Device for detecting radiation in the mid-wavelength infrared band, a method of manufacturing such a device and an ir camera comprising an array of such devices

Abstract

A device (100) for detecting radiation at a target wavelength within the mid-wavelength infrared (MWIR) band is presented. The device comprising: a nanowire (110) made of semiconductor material, wherein the nanowire comprises a first doped portion (112) and a second doped portion (114) separated by a barrier portion (116), wherein both the first doped portion and the second doped portion are either n-doped or p-doped forming a nBn or pBp-structure of the nanowire, wherein the semiconductor material of the nanowire is selected such that it has virtually no absorption of photons at the target wavelength; an antenna (120) connected with the first doped portion of the nanowire, wherein the antenna is arranged to absorb photons at the target wavelength; a first electrode (140) arranged in contact with a first end (111) of the nanowire; and a second electrode (130) arranged in contact with a second end (113) of the nanowire. The antenna and the nanowire are enclosed in a dielectric material body (160). A method of manufacturing the device is also presented as well as an IR-camera comprising an array of such devices.

Description

[0001] DEVICE FOR DETECTING RADIATION IN THE MID-WAVELENGTH INFRARED BAND, A METHOD OF MANUFACTURING SUCH A DEVICE AND AN IR CAMERA COMPRISING AN ARRAY OF SUCH DEVICES

[0002] TECHNICAL FIELD

[0003] The present invention relates to detecting radiation in the mid-wavelength infrared, MWIR, band. Especially, a device for optically detect MWIR radiation is presented. A method of manufacturing the device is also presented as well as an IR- camera comprising an array of such devices.

[0004] BACKGROUND

[0005] Photon detection in the mid-wavelength infrared (MWIR) band (3-7 pm) is used for thermal imaging, communication, and sensing of environmentally relevant gases such as CH4 (3.3 pm), CO2 (4.3 pm), CO (4.67 pm) and NOx (5.4 pm). Low-cost and sensitive monitoring of these gases is vital to achieve a carbon-neutral society by providing accurate and detailed greenhouse gas emission data and for early detection of leaks in industrial processes. In addition, detection of MWIR wavelengths are highly relevant for military applications such as night vision and to see through fog. MWIR detection can be done indirectly via various side effects caused by the absorption of MWIR radiation, such as temperature rise, a thermoelectric or pyroelectric signal such devices may be referred to as thermal detectors. MWIR detection can also be done directly by direct detection of photons. Such optical detectors are the most sensitive type of detectors in the MWIR band. Optical detectors made of HgCdTe alloys dominate the market. The major drawback of optical MWIR detectors is that they require cryogenic cooling to avoid obscuring the signal by thermal noise. In addition, the instability and highly toxic constituents of HgCdTe make the material a significant environmental risk.

[0006] Thermal detectors can operate at room temperature but are limited in their response speed to video frequency (25-50 Hz) as well as their sensitivity which is orders of magnitude below the optical detectors.

[0007] The lll-V semiconductors InAs and InSb are promising alternative materials to HgCdTe in the MWIR band. The conventional methods to fabricate 111 -V-based photodetectors based on epitaxial thin film growth on expensive lll-V substrates, or bonding of full lll-V crystals to a read-out chip, lead to a high cost and unsustainable consumption of rare In.

[0008] In Fig. 1 a comparison of various IR detector technologies in terms of detectivity at different wavelengths is presented. Ideal detector behavior at 300K is indicated, highlighting a targeted performance.

[0009] To date, improvements to the signal-noise ratio for optical detectors has been achieved primarily focusing on the effective bandgaps in semiconductor 5 wherein the photons are absorbed. US 8,450,773 Bl teaches for example how strains can be imposed on the absorbing semiconductor in order to reduce its effective bandgap and hence allow the absorption of photons with lower energy, i.e. longer wavelengths, and thereby increasing the signal-noise ratio. Similarly, US 7,737,411 B2 adopts a gradient of As in a nBn heterojunction in order to widen the 10 energy range of the detectable (absorbing) photons. US 11,164,985 B2 discloses the use of a highly doped semiconductor layer beneath an absorption layer, optionally in combination with a metal antenna on top of the absorption layer, in so focusing the incoming electromagnetic radiation to the semiconductor absorption layer and thereby achieving a larger signal-noise ratio. Despite recent improvement to the 15 technology there is a need to improve the performance.

