JP2012199554A - Light-receiving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-receiving device in which image formation disabled state does not occur even for an optical input of high luminance or the instantaneous increase in brightness of a subject.SOLUTION: The light-receiving device comprises a light-receiving element array 10, and a multiplexer having a signal input part and a body part for receiving a signal passing through the signal input part. In the light-receiving element array 10, a monitor light-receiving part M is located between light-receiving elements S and forms a pin-type photodiode. Electrodes of the monitor light-receiving part and the light-receiving element are connected separately with the signal input part. In the signal input part, a signal direct from the light-receiving element is subjected to gain control or on/off control based on a signal direct from the monitor light-receiving part, and then output to the body part.

Description

  The present invention relates to a light receiving device, and more specifically to a light receiving device having a light receiving sensitivity on the long wavelength side even in the near infrared region.

Group III-V compound semiconductors have attracted attention as compound semiconductors having band gap energy corresponding to the near-infrared wavelength region or longer wavelength side, and research and development are in progress. For example, a night vision camera is disclosed that receives natural light from the universe using a light receiving element array in which light receiving elements having InGaAs lattice-matched to InP in a light receiving layer are arranged on the InP substrate (Non-Patent Document 1). ). As a result, it is possible to capture images with natural light without using artificial lighting at night and in the rain.
Marshall J. Cohen and Gregory H. Olsen "Near-IR imaging cameras operate at roomtemperature", LASER FOCUS WORLD, June 1993, pp.109-113

  However, when the above-mentioned night vision camera forms an image output with relatively small input light, halation occurs when light with high luminance enters the field of view, and an image cannot be obtained until the carrier disappears from the light receiving element. For this reason, for example, when the luminance changes greatly during imaging of a moving image, a state in which image formation becomes impossible tends to occur. In the near-infrared imaging devices (sensors) that are expected to be used in a variety of applications in the future, it is not preferable that the above-mentioned image formation impossible state occurs, and it should be overcome.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a light receiving device that does not cause a state in which an image cannot be formed even when a light input with high luminance or an instantaneous brightness increase of a subject is generated.

The light-receiving device of the present invention includes a light-receiving element array in which a plurality of light-receiving elements are arranged in a semiconductor laminate including a light-receiving layer, and a multiplexer having a signal input unit and a main body unit that receives a signal passing through the signal input unit. A light receiving device. The light receiving device includes one or more monitor light receiving units positioned between the plurality of light receiving elements in the light receiving element array, and each of the plurality of light receiving elements and the monitor light receiving unit is one of the semiconductor stacked bodies. And an electrode in ohmic contact with the impurity region, and each of the light receiving element and the monitor light receiving part forms a pin type photodiode. The back-illuminated type in which light is incident from the back surface opposite to the front surface of the semiconductor laminate, and the monitor light-receiving unit and the electrode of the light-receiving element are individually connected to the signal input unit of the multiplexer. The direct signal from the element is subjected to gain control or on / off control based on the direct signal from the monitor light receiving unit, and is output to the main body of the multiplexer. To.
Here, the conductivity type of the light receiving layer is not limited and may be the first conductivity type or intrinsic.

With the above configuration, the monitor light-receiving unit can receive incident light and monitor and output the intensity of the light in a state where a depletion layer is formed at the pn junction as in the light-receiving element. Based on this light intensity output signal, an external circuit (driving circuit) can issue a signal for controlling the gain or on / off of the light receiving element. In other words, each of the light receiving element and the monitor light receiving unit forms a pin type photodiode, thereby greatly expanding the depletion layer from the pn junction or the pi junction by applying a low reverse bias voltage or no voltage. On the other hand, avoiding an image formation impossible state due to high luminance input while increasing the light receiving sensitivity in the image sensor can be performed by controlling the gain or the like with the monitor light receiving unit and an external drive circuit.
As a result, it is possible to obtain a light receiving device that avoids the occurrence of an image formation impossible state due to the persistence of the carrier saturation state due to the input of high luminance light.

In the signal input unit, the direct signal from the monitor light receiving unit is passed through an amplification + differentiation circuit to obtain a time gradient of brightness, and (1) the height of the signal of the time gradient exceeds a predetermined reference value. In this case, an output for turning off the direct signal from the light receiving element or an output for performing automatic gain control according to the height can be performed.
Before entering the multiplexer body, the output of the light receiving element array can be controlled immediately.

