Thermoelectric photodetector device

Abstract

There is provided a thermoelectric photodetector device including: a substrate; an array of resonant nanostructures formed at a portion of the substrate; a first thin film of thermoelectric material of a first conductivity type including a thermocouple portion disposed over the array of resonant nanostructures, the first thin film extends from the thermocouple portion to connect to an electrode; and a second thin film of thermoelectric material of a second conductivity type including a thermocouple portion disposed over the array of resonant nanostructures, the second thin film extends from the thermocouple portion to connect to another electrode. In particular, the thermocouple portion of the first thin film and the thermocouple portion of the second thin film overlap with each other to form a thin film stack coating the array of resonant nanostructures. In this regard, the thin film stack constitutes a thermocouple region including a thermoelectric junction. There is also provided a method of fabricating the thermoelectric photodetector device.

Description

THERMOELECTRIC PHOTODETECTOR DEVICECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore Patent Application No. 10202400596T, filed 5 March 2024, the content of which being hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] The present invention generally relates to a thermoelectric photodetector device and a method of fabricating the thermoelectric photodetector device.BACKGROUND

[0003] Photodetection is a critical process used in various devices and technologies such as cameras, light sensors, solar cells, and optical communications. The applications exploit a broad spectrum of light from visible to far-infrared wavelengths. Traditional photodetectors primarily utilize semiconductors or resistive bolometers. Semiconductors are known for their speed and sensitivity but are ineffective at detecting lower energy light beyond their bandgap. For wavelengths below this threshold, conventionally, resistive bolometers are used, offering efficient detection but with slow speed. More recently, a photodetector design has emerged, combining the thermoelectric effect and optical resonance effects to enable rapid light detection without a wavelength cutoff (see Mauser, et al., “Resonant Thermoelectric Nanophotonics”, Nature Nanotechnology, August 2017, 12(8): pages 770-775 (hereinafter referred to as the Mauser reference)). In this photodetector design, localized absorption occurs in thermoelectric nanowires, leading to localized heating and the generation of substantial thermal gradients under non-focused optical excitation.

[0004] Due to the Seebeck effect, these thermal gradients lead to a non-uniform distribution of charge carriers, resulting in an electric potential difference. However, the primary limitation of conventional thermoelectric photodetectors has been their relatively low photosensitivity, which limits their practical applications. Therefore, enhancing the optical absorption of thermoelectric materials is a key factor for improving detection efficiency. Previous reports have explored methods such as using metasurfaces made of metals as an absorber material (i.e , a metasurface absorber), essentially using an indirect absorption approach. In addition, as mentioned above, there was previously reported a thermoelectric photodetector based onthermocouple nanowires using engineered thermoelectric material with resonance itself as the absorber (see the above-mentioned Mauser reference). Nonetheless, the overall optical absorptance has remained below 60% in the visible range.

[0005] A need therefore exists to provide a thermoelectric photodetector device (or simply referred to as a thermoelectric photodetector) that seek to overcome, or at least ameliorate, one or more of the deficiencies of conventional thermoelectric photodetectors, and more particularly, with enhanced optical absorption for improving photosensitivity or detection efficiency. It is against this background that the present invention has been developed.SUMMARY

[0006] According to a first aspect of the present invention, there is provided a thermoelectric photodetector device comprising: a substrate; an array of resonant nanostructures formed at a portion of the substrate; a first thin film of thermoelectric material of a first conductivity type comprising a thermocouple portion disposed over the array of resonant nanostructures, the first thin film extends from the thermocouple portion to connect to an electrode; and a second thin film of thermoelectric material of a second conductivity type comprising a thermocouple portion disposed over the array of resonant nanostructures, the second thin film extends from the thermocouple portion to connect to another electrode, wherein the thermocouple portion of the first thin film and the thermocouple portion of the second thin film overlap with each other to form a thin film stack coating the array of resonant nanostructures, the thin film stack constituting a thermocouple region comprising a thermoelectric junction.

[0007] According to a second aspect of the present invention, there is provided a method of fabricating a thermoelectric photodetector device, the method comprising: providing a substrate; forming an array of resonant nanostructures at a portion of the substrate; forming a first thin film of thermoelectric material of a first conductivity type comprising a thermocouple portion disposed over the array of resonant nanostructures, the first thin film extends from the thermocouple portion to connect to an electrode; andforming a second thin film of thermoelectric material of a second conductivity type comprising a thermocouple portion disposed over the array of resonant nanostructures, the second thin film extends from the thermocouple portion to connect to another electrode, wherein the thermocouple portion of the first thin film and the thermocouple portion of the second thin film overlap with each other to form a thin film stack coating the array of resonant nanostructures, the thin film stack constituting a thermocouple region comprising a thermoelectric junction.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Embodiments of the present invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:FIG. 1 depicts a schematic drawing of a side cross-sectional view of a thermoelectric photodetector device, according to various embodiments of the present invention;FIG. 2 depicts a schematic diagram of a method of fabricating a thermoelectric photodetector device, according to various embodiments of the present invention;FIG. 3 depicts a schematic drawing of a side cross-sectional view of an example thermoelectric photodetector with example materials shown, according to various example embodiments of the present invention;FIGs. 4A and 4B depict SEM (scanning electron microscope) images of a portion of an array of Sb2Te3-coated nanoposts at different imaging angles, whereby FIG. 4A shows the plane-view and FIG. 4B shows the 55-degrees tilted view;FIGs. 4C and 4D depict SEM images of a portion of an array of SbiTej-coated nanorings at different imaging angles, whereby FIG. 4C shows the plane-view and FIG. 4D shows the 55- degrees tilted view;FIG. 5 depicts a reflection image (captured by a microspectrophotometer) of a top view of an example thermoelectric photodetector (which may be referred to as a cascaded thermoelectric photodetector) with multiple arrays of resonant nanostructures formed at example multiple portions of the substrate, according to various example embodiments of the present invention;FIG. 6A shows a plot of the optical absorbance of Sb2Te3 / Bi2Te3 films, with and without nanostructures;FIG. 6B shows the enhancement factor for the optical absorption of Sb2Te3 / Bi2Te3 films with nanostructures compared to that without nanostructures; andFIGs. 7A and 7B depict plots of reversible switching of the example cascaded thermoelectric photodetector illuminated at 405 nm and 605 nm wavelengths, respectively.DETAILED DESCRIPTION|0009| Various embodiments of the present invention provide a thermoelectric photodetector device and a method of fabricating the thermoelectric photodetector device.

