JP2008124182A - Optical detector and field of view supporting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical detector, capable of having sufficiently high photosensitivity from near-infrared region to visible region, and a view supporting device employing it. <P>SOLUTION: The photodetector 10 of this invention is equipped with the GaInNAs light receiving layer 3 of an epitaxial layer having an absorption end between a near-infrared region and an infrared region and an AR (anti-reflection) multi-layer film, that is, a semiconductor multi-layers film 12 positioned in the surface of incidence of light into the GaInNAs light receiving layer 3 while the AR multi-layer film has a reflection factor lower than that of the semiconductor layer which the AR multi-layer film contacts, in a wavelength region from visible wavelength to a near-infrared wavelength. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light detection device and a field-of-view support device, and more specifically to a light detection device and a field-of-view support device used for various analysis devices and night vision support of automobiles.

  A light receiving element using a compound semiconductor InGaAs has a high light receiving sensitivity to near infrared light in a wavelength range of 900 nm to 1700 nm, and therefore is widely used for commercial and military purposes. The wavelength range is also included in a part of the cosmic light that reaches from the universe to the surface of the earth. Therefore, it is also used for night vision assistance devices for automobiles that use the reflection of cosmic light from objects at night.

  Under such circumstances, as a light receiving element using InGaAs, an InGaAs light receiving element having light receiving sensitivity from the near infrared region to a shorter wavelength region, specifically, the visible region has been proposed (Non-Patent Document 1). . The structural features and manufacturing process of this InGaAs light receiving element are not disclosed. However, an AR (Anti-Reflection) film provided on the entrance surface for preventing reflection is effective for near-infrared light, but becomes an obstacle to visible light. It is described that an InGaAs light receiving element was manufactured. In the wavelength range shorter than 900 nm, the conventional light receiving element has shown little sensitivity. However, according to the above InGaAs light receiving element, the sensitivity decreases sharply even in the wavelength range shorter than the wavelength of 900 nm, but the light receiving sensitivity in the visible range. Data having the following is disclosed.

  In addition to the above, an imaging apparatus having sensitivity in the visible region and the near infrared region has been presented (Non-Patent Document 2). This mechanism also does not indicate what kind of mechanism increases the sensitivity to the visible range, but the standard InGaAs light receiving element has a wavelength of 900 nm or less and has no sensitivity at all. Data showing quantum efficiency of about 50% at a wavelength of 800 nm, 20% at a wavelength of 600 nm, and a little over 5% at a wavelength of about 500 nm are disclosed. In the non-patent documents 1 and 2 described above, the mechanism by which the light-receiving sensitivity in the visible region is improved is explained only in the non-patent document 1 that the AR film is not used. Is not shown.

In the imaging apparatus, generally, the response time is shortened and the light receiving sensitivity is in a trade-off relationship. For example, when the thickness of the InGaAs light receiving layer is increased in order to increase the light receiving sensitivity in the visible region, the response speed is deteriorated. In the back-incidence flip-chip mounted light receiving element of the InP substrate, a microlens is formed on the back surface of the InP substrate coated with a silicon nitride film as an AR coating film, and a reflective portion is locally provided on the microlens and re-reflected. There has been proposed an InGaAs light receiving element that improves both response speed and light receiving sensitivity by effectively utilizing light (Patent Document 1).
Theodore R. Hpelter & Jeffrey B. Barton (Indigo SystemCorporation, 50 Castilian Drive, Goleta, CA USA 93117), "Extended shortwavelength spectral response from InGaAs focal plane arrays", Published inthe Infrared Technology and Applications XXIX SPIE Vol.5074 (2003) , Copyright2003 Society of Photo-Optical Instrumentation Engineers. Goodrich: Near-infrared camera SU640SDVVis-1.7RT (High Resolution InGaAs Visible SWIR AreaCamera) http://www.sensorship.com/specs_SU640SDVVis.html JP-A-6-77518

  According to the above prior art, a general mechanism that can improve both the light receiving sensitivity and the response speed is disclosed (Patent Document 1). However, no effective measures for expanding the light receiving sensitivity from the near infrared region to the visible region are disclosed.

  It is an object of the present invention to provide a photodetection device capable of receiving light sensitivity from the near infrared region to the visible region and a visual field support device using the same.