[0010] SUMMARY OF THE INVENTION

[0011] It is an object to provide a MWIR detector that at least alleviate one or more of the above problems pertaining to MWIR detectors.

[0012] The invention is set out in the appended set of claims. This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description.

[0013] According to a first aspect a device for detecting radiation at a target wavelength within the mid-wavelength infrared, MWIR, band, is provided. The device comprises a nanowire made of semiconductor material and an antenna. The nanowire comprises a first doped portion and a second doped portion separated by a barrier portion. Both the first doped portion and the second doped portion are either n-doped or p-doped forming a nBn or pBp-structure of the nanowire. The semiconductor material of the nanowire is selected such that it has virtually no absorption of photons at the target wavelength. The antenna is connected with the first doped portion of the nanowire. The antenna is arranged to absorb photons at the target wavelength. The device further comprises a first electrode arranged in contact with a first end of the nanowire and a second electrode arranged in contact with a second end of the nanowire. The antenna and the nanowire are at least partly enclosed in a dielectric material body.

[0014] The combined use of having a nanowire of semiconductor material being virtually transparent to photons at the target wavelength within the MWIR band and a antenna being arranged to absorb photons at the target wavelength within the MWIR band is that absorption of MWIR band photons will only occur in the antenna. Further, the electron-hole pairs being a result from the photon absorption in the antenna can be injected into the first doped portion of the nanowire through hot carrier injection. This allows the semiconductor to have up to twice the band gap of the photon energy of the absorbed photons. Moreover, the nBn or pBp structured nanowire allow for a low dark current running through the device which in turn allow for operating the device at as high temperatures as room temperature. In case of a nBn structure the conduction band of the barrier portion in the nBn structure prevents electrons from passing the barrier portion while holes may pass the barrier portion. In case of a pBp structure, the valence band of the barrier portion in the pBp structure prevents holes from passing the barrier portion while electrons may pass the barrier portion.

[0015] The dielectric material body may be transparent to photons in the MWIR band.

[0016] The dielectric material body may be made from a material selected form one or more of SijIX , SiCh, SiOC, SiC, SiOF or SiCN.

[0017] At least one of the first electrode and the second electrode may be structured and arranged as to substantially not obscure incoming photons in the MWIR band.

[0018] The semiconductor material of the nanowire may have a bandgap which is up to twice of the energy corresponding to the target wavelength.

[0019] The first and second doped portions may consist of InAs or InSb. Alternatively, InAsSb may be used for the first and second doped portions. The barrier portion may consist of one or more of InGaAs, AlAsSb and GaAsSb.

[0020] The antenna may comprise a plurality of antenna portions. Each antenna portion may be connected to the first doped portion of the nanowire.

[0021] According to a second aspect a method of manufacturing the device according to the first aspect is provided. The method comprises: providing a dielectric material body enclosing an antenna metal layer and a bottom electrode; forming, from a top of the dielectric material body down to the bottom electrode, a cavity in the dielectric material body, the cavity intersecting the antenna metal layer; and growing a nanowire in the cavity. The nanowire being grown such that: the nanowire comprises a first doped portion and a second doped portion separated by a barrier portion, wherein both of the first doped portion and the second doped portion are either n-doped or p-doped, the nanowire integrates with the antenna metal layer, thereby forming a antenna integrated with the nanowire, and a bottom end of the nanowire is arranged in contact with the bottom electrode.

[0022] The method further comprises arranging a top electrode at a top end of the nanowire.

[0023] A further scope of applicability will become apparent from the detailed description given below. However, it should be understood that the detailed description and specific examples are given by way of illustration only.

