not performed. After the second state and the third state are repeated to recombine electrons and holes, the state shifts to the fourth state.

  In the above-described example, electrons and holes are recombined by repeating the second state and the third state in the lighting period, but the received light amounts A0 to A3 are controlled by controlling the sensitivity in the second state. After the electrons corresponding to any of the above are integrated, the light source 2 may be turned off, and the voltages in the second state and the third state may be repeatedly applied for recombination. Further, after the electrons corresponding to any one of the received light amounts A0 to A3 are accumulated by controlling the sensitivity in the second state, the second state and the third state are repeated while the light source 2 is turned on. And the operation of repeating the second state and the third state in a state where the light source 2 is turned off. Other configurations and operations are the same as those of the third embodiment. Further, in both the third and fourth embodiments, the buried layer 23 may be provided at the bottom of the well region 31 as in the first embodiment.

1 is a schematic configuration diagram illustrating a first embodiment. It is operation | movement explanatory drawing which shows one operation | movement same as the above. It is operation | movement explanatory drawing which shows one operation | movement same as the above. It is a block diagram which shows the principal part of the distance measuring device using the same as the above. It is principle explanatory drawing same as the above. It is a schematic block diagram which shows the modification same as the above. It is operation | movement explanatory drawing which shows the other operation example of the distance measuring device using the same as the above. It is a block diagram which shows the principal part of the distance measuring device using Embodiment 2. FIG. 6 is a schematic configuration diagram showing a third embodiment. It is operation | movement explanatory drawing which shows one operation | movement same as the above. It is operation | movement explanatory drawing which shows one operation | movement same as the above. It is a schematic block diagram which shows the modification same as the above. It is a schematic block diagram which shows the other modification same as the above. FIG. 6 is a schematic configuration diagram showing a fourth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photodetection element 2 Light source 10 Timing control part 11 Photosensitive part 11a, 11b Photosensitive part 12 Carrier discriminating part 13 Hole holding part 14 Electron holding part 15 Recombination part 16 Output part 17 Switch element 18 Discarding part 21 Substrate 22 Element formation layer 23 buried layer 24 insulating layer 25 surface electrode 26 control electrode 27 gate electrode 28 control electrode for withdrawal 29 intermediate layer 31 well region 32 electron holding region 33 hole holding region 34a, 34b drain region 35a, 35b drain electrode 36 charge transfer region 38a, 38b Gate part 39 Transfer electrode

Claims (15)

