JP2007123587A - Light receiving element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple and a reliable light-receiving element that can maximize the light receiving area, and moreover can be manufactured inexpensively. <P>SOLUTION: The semiconductor light receiving element 1 comprises a crystal substrate 2 made of a conductive Si-based semiconductor; a buffer layer 3 formed on a surface at one side of the crystal substrate 2; at least one photosensitive layer 4, that is formed on the buffer layer 3, and is made of an insulating GaN-based material; a Schottky electrode 5 that is provided on a surface at one side of the photosensitive layer 4 that serves as a light receiving surface 4a, and is an electrode on one side for constituting the light reception element; and an electrode 7 at the other side for composing the light-receiving element 1, while being provided on a surface at the other side of the crystal substrate 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion element, a so-called light receiving element.

At present, semiconductor light-receiving elements based on photodiodes (PDs) are widely used for various applications, and the types are various.
However, in order to obtain a semiconductor light receiving element capable of receiving light of a desired wavelength selected from a wide range from infrared to ultraviolet with a simple manufacturing process while ensuring sufficient performance, There were the following two problems that could not be solved.

The first problem relates to a light receiving element using silicon (Si) as a photosensitive layer.
First, in general, semiconductors have a characteristic that they are sensitive to photons having energy equal to or higher than the band gap value, but are significantly less sensitive to photons that are overwhelmingly larger than the band gap. Therefore, for example, the photosensitive layer of the light receiving element of ultraviolet rays (Ex. Near ultraviolet region having a wavelength of 300 to 390 nm is displayed in electron volt units is 3.18 to 4.13 eV) is made of silicon (band gap is about 1 at room temperature). .12 eV) has a problem that the sensitivity is remarkably lowered.
Moreover, since silicon has a small band gap value, light (visible light) having an energy value less than or equal to the desired light has to be cut by a separate filter, which further reduces the sensitivity. .

In order to solve the first problem, a group III nitride material such as a GaN-based or InGaAlN-based material, for example, Al _x Ga _y In _(1-xy) N (0 ≦ x ≦ 1, 0 A light receiving element using ≦ y ≦ 1 and x + y ≦ 1) for the photosensitive layer has already been developed (see Patent Document 1 and Non-Patent Document 1). This has the feature that the band gap can be tuned to all photon energies from infrared to ultraviolet by varying x and y. Therefore, at present, this group III nitride device is generally used as a semiconductor light-receiving element capable of receiving light in the ultraviolet region or a wavelength corresponding to purple to blue to green.

  Here, the semiconductor light-receiving elements listed in Patent Document 1 and Non-Patent Document 1 are Schottky barrier PDs that receive ultraviolet rays. FIG. 2 shows an outline of these conventional structures. As described in Non-Patent Document 1, some PDs are based on many light receiving principles, and one of them is a Schottky barrier type PD.

As shown in FIG. 2, in these PDs, a GaN-based crystal is grown on a sapphire substrate via a buffer layer made of AlN or the like, and a Schottky electrode (Schottky barrier is formed on the GaN-based crystal. And the ohmic electrode are provided to form a PD (see FIG. 4 of Patent Document 1 and FIG. 2 of Non-Patent Document 1).
FIG. 2A is a cross-sectional structure diagram showing an example (20) of a conventionally known semiconductor light receiving element, and an n-type group III nitride is formed on a substrate 21 made of sapphire via a buffer layer grown at a low temperature. A semiconductor layer (n-GaN) 22 is grown, a photosensitive layer 23 made of a non-doped group III nitride material (GaN) is formed thereon, and a transparent Schottky electrode 25 is formed on the photosensitive layer 23. And an ohmic electrode 27 provided on the edge of the n-type nitride semiconductor layer 22.
FIG. 2B is a cross-sectional structural view showing another example (30) of a conventionally known semiconductor light receiving element, as in FIG. 2A, and Si is formed on the sapphire substrate 31 through a buffer layer. An added n-GaN layer 32 and an undoped GaN layer 33 are sequentially formed, and electrodes 35 and 37 are provided on the undoped GaN layer 33 and the n-GaN layer 32, respectively. The electrode 35 in FIG. 2B is a comb-shaped Schottky electrode provided on the non-doped GaN layer 33.
2 (a) and 2 (b), n-type nitride semiconductor layers 22 and 32 in which part of the edges of the upper layers 23 and 33 made of a non-doped nitride material are formed on the lower side thereof. The portions (24, 34) that are bent up to reach the point are called mesa structures, and are formed to provide ohmic electrodes 27, 37 on the surfaces of the n-type nitride semiconductor layers 22, 32. Is. The mesa structure is formed by reactive ion etching (RIE) or the like.
Normally, reverse biases 26 and 36 are applied when each element shown in FIG. 2 is used.