[0010] As discussed in the background, conventional thermoelectric photodetectors have relatively low photosensitivity, which limits their practical applications. Therefore, enhancing optical absorption of thermoelectric materials is a key factor for improving photosensitivity or detection efficiency Tn this regard, various embodiments of the present invention provide a thermoelectric photodetector device that seek to overcome, or at least ameliorate, one or more of the deficiencies of conventional thermoelectric photodetectors, and more particularly, with enhanced optical absorption for improving photosensitivity or detection efficiency.

[0011] FIG. 1 depicts a schematic drawing of a side cross-sectional view of a thermoelectric photodetector device 100, according to various embodiments of the present invention. The thermoelectric photodetector device 100 comprises: a substrate 110; an array 120 (e.g., two- dimensional (2D) array) of resonant nanostructures formed at a portion of the substrate 1 10; a first thin film 130 of thermoelectric material of a first conductivity type (e.g., n-type) comprising a thermocouple portion 132 disposed over the array 120 of resonant nanostructures, the first thin film 130 extends from the thermocouple portion 132 to connect to an electrode 140; and a second thin film 150 of thermoelectric material of a second conductivity type (e.g., p-type) comprising a thermocouple portion 152 disposed over the array 120 of resonant nanostructures, the second thin film 150 extends from the thermocouple portion 152 to connect to another electrode 160. In particular, the thermocouple portion 132 of the first thin film 130 and the thermocouple portion 152 of the second thin film 150 overlap with each other (or are stacked over each other) to form a thin film stack coating the array 120 of resonant nanostructures. Accordingly, the thin film stack comprises the thermocouple portion 132 of the first thin film 130 and the thermocouple portion 152 of the second thin film 130 formed to overlap (e g., substantially or fully overlap) and be in contact (the two contact surfaces of the thermocouple portions 132, 152 facing each other) with each other. Accordingly, the thin film stack constitutes a thermocouple region comprising a thermoelectric junction formed betweenthe thermocouple portions 132, 152 (between the two contact surfaces of the thermocouple portions 132, 152). As a result of forming the thin film stack to coat the array 120 of resonant nanostructures, the thin film stack conforms to, or is shaped by, the extemal / exterior shape of the array 120 of resonant nanostructures, thereby forming nanopattemed or nanostructured thermoelectric material thin films (at the thermocouple region) and resulting in the array of thin film coated resonant nanostructures.100121 Accordingly, with the thin film stack configured to constitute a thermocouple region comprising a thermoelectric junction formed between the thermocouple portions 132, 152 (which may be referred to as a thermocouple pair), it can be understood by a person skilled in the art that the thermoelectric photodetector device 100 operates based on the photo- thermoelectric (PTE) effect. The PTE effect is known to a person skilled in the art and thus need not be described in detail herein. In general, the PTE effect is based on the photothermal conversion and thermoelectric effect (i.e., the Seebeck effect). Light incident on the thin film stack (thermocouple region) is absorbed and converted into heat at the thermoelectric junction (or the thermoelectric p-n junction), which may be referred to as the photothermal response. This increase in temperature at the thermoelectric junction produces a temperature gradient to the two thermoelectric leads (e.g., a first thermoelectric lead portion corresponding to a portion (non-resonant portion) of the first thin film 130 extending from the thermocouple portion 132 to the electrode 140 and a second thermoelectric lead portion corresponding to a portion (non- resonant portion) of the second thin film 150 extending from the thermocouple portion 152 to the other electrode 160), thereby establishing an electric potential (known as the Seebeck voltage) across the temperature gradient, which may be referred to as the thermoelectric response. Accordingly, in various embodiments, the thermoelectric photodetector device 100 is configured to enable region selective photo-absorption whereby photo-absorption is large, enhanced or maximized at the thin film stack (thermocouple region) and minimal at the thermoelectric lead portions.

[0013] The thermoelectric photodetector device 100 advantageously possesses enhanced optical absorption, and thus, also possesses improved photosensitivity or detection efficiency. In particular, various embodiments of the present invention found that by forming the thin film stack (comprising the thermocouple portions 132, 152 of the first and second thin films 130, 150 of thermoelectric materials) over the array 120 of resonant nanostructures, thereby coating the array 120 of resonant nanostructures with the thin film stack, an array of thin film coated resonant nanostructures is advantageously formed with the thin film stack conforming to, orshaped by, the external / exterior shape of the array 120 of resonant nanostructures. Such an array of thin film coated resonant nanostructures, or such a configuration of the thin film stack (nanopatterned or nanostructured thermoelectric material thin films), has been surprisingly found to significantly enhance optical absorption, thereby significantly improving photosensitivity or detection efficiency of the thermoelectric photodetector device 100. In particular, such a configuration of the thin film stack with the array 120 of resonant nanostructures has been found to significantly enhance optical absorption of the thin film stack comprising the thermocouple portions 132, 152 of the first and second thin films 130, 150 of thermoelectric materials. These advantages or technical effects, and / or other advantages or technical effects, will become more apparent to a person skilled in the art as the thermoelectric photodetector device 100 is described in more detail according to various embodiments and example embodiments of the present invention.

[0014] In various embodiments, the thermoelectric photodetector device 100 further comprises one or more additional arrays (e.g., 2D array) of resonant nanostructures (not shown in FIG. 1) formed at one or more additional portions of the substrate 110, respectively. In various embodiments, each additional array of resonant nanostructures may have the same or similar configuration as the above-mentioned array 120 (which may be referred to as a first array) of resonant nanostructures. For each additional array of resonant nanostructures, the thermoelectric photodetector device 100 further comprises: a first thin film of thermoelectric material of the first conductivity type (e.g., n-type) comprising a thermocouple portion disposed over the additional array of resonant nanostructures, the first thin film extends from the thermocouple portion to connect to an electrode; and a second thin film of thermoelectric material of the second conductivity type (e.g., p-type) comprising a thermocouple portion disposed over the additional array of resonant nanostructures, the second thin film extends from the thermocouple portion to connect to another electrode. In the same or similar manner as the first and second thin films 130, 150 associated with the array 120 of resonant nanostructures described above, the thermocouple portion of the first thin film and the thermocouple portion of the second thin film associated with the additional array of resonant nanostructures overlap with each other to form a thin film stack coating the additional array of resonant nanostructures. Accordingly, the thin film stack constitutes a thermocouple region comprising a thermoelectric junction formed between the thermocouple portions (between the two contact surfaces of the thermocouple portions) of the first and second thin films. In the same or similar manner as the first and second thin films 130, 150 associated with the array 120 of resonant nanostructuresdescribed above, as a result of forming the thin film stack to coat the additional array of resonant nanostructures, the thin film stack conforms to, is shaped by, the extemal / exterior shape of the additional array of resonant nanostructures, thereby forming nanopatterned thermoelectric material thin films (at the thermocouple region) and resulting in the additional array of thin film coated resonant nanostructures. Tn various embodiments, each additional array of thin film coated resonant nanostructures is configured in the same or similar manner as the array of thin film coated resonant nanostructures described above. Therefore, in the same or similar manner as the array of thin film coated resonant nanostructures described above, each additional array of thin film coated resonant nanostructures also has significantly enhanced optical absorption, thereby significantly improving photosensitivity or detection efficiency of the thermoelectric photodetector device 100.