[0024] It is to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It must be noted that, as used in the specification and the appended claim, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements unless the context clearly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other aspects will now be described in more detail, with reference to appended figures. The figures should not be considered limiting; instead they are used for explaining and understanding.

[0027] As illustrated in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures. Like reference numerals refer to like elements throughout.

[0028] Fig. 1 illustrate a comparison of various IR detector technologies in terms of detectivity at different wavelengths.

[0029] Fig. 2 illustrates a device for radiation detection at a target wavelength within the mid-wavelength infrared, MWIR, band.

[0030] Fig. 3a illustrates a nBn heterostructure in a nanowire.

[0031] Fig. 3b illustrates hot carrier injection from a metal to a semiconductor.

[0032] Figs. 4 is a carton strip illustrating a method of manufacturing the device for radiation detection in the mid-wavelength infrared, MWIR, band illustrated in Fig. 2.

[0033] Fig. 5 is a block diagram of the method of manufacturing the device for radiation detection in the mid-wavelength infrared, MWIR, band.

[0034] Fig. 6a is a cross-sectional electron microscopy image of an InAs nanowire grown by TASE on W metal.

[0035] Fig 6b is an electron microscopy image at 70° tilt, and electron backscatter diffraction, EBSD, maps of InAs nanowires after SisN4 back-etching, verifying single crystallinity of the nanostructures with occasional twin defects.

[0036] Fig. 6c is an electromagnetic simulation of a device geometry resulting in focused electric field at the semiconductor-metal interface and absorption max at 4.7 pm. DETAILED DESCRIPTION

[0037] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms.

[0038] Fig. 2 illustrates a device 100 for radiation detection in the mid-wavelength infrared, MWIR, band. The MWIR band is in the range of 3-7pm. For example, the device 100 may be arranged for radiation detection at a target wavelength within the MWIR band. The target wavelength may be 5,5pm. Particularly, the device is configured for optical detection. The device 100 comprises a nanowire 110 and an antenna 120. The range of optical detection of the device 100 may be stretched outside the MWIR band. The range of optical detection of the device 100 depend on a selection of materials used for the antenna 120 and the nanowire 110. Also a shape of the antenna 120 and dimensions on the nanowire 110 and the antenna 120 will affect the range of optical detection of the device 100. For example, the device may perform optical detection in the range of 2 pm to 9 pm. Multiple devices 100 can be used to make up an array of detectors for e.g. an IR camera.

[0039] The nanowire 110 is made of semiconductor material. The nanowire 110 comprises a first doped portion 112 and a second doped portion 114 separated by a barrier portion 116. Both of the first doped portion 112 and the second doped portion 114 are either n-doped or p-doped. Hence, the nanowire 110 is forming a nBn or pBp-structure. The nanowire 110 may be single-crystalline. The nanowire 110 is typically straight. The nanowire 110 is typically arranged perpendicular in relation to a substrate 150 supporting the device 100.

[0040] The semiconductor material of the nanowire 110 is selected such that it has virtually no absorption of photons at the target wavelength. By virtually no absorption of photons is meant that the material of the nanowire absorbs less than 1% of photons at the target wavelength. Hence, the nanowire is to made insensitive to the incoming radiation that the device 100 is supposed to detect. The selection of semiconductor material depends on the target wavelength which depends on the bandgap of the semiconductor. The target wavelength is decided by half the bandgap. The selection of semiconductor material shall also be done taking into account the atomic lattice constant of the barrier material of the barrier portion 116. This in order to avoid stress in the heterostructure which can lead to crystal defects.

[0041] For detection at a target wavelength of 5.5 pm InAs is a good selection of semiconductor material for the first and second doped portions 112, 114. This since it has a bandgap, Eg, of 0.37 eV at room temperature --> Eg / 2 = 0.185 eV --> wavelength of 6.6 pm. Further, using InAs for the first and second doped portions 112, 114, the barrier portion 116 can be made by alloying with Ga --> InGaAs. Alternatively, the barrier portion 116 can be made out of AlAsSb since InAs is almost lattice matched to AlAsSb. Yet alternatively, GaAsSb can be used for the barrier portion 116. A benefit with using InAs as the semiconductor material for the first and second doped portions 112, 114 is that the device 100 can be operated at room temperature.