As described above, most of the conventionally known group III nitride devices are crystal growth using MOCVD (metal organic chemical vapor deposition) or MBE (molecular beam crystal growth) on a sapphire substrate. It is produced by.
However, as a problem when using sapphire as a substrate, there is an increase in crystal defects due to a large difference in thermal expansion coefficient and lattice constant from the group III nitride. For this reason, the problem that a device characteristic is bad, for example, it is difficult to lengthen the lifetime of a light emitting device, or the problem that an operating power becomes large may arise.

Furthermore, in the case of a sapphire substrate, since it is insulative, it is impossible to take out an electrode from the substrate side like a conventional light emitting device, and it is necessary to take out an electrode from the nitride crystal thin film surface side where the crystal has grown. Become. That is, it is necessary to place both electrodes of the diode on the surface of the Al _x Ga _y In _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1). Further, it is necessary to add a complicated process such as etching on the surface side of the nitride crystal thin film (see FIG. 2). As a result, not only the manufacturing process becomes complicated, but also the light receiving area is narrowed due to structural reasons, so when trying to secure the desired light receiving area, the device area increases enormously, leading to high costs. there were. This is the second problem.
In addition, the portion having the mesa structure is likely to be a blind spot on the light receiving surface, which causes variations in light receiving sensitivity on the light receiving surface.

In such circumstances, recently, a group III nitride crystal (for example, GaN) is used instead of a sapphire substrate to form a substrate, and another group III nitride crystal thin film is grown on the group III group. There has also been an attempt to solve the second problem by using a nitride semiconductor multilayer structure (see Patent Document 2).
However, group III nitride crystal substrates such as GaN substrates are absolutely extremely expensive in nature, and there is a problem that it is impossible to provide a general-purpose device at a low cost.

  Further, Patent Document 3 discloses a configuration in which an ohmic electrode is provided on one surface of a substrate made of a material exhibiting conductivity instead of a sapphire substrate (FIG. 3C, [0030], [0030], [Patent Document 3]. This is a configuration in which a non-patent document 1 is provided with an opaque Schottky electrode having a comb-shaped pattern on the light receiving surface, and still has the second problem that the effective light receiving area on the light receiving surface is still small. It was something that could not be resolved.

In short, it can receive light of a desired wavelength selected from a wide range from infrared to ultraviolet, and it can be manufactured at a low cost with a simple process while ensuring sufficient performance. No semiconductor light receiving element has been provided so far.
JP 2003-23175 A JP 2004-307322 A JP 2000-101130 A Koto et al., "Development of AlGaN-based ultraviolet light-receiving element", Mitsubishi Cable Industrial Time Report No. 97, January 2001

  Accordingly, it is an object of the present invention to provide a simple and reliable semiconductor light receiving element that does not require a complicated manufacturing process such as etching and can be manufactured at low cost. It is another object of the present invention to provide a semiconductor light receiving element that can maximize the light receiving area and can ensure sufficient performance while being small.

  As a result of various studies to solve the above-mentioned problems, the present inventor has found that a Si-based material that is electrically conductive and that is much easier to obtain and cheaper than a crystal substrate made of a nitride material such as GaN is a crystal substrate. The electrode provided above the photosensitive layer grown on one side of the substrate is a so-called transparent electrode, and the other side electrode constituting the light receiving element is provided on the other side of the substrate. It has been found that the above problems can be solved by providing, and the present invention has been completed.