  The light detection device of the present invention is a light comprising an epitaxial light-receiving layer having an absorption edge in the near-infrared region to the infrared region, and an AR (Anti-Reflection) film located on a light incident surface to the light-receiving layer. It is a detection device. The AR film is characterized by being a multilayer film having a lower reflectance in the wavelength region from visible to near infrared than the semiconductor layer in contact with the AR film.

  By making the AR film a multilayer film, it not only suppresses reflection with respect to light in the near infrared region, but also suppresses reflection with respect to visible light and promotes transmission. For this reason, according to said structure, the wavelength range shorter than a near infrared region, ie, more visible light (wavelength lower limit 390 nm) can be introduce | transduced into a light receiving layer by the effect | action of AR multilayer film, The light receiving sensitivity in the visible range can be increased. In the above configuration, the photodetector may be epi-up mounted with the AR multilayer film disposed on the top side of the epitaxial layer, or may be epi-down mounted with the AR multilayer film disposed on the back side of the substrate. .

  An epitaxial layer n-type buffer layer is provided between the light-receiving layer and the AR film, and the light-receiving layer is epi-down mounted so as to be closer to the mounting surface than the n-type buffer layer. It can take a structure without. As a compound semiconductor substrate having an absorption edge in the near infrared region, a compound semiconductor substrate such as InP is used. The compound semiconductor substrate has an absorption band in the visible region. However, according to the above configuration, since the semiconductor substrate is not removed, it is possible to prevent light from being absorbed by the semiconductor substrate before reaching the light receiving layer, and to improve the sensitivity to visible light. .

  According to the configuration described above, epi-down mounting or flip-chip mounting is performed, and the epitaxial layer window layer is provided on the light-receiving layer mounting side (opposite to the n-type buffer layer). A plurality of p-type regions into which p-type impurities are introduced are provided in a lattice arrangement so as to reach the light receiving layer through the window layer, and a p-part electrode is provided for each p-type region. This p-type region forms a pixel region, and a different current flows for each pixel region corresponding to the position received by the light receiving layer and is received by each p-part electrode, so that an image is formed.

  The light receiving layer may be made of any one of GaInNAs, GaInNAsSb, and GaInNAsP, or a combination thereof. With this configuration, it is possible to obtain a photodetection device having light receiving sensitivity in the visible region after detecting light in the near infrared region having a wavelength of 0.4 μm to 2.5 μm.

The AR film may be a semiconductor multilayer film as an epitaxial layer. The AR film may be a dielectric multilayer film. With this configuration, the light receiving sensitivity can be ensured over the visible region to the near infrared region. When the AR multilayer film is an epitaxial semiconductor multilayer film, the semiconductor multilayer film can be epitaxially grown directly on the semiconductor substrate, and the n-type buffer layer can be epitaxially grown on the semiconductor multilayer film. After forming the semiconductor substrate, the semiconductor substrate can be removed. As the semiconductor multilayer film, a multilayer film such as GaP or AlN can be used. On the other hand, when the AR multilayer film is a dielectric multilayer film, the above-mentioned epitaxial multilayer structure is formed on the semiconductor substrate, the semiconductor substrate is removed, and then the dielectric multilayer film is placed on the n-type buffer layer. Form. As the dielectric multilayer film, a multilayer film of Al ₂ O ₃ , TiO ₂ or the like can be used.

  In addition, a visual field support device according to the present invention uses any one of the above-described light detection devices. Since the above-mentioned light detection device has sensitivity in the visible region to the near infrared region, for example, when used in a vehicle vision support device, it has sensitivity in the near infrared region, so that an object can be imaged by reflection of space light at night. In addition, since it has sensitivity in the visible range, it is possible to distinguish red, blue, and green traffic signals for imaging. For this reason, the visual field assistance apparatus useful for traffic safety ensuring can be comprised compactly.

  ADVANTAGE OF THE INVENTION According to this invention, the optical detection apparatus and visual field assistance apparatus which can cover from a near infrared region to a visible region can be provided using AR multilayer film.

(Embodiment 1)
FIG. 1 is a diagram showing a photodetection device 10 according to Embodiment 1 of the present invention. In FIG. 1, the photodetection device 10 is mounted epi-down, and the light incident surface is formed by a semiconductor multilayer film 12 which is an AR multilayer film. An n-type InP buffer layer 2 is located under the semiconductor multilayer film 12, a light-receiving layer GaInNAs layer 3 is located thereunder, and an InP window layer 4 is further provided thereunder.