[0015] Tt will be appreciated by a person skilled in the art that the present invention is not limited to any particular or specific number of arrays of resonant nanostructures (and thus, any particular or specific number of arrays of thin film coated resonant nanostructures) formed at the substrate 110, which may be determined or configured as desired or as appropriate. Furthermore, it will also be appreciated by a person skilled in the art that the present invention is not limited to any particular or specific portion(s) of or locations at the substrate 110 to form the array(s) of resonant nanostructures, which may be determined or configured as desired or as appropriate.

[0016] In various embodiments, the first and second thin films 130, 150 associated with the array 120 of resonant nanostructures together form a first strip of thin films (e.g., extending between the corresponding opposite electrodes 140, 160). Similarly, for each additional array of resonant nanostructures, the first and second thin films associated with the additional array of resonant nanostructures together form an additional strip of thin films (e g., extending between the corresponding opposite electrodes). Furthermore, in various embodiments, the first strip of thin films and each additional strip of thin films are connected in series. For example, the first strip of thin films and each additional strip of thin films may be connected in series to have a cascaded configuration, and such a thermoelectric photodetector may be referred to as a cascaded thermoelectric photodetector.

[0017] In various embodiments, the thermoelectric material of the first conductivity type is an n-type thermoelectric material, and the thermoelectric material of the second conductivity type is a p-type thermoelectric material.

[0018] In various embodiments, the n-type thermoelectric material comprises or is n-type bismuth telluride (Bi2Te3) thermoelectric material, and the p-type thermoelectric material comprises or is p-type antimony telluride (Sb2Te3) thermoelectric material. Although Bi2Te3 and SbiTes may be preferred or particularly suitable for the thermoelectric photodetector device 100 according to various embodiments of the present invention, such as due to their thermoelectric properties being particularly suitable for producing the photo-thermoelectric (PTE) effect, it will be understood by a person skilled in the art that the thermoelectric photodetector device 100 is not limited to such specific materials for the first and second thin films and other materials may be utilized as desired or as appropriate, such as based on various material properties (e g., Seebeck coefficients, electrical conductivities and thennal conductivities). In general, any thermoelectric materials that can be nanostructured to enhance optical absorption can be used, such as but not limited to, GeTe, Bi2Se3, PbTe, Si-Ge alloys, SnSe and so on.

[0019] In various embodiments, the resonant nanostructures are each configured as a nanopillar. In various embodiments, the nanopillar is a nanopost, a nanoring or a nanoellipse. It will be appreciated by a person skilled in the art that, while certain types or geometries of nanopillar may have certain corresponding advantages, the present invention is not limited to any particular or specific type of nanopillar, which may be configured or chosen as desired or as appropriate. For example, various types or geometries may be configured for supporting field enhancement to further enhance or optimize device functionality. As an illustrative example, the resonant nanostructures may be configured as nanoellipses, whereby the ellipse orientation and elongation may be configured or controlled to optimize polarization-dependent optical effects in photonic applications. In various embodiments, the resonant nanostructures are each configured to be the same (same type, geometry and size).

[0020] In various embodiments, the array 120 of resonant nanostructures is a periodic array of resonant nanostructures. In various embodiments, each additional array of resonant nanostructures is a periodic array of resonant nanostructures. It will be appreciated by a person skilled in the art that the present invention is not limited to any particular or specific array size for the resonant nanostructures, which may be determined or configured as desired or as appropriate. It will also be appreciated by a person skilled in the art that the arrangement of resonant nanostructures (e g., within an array) on the substrate 1 10 may be configured or optimized for device performance, by influencing properties such as light trapping and plasmonic resonance For example, in addition to the geometry of the resonant nanostructures,the periodicity and pitch size of the resonant nanostructures within an array may be configured or optimized for device performance, as they directly influence optical interference and electronic properties. For example, pitch sizes in the range of 200-500 nm may optimize lightmatter interactions, while sub-200 nm features may enhance quantum confinement effects in semiconductor applications Therefore, it will be appreciated by a person skilled in the art that various properties of the array(s) of resonant nanostructures may be configured or optimized as desired or as appropriate, such as but not limited to, with respect the geometry, periodicity and pitch size, without going beyond the scope of the present invention. In various embodiments, any type of nanostructured surface that exhibits field enhancements is within the scope of the present invention.

[0021] It can be understood by a person skilled in the art that nanostructures refer to structures having geometrical dimensions (e.g., at least a width) of 10'9to 10'6m (i.e., nanoscale). It will be appreciated by a person skilled in the art that the size or dimension (e.g., a width) of the nanostructures may be configured or optimized as desired or as appropriate, such as based on the optical properties of the material used, the type of resonant absorption, and / or the range of wavelengths that the nanostructures are designed for. Therefore, it will be appreciated by a person skilled in the art that the resonant nanostructures described herein according to various embodiments are not limited to any specific nanoscale size, which may be configured or optimized as desired or as appropriate As an illustrative example, in the case of SbiTe^ and BijTes nanostructures, which exploit plasmonic resonances for wavelengths 400- 800 nm, the size of the nanostructures may range from 50-250 nm, and the thickness of the thin films may range from 10-100 nm. Therefore, the thicknesses of the thin films described herein according to various embodiments are also not limited to any specific nanoscale size, which may be configured or optimized as desired or as appropriate. For example and without limitation, the size of the nanostructures may increase with the wavelength of light intended to be detected, and for example, nanostructures designed for infrared wavelengths may have sizes ranging from 500-1000 nm.

[0022] FIG. 2 depicts a schematic diagram of a method 200 of fabricating a thermoelectric photodetector device, according to various embodiments of the present invention, and more particularly, for fabricating the thermoelectric photodetector device 100 as described hereinbefore according to various embodiments of the present invention. The method 200 comprises: providing (at 202) a substrate 110; forming (at 204) an array 120 of resonant nanostructures at a portion of the substrate 1 10; forming (at 206) a first thin film 130 ofthermoelectric material of a first conductivity type (e.g., n-type) comprising a thermocouple portion 132 disposed over the array 120 of resonant nanostructures, the first thin film 130 extends from the thermocouple portion 132 to connect to an electrode 140; and forming (at 208) a second thin film 150 of thermoelectric material of a second conductivity type (e.g., p-type) comprising a thermocouple portion 152 disposed over the array 120 of resonant nanostructures, the second thin film 150 extends from the thermocouple portion 152 to connect to another electrode 160. In particular, as described above, the thermocouple portion 132 of the first thin film 130 and the thermocouple portion 152 of the second thin film 130 overlap with each other (or are stacked over each other) to form a thin film stack coating the array 120 of resonant nanostructures. Accordingly, the thin film stack constitutes a thermocouple region comprising a thermoelectric junction formed between the thermocouple portions 132, 152.