The light-receiving element of the present invention that can solve the above-mentioned problems is (1) a semiconductor light-receiving element, which is a crystal substrate made of a Si-based semiconductor exhibiting conductivity, and a buffer formed on one surface of the crystal substrate A light-sensitive layer made of an insulating group III nitride material, formed on at least one layer above the buffer layer, and provided on one surface of the light-sensitive layer serving as a light-receiving surface; A Schottky electrode as one electrode constituting the light receiving element and an electrode on the other side constituting the light receiving element provided on the other surface of the crystal substrate. .
In the light receiving element of the present invention, (2) the crystal substrate is made of n-type SiC, and the buffer layer is made of n-type Al _y Ga _1-y N (0 ≦ y ≦ 1), or (3 It is preferable that the crystal substrate is made of n-type Si and the buffer layer is made of n-type SiC.
Alternatively, in the light receiving element of the present invention, (4) the crystal substrate is made of n-type Si, and the buffer layer is n-type Al _u Ga _1-u N (0 ≦ u ≦ 1) and n-type Al _v Ga. _1-v N (0 ≦ v ≦ 1, v ≠ u), or (5) the crystal substrate is made of n-type Si, and the buffer layer is made of n-type SiC and n-type Al. is preferably made of _{u Ga 1-u n (0} ≦ u ≦ 1) and the n-type _Al v _{Ga 1-v} superlattice structure of n (0 ≦ v ≦ 1, v ≠ u).

In the light receiving element of the present invention, (6) the photosensitive layer is a group III nitride material, particularly preferably Al _x Ga _y In _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y < 1, x + y ≦ 1).

  Further, in the light receiving element of the present invention, (7) the Schottky electrode is made of a light-transmitting metal thin film that is transparent to the wavelength of light to be detected, and covers substantially the entire surface of the light receiving surface. It is preferable to be formed. On the other hand, (8) the electrode on the other side is preferably an ohmic electrode.

  In addition, in the light receiving element of the present invention, (9) a P-type group III nitride semiconductor layer is further provided between the photosensitive layer and the one side electrode, and the one side electrode is used as an ohmic electrode. It doesn't matter.

  In the light receiving element of the present invention according to the above (1) to (9), (10) the photosensitive layer is formed by metal organic chemical vapor deposition (MOCVD), molecular beam growth (MBE) or hydride ( HVPE) is preferably produced by at least one growth method.

  In the present invention, the light receiving surface refers to a surface on the light receiving side of both surfaces of the photosensitive layer. A Schottky electrode is provided so as to cover the light receiving surface.

A Schottky electrode generally refers to an electrode in a state where a potential barrier called a Schottky barrier is generated by a junction between a metal and a semiconductor. Since the height qφ of the Schottky barrier is generally a difference between the work function φ _{m of the} metal and the electron affinity χ of the semiconductor, qφ = q (φ _m −χ), and a relatively large material of φ _m Is desired.
Preferably, a transparent (translucent metal thin film) electrode is used as the Schottky electrode. At this time, the light transmitted through the electrode is absorbed by the depletion layer and the insulating photosensitive layer at the electrode / semiconductor interface junction, and generates a photocurrent.
Here, “transparent” means transparent to the wavelength of light to be detected (for example, UV transparent if the detection target is ultraviolet).

  The ohmic electrode is a state in which the contact between the metal and the semiconductor does not exhibit rectifying characteristics (regardless of the direction of the applied voltage) and the contact resistance is almost negligible. The contact between the highly doped semiconductor and the metal is likely to be ohmic because the width of the depletion layer formed is significantly narrowed and a tunneling current easily flows.

  According to the present invention, complicated manufacturing processes such as the above-described etching can be omitted, and not only the manufacturing is simplified, but also the light receiving area can be maximized. Furthermore, according to the present invention, it is possible to provide a light receiving element having a simple and excellent structure at low cost.