  A p-type impurity is introduced to reach the GaInNAs light-receiving layer 3 from the opening of the diffusion mask 23 through the InP window layer 4 and the p-type region 5 is formed. The openings of the diffusion mask 23 are arranged in a lattice pattern, and the p-type region 5 is a pixel unit (pixel). A p-part electrode (not shown) is provided for each p-type region, and the current generated by light reception in the GaInNAs light-receiving layer 3 is detected for each p-type region corresponding to the light-receiving position, and the location of the received light intensity. A distribution, i.e. an image, can be formed.

  There are two points of the light detection apparatus 10 in the present embodiment. One is that an AR multilayer film, that is, a semiconductor multilayer film 12 is used instead of a silicon nitride single layer film or a SiON single layer film as in the prior art. Whether or not the semiconductor multilayer film 12 is necessarily an epitaxial film depends on the manufacturing method of the photodetector 10 and will be described later. One period of the AR multilayer film may be any period as long as it has periodicity such as (a layer / b layer), (a layer / b layer / c layer), (more complicated long period), etc. . Another point is that the InP substrate used for forming the epitaxial laminated structure is excluded.

  A method for manufacturing the photodetector 10 illustrated in FIG. 1 will be described with reference to FIGS. First, the semiconductor multilayer film 12 is epitaxially grown on the InP substrate 1. The semiconductor multilayer film 12 is preferably a GaP / AlN multilayer film (4 cycles). Next, the n-type InP layer 2 is epitaxially grown on the semiconductor multilayer film 12, and the GaInNAs light-receiving layer 3 and the InP window layer 4 are sequentially epitaxially grown thereon. Thereafter, p-type impurities are diffused and introduced so as to reach the GaInNAs light-receiving layer 3 from the opening of the diffusion mask 23 through the InP window layer 4. As a result, a pin type photodiode is formed by (p type region 5 / GaInNAs light receiving layer 3 / n type InP buffer layer 2). As described above, the p-type region constitutes a pixel.

  Next, the InP substrate 1 is removed by backside polishing so that the semiconductor multilayer film 12 is exposed. The photodetector 10 thus manufactured is epi-down mounted with the p-type region 5 side disposed on the mounting substrate side, and light is incident from the semiconductor multilayer film 12 side. When light is received by the GaInNAs light receiving layer 3, electric charge is generated and a current flows, but imaging is performed as a result of the current being different for each p-type region corresponding to the light receiving position.

In the photodetector 10 of FIG. 1, since the AR multilayer film is formed of the semiconductor multilayer film 12, the visible light is not strongly reflected unlike the conventional SiON film. FIG. 3 shows a (GaP / AlN) semiconductor multilayer film which is an AR multilayer film according to the first embodiment, and an (Al ₂ O ₃ / TiO ₂ ) dielectric which is an AR multilayer film according to a second embodiment which will be described later. It is a figure which shows the reflectance R of a multilayer film with respect to wavelength (lambda), respectively. The comparative example shows the SiON single-layer AR film, and the reference example also shows the reflectance of InP. InP corresponds to the semiconductor layer (buffer layer 2) in contact with the semiconductor multilayer film 12 which is an AR multilayer film.

  According to FIG. 3, InP has a large reflectance with respect to the wavelength in the visible region, and the SiON film also has a large reflectance peak in the visible region. On the other hand, in the (GaP / AlN) semiconductor multilayer film in the first embodiment, the peak value of the reflectance in the visible region is small. In addition, the reflectance increases in the vicinity of a wavelength of 300 nm, but it is out of the visible range and does not substantially affect the light receiving sensitivity in the visible range. For this reason, the light receiving sensitivity in the visible region can be improved as compared with the case where the AR film of the SiON single layer film is used.

  The photodetector shown in FIG. 1 is also characterized in that the InP substrate is removed, and the absorption of visible light by the InP substrate is usually eliminated by removing the InP substrate having a thickness of about 200 μm. be able to. As a result, the light receiving sensitivity in the visible range can be further improved.

