Ultraviolet detector

Abstract

This ultraviolet detector comprises an n-type semiconductor layer composed of silicon doped with at least one element selected from the group consisting of a group V element and a group VI element, and an uneven structure including silicon in which a period p is set so that surface plasmon resonance is excited by ultraviolet rays is provided on a light irradiation surface.

Description

UV detector

[0001] The present disclosure relates to ultraviolet detectors.

[0002] Recent advances in semiconductor lithography technology have led to an increasing demand for ultraviolet sensors in biomedical applications, such as the detection of microorganisms. Photoconductive detectors using wide bandgap semiconductors such as GaN and CdS have been developed as highly sensitive ultraviolet sensors (see, for example, Non-Patent Document 1).

[0003] Abhishek Dubey et al., “Aluminum Plasmonics Enriched Ultraviolet GaN Photodetector with Ultrahigh Responsibility, Detectivity, and Broad Bandwidth”, Adv.Sci. 2020 7, 2002274

[0004] Photoconductive detectors using wide bandgap semiconductors such as GaN and CdS, as described in Non-Patent Document 1, have high detection sensitivity but high material and manufacturing costs, limiting their applications. For this reason, silicon (Si) photodiodes, which are used as visible light sensors, are commonly used in consumer ultraviolet sensors. However, the Si photodiode's pn junction provides a surface p-type semiconductor layer (insensitive layer) that absorbs most of the ultraviolet light, resulting in low detection sensitivity. In order to increase detection sensitivity, it is necessary to inject dopants (impurities) to form an extremely thin surface p-type semiconductor layer, but this is technically difficult.

[0005] The present disclosure has been made in view of the above, and aims to provide an ultraviolet detector that can achieve both cost reduction and high detection sensitivity.

[0006] Specific means for achieving the above object are as follows. <1> An ultraviolet detector including an n-type semiconductor layer made of silicon doped with at least one element selected from the group consisting of group V elements and group VI elements, wherein a silicon-containing concavo-convex structure having a period p set so that surface plasmon resonance is excited by ultraviolet light is provided on a light irradiation surface. <2> The ultraviolet detector according to <1>, wherein the concavo-convex structure is provided on the light irradiation surface of the n-type semiconductor layer. <3> The ultraviolet detector according to <1> or <2>, wherein the concavo-convex structure has periodicity in one direction in plan view. <4> The ultraviolet detector according to any one of <1> to <3>, wherein the period p is 100 nm to 300 nm. <5> The ultraviolet detector according to any one of <1> to <4>, wherein the doped element is at least one selected from the group consisting of phosphorus, arsenic, antimony, and selenium. <6> The ultraviolet detector according to any one of <1> to <5>, wherein the duty ratio of the concavo-convex structure is 0.1 to 0.9. <7> The ultraviolet detector according to any one of <1> to <6>, wherein the height of the convex portions in the concave-convex structure is 10 nm to 100 nm.

[0007] The present disclosure can provide an ultraviolet detector that can achieve both cost reduction and high detection sensitivity for ultraviolet light.

[0008] 1 is a schematic diagram showing a photoconductive detector in which an uneven structure is provided on the light irradiation surface of an n-type semiconductor layer made of silicon. 2 is a graph showing the analysis results of the reflection spectrum of TM incident light in the photoconductive detector of the example. 3 is a graph showing the results of the ultraviolet output and the detected photocurrent value in the ultraviolet detectors of the example and the comparative example.

[0009] Modes for carrying out the present disclosure are described in detail below. However, the present disclosure is not limited to the following embodiments. In the present disclosure, components (including elementary steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples. In the present disclosure, the terms "layer" or "film" include cases where the layer or film is formed over the entire region when the region where the layer or film is present is observed, as well as cases where the layer or film is formed only over a portion of the region. In the present disclosure, the height of a protrusion is defined as the arithmetic average of the heights of five protrusions measured. The ultraviolet light irradiated onto the ultraviolet detector is, for example, light in the wavelength range of 100 nm to 400 nm, and may be light in the wavelength range of 100 nm to 280 nm. In the examples described below, light in the wavelength range of 266 nm is used as an example, but the present disclosure is not limited to this.

[0010] The ultraviolet detector of the present disclosure includes an n-type semiconductor layer made of silicon doped with at least one element selected from the group consisting of group V elements and group VI elements, and a concavo-convex structure including silicon with a period p set so that surface plasmon resonance is excited by ultraviolet light is provided on the light irradiation surface.

[0011] The ultraviolet detector disclosed herein has improved sensitivity to ultraviolet light compared to a detector without a textured structure on the light irradiation surface. The reason for this is presumed to be as follows: When light is irradiated onto a metal surface with a periodic textured structure, surface plasmon resonance is excited by the resonant vibration of the light electric field and free electrons, and an enhanced electric field is formed near the metal surface. Silicon has a negative dielectric constant in the deep ultraviolet region and exhibits a metallic response to deep ultraviolet light. In light of these properties, by providing a textured structure containing silicon on the light irradiation surface, surface plasmon resonance is excited by ultraviolet light, improving the detection sensitivity of ultraviolet light.