  Hereinafter, a configuration example of the light receiving element of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing a configuration example of a light receiving element of the present invention. FIG. 1 is an end view when the light receiving element 1 of the present embodiment is cut at an appropriate position. Hatching is applied to identify the electrodes.

[Constitution]
As shown in FIG. 1, a semiconductor light receiving element (hereinafter “light receiving element”) 1 of the present invention is a PD having a so-called MIS type configuration. Accordingly, the Schottky electrode and the other electrode provided corresponding to the Schottky electrode are arranged in a manner that can function as a light receiving element. The other electrode is preferably an ohmic electrode. Details of each electrode will be described later. The mechanism of light detection using a Schottky barrier is the same as that of a conventional Schottky barrier type PD.
The light receiving element 1 according to the present embodiment is one in which the crystal substrate 2 is made of a Si-based material exhibiting conductivity, and the electrodes on one side and the other side are at least sandwiched between the Si-based crystal substrates. It is formed.

The light-receiving element according to the present invention is preferably configured as a laminate formed by crystal growth of a layer of a group III nitride material on a crystal substrate. At this time, the photosensitive layer 4 is located in the uppermost layer of the laminate. The structure of this laminate and the positional relationship between each electrode (Schottky electrode 5 and ohmic electrode 7) are as shown in FIG.
In FIG. 1, 2 is an n-type semiconductor crystal substrate showing conductivity, 3 is a buffer layer made of an n-type group III nitride semiconductor, and 4 is a photosensitive layer made of an insulating or non-doped group III nitride material. Reference numeral 5 denotes a transparent Schottky electrode which is one electrode constituting the light receiving element. Reference numeral 7 denotes an ohmic electrode as an electrode on the other side constituting the light receiving element. In FIG. 1, L is light to be detected.

  As shown in FIG. 1, the light receiving element 1 of the present embodiment has a layer made of a non-doped group III nitride material as a photosensitive layer 4. Further, a surface on one side of the photosensitive layer 4 is a light receiving surface 4a, and a Schottky electrode 5 is provided on the light receiving surface 4a.

The group III nitride material used for the photosensitive layer 4 is a compound determined by the formula Al _x Ga _y In _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y <1, x + y ≦ 1) Is preferred. Such a group III nitride material has much stronger chemical bond strength than Si and has mechanical and thermal properties.
Here, the optimum composition of the group III nitride material used for the photosensitive layer 4 is determined by the value at the long wavelength end in the wavelength range of light to be detected. For example, InGaN when targeting light in the blue region (near 480 nm) and shorter wavelength regions, only InGaN with a small In composition and ultraviolet light of 365 nm or less when targeting light in the short wavelength region of 400 nm or less even with ultraviolet light AlGaN is selected when targeting.

In the present embodiment, a transparent (translucent metal thin film) electrode is used for the Schottky electrode 5. Transparent means transparent to the wavelength of light to be detected. Examples of the material of the Schottky electrode 5 include Au, Pt, TiW, or a combination thereof (Ni / Pt, Ni / Au, etc.). The transparent Schottky electrode 5 is formed so as to cover substantially the entire light receiving surface 4a.
In the present embodiment, a pad electrode 6 made of Au is added to the upper surface of the Schottky electrode 5 in order to facilitate the connection between the transparent Schottky electrode 5 made of a translucent metal thin film and the outside. Yes.

Examples of the material of the ohmic electrode 7 include Al / Ti, Au / Ti, Ti, or a combination thereof. In addition, since the voltage is applied so that the Schottky electrode 5 side is reverse-biased, even if the ohmic electrode 7 side has a Schottky barrier, it does not become a big problem. This means that even if both electrodes are formed by Schottky electrodes, when a reverse bias voltage is applied to the electrode on the light receiving surface, the other electrode is in a forward bias state, resulting in an ohmic electrode. It means to work equivalently.
In this embodiment, since the one-side electrode is the ohmic electrode 7, the internal electric field can be used, and the principle advantage that the electron-hole pair is separated even when the applied voltage is zero is obtained. That is, according to the present embodiment, since the one-side electrode is an ohmic electrode, it can be expected that carriers are separated by an internal electric field and can be taken out as a photocurrent without an applied voltage.