  As viewed in a plan view, the area of light received by the monitor light receiving unit can be made smaller than that of the light receiving element. As a result, the monitor light receiving unit is saturated earlier than the light receiving element, and signal processing can be performed at high speed by the wired logic circuit regardless of microcomputer control. Further, when the microcomputer control is performed, the microcomputer control is easily performed.

  Said semiconductor laminated body can be comprised with a III-V group compound semiconductor, and a 2nd conductivity type impurity can be made into Zn. This facilitates selective diffusion of Zn, which has been proven so far, into the semiconductor stack to form a pn junction in the light receiving layer.

The light-receiving layer can be composed of a III-V group compound semiconductor having band gap energy corresponding to the near infrared region or longer wavelength side.
As a result, it is possible to obtain a light receiving device that has sensitivity in the near-infrared region or a longer wavelength side and that avoids the occurrence of an image incapable state due to the continuation of the carrier saturation state due to high-luminance light input.

  According to the light receiving device of the present invention, it is possible to avoid the occurrence of an image formation impossible state due to the persistence of the carrier saturation state due to the high luminance light input.

  FIG. 1 is a partial cross-sectional view of an end portion of a light receiving element array 10 in a light receiving device according to an embodiment of the present invention. In FIG. 1, the light receiving element array 10 includes (InP substrate 1 / n type (first conductivity type) InP buffer layer 2 / GaInNAs light receiving layer 3 / InP window layer 4) of one semiconductor laminate. FIG. 2 is a top view of the light receiving element array 10. The light receiving element array 10 includes a sensing unit S, which is a light receiving element periodically disposed, and a monitor light receiving unit M disposed in one or more in the plan view. Here, the light receiving device in the present invention is not limited to the name as long as it has the configuration of the present invention, such as an imaging device and a detection device, and may be anything.

  In FIG. 1, the impurity diffusion mask pattern 5 is made of SiN, and is located on the InP window layer 4 so that the sensing part S and the monitor light-receiving part M have openings. Both the sensing unit S and the monitor light receiving unit M are formed with a p-type (second conductivity type) region 16 in which Zn diffused and introduced from the opening of the mask pattern 5 is distributed. As shown in FIGS. 1 and 2, the area of the monitor light receiving unit M is formed smaller than the area of the sensing unit S, but can be adjusted by the control of the control circuit. It may be an area. By making the size of the monitor light-receiving part M smaller than that of the sensing part S, (1) the monitor light-receiving part M is more likely to saturate earlier than the sensing part S when large input light is incident, and the intensity of the input light The advantage that the halation can be prevented only by the wired logic circuit (hardware) without applying the microcomputer control to the sensing unit, and (2) the monitor light receiving unit M is arranged between the sensing S of the periodic array. Produces the advantage, which becomes easier.

  FIG. 3 is a plan view showing an imaging device 50 in which a light receiving element array and a multiplexer are combined, and the sensing unit S and the monitor light receiving unit M are indicated by solid lines. As shown in FIG. 3, the monitor light receiving unit M is irrelevant to the number of sensing units S, and may be one for the entire light receiving element array, or suitable for input monitoring at the center and four corners. Can be placed in position. In short, any arrangement that can monitor the incidence of light may be used so that it is possible to avoid a state in which an image cannot be formed during a charge full state due to high luminance light input.

  4 is a cross-sectional view taken along line IV-IV in FIG. The p-part electrode 11 of each sensing part is electrically connected to the input terminal 56 of the multiplexer 51 using a solder bump (not shown), and an n-part electrode (not shown) to which a common ground potential is applied is provided. Similarly, a ground potential terminal (not shown) of the multiplexer 51 is electrically connected. The multiplexer 51 is preferably a CMOS multiplexer.

  The p-part electrode 11 of the monitor light-receiving part M is electrically connected to the monitor terminal 59 of the multiplexer 51 using a solder bump or the like (not shown). The multiplexer 51 is provided with a signal processing circuit (control circuit), and controls the light receiving operation of the sensing unit S based on the light receiving signal input from the monitor light receiving unit M via the p unit electrode 11. The control of the light receiving operation of the sensing unit S may be an on / off control that blocks a light reception signal from the sensing unit S to the main body of the multiplexer 51, or may be a gain control of the sensing unit S.