[0012] It is possible to form a textured structure on the surface of silicon using CMOS transistor lithography technology, and the ultraviolet detector of the present disclosure can be easily fabricated compared to ultraviolet detectors that use wide bandgap semiconductors such as GaN and CdS, or metal nanostructures, etc., allowing for reduced manufacturing costs.

[0013] The ultraviolet detector of the present disclosure can be used as an ultraviolet sensor for biomedical applications, microbial detection, and the like.

[0014] The ultraviolet detector of the present disclosure has a silicon-containing uneven structure provided on the light irradiation surface, and for example, the uneven structure may be provided on the light irradiation surface of an n-type semiconductor layer. This makes the ultraviolet detector of the present disclosure a photoconductive ultraviolet detector. Photoconductive ultraviolet detectors can be manufactured more inexpensively because they do not require techniques such as dopant injection into an ultrathin p-type semiconductor layer or pn junction technology.

[0015] The ultraviolet detector of the present disclosure may be a photovoltaic ultraviolet detector including an n-type semiconductor layer and a p-type semiconductor layer and having a p-n junction. In this case, the p-type semiconductor layer may be located on the light irradiation surface side, and the light irradiation surface of the p-type semiconductor layer may be provided with an uneven structure.

[0016] The method for forming the n-type semiconductor layer and the p-type semiconductor layer is not particularly limited, and examples thereof include a dopant injection method, etc. The method for forming the uneven structure is not particularly limited, and examples thereof include techniques such as lithography and dry etching.

[0017] In the preparation of the n-type semiconductor layer, the element doped into silicon is preferably at least one selected from the group consisting of phosphorus, arsenic, antimony, and selenium, and from the viewpoint of cost, is more preferably phosphorus or arsenic.

[0018] In the preparation of the p-type semiconductor layer, the element doped into silicon may be at least one element selected from the group consisting of group II elements and group III elements. Examples of the element doped into silicon include boron, aluminum, and indium, and boron is more preferred from the viewpoint of cost.

[0019] The shape of the uneven structure provided on the light irradiation surface of the ultraviolet detector is not particularly limited, and examples thereof include the shape of the convex or concave portions in the uneven structure being a polygonal shape such as a quadrangular prism, a triangular prism, a cylindrical shape, etc. The uneven structure may have convex or concave portions two-dimensionally arranged in a triangular lattice or a square lattice. This makes it possible to obtain an ultraviolet detector that is not polarization dependent. The uneven structure may have periodicity in one direction in a plan view, and for example, slit-shaped convex portions may be arranged in the vertical or horizontal direction. This makes it possible to obtain an ultraviolet detector that is polarization dependent.

[0020] The period p is preferably 100 nm to 300 nm, and more preferably 150 nm to 250 nm. The period p of the concave-convex structure is not particularly limited as long as it is set to a value that allows surface plasmon resonance to be excited at the interface between air and the silicon-containing concave-convex structure by ultraviolet light. As shown in the examples described below, the period p of the concave-convex structure described above is a value that varies when the wavelength of incident light, the angle of incidence, the material of the concave-convex structure, etc. are changed. The period p may be a value calculated from the conditional expression for surface plasmon resonance described below. Furthermore, the period p does not need to strictly match the value calculated from the conditional expression for surface plasmon resonance described below. When the calculated value is taken as p', p may be adjusted within a range satisfying 0.8×p'≦p≦1.2×p', or within a range satisfying 0.9×p'≦p≦1.1×p'.

[0021] The duty ratio of the concave-convex structure is preferably 0.1 to 0.9, and more preferably 0.25 to 0.75. The duty ratio refers to w / p, which is the ratio of the width w of the convex portions in the concave-convex structure to the period p of the concave-convex structure.

[0022] The height of the convex portions in the concave-convex structure is preferably 10 nm to 100 nm, and more preferably 30 nm to 100 nm.

[0023] The width of the convex portions in the concave-convex structure is preferably 30 nm to 200 nm, and more preferably 50 nm to 150 nm.

[0024] The ratio of the total area of ​​the convex portions in a plan view of the concave-convex structure to the total area of ​​the concave-convex structure (total area of ​​the convex portions and concave portions) may be, for example, 0.2 to 0.8, or 0.4 to 0.6.

[0025] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to the following examples.

[0026] Example: A photoconductive detector 10 was investigated, in which a concave-convex structure 2 was provided on the light-irradiated surface of an n-type semiconductor layer 1 made of silicon, as shown in FIG. 1 . First, a concave-convex structure was formed on the surface of an n-type semiconductor substrate made of silicon using lithography. Specifically, resist patterning was performed using electron beam lithography, and a concave-convex structure corresponding to the resist pattern was fabricated using reactive ion etching (RIE). While patterning was performed using electron beam lithography, this method is not limited thereto; for example, semiconductor lithography techniques for CMOS processes may also be used. The fabricated concave-convex structure had slit-shaped convex portions arranged in one direction in a planar view, with a period p of 210 nm, a convex width of 100 nm, a convex height of 35 nm, and a duty ratio of 0.5. Here, the period p refers to the sum of the widths of adjacent convex portions and concave portions at their bottoms. The period p was investigated so that surface plasmon resonance is excited at the interface between air and the concave-convex structure for TM light with a wavelength of 266 nm incident from above the concave-convex structure. The conditional expression for surface plasmon resonance at the interface between air and the concave-convex structure (also referred to as the Air / Si interface) is given by the following formula (1):