The crystal substrate 2 is a conductive Si-based semiconductor substrate capable of crystal growth of a group III nitride material. Suitable substrates include those made of n-type SiC or n-type Si. In the present embodiment, a photosensitive layer 4 made of a non-doped group III nitride crystal is grown on the crystal substrate 2 via a buffer layer 3. In general, the buffer layer 3 is deposited at a temperature lower than the crystal growth temperature of the group III nitride material grown thereon.
For convenience, the surface of the crystal substrate 2 made of n-type SiC or n-type Si has n-type Al _y Ga _1-y N (for relaxing the difference in lattice constant and thermal expansion coefficient from the group III nitride crystal). 0 ≦ y ≦ 1) [in the case of n-type SiC substrate] or n-type SiC [in the case of n-type Si substrate] provided with a buffer layer 3 may be regarded as a substrate, and further a photosensitive layer thereon 4 may be regarded as a substrate having a group III nitride crystal thin film different from 4 (for example, one having a doping concentration different from that of the substrate or the like).
In any case, in this embodiment, the layers below the buffer layer 3 (the buffer layer 3, the crystal substrate 2, and the ohmic electrode 7) with the photosensitive layer 4 as a boundary may be handled as electrodes integrally. Is possible.

The light to be received by the light receiving element of the present invention can be selected at any wavelength depending on the composition of the group III nitride material used for the photosensitive layer 4, but from blue to ultraviolet and X-rays. The utility of the present invention is particularly remarkable when light of short wavelengths is used.
For example, light with a short wavelength, such as light with a wavelength of 248 nm emitted from a KrF excimer laser device or light with a wavelength of 193 nm emitted from an ArF excimer laser device, is a light having intense energy. High durability and reliability were strongly demanded.
However, according to the present invention, an element having a structure that does not require a complicated manufacturing process, is simple and can take up the light receiving area to the maximum, and can withstand light of a short wavelength such as ultraviolet rays, is a group III. Since a nitride material can be used for the photosensitive layer, it is possible to provide a light receiving element that is excellent in durability and reliability in addition to ultraviolet resistance. According to the present invention, it is possible to provide a high-performance element at low cost by using a Si-based material for the substrate.

[Operation]
In the following, the operation of the light receiving element 1 of the present embodiment will be described. First, a negative voltage is applied to the transparent Schottky electrode 5 side, and a positive voltage is applied to the n-type layer side, that is, the ohmic electrode 7 to place the element in a reverse bias state. The light L incident from the upper side of the figure passes through the transparent Schottky electrode 5 and is absorbed when reaching the photosensitive layer 4, generating electrons in the conduction band and holes in the valence band. At this time, electrons move to the crystal substrate 2 which is an n-type semiconductor layer by an electric field, while holes move to the transparent Schottky electrode 5 and are taken out as photocurrent through the electrodes. In other words, electrons are guided to the ohmic electrode 7 and holes are guided to the Schottky electrode 5 to be taken out as photocurrent.
Here, by increasing the reverse bias voltage, an avalanche effect is caused, and it may be used as a current amplification type element.

  Next, the light receiving element of the present invention having the above configuration will be described with reference to an example in which the light receiving element of the present invention is actually made as an ultraviolet sensor that receives light in the ultraviolet region.

[First example]
Similar to the above embodiment, the light receiving element 1 of the present example has the structure shown in FIG. 1, and n-type Al _y Ga _1-y N (0 ≦ y) serving as a buffer layer on the n-type SiC substrate 2. ≦ 1) Photosensitive layer 4 made of layer 3 and insulating non-doped Al _x Ga _y In _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y <1, x + y ≦ 1) are sequentially laminated. The MIS type light receiving element having a transparent Schottky electrode 5 made of Ni / Au formed thereon.