  FIG. 5 is a circuit diagram in the case of performing on / off control for blocking the light reception signal from the sensing unit S to the main body of the multiplexer 51. When the subject becomes very bright instantaneously, the signal processing circuit performs control of the switch of the sensing unit S or on / off control based on the output of the monitor light receiving unit M (light receiving element or photodiode). In order to quantify the degree of instantaneous brightness increase in the signal processing, the output of the monitor light receiving unit M should have a time gradient of brightness increase by an amplification + differential circuit as shown in FIG. . Since the time gradient of the increase in brightness becomes a spike through the differentiation circuit, the output Sout to the main body of the multiplexer 51 is turned off when the height of the spike exceeds a predetermined reference value.

  FIG. 6 is a circuit diagram in the case where the intensity of the light reception signal from the sensing unit S to the main body of the multiplexer 51 is controlled based on the light reception signal of the monitor light reception unit M. As for the output of the monitor light receiving unit M, the time gradient for increasing the brightness by the amplification + differential circuit is the same as in the case of FIG. Since the time gradient of the increase in brightness becomes a spike after passing through the differentiation circuit, the automatic gain control (AGC Auto Gain Control) of the output Sout to the multiplexer 51 main body is performed according to the height of the spike. A commonly used control method can be used for the control circuit mounted in the multiplexer 51 or other driving unit.

  5 and 6 show a case where the output control of one sensing unit S is performed by one monitor light receiving unit M. FIG. However, it can be considered that one sensing unit S is regarded as any one light receiving element of the light receiving element array and output control of all the light receiving elements S is performed by one monitor light receiving unit M. It can also be considered that output control of a plurality of sensing units S within the range covered by one monitor light receiving unit M is performed. In any case, since the output of the sensing unit S is controlled by the monitor light receiving unit M, it is possible to prevent the occurrence of an image formation impossible period due to high luminance light input with respect to large input light incidence.

Next, a method for manufacturing the light receiving element array 10 and the imaging device 50 will be described. First, the n-type InP buffer layer 2 is formed on the n-type InP substrate 1. The n-type InP substrate 1 and the n-type InP buffer layer 2 are preferably doped with n-type impurity Si so as to have a high carrier concentration of 3 × 10 ¹⁸ cm ⁻³ . The n-type InP substrate 1 may be doped with Fe. The n-type InP buffer layer 2 can be formed by a known method such as MBE (Molecular Beam Epitaxy) method or OMVPE (Organo Metallic Vapor Phase Epitaxy) method. However, in the case of using a film formation method that increases the hydrogen concentration, such as the OMVPE method, it is preferable to perform heat treatment for dehydrogenation.

Next, a GaInNAs light receiving layer 3 is grown on the n-type InP buffer layer 2. Impurities need not be added, but n-type impurity Si may be added so as to have a carrier concentration of about 3 × 10 ¹⁵ cm ⁻³ . From the point of reducing the hydrogen concentration, it is preferable to grow by the MBE method. However, if the hydrogen concentration is high, the dehydrogenation treatment may be performed by heat treatment. The GaInNAs light receiving layer 3 may contain Sb in order to improve crystallinity. An InP window layer 4 is grown in contact with the GaInNAs light receiving layer 3. The GaInNAs light receiving layer 3 has light receiving sensitivity on the long wavelength side in the near infrared region, but may contain Sb and / or P. Sb is added to improve crystallinity. In addition, in the case where the light receiving sensitivity on the long wavelength side in the near infrared region is not so much required, it may be a GaInAs light receiving layer that does not contain N. The window layer 4 may be anything other than InP as long as it is lattice-matched with the light receiving layer 3 and has a larger band gap than the light receiving layer 3. The semiconductor stacked body is formed of the following compound semiconductor layers.
Semiconductor laminated body: (InP substrate 1 / n ⁺ InGaAs buffer layer 2 / GaInNAs light receiving layer 3 / InP window layer 4)
The thickness of each layer is roughly 1 μm to 2 μm for the InGaAs buffer layer 2, 2 μm to 3 μm for the GaInNAs light receiving layer 3, and 0.5 μm to 1.5 μm for the InP window layer 4. On the InP window layer 4, a mask pattern 5 having openings in the sensing part S and the monitor light receiving part M is formed of SiN, and p-type impurity Zn is introduced from each opening through the InP window layer 4 to form a p-type region. 16 is formed. The p-type region 16 reaches the GaInNAs light receiving layer 3 and forms a pn junction or a pin junction at the tip. Thereafter, the p-type electrode 11 in ohmic contact is formed on the p-type region 16 of the InP window layer 4 by PtTi or the like, and the n-part electrode 12 that is ohmically connected to the peripheral part of the InP substrate 1 or the InGaAs buffer layer 2 by AuGeNi or the like. Form each one.