  Control of the voltage applied to the discrimination control electrode having a control electrode for discrimination and a photosensitive portion made of a semiconductor capable of receiving light emitted from the light source and generating a number of holes and electrons according to the amount of received light And a carrier discriminating part for separating a target carrier which is one of holes and electrons generated in the photosensitive part and a non-target carrier which is the other, and a coupling control electrode, which is applied to the coupling control electrode A recombination unit that recombines a target carrier generated in the photosensitive unit during the light source lighting period and a non-target carrier generated in the photosensitive unit during the light source extinction period at a predetermined timing by voltage control, and a recombination unit. An optical detection element comprising an output portion for taking out a target carrier remaining after being coupled to the outside as one semiconductor device.   In the carrier discriminating unit, the number of target carriers generated during the lighting period and involved in recombination in the recombination unit is greater than the number of non-target carriers generated during the extinguishing period and involved in recombination in the recombination unit. The light detection element according to claim 1, wherein the light detection element is adjusted as follows.   A target carrier holding unit for collecting and holding the target carriers generated in the photosensitive unit until recombination and a non-target carrier holding unit for collecting and holding the non-target carriers generated in the photosensitive unit until recombination are added. 3. The light according to claim 1, wherein the recombination unit recombines the target carrier held by the target carrier holding unit and the non-target carrier held by the non-target carrier holding unit. Detection element.   The light detection element according to claim 3, wherein the carrier discriminating unit includes a switch element that discards the target carrier held in the target carrier holding unit.   5. The photodetecting element according to claim 1, wherein the output unit has an integration function of integrating a target carrier remaining due to recombination in the recombination unit.   A first conductivity type element forming layer formed on a main surface of a substrate made of a semiconductor, a second conductivity type well region provided on the main surface side of the element forming layer, and at least a well on the main surface of the element forming layer A surface electrode which is opposed to the region through an insulating layer and can transmit light; a first holding region of the second conductivity type which is provided on the main surface side of the element forming layer in the well region and serves as the target carrier holding portion; A first holding type second holding region provided on the main surface side of the element forming layer in the first holding region and serving as the non-target carrier holding portion, and corresponding to the second holding region of the main surface of the element forming layer. And a control electrode that is used as the discrimination control electrode and the coupling control electrode and is capable of transmitting light. Generate holes, as the recombination part 1 holding region and a light detecting element according to claim 3, characterized by using at least one of the second holding region.   A drain region of a second conductivity type formed adjacent to the well region on the main surface side of the element formation layer and capable of discarding the target carrier from the target carrier holding portion, and a first ohmic connected to the drain region The photodetecting element according to claim 6, further comprising a drain electrode to which a voltage is applied so that a target carrier is discarded from the holding region to the drain region.   A first conductivity type element forming layer formed on a main surface of a substrate made of a semiconductor; a second conductivity type well region provided on the main surface side of the element forming layer and serving as the target carrier holding portion; and an element forming layer A surface electrode facing at least the well region through the insulating layer and transmitting light on the main surface of the first surface, and a first conductivity type provided on the main surface side of the element forming layer in the well region and serving as the non-purpose carrier holding portion Of the main surface of the element formation layer and an electrode facing each other through an insulating layer at a portion corresponding to a part of the holding region, which is used as both the discrimination control electrode and the coupling control electrode. And the photosensitive part generates electrons and holes in the element formation layer, and at least one of the inside and outside of the holding area is used in the well area as the recombination part. Claim 3 Of the light detection element.   A second conductivity type element forming layer formed on the main surface of the substrate made of the second conductivity type semiconductor via the first conductivity type intermediate layer, and the target carrier holding provided on the main surface side of the element forming layer A well region of the second conductivity type to be a part, a surface electrode that is opposed to at least the well region via an insulating layer on the main surface of the element forming layer, and allows light to pass through, and on the main surface side of the element forming layer in the well region A first conductivity type holding region that is provided on the non-target carrier holding portion, and an electrode facing the part of the main surface of the element forming layer corresponding to a part of the holding region with an insulating layer interposed therebetween, A control electrode which can be used as a discrimination control electrode and the coupling control electrode and can transmit light; the photosensitive portion generates electrons and holes in the element formation layer; At least inside and outside of the holding area Light detecting element of claim 3, wherein the use of one.   The well region has a depth that does not reach the substrate in the element formation layer, and a buried layer is formed at the bottom of the well region to increase a potential barrier between the well region and the element formation layer. The photodetecting element according to any one of claims 6 to 9, wherein:   4. The method of controlling a photodetecting element according to claim 3, wherein the target carrier is accumulated in the target carrier holding unit during the lighting period, the non-target carrier is discarded, and the non-target carrier holding part is not used during the extinguishing period. A method for controlling a photodetecting element, comprising: controlling a voltage applied to a control electrode for discrimination so as to accumulate target carriers and discard the target carriers.   11. A method for controlling a photodetecting element according to claim 6, wherein a target carrier is held in the target carrier holding part, and a non-target carrier is held in the non-target carrier holding part. After applying a voltage to the control electrode, the voltage applied to the control electrode is changed to move at least one of the target carrier held by the target carrier holding unit and the non-target carrier held by the non-target carrier holding unit A method for controlling a photodetecting element, wherein the photodetecting element is recombined.   10. The method for controlling the photodetecting element according to claim 8, wherein a voltage for holding the target carrier in the target carrier holding unit and holding the non-target carrier in the non-target carrier holding unit is applied to the control electrode. After the application, by changing the voltage applied to the control electrode a plurality of times, the target carrier is reciprocated in and out of the holding region in the well region, and the non-target carrier is controlled with the control electrode in the holding region. A method for controlling a photodetecting element, wherein a target carrier and a non-target carrier are recombined by reciprocating between an opposing part and a non-opposing part.   10. A method for controlling a photodetecting element according to claim 8 or claim 9, wherein non-target carriers are accumulated in the holding region during the extinguishing period and the target carriers are discarded, and the target carrier is discarded in the holding region during the lighting period. A method for controlling a photodetecting element, comprising: controlling voltages applied to the surface electrode, the control electrode, and the substrate so as to accumulate carriers and discard non-target carriers.   In the state where target carriers are accumulated in the lighting period and the state where non-target carriers are accumulated in the extinguishing period, the polarity of each voltage applied to the surface electrode and the control electrode is opposite to the polarity of the voltage applied to the substrate. In the state in which the target carrier and the non-target carrier are recombined in at least one of the lighting period and the light-off period, the polarity of the voltage applied to the control electrode is reversed a plurality of times and remains in the well region after recombination. 15. The method of controlling a photodetecting element according to claim 14, wherein the target carrier is taken out.

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