[0023] In various embodiments, the method 200 is for fabricating the thermoelectric photodetector device 100 as described hereinbefore according to various embodiments of the present invention, therefore, various steps or operations of the method 200 may correspond to forming, providing or configuring various components or portions of the thermoelectric photodetector device 100 as described herein according to various embodiments, and thus such corresponding steps or operations need not be described or repeated with respect to the method 200 for clarity or conciseness. In other words, various embodiments described herein in the context of the thermoelectric photodetector device 100 are analogously valid for the method 200 (e.g., for fabricating the thermoelectric photodetector device 100 having various components, portions and / or configurations as described hereinbefore according to various embodiments), and vice versa. It will also be appreciated by a person skilled in the art that the method 200 for fabricating the thermoelectric photodetector device 100 is not limited to any particular order of operations / steps, and may be performed in any order as desired or as appropriate. For example, FIG. 2 merely shows the presence of various operations / steps of the method 200 for fabricating the thermoelectric photodetector device 100, but does not limit the method 200 to any particular order of operations / steps. For example, referring to the thermoelectric photodetector device 100 shown in FIG. 1 as an illustrative example, in the case of the first and second thin films 130, 150 being formed using magnetron sputtering, it can be understood by a person skilled in the art that the second thin film 150 is deposited first, and then subsequently, the first thin film 130 is deposited

[0024] In various embodiments, the method 200 further comprises: forming one or more additional arrays of resonant nanostructures at one or more additional portions of the substrate110, respectively. In various embodiments, each additional array of resonant nanostructures may have a same or similar configuration as the above-mentioned array 120 (e.g., may be referred to as a first array) of resonant nanostructures. For each additional array of resonant nanostructures, the method 200 further comprises: forming a first thin film of thermoelectric material of the first conductivity type (e g., n-type) comprising a thermocouple portion disposed over the additional array of resonant nanostructures, the first thin film extends from the thermocouple portion to connect to an electrode; and forming a second thin film of thennoelectric material of the second conductivity type (e.g., p-type) comprising a thermocouple portion disposed over the additional array of resonant nanostructures, the second thin film extends from the thermocouple portion to connect to another electrode In the same or similar manner as the first and second thin films 130, 150 associated with the array 120 of resonant nanostructures described above, the thermocouple portion of the first thin film and the thermocouple portion of the second thin film associated with the additional array of resonant nanostructures overlap with each other to form a thin film stack coating the additional array of resonant nanostructures. Accordingly, the thin film stack constituting a thermocouple region comprising a thermoelectric junction formed between the thermocouple portions (between the two contact surfaces of the thermocouple portions) of the first and second thin films. For example, in the case that the first and second thin films associated with all arrays are formed using magnetron sputtering, it can be understood by a person skilled in the art that the second thin films associated with all arrays may be simultaneously deposited first, and then subsequently, the first thin films associated with all arrays may be simultaneously deposited.

[0025] In various embodiments, the array 120 of resonant nanostructures is formed at the portion of the substrate 110 based on electron-beam lithography (EBL), plasma etching, nanoimprint lithography (NIL), focused ion beam (FIB) milling or self-assembly. In various embodiments, each additional array of resonant nanostructures is also formed in the same or similar manner as the array 120 of resonant nanostructures. For example, Hydrogen Silsesquioxane (HSQ) is commonly used as a negative resist in EBL due to its high resolution, excellent etch resistance, and desirable optical properties such as a low refractive index and high transparency in the visible and near-infrared spectrum. However, it will be appreciated by a person skilled in the art that there are other materials that have similar properties to HSQ and may instead be applied to form the nanostructures on the substrate 1 10. For example, Polymethyl Methacrylate (PMMA), although a positive resist, can be modified for negativetone applications and is known for its transparency in the UV and visible spectra, making ituseful for optoelectronic devices. For example, EBL remains a high-resolution technique, however, other techniques may be applied instead as desired or as appropriate. For example, NIL is suitable for large-area replication of nanoscale features, providing a cost-effective alternative to EBL . FIB milling allows direct patterning of nanostructures without the need for resist materials, making it particularly useful for rapid prototyping. Self-assembly techniques can lead to spontaneous formation of nanopattems, reducing the reliance on lithography, while plasma etching provides high precision in defining nanoscale geometries. Accordingly, it will be appreciated by a person skilled in the art that the present invention is not limited to any particular or specific technique, or any particular or specific materials associated with the technique, for forming the resonant nanostructures on the substrate 110, and any technique or material may be used as desired or as appropriate.

[0026] In various embodiments, the first and second thin films 130, 150 associated with the array 120 of resonant nanostructures are formed based on magnetron sputtering (e.g., RF magnetron sputtering). In various embodiments, the first and second thin films associated with each additional array of resonant nanostructures are formed in the same or similar manner as the first and second thin films 130, 150 associated with the array 120 of resonant nanostructures.

[0027] It will be appreciated by a person skilled in the art that the terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0028] Any reference to an element or a feature herein using a designation such as “first”, “second” and so forth does not limit the quantity or order of such elements or features, unless stated or the context requires otherwise. For example, such designations may be used herein as a convenient way of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not necessarily mean that only two elements can be employed, or that the first element must precede the second element, unless stated or the context requires otherwise. In addition, a phrase referring to “at least one of’ a list of items refers to any single item therein or any combination of two or more items therein.

[0029] In order that the present invention may be readily understood and put into practical effect, various example embodiments of the present invention will be described hereinafter by way of examples only and not limitations. It will be appreciated by a person skilled in the art that the present invention may, however, be embodied in various different forms or configurations and should not be construed as limited to the example embodiments set forth hereinafter. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0030] In particular, for better understanding of the present invention and without limitation or loss of generality, various example embodiments of the present invention will now be described with respect to example thermoelectric photodetectors whereby the above-mentioned first thin film of thermoelectric material of the first conductivity type is n-type bismuth telluride (BizTes) thermoelectric material and the above-mentioned second thin film of thermoelectric material of the second conductivity type is p-type antimony telluride (SbiTes) thermoelectric material. As explained hereinbefore, it will be understood by a person skilled in the art that the thermoelectric photodetector is not limited to such specific materials for the first and second thin films and other materials may be utilized as desired or as appropriate.