[0027]

[0028] In the above formula (1), k ｓｐ is the wave number of the surface plasmon, and k ０ is the wave number of the incident light, θ is the angle of incidence, m is the diffraction order, p is the period of the uneven structure, and ε Air is the dielectric constant of air, and ε Ｓｉ is the dielectric constant of the silicon that forms the concave-convex structure. As shown in equation (2), for TM incident light (θ=0) with a wavelength of 266 nm from above the concave-convex structure, the wave number K of the structural period vector and the wave number k of the first-order (m=1) surface plasmon ＳＰ We investigated how to improve the light absorption rate by matching the

[0029]

[0030] The period p of the concave-convex structure was calculated based on formula (2) and was found to be 252 nm. Note that the period p of the concave-convex structure that satisfies the surface plasmon resonance condition is a value that varies when the wavelength of the incident light, the angle of incidence, the diffraction order, the material of the concave-convex structure, etc. are changed, and is not limited to the above value in the present invention. Furthermore, the wave number K of the structural period vector and the wave number k of the surface plasmon other than the first order (e.g., second order, third order) are ＳＰ Even when the above two materials are matched, the light absorption rate can be improved.

[0031] (Analysis of Reflection Spectrum of TM Incident Light) The reflection spectrum of TM incident light was analyzed for each structural parameter determined as described above. The results are shown in FIG. 2. The spectral characteristics of the reflectance (Reflectance) for TM incident light at each wavelength (220 nm to 500 nm) are indicated by (2) in FIG. 2. As shown in FIG. 2, the reflectance exhibited a minimum value near a wavelength of 266 nm, and ultraviolet absorption increased. The results in FIG. 2 confirmed that surface plasmon resonance was excited at a wavelength of 266 nm, reducing the reflectance and improving the absorption efficiency. Furthermore, although the period p of the concave-convex structure calculated from equation (2) was 252 nm, it was confirmed that even when the period p of the concave-convex structure was 210 nm as in the experiment, the absorption efficiency improved due to excitation of surface plasmon resonance at a wavelength of 266 nm. These results confirmed that the effects of the present invention can be obtained even without setting the period p to completely satisfy the conditional expression for surface plasmon resonance. For example, when the period obtained from the conditional equation for surface plasmon resonance is p' (252 nm in this embodiment) and the period of the actual uneven structure is p (210 nm in this embodiment), p may be adjusted within a range of 0.8×p'≦p≦1.2×p', or within a range of 0.9×p'≦p≦1.1×p'. Note that (1) in Figure 2 shows the spectral characteristics of the reflectance for TE incident light of each wavelength for reference.

[0032] The sensitivity to ultraviolet light with a wavelength of 266 nm was examined for a photoconductive detector (Example) in which a textured structure was provided on the light-irradiated surface of an n-type semiconductor layer made of silicon as shown in FIG. 1 , and an n-type semiconductor made of silicon (Comparative Example) in which a textured structure was not provided on the light-irradiated surface. The ultraviolet sensitivity was determined from the photocurrent values ​​detected when the ultraviolet detectors of the Example and Comparative Example were irradiated with ultraviolet light having the output shown in FIG. 3 . The applied voltage was 7 V. The ultraviolet detector of the Example had an ultraviolet sensitivity of 180.8 mA / W, while the ultraviolet detector of the Comparative Example had an ultraviolet sensitivity of 56.3 mA / W. The Example achieved an ultraviolet sensitivity approximately 3.2 times higher than that of the Comparative Example. It is believed that this is because the silicon surface was provided with a periodic textured structure, which excited surface plasmon resonance and improved ultraviolet sensitivity.

[0033] The disclosure of Japanese Patent Application No. 2023-192445, filed November 10, 2023, is incorporated herein by reference in its entirety.

[0034] 1 n-type semiconductor layer 2 uneven structure 10 photoconductive detector

Claims

1. An ultraviolet detector comprising an n-type semiconductor layer made of silicon doped with at least one element selected from the group consisting of group V elements and group VI elements, wherein a surface plasmon structure containing silicon with a period p set so as to excite surface plasmon resonance by ultraviolet light is provided on the light irradiation surface between electrodes of the n-type semiconductor layer.

2. An ultraviolet detector having a pn junction comprising an n-type semiconductor layer made of silicon doped with at least one element selected from the group consisting of group V and group VI elements, and a p-type semiconductor layer made of silicon doped with at least one element selected from the group consisting of group II and group III elements, wherein a surface plasmon resonance is excited by ultraviolet light, and a surface irradiation surface containing silicon with a period p is provided on the light irradiation surface between the electrodes of the n-type semiconductor layer or the light irradiation surface between the electrodes of the p-type semiconductor layer.

3. The ultraviolet detector according to claim 1 or claim 2, wherein the uneven structure is an uneven structure having periodicity in one direction when viewed from above.