Specifically, in the light receiving element 1 of this embodiment, a buffer layer 3 made of n-type Al _y Ga _1-y N (0 ≦ y ≦ 1) is formed on an n-type SiC substrate 2 manufactured by a sublimation method or the like. Further, the photosensitive layer 4 made of insulating non-doped Al _x Ga _y In _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y <1, x + y ≦ 1) is formed on the crystal. It is made up of growth. In this example, the above laminated structure was produced by metal organic chemical vapor deposition (MOCVD) by introducing a known method.

In addition, regarding the insulating non-doped Al _x Ga _y In _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y <1, x + y ≦ 1) group III nitride material constituting the photosensitive layer 4 The optimum composition is determined according to the wavelength band of light to be detected. The ratio of x and y corresponding to the wavelength band of light to be detected and others are well known in the art. In this example, the light-sensitive layer 4 was formed of AlGaN in order to obtain a sensor having sensitivity to light having a wavelength of about 340 nm in the ultraviolet region.

As shown in FIG. 1, an ohmic electrode 7 made of Ti / Al is formed on the back surface of the n-type SiC substrate 2, and a pad electrode 6 made of Au is formed on a part of the light receiving surface of the transparent Schottky electrode 5. Is formed.
In the light receiving element 1 of this embodiment, when light (ultraviolet light) L is incident from the transparent Schottky electrode 5 side, carriers are generated and a photocurrent is taken out from the electrodes 5 and 7.

[Second example]
Subsequent to the first example, a second example having the same laminated structure was produced.
In the light receiving element 1 of the second example, an n-type Si substrate is used instead of the n-type SiC substrate, a buffer layer 3 made of n-type SiC is formed thereon, and an insulating non-doped Al is further formed thereon. is the _{x Ga y in (1-x} -y) N (0 ≦ x ≦ 1,0 ≦ y <1, x + y ≦ 1) light sensitive layer 4 made of a group III nitride material that has been configured by crystal growth .
Similar to the first example, in the second example, the upper laminated structure was formed by metal organic chemical vapor deposition (MOCVD). The composition of the photosensitive layer 4 was the same as in the first example.
A method for crystal growth of a layer made of a group III nitride material on SiC substrate via SiC (3C-SiC) is described in T.W. This is known from a report by Takeuchi et al. (See J. Cryst. Growth 115, 634 (1991)).

Regarding the method of growing a group III nitride crystal on a Si crystal substrate, in addition to the above, i) a buffer layer made of a GaN-based semiconductor containing at least In is deposited on a substrate of Si or the like, and a GaN-based semiconductor is deposited thereon. A method of crystal growth of a semiconductor layer (see JP-A-11-145514), or ii) forming a Ga thin film on the Si substrate by MBE, and then forming a nitride layer 13 on the Ga thin film, Further, a method of growing a GaN crystal thereon (see Japanese Patent Laid-Open No. 9-134878), iii) having an intermediate lattice constant between Si and a group III nitride semiconductor (to be formed on the buffer layer), At least selected from II-III-VI group compound semiconductors, I-III-VI group compound semiconductors and II-IV-V group compound semiconductors, and GaN-based nitride semiconductors A method of growing a group III nitride semiconductor on a Si substrate by stacking two kinds of compound semiconductors so as to constitute a superlattice structure and forming a buffer layer therebetween (Japanese Patent Laid-Open No. 2004-63762) Iv) a method of interposing an intermediate layer made of AlN or AlGaN / AlN (see Umeno et al. “Heteroepitaxy on Si substrate”, Applied Physics Vol. 72, No. 3, P280-281 (2003)). It has been reported and proposed so far.
Furthermore, v) a method of growing high-quality AlGaN on a Si substrate by gas source MBE using an AlGaN / AlN superlattice (SA Nikishin et al., Appl. Phys. Lett. 76, 3028 (2000) Vi)), and vi) there are reported examples of producing a GaInN / GaN device (MQW LED) by introducing an AlGaN / GaN multilayer on a Si substrate (A. Dadgar et al., Appl. Phys. Lett. 78). 2211 (2001)).