[0031] Conventional photodetectors commonly use semiconductors that absorb photons with energies above the material bandgap. Unlike semiconductors, thermoelectric materials are not bandgap limited and have the potential to absorb photons across a much wider bandwidth. The photo-thermoelectric (PTE) effect, which converts light energy into electrical energy, holds great promise in optical detection. This technology finds applications in various fields, such as but not limited to, sensing, optoelectronic communications, and wide-temperature-range measurements However, practical applications involving conventional thermoelectric photodetectors have been limited due to the low photosensitivity. The initial step in photo- thermoelectric photodetection involves optical absorption, and thus, enhancing this optical absorption is a key factor for improving detection efficiency. In this regard, various example embodiments provide a thermoelectric photodetector device (or simply be referred to as a thermoelectric photodetector) that seek to overcome, or at least ameliorate, one or more of the deficiencies of conventional thermoelectric photodetectors, and more particularly, with enhanced optical absorption for improving photosensitivity or detection efficiency.

[0032] Various example embodiments address the technical challenge of low photosensitivity in conventional thermoelectric photodetectors by focusing on enhancing theoptical absorption of thermoelectric materials. While previous research has explored methods such as nanowire fabrication (the Mauser reference discussed in the background) and metasurfaces, various example embodiments introduce highly absorptive resonant nanostructures, comprising thermoelectric materials, formed on a substrate, and more particularly, resonant nanostructures coated with thin films of n-type ther oelectric material (e.g., n-type bismuth telluride (BizTes)) and p-type thermoelectric material (e.g., p-type antimony telluride (SbjTes)). In this manner, as a result of the thin film coated resonant nanostructures, nanopatterned or nanostructured thermoelectric material thin films (at the thermocouple region) are formed, which have been found to substantially improve optical absorption, reaching approximately 90%, thereby significantly improving photosensitivity or detection efficiency, and thus, significantly enhancing practical applications. For example, in experiments conducted as will be discussed later below, an example thermoelectric photodetector, comprising resonant nanostructures coated with thin films of n-type Bi? ei and p-type SbiTei, according to various example embodiments of the present invention demonstrated responsivities of about 2.0 V / W and 4.7 V / W illumination at 405 nm and 650 nm wavelengths, respectively.

[0033] In various example embodiments, the thermoelectric photodetector is advantageously capable of bidirectional photodetection. In this regard, the resonant nanostructures developed is not only capable of capturing light from the top side of the substrate (the side at which the resonant nanostructures are formed) but also from the bottom side of the substrate. This bidirectional photodetection feature adds versatility to the thermoelectric photodetector, making it suitable for a wider range of applications. For example, previous thermoelectric photodetectors may rely on external absorber materials that are unidirectional. In contrast, according to various example embodiments, the thermocouple portions of thermoelectric materials are directly fabricated or configured with nanostructures (nanopatterned or nanostructured thermoelectric material thin films) which provide intrinsic optical absorption within the thermocouple portions of the thermoelectric materials, which allows bidirectional capability of capturing light when they are fabricated on, for example, a transparent substrate.

[0034] FIG. 3 depicts a schematic drawing of a side cross-sectional view of an example thermoelectric photodetector 300 with example materials shown, according to various example embodiments of the present invention. The thermoelectric photodetector 300 comprises: a substrate 310; an array 320 (2D array) of resonant nanostructures formed at a portion of thesubstrate 310; a first thin film 330 of n-type BizTe3 comprising a thermocouple portion 332 disposed over the array 320 of resonant nanostructures, the first thin film 330 extends from the thermocouple portion 332 to connect to an electrode 340 (e.g., gold film); and a second thin film 350 of p-type SbiTes comprising a thermocouple portion 352 disposed over the array 320 of resonant nanostructures, the second thin film 350 extends from the thermocouple portion 352 to connect to another electrode 360 (e.g., gold film). As an illustrative example and without limitation, the first and second thin films 330, 350 may each have a thickness t of about 50 nm. For example, the electrodes 340, 360 may also each have a thickness t of about 50 nm. As explained hereinbefore, it will be appreciated by a person skilled in the art that the thicknesses of the first and second thin films 330, 350 and the electrodes 340, 360 may be configured as appropriate. As shown in FIG. 3, the thermocouple portion 332 of the first thin film 330 and the thermocouple portion 352 of the second thin film 350 overlap with each other (or are stacked over each other) to form a thin film stack coating the array 320 of resonant nanostructures. Accordingly, the thin film stack comprises the thermocouple portion 332 of the first thin film 330 and the thermocouple portion 352 of the second thin film 330 formed (e.g., deposited over the glass substrate 310) to overlap (e.g., substantially or fully overlap) and be in contact (the two contact surfaces of the thermocouple portions 332, 352 facing each other) with each other. Accordingly, the thin film stack constitutes a thermocouple region comprising a thermoelectric junction formed between the thermocouple portions 332, 352 (between the two contact surfaces of the thermocouple portions 332, 352). As a result of forming the thin film stack to coat the array 320 of resonant nanostructures, the thin film stack conforms to, or is shaped by, the extemal / exterior shape of the array 320 of resonant nanostructures, thereby forming nanopattemed or nanostructured thermoelectric material thin films (at the thermocouple region) and resulting in the array of thin film coated resonant nanostructures

[0035] Accordingly, the thermoelectric photodetector 300 is configured to operate based on the photo-thermoelectric (PTE) effect. In this regard, light incident on the thin film stack (thermocouple region) is absorbed and converted into heat at the thermoelectric p-n junction. This increase in temperature at the thermoelectric junction produces a temperature gradient to the two thermoelectric leads (e.g., a first thermoelectric lead portion corresponding to a portion (non-resonant portion) of the first thin film 330 extending from the thermocouple portion 332 to the electrode 340 and a second thermoelectric lead portion corresponding to a portion (non- resonant portion) of the second thin film 350 extending from the thermocouple portion 352 tothe other electrode 360), thereby establishing an electric potential (known as the Seebeck voltage) across the temperature gradient.

[0036] Accordingly, in various example embodiments, a thin film stack (comprising the thermocouple portions 332, 352 of the first and second thin films 330, 350 of n-type BizTes and p-type SbzTe;, respectively) is formed over the array 320 of resonant nanostructures to coat the array 320 of resonant nanostructures to form an array of thin film coated resonant nanostructures with the thin film stack conforming to the extemal / exterior shape of the array 320 of resonant nanostructures. Accordingly, in various example embodiments, the substrate 310 has a nanostructured surface at the above-mentioned portion thereof that is configured to exhibit or provide field enhancements. Such an array of thin film coated resonant nanostructures, or such a configuration of the thin film stack (nanopatterned thermoelectric material thin films), has been surprisingly found to significantly enhance optical absorption of the thin film stack, thereby significantly improving photosensitivity or detection efficiency of the thermoelectric photodetector device 300.