  According to the above light receiving element array and an image pickup apparatus using the same, even if there is an instantaneous increase in brightness of the subject or high luminance light input, the light receiving signal of the light receiving element (sensing unit) is monitored by monitoring the monitor light receiving unit. Since the output is controlled, it is possible to avoid a state where an image cannot be formed, and a clear image such as a subject can always be obtained.

  Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is the implementation of these inventions. It is not limited to the form. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  According to the light receiving element array and the imaging device of the present invention, it is possible to obtain a clear image without causing a state incapable of forming an image with respect to high luminance light input or instantaneous brightness increase of a subject.

It is sectional drawing which shows the light receiving element array in embodiment of this invention. FIG. 2 is a top view of the light receiving element array in FIG. 1. It is a top view which shows the imaging device which combined the light receiving element array and the multiplexer. It is sectional drawing which follows the IV-IV line of FIG. In the imaging device of the present invention, it is a circuit diagram in the case of performing on / off control of the light reception signal output of the sensing unit based on the light reception signal of the monitor light reception unit. FIG. 6 is a circuit diagram in the case of performing automatic gain control of the light reception signal output of the sensing unit based on the light reception signal of the monitor light reception unit in the imaging apparatus of the present invention.

1 InP substrate, 2 n-type InP buffer layer, 3 GaInNAs light-receiving layer, 4 InP window layer, 5 mask pattern, 10 light-receiving element array, 11 p-part electrode, 12 n-part electrode, 16 p-type area, 50 imaging device, 51 Multiplexer, 56 Multiplexer input terminal, 59 Monitor input terminal of multiplexer, S sensing unit (light receiving element), M Monitor light receiving unit.

Claims (5)

A light receiving device including a light receiving element array in which a plurality of light receiving elements are arranged in a semiconductor stacked body including a light receiving layer, and a multiplexer having a signal input unit and a main body unit that receives a signal passing through the signal input unit,
In the light receiving element array, comprising one or more monitor light receiving units located between the plurality of light receiving elements,
Each of the plurality of light receiving elements and the monitor light receiving unit includes an impurity region positioned so as to reach the light receiving layer from a surface that is one surface of the semiconductor stacked body, and an electrode that is in ohmic contact with the impurity region; Have
Each of the light receiving element and the monitor light receiving unit forms a pin type photodiode,
It is a back-side incident type in which light is incident from the back side opposite to the surface of the semiconductor laminate,
The monitor light receiving unit and the electrode of the light receiving element are separately connected to the signal input unit of the multiplexer, and in the signal input unit, a direct signal from the light receiving element is a direct signal from the monitor light receiving unit. Gain control or on / off control based on the output and output to the main body of the multiplexer.   In the signal input unit, a direct signal from the monitor light receiving unit is passed through an amplification + differential circuit to obtain a time gradient of brightness, and (1) a reference value having a predetermined height of the signal of the time gradient 2. The light receiving device according to claim 1, wherein an output for turning off a direct signal from the light receiving element when exceeding a value or (2) an output for performing an automatic gain control according to a height is performed. apparatus.   3. The light receiving device according to claim 1, wherein an area of light received by the monitor light receiving unit is smaller than that of the light receiving element when viewed in a plan view.   4. The light receiving device according to claim 1, wherein the semiconductor stacked body of the light receiving element array is made of a group III-V compound semiconductor, and the impurity is zinc (Zn). 5. The said light receiving layer is comprised from the III-V group compound semiconductor which has the band gap energy corresponding to a near-infrared region or a long wavelength side from it, The any one of Claims 1-4 characterized by the above-mentioned. Light receiving device.

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