  In the manufacturing method of the photodetector shown in the first embodiment, the semiconductor multilayer film is limited to the one that is epitaxially grown on the InP substrate 1. However, the semiconductor multilayer film used for the AR multilayer film can be formed without using the process through (the structure in FIG. 2 → the structure in FIG. 1). The light detection device provided with the semiconductor multilayer film can also be manufactured by the manufacturing method shown in the following second embodiment. In this case, the semiconductor multilayer film is not necessarily an epitaxial film.

(Embodiment 2)
FIG. 4 is a diagram showing a light detection apparatus according to Embodiment 2 of the present invention. In FIG. 4, the point that the dielectric multilayer film 13 is used for the AR multilayer film is only different from the photodetector in the first embodiment shown in FIG. 1, and the other parts are the same. The dielectric multilayer film 13 is formed of a three-cycle multilayer film of (Al ₂ O ₃ / TiO ₂ ).

  The manufacturing method of the photodetection device 10 shown in FIG. 4 is as follows. First, an epitaxial laminated structure of (InP substrate 1 / n-type InP buffer layer 2 / GaInNAs light receiving layer 3 / InP window layer 4) is formed (see FIG. 5). Thereafter, the p-type region 5 is formed by diffusing and introducing p-type impurities so as to reach the GaInNAs light-receiving layer 3 from the opening of the diffusion mask 23 through the InP window layer 4. As a result, a pin type photodiode is formed by (p type region 5 / GaInNAs light receiving layer 3 / n type InP buffer layer 2). The p-type region constitutes a pixel. Next, the InP substrate 1 is removed by back surface polishing (see FIG. 6). The InP substrate may be removed before introducing the p-type impurity.

Thereafter, the dielectric multilayer film 13, specifically, (Al ₂ O ₃ / TiO ₂ ) multilayer film is formed on the n-type InP buffer layer 2. As shown in FIG. 3, the (Al ₂ O ₃ / TiO ₂ ) multilayer film is an InP corresponding to the semiconductor layer in contact with the (Al ₂ O ₃ / TiO ₂ ) multilayer film, which is an AR multilayer film, particularly in the visible region. And lower reflectivity than SiON films. Further, in the visible region and the near infrared region, the reflectance is slightly lower than that of the (GaP / AlN) semiconductor multilayer film. Therefore, by using the (Al ₂ O ₃ / TiO ₂ ) multilayer film as the AR multilayer film, the light receiving sensitivity in the near infrared region to the visible region can be greatly improved.

  As described above, when the semiconductor multilayer film is used for the AR multilayer film, the dielectric multilayer film 13 is not limited to the manufacturing method shown in the first embodiment (the structure in FIG. 5 → the structure in FIG. 6 → the structure in FIG. 7). The structure can be manufactured through the process of the structure substituted with the semiconductor multilayer film 12. In this case, the semiconductor multilayer film is not necessarily epitaxially grown on the epitaxial n-type buffer layer. In many cases, the surface property of the base (epitaxial n-type buffer layer) is not suitable for epitaxial growth, so that it is non-epitaxial. Become a layer.

(Embodiment 3)
FIG. 7 is a diagram showing a field-of-view assistance apparatus according to Embodiment 3 of the present invention. This visual field support device is mounted on a vehicle in order to support a driver's forward visual field when driving a car at night. The vehicle includes an imaging device 70 including the light detection device 10 described in the first and second embodiments, an optical element such as a lens (not shown), a display monitor 65 that displays a captured image, and drive control thereof. A control device 60 is mounted. FIG. 8 is a diagram showing a night vision support device mounted on a vehicle in order to support the driver's rear vision in driving the automobile at night. An image captured by the imaging device 70 including the optical detection device of the first and second embodiments, the lens, and the like, which is attached to the rear portion of the automobile in a rearward direction, is displayed on the display device 65 in the upper front of the driver. . The imaging device 70 and the display device 65 are driven and controlled by the control device 60.

  In the conventional vehicular field-of-view assistance device, reflected light or emitted light in the infrared region from an object is received and used as an image, and thus has the following problems. When using reflected light, a light source is required, a mounting space is required, and the cost is increased. In addition, when using the radiant heat of an object, it is difficult to recognize a pedestrian or the like wearing a non-heating element other than a person or a cold protection device, so it is necessary to use it together with a recognition means other than an infrared camera. In addition, when using a light source, it is necessary to take measures against the human body, that is, eye-safe measures depending on the wavelength range to be used. Moreover, even if the traffic signal can be distinguished from light emission and non-light emission, the light emission color of the traffic signal cannot be identified.