As described above, there are various methods for growing a group III nitride crystal on a Si crystal substrate. As a preferable method that can be substituted for the method of forming the buffer layer 3 made of n-type SiC, n and a method of using a buffer layer of a superlattice structure of the type _{Al u Ga 1-u n (} 0 ≦ u ≦ 1) and the n-type _{Al v Ga 1-v n (} 0 ≦ v ≦ 1, v ≠ u), Buffer layer having a superlattice structure of n-type SiC, n-type Al _u Ga _1-u N (0 ≦ u ≦ 1) and n-type Al _v Ga _1-v N (0 ≦ v ≦ 1, v ≠ u) The method using is mentioned.
The superlattice structure refers to an artificial structure formed by repeating heterojunctions at a constant period of several to several tens of atomic layers. When a semiconductor superlattice is formed with a sufficiently short period (short-period superlattice), it is known that the laminated structure works substantially the same as a mixed crystal having an average composition determined by the dimensions of the superlattice.

With respect to the ultraviolet sensors of the present embodiment obtained as the first and second examples, light of various wavelengths is irradiated from the direction perpendicular to the light receiving surface in a state in which a reverse bias is applied between the electrodes 5 and 7. Then, when the performance of light reception was examined, it was found that there was sensitivity to light in the ultraviolet region, that is, light having a wavelength of about 340 nm or less. For the wavelength region of 340 nm or less, the light absorption characteristics of AlGaN, which is a problem when light is incident from the substrate side in the prior art, directly contributes to the light receiving sensitivity in the present invention. It became a flat characteristic. Further, with respect to light having a wavelength range longer than 340 nm, the photosensitive layer 4 is not sensitive, so there is no sensitivity at all and no significant temperature rise of the device was observed.
Furthermore, in the ultraviolet sensor of the present embodiment, since it is not necessary to employ a mesa structure, there is no blind spot on the light receiving surface, and variations in light receiving sensitivity on the light receiving surface are eliminated.

As described above, since the light receiving element of the present invention uses a group III nitride material for the photosensitive layer, it has excellent resistance to ultraviolet rays. The light receiving element of the present invention is a Schottky barrier type PD using a transparent electrode made of a translucent metal thin film, and has a structure for receiving light from the upper surface side of the Schottky electrode. That is, the light to be received can directly enter the photosensitive layer from the electrode side without passing through the substrate layer.
As described above, according to the present invention, it is possible to obtain a light receiving element having excellent sensitivity to light having a wavelength in the blue to ultraviolet range. In addition, according to the present invention, a remarkable effect can be obtained that the sensitivity does not decrease even when the wavelength is shortened.

[Modification]
Although the present invention has been specifically described with reference to one embodiment and the like, the present invention is not limited to the configuration described in the embodiment and the like, and various design changes are possible.

For example, in each of the embodiments described above, the photosensitive layer 4 is made of a composition having sensitivity to ultraviolet rays. However, the composition of the photosensitive layer 4 is not limited to this, and the wavelength band of light to be detected is set. It does not matter if the composition has an optimum composition. The photosensitive layer is not limited to a single layer, and may be formed by laminating a plurality of layers having different compositions. The general formula is not limited to Al _x Ga _y In _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y <1, x + y ≦ 1), but Al _x Ga _1-x N (0 <x ≦ 1) etc.
The buffer layer 3 and its formation method are not limited to those described in the above embodiments, and any appropriate ones reported and proposed so far can be used.

  Further, as described above, the other side electrode 7 forming the light receiving element 1 provided on the other side of the crystal substrate 2 may be a so-called Schottky electrode having a Schottky barrier.

Furthermore, in each of the above embodiments, the laminated structure on the substrate is formed by metal organic chemical vapor deposition (MOCVD). However, the method for forming the laminated structure is not limited to this, and another known crystal can be used. A growth method such as a molecular beam growth method (MBE) or a hydride method (HVPE) may be used.
The electrode material is not limited to those described in the above embodiments. Also, appropriate values can be selected for the film thickness of each layer and the electrode thickness.