[0037] In various example embodiments, the resonant nanostructures are each configured as a nanopillar. For example, the nanopillar may be a nanopost, a nanoring (which may also be referred to as a nano-hole) or a nanoellipse. As an illustrative example, in the case of nanoposts, each nanopost may have a width of about 80 nm when uncoated. For example, after depositing about 50 nm of SbzT e3 to coat the nanoposts, the width of each nanopost increased to about 125 nm. As a further illustrative example, in the case of nanorings, each nanoring may have a width of about 120 nm when uncoated. For example, after depositing about 50 nm of SbzTes to coat the nanorings, the width of each nanoring increased to about 210 nm. It will be appreciated by a person skilled in the art that the present invention is not limited to any particular or specific type of nanopillar and any particular or specific size of the nanopillars, which may be configured or optimized as appropriate. For illustration purpose, SEM imaging (e.g., using JEOL JSM-7600F system) was used to examine the structural characteristics of the nanostructures. FIGs. 4A and 4B depict SEM images of a portion of an array of SbzTe^-coated nanoposts at different imaging angles, whereby FIG. 4A shows the plane-view and FIG. 4B shows the 55-degrees tilted view. FIGs. 4C and 4D depict SEM images of a portion of an array of SbzTes-coated nanorings at different imaging angles, whereby FIG. 4C shows the plane-view and FIG. 4D shows the 55-degrees tilted view.

[0038] In various example embodiments, multiple arrays (2D arrays) of resonant nanostructures are formed at multiple portions of the substrate, respectively. As an illustrativeexample, FIG. 5 depicts a reflection image (captured by a microspectrophotometer) of a top view of an example thermoelectric photodetector 500 with multiple arrays 520 of resonant nanostructures formed at example multiple portions of the substrate 510 (e g., five arrays formed at five portions, respectively, of the substrate 510 are shown in FIG. 5), according to various example embodiments of the present invention. In various example embodiments, each array 520 of resonant nanostructures is configured in the same or similar manner as the above- mentioned array 320 of resonant nanostructures described above. For each array 520 of resonant nanostructures, the thennoelectric photodetector 500 further comprises a first thin film 530 of n-type Bi2Te3 comprising a thermocouple portion disposed over the array 520 of resonant nanostructures, the first thin film 530 extends from the thermocouple portion to connect to an electrode 540; and a second thin film 550 of p-type Sb2Tes comprising a thermocouple portion disposed over the array 520 of resonant nanostructures, the second thin film 550 extends from the thermocouple portion to connect to another electrode 560. The thermocouple portion of the first thin film 530 and the thermocouple portion of the second thin film 550 are configured to overlap with each other to form a thin film stack coating the array 520 of resonant nanostructures, thereby forming nanopattemed or nanostructured thermoelectric material thin films (at the thermocouple region) and resulting in the array 520 of thin film coated resonant nanostructures, in the same or similar manner as the first and second thin films 330, 350 described above and thus need not be repeated for clarity and conciseness.

[0039] In various example embodiments, as can be seen in FIG. 5, for each array 520 of resonant nanostructures, the first and second thin films associated with the array 520 of resonant nanostructures together form a strip of thin films extending between the corresponding opposite electrodes 540, 560. Furthermore, as illustrated in FIG. 5, the strips of thin films associated with the arrays 520 of resonant nanostructures are connected in series to have a cascaded configuration, and thus, the example thermoelectric photodetector 500 may be referred to as a cascaded thermoelectric photodetector. In the cascaded configuration, as illustrated in FIG. 5, the two adjacent strips of each pair of adjacent strips of thin films may be connected to each other at one end thereof via a same or shared electrode in an alternating manner such that the strips of thin films are connected in series to have the cascaded configuration. For example, for a first pair of adjacent strips of thin films, a first end of the first pair of adjacent strips may be connected to each other via a first electrode. For the next pair (with respect to the first pair, which may be referred to as a second pair) of adjacent strips of thin films, a second end (opposite side to the first end with respect to the array 520 of resonant nanostructures) of the second pairof adjacent strips may be connected to each other via a second electrode. For the next pair (with respect to the second pair, which may be referred to as a third pair) of adj acent strips of thin films, a first end (same side as the first end of the first pair with respect to the array 520 of resonant nanostructures) of the third pair of adjacent strips may be connected to each other via a third electrode, and so on. For example, as illustrated in FIG 5, the two electrodes at opposite ends of the cascaded structure may be thermoelectric contact pads. For example, a thermocouple region of two thin films of thermoelectric materials 530, 550 with different Seebeck coefficients (e g., Sb2Te3 and Bi2Te3) are connected at a thermoelectric junction therebetween. The thermocouple region, comprising the thermoelectric junction, of the thermoelectric materials is configured with nanostructures (nanopatterned or nanostructured thermoelectric material thin films) to enhance light absorption. When light is incident on the nanostructured thermocouple region, the nanostructured thermocouple region absorbs more light and becomes hotter than the non-nanostructured or plain region of the thermoelectric materials. The temperature difference that is established in the thermoelectric photodetector device 500 results in a thermoelectric voltage generated by the Seebeck effect due to the different Seebeck coefficients of the thermoelectric materials. By cascading multiple nanostructured thermocouple regions, each comprising a thermoelectric junction, the photovoltage that is generated can thus be scaled by the number of thermoelectric junctions. The cascaded thermoelectric photodetector 500 thus advantageously provides a stronger photoresponse signal compared to a single thermoelectric junction photodetector.

[0040] In various example embodiments, the substrate 310 / 510 is a quartz substrate to avoid the requirement for surface passivation, which has lower thermal conductivity compared to other substrate material, so as to optimize the performance of the thermoelectric photodetectors 300 / 500. For example, a quartz substrate with a low thermal conductivity of 1.46 W / (mK) may be used.