In the visual field support device according to the present embodiment, the extra light source and the eye-safe measures as described above are unnecessary. Moreover, it does not matter whether the imaging target is heated or not. Furthermore, a clear image of the object can be obtained even in an environment containing moisture such as in fog. For this reason, the visual field assistance apparatus for vehicles excellent at night can be provided. This is the short wavelength infrared region from the object (Short
Wavelength Infrared SWIR (included in the visible to near-infrared range) is a light-receiving element that uses reflected light of cosmic light, has a sufficiently low dark current, and has an excellent dynamic range (S / N). It is. In addition, it should be noted that the light receiving sensitivity of one photodetection device has been increased from the near infrared region to the visible region, so that not only imaging of objects with space light in the SWIR region, but also the emission color of traffic signals (visible region). Can be identified. For this reason, the visual field assistance apparatus which can greatly improve the safety | security in an intersection etc. can be formed compactly.

(Another aspect of the present photodetection device)
(1) Mounting In the above-described embodiment of the present invention, only the epi-down mounting mode has been described. However, it is possible to adopt a structure in which the AR multilayer film is arranged on the top of the epitaxial layer by epi-up mounting. In this case, for example, when a method of forming an image by obtaining a received light current with each p-type electrode in ohmic contact with each p-type region, the p-type electrode may interfere with incident light. It is possible to obtain an advantage that it is not necessary to perform back surface polishing in order to remove the substrate.
(2) Application The light detection device of the present invention can be applied not only to a visual field support device but also to various image analysis devices such as a biological recognition device, a biomedical device, and a foreign object recognition device. Since the apparatus to which the present photodetection device is applied is very wide, not all of them can be specifically mentioned here, but may be applied to a device realized in the future.

  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.

  Since the light detection device of the present invention has sufficiently high detection sensitivity in the near infrared region to the visible region, it can be used for a vehicle field of view support device, other image analysis devices, and the like.

It is a figure which shows the photon detection apparatus in Embodiment 1 of this invention. It is a figure for demonstrating the manufacturing process of the photon detection apparatus of FIG. It is a figure which shows the wavelength characteristic of the reflectance of AR multilayer film in Embodiment 1 and 2 of this invention. It is a figure which shows the photon detection apparatus in Embodiment 2 of this invention. FIG. 5 is a diagram for explaining a manufacturing process of the photodetector in FIG. 4 (epitaxial layer formation stage). FIG. 5 is a diagram for explaining a manufacturing process of the photodetecting device of FIG. 4 (p-type impurity introduction and back surface polishing end stage). It is a figure which shows the visual field assistance apparatus in Embodiment 3 of this invention. It is a figure which shows the modification of the visual field assistance apparatus of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 InP board | substrate, 2 n-type InP buffer layer, 3 GaInNAs light receiving layer, 4 InP window layer, 5 p-type area | region, 10 photodetector, 12 Semiconductor multilayer film, 13 Dielectric multilayer film, 23 Diffusion mask, 60 Control apparatus 65 Display device, 70 Imaging device.

Claims (6)

A light-receiving layer of an epitaxial layer having an absorption edge in the near-infrared region;
An optical detection device comprising an AR (Anti-Reflection) film positioned on a light incident surface to the light receiving layer,
The AR film is a multilayer film having a lower reflectivity in a wavelength region from visible to near infrared than a semiconductor layer in contact with the AR film.   An epitaxial n-type buffer layer is provided between the light-receiving layer and the AR film, and the light-receiving layer is epi-down mounted so as to be closer to the mounting surface than the n-type buffer layer. The photodetection device according to claim 1, wherein there is no substrate.   The photodetection device according to claim 1, wherein the light receiving layer is made of any one of GaInNAs, GaInNAsSb, and GaInNAsP, or a combination thereof.   The photodetecting device according to claim 1, wherein the AR film is an epitaxial semiconductor multilayer film.   The photodetecting device according to claim 1, wherein the AR film is a dielectric multilayer film. 6. A visual field support device using the light detection device according to claim 1.

Images