In other embodiments, the light receiving element 1 has a MIS configuration in which the buffer layer 3, the non-doped photosensitive layer 4 and the Schottky electrode 5 are sequentially formed on the conductive n-type crystal substrate 2. However, various modifications can be made such as a PIN type configuration in which a P-type group III nitride semiconductor is provided on the photosensitive layer 4 and an appropriate electrode (for example, an ohmic electrode) is provided thereon. As the P-type group III nitride semiconductor, AlGaN having an arbitrary composition ratio can be used. The P-type layer is not limited to a single layer, and may be configured by stacking a plurality of layers having different compositions and doping ratios. In any case, the other side surface (ohmic electrode) constituting the light receiving element is provided on the other side surface of the crystal substrate.
In short, the present invention can maximize the light receiving area by forming the electrodes on one side and the other side with the Si-based crystal substrate having conductivity interposed therebetween, and also troublesome processes such as etching. This is intended for a light receiving element that can be omitted.

  As described above, the present invention is not limited to the configurations described in the above embodiments and the like, and those skilled in the art can devise various modifications based on the basic technical idea and teachings disclosed above. Things are self-explanatory.

  As described above, the present invention can receive light of a desired wavelength selected from a wide range from infrared to ultraviolet, and is manufactured at a low cost with a simple process while ensuring sufficient performance. It is clear that this is a new and useful device that can provide a simple and reliable semiconductor light-receiving element.

It is a figure which shows the example of 1 structure of the light receiving element of this invention. It is a figure which shows a conventional structure.

Explanation of symbols

L incident light 1 light receiving element 2 crystal substrate 3 buffer layer 4 light sensitive layer 4a light receiving surface 5 Schottky electrode 6 pad electrode 7 electrode on the other side 20, 30 light receiving element 21, 31 substrate 22, 32 n-GaN layers 23, 33 Photosensitive layer 24, 34 Mesa structure 25, 35 Schottky electrode 26, 36 Bias power supply 27, 37 Ohmic electrode

Claims (10)

A semiconductor light receiving element,
A crystal substrate made of a Si-based semiconductor exhibiting conductivity;
A buffer layer formed on one surface of the crystal substrate;
A photosensitive layer made of an insulating group III nitride material, formed at least one layer above the buffer layer;
A Schottky electrode, which is provided on one surface of the light-sensitive layer serving as a light-receiving surface, and is one electrode constituting the light-receiving element;
An electrode on the other side constituting a light receiving element provided on the other surface of the crystal substrate;
A light receiving element comprising: The light receiving element according to claim 1, wherein the crystal substrate is made of n-type SiC, and the buffer layer is made of n-type Al _y Ga _1-y N (0 ≦ y ≦ 1).   The light receiving element according to claim 1, wherein the crystal substrate is made of n-type Si, and the buffer layer is made of n-type SiC. The crystal substrate is made of n-type Si, and the buffer layer is made of n-type Al _u Ga _1-u N (0 ≦ u ≦ 1) and n-type Al _v Ga _1-v N (0 ≦ v ≦ 1, v ≠ u The light receiving element according to claim 1, wherein the light receiving element has a superlattice structure. The crystal substrate is made of n-type Si, and the buffer layer is made of n-type SiC, n-type Al _u Ga _1-u N (0 ≦ u ≦ 1), and n-type Al _v Ga _1-v N (0 ≦ v ≦ 1). , V ≠ u), and the light receiving element according to claim 1. The photosensitive layer is made of Al _x Ga _y In _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y <1, x + y ≦ 1). The light receiving element according to item 1.   The Schottky electrode is formed of a light-transmitting metal thin film that is transparent to the wavelength of light to be detected, and is formed so as to cover substantially the entire surface of the light receiving surface. The light receiving element according to any one of 6.   The light receiving element according to claim 1, wherein the electrode on the other side is an ohmic electrode.   The P-type group III nitride semiconductor layer is further provided between the photosensitive layer and the electrode on the one side, and the electrode on the one side is an ohmic electrode. The light receiving element according to claim 1.   10. The photosensitive layer is formed by at least one growth method of metal organic chemical vapor deposition (MOCVD), molecular beam growth (MBE), or hydride method (HVPE). The light receiving element according to any one of the above.

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