[0041] For example, referring to the example thermoelectric photodetector 500 shown in FIG. 5, a temperature gradient is established between the thermoelectric pads and the arrays 520 of thin film coated nanostructures. In this regard, for the thermoelectric photodetector 500 to generate a voltage by the thermoelectric effect, a temperature gradient is required between the thermoelectric pads and the nanostructure arrays 520. Because the nanostructure arrays 520 (nanostructured thermocouple regions) absorb more light than the thermoelectric pads, the nanostructured thermocouple regions become hotter than the thermoelectric pads, and the necessary temperature gradient is formed. From the reflection image shown in FIG. 5, it can beseen that the color of the reflected light at the arrays 520 of thin film coated nanostructures (i.e., at the nanostructured thermocouple regions) of the thermoelectric photodetector 500 differs from that of Au electrodes 540 (including the electrodes corresponding to the thermoelectric pads at opposite ends of the cascaded structure), thereby confirming the intensified light absorption by the arrays 520 of resonant nanostructures at the nanostructured thermocouple regions of the thermoelectric photodetector 500. In FIG. 5, Tcindicates a region with a lower relative temperature compared to Th, which indicates a region with a higher relative temperature. Accordingly, various example embodiments advantageously enable region selective photo-absorption whereby photo-absorption is large, enhanced or maximized at the nanostructured thermocouple regions (at the arrays 520 of thin film coated nanostructures) and less or minimal at other portions, such as the thermoelectric lead portions and the electrodes 540.

[0042] Experiments were conducted to demonstrate the significantly enhanced optical absorption of the thermoelectric photodetectors according to various example embodiments of the present invention. In particular, experiments were conducted on: (1) thin film (Bi2Te3 / Sb2Te3 stack) coated nanoposts, (2) thin film (BijTci / SbGc' stack) coated nanorings (which may also be referred to as nanoholes), a plain thin film (flat, without being nanopattemed or nanostructured by nanostructures) of BfiTei and a plain thin film of Sb2Te3. The experiments conducted were purely optical measurements to demonstrate and compare the optical absorption capability of thin film coated nanostructures and plain thin films prepared on separate samples. The optical absorption measurements were conducted at room temperature with a CRAIC microspectrophotometer. Photo induced voltage measurements were carried out under room temperature conditions, using a Keithley 2612B source meter. The light sources employed for these measurements were 405 and 650 nm diode lasers with a time-averaged power output of 0.65 mW and 1.28 mW, respectively. The laser beam had a diameter of 120 micrometers which illuminated the whole device.

[0043] FIG. 6A shows a plot of the optical absorbance (absorption spectra in the visible spectrum (380 to 700 nm wavelength)) of the thin film (Bi2Te3 / Sb2Te3 stack) coated nanoposts for light incident on the air interface (i.e., light from the top side of substrate) (denoted by 602) and for light incident on the glass interface (i.e., light from the bottom side of the substrate) (denoted by 604), the thin film (Bi2Te3 / Sb2Te3 stack) coated nanorings for light incident on the air interface (denoted by 606) and for light incident on the glass interface (denoted by 608), the plain thin film ofBi2Te3 (denoted by 610) and the plain thin film of Sb2Te3 (denoted 612). FromFIG. 6A, pronounced resonance peaks and a significant increase in absorption of both the thin film (Bi2Te3 / Sb2Te3 stack) coated nanoposts and nanorings reaching approximately 90%, compared to the plain thin films, are observed at both the air and glass interfaces. This demonstrates that the thermoelectric photodetector according to various example embodiments of the present invention is advantageously capable of bi di recti on al photodetection, whereby the thin film coated resonant nanostructures developed is not only capable of capturing light from the top side of the substrate (the side at which the resonant nanostructures are formed) but also from the bottom side of the substrate.

[0044] FIG. 6B shows a plot of the absorption enhancement factor of the thin film coated nanoposts and the thin film coated nanorings compared to the plain thin film Bi2Te3 and the plain thin film Sb2Te . In other words, FIG. 6B shows the enhancement factor for the optical absorption of the Sb2Te3 / Bi2Te3 films, with and without the nanostructures From FIG 6B, it can be seen that the films’ optical absorption is found to be 2 and 2.2 times higher for the Sb2Te3 / Bi2Te3 films (thin film stack) with nanorings and nanoposts, respectively, compared to the plain thin films Bi2Te3 and Sb2Te3.

[0045] In addition, the responsivity of the cascaded thermoelectric photodetector 500 was measured for two different illumination wavelengths, 405 and 650 nm. Notably, the resonant nanostructures, comprising thin films of Sb2Te3 / Bi2Te3, (nanostructured thermoelectric material thin films) according to various example embodiments of the present invention exhibit responsivity values of approximately 2.017 and 4.737 V / W for illumination at 405 and 650 nm, respectively. FIGs. 7A and 7B depict plots of reversible switching of the cascaded thermoelectric photodetector 500 illuminated at 405 nm (FIG. 7A) and 605 nm (FIG. 7B) wavelength.

[0046] As an illustrative example, an example method of fabricating the thermoelectric photodetector 500 will now be described, according to various example embodiments of the present invention. The array(s) 320 / 520 of resonant nanostructures at portion(s) of the substrate 510 may be formed based on electron-beam lithography (EBL). For example, to achieve a 100 nm thick hydrogen silsesquioxane (HSQ) film, a 6% HSQ solution may be applied using a spin coating method onto a glass substrate. Subsequently, EBL may be employed to pattern array(s) of nanostructures (e.g., nanoscale posts, rings / holes or ellipses), which may then be developed using a salty developer. For example, nanoposts or nanorings measuring 80 nm and 120 nm in width, respectively, may be fabricated. The thin films of Sb2Te3 and Bi2Te3 (e.g., 50 nm in thickness each) may be fabricated or deposited based on RF magnetron sputtering (e.g., usingan AJA Orion 5 system). For example, the deposition power and pressure may be set to 20 W and 0.5 Pa, respectively. The same RF magnetron sputtering system used for forming the thin films of Sb2Te3 and Bi2Te3 may also be used to form the electrode connections. For example, a 50 nm thick gold (Au) film may be deposited to form the electrode using the DC gun with a power of 50 W and deposition pressure of 0.5 Pa For example, the deposition of the films may be performed in a base vacuum pressure of 2.7x 10'5Pa.|0047| Accordingly, various example embodiments provide nanostructure resonators coated with thin films of thermoelectric materials for enhanced absorption in thermoelectric photodetectors. In particular, according to various example embodiments of the present invention, resonant nanostructures are advantageously utilized to enhance the optical absorption of thin films of thermoelectric materials (e.g., Sb2Te3 / Bi2Te3) by forming nanopattemed or nanostructured thermoelectric material thin films, and more specifically, at the thermocouple region thereof. As discussed above, the optical absorption analysis demonstrates enhanced absorption of the nanostructured thermocouple region in the visible spectrum (380 to 700 nm wavelength), with sharp resonance peaks. As also discussed above, as an illustrative example, the optical absorption of the nanopatterned Sb2Te3 / Bi2Te3 films has demonstrated 2 to 2.2 times improvement compared to the plain thin films of Sb2Te3 and Bi2Te3. For example, the thermoelectric photodetector 500 comprising resonant nanostructures comprising Sb2Te3 / Bi2Te3 was measured for two different illumination wavelengths, exhibiting responsivity values of 2.017 and 4.737 V / W for illumination at 405 and 650 nm, respectively. Accordingly, various example embodiments demonstrated the use of highly absorptive resonant nanostructures comprising thin films of thermoelectric materials (e.g., Sb2Te3 / Bi2Te3) (nanostructured thermoelectric material thin films) for thermoelectric photodetectors. Therefore, the thermoelectric photodetectors 300 / 500 according to various example embodiments of the present invention advantageously possesses enhanced optical absorption, and thus, also possesses improved photosensitivity or detection efficiency. Accordingly, the thermoelectric photodetectors 300 / 500 advance photodetection technology, thereby significantly enhancing practical applications, such as but not limited to, cameras, sensors, solar cells, and optical communications.

[0048] While embodiments of the invention have been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims. The scope of the invention is thus indicatedby the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

CLAIMS1. A thermoelectric photodetector device comprising: a substrate; an array of resonant nanostructures formed at a portion of the substrate; a first thin film of thermoelectric material of a first conductivity type comprising a thermocouple portion disposed over the array of resonant nanostructures, the first thin film extends from the thermocouple portion to connect to an electrode; and a second thin film of thermoelectric material of a second conductivity type comprising a thermocouple portion disposed over the array of resonant nanostructures, the second thin film extends from the thermocouple portion to connect to another electrode, wherein the thermocouple portion of the first thin film and the thermocouple portion of the second thin film overlap with each other to form a thin film stack coating the array of resonant nanostructures, the thin film stack constituting a thermocouple region comprising a thermoelectric junction.

2. The thermoelectric photodetector device according to claim 1, further comprising: one or more additional arrays of resonant nanostructures formed at one or more additional portions of the substrate, respectively; and for each additional array of resonant nanostructures, the thermoelectric photodetector device further comprises: a first thin film of thermoelectric material of the first conductivity type comprising a thermocouple portion disposed over the additional array of resonant nanostructures, the first thin film extends from the thermocouple portion to connect to an electrode; and a second thin film of thermoelectric material of the second conductivity type comprising a thermocouple portion disposed over the additional array of resonant nanostructures, the second thin film extends from the thermocouple portion to connect to another electrode, wherein the thermocouple portion of the first thin film and the thermocouple portion of the second thin film overlap with each other to form a thin film stack coating the additional array of resonant nanostructures, the thin film stack constituting a thermocouple region comprising a thermoelectric junction.

3. The thermoelectric photodetector device according to claim 2, wherein the first and second thin films associated with the array of resonant nanostructures together form a first strip of thin films, for said each additional array of resonant nanostructures, the first and second thin films associated with the additional array of resonant nanostructures together form an additional strip of thin films, and the first strip of thin films and each additional strip of thin films are connected in series.

4. The thermoelectric photodetector device according to any one of claims 1 to 3, wherein the thermoelectric material of the first conductivity type is an n-type thermoelectric material, and the thermoelectric material of the second conductivity type is a p-type thermoelectric material.

5. The thermoelectric photodetector device according to claim 4, wherein the n-type thermoelectric material comprises n-type bismuth telluride (Bi2Te3) thermoelectric material, and the p-type thermoelectric material comprises p-type antimony telluride (SbzTes) thermoelectric material.

6. The thermoelectric photodetector device according to any one of claims 1 to 5, wherein the resonant nanostructures are each configured as a nanopillar.

7. The thermoelectric photodetector device according to claim 6, wherein the nanopillar is a nanopost, a nanoring or a nanoellipse.

8. The thermoelectric photodetector device according to any one of claims 1 to 7, wherein the array of resonant nanostructures is a periodic array of resonant nanostructures.

9. A method of fabricating a thermoelectric photodetector device, the method comprising: providing a substrate; forming an array of resonant nanostructures at a portion of the substrate;forming a first thin film of thermoelectric material of a first conductivity type comprising a thermocouple portion disposed over the array of resonant nanostructures, the first thin film extends from the thermocouple portion to connect to an electrode; and forming a second thin film of thermoelectric material of a second conductivity type comprising a thermocouple portion disposed over the array of resonant nanostructures, the second thin film extends from the thermocouple portion to connect to another electrode, wherein the thermocouple portion of the first thin film and the thermocouple portion of the second thin film overlap with each other to form a thin film stack coating the array of resonant nanostructures, the thin film stack constituting a thermocouple region comprising a thermoelectric junction.

10. The method according to claim 9, further comprising: forming one or more additional arrays of resonant nanostructures at one or more additional portions of the substrate, respectively; and for each additional array of resonant nanostructures, the method further comprises: forming a first thin film of thermoelectric material of the first conductivity type comprising a thermocouple portion disposed over the additional array of resonant nanostructures, the first thin film extends from the thermocouple portion to connect to an electrode; and forming a second thin film of thermoelectric material of the second conductivity type comprising a thermocouple portion disposed over the additional array of resonant nanostructures, the second thin film extends from the thermocouple portion to connect to another electrode, wherein the thermocouple portion of the first thin film and the thermocouple portion of the second thin film overlap with each other to form a thin film stack coating the additional array of resonant nanostructures, the thin film stack constituting a thermocouple region comprising a thermoelectric junction.

11. The method according to claim 10, wherein the first and second thin films associated with the array of resonant nanostructures together form a first strip of thin films,for said each additional array of resonant nanostructures, the first and second thin films associated with the additional array of resonant nanostructures together form an additional strip of thin films, and the first strip of thin films and each additional strip of thin films are connected in series.

12. The method according to any one of claims 9 to 11, wherein the thermoelectric material of the first conductivity type is an n-type thermoelectric material, and the thermoelectric material of the second conductivity type is a p-type thermoelectric material.

13. The method according to claim 12, wherein the n-type thermoelectric material comprises n-type bismuth telluride (BiiTes) thermoelectric material, and the p-type thermoelectric material comprises p-type antimony telluride (SbzTes) thermoelectric material.

14. The method according to any one of claims 9 to 13, wherein the resonant nanostructures are each configured as a nanopillar15. The method according to claim 14, wherein the nanopillar is a nanopost, a nanoring or a nanoellipse.

16. The method according to any one of claims 9 to 15, wherein the array of resonant nanostructures is a periodic array of resonant nanostructures.

17. The method according to any one of claims 9 to 16, wherein the array of resonant nanostructures is formed at the portion of the substrate based on electron-beam lithography, plasma etching, nanoimprint lithography, focused ion beam milling or self-assembly.

18. The method according to any one of claims 9 to 17, wherein the first and second thin films associated with the array of resonant nanostructures are formed based on magnetron sputtering.

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