[0042] Alternatively, InSb can be used as the semiconductor material for the first and second doped portions 112, 114. Using InSb will allow for reaching even further out in wavelength. Using InSb as the semiconductor material for the first and second doped portions 112, 114, AlSb can be used for the barrier portion 116.

[0043] Alternatively, InAsSb, being an alloy of InAs and InSb, may be used for the first and second doped portions 112, 114.

[0044] Another alternative of semiconductor material for the first and second doped portions 112, 114 is GaSb, especially p-doped GaSb. If so, the barrier portion 116 can be made out of AIGaAs, then the nanowire 110 will be formed as a p Bp-structure.

[0045] Regarding the barrier portion 116, an important aspect is that the barrier material of the barrier portion 116 introduces a barrier that is larger than the band gap of the absorption material of the first and second doped portions 112, 114. This without having a too large lattice mismatch between the materials. AlAsSb is a good candidate for the barrier material of the barrier portion 116 having a band gap of ~1.5 eV. Further, there is almost no stress between AlAsSb and InAs since AlAsSb is almost lattice matched to InAs. But it is challenging to grow AlAsSb with high quality using selective epitaxy techniques, especially at low temperature. InGaAs is an alternative material to be used for the barrier portion 116. This since InGaAs is easy to grow simply adding Ga to the InAs growth process. However, using InGaAs the barrier portion 116 comes with the potential issue that a tensile stress will be introduced. For example, lno.5Gao.5As will be tensile stressed (3.3%) and will give a bandgap barrier of ~0.4 eV.

[0046] As mentioned above, GaAsSb is yet an alternative material for the barrier portion 116. For example, using GaAs0.6Sb0.4 provide ~0.8 eV barrier but even larger tensile stress, 3.8%.

[0047] The antenna 120 is connected with the nanowire 110 at the first doped portion 112 of the nanowire 110. Preferably, the antenna 120 is oriented perpendicularly to the semiconductor nanowire 110. Hence, the antenna 120 is typically parallel arranged in relation to the substrate 150 supporting the device 100. The antenna 120 may comprise a plurality of antenna portions 122a, 122b, wherein each such antenna portion 122a, 122b is connected to the first doped portion 112 of the nanowire 110. A shape of the antenna 120 will decide the interaction of the antenna 120 with the radiation of interest to detect. The antenna 120 is to be designed to focus incoming radiation at the target wavelength to the vicinity of the nanowire, such that absorption is maximized in the antenna 120 close to the nanowire 110.

[0048] Importantly to notice, the material of the nanowire 110 itself is supposed to be insensitive to the target wavelength and thus not absorb the incoming target radiation. An example of a suitable shape is a bow-tie antenna where the nanowire 110 is placed in the center of the bow tie. Such an exemplary embodiment of the antenna 120 is illustrated in Fig. 2. It is however understood that alternative shapes may as well be used for the antenna 120. In summary, around the nanowire 100 an antenna is integrated.

[0049] The antenna 120 is arranged to absorb photons in the MWIR band and specifically at the target wavelength within the MWIR band. The antenna may be a metallic antenna. The metallic antenna 120 may be made from W, Cr, TiN. The antenna may be a metasurface antenna. However, any material can be used as long as the material is a good absorber of photons at the target wavelength. By being a good absorber of photons at the target wavelength is meant that the material of antenna 120 absorbs more than 50% of photons at the target wavelength. Another aspect to consider in selecting the material for the antenna 120 is that crystal growth of the semiconductor material used for the nanowire 110 is not supposed to start at the antenna 120, but instead at a bottom electrode 132. Reference is made to Figs 4 and 5 for a discussion about a method for manufacturing the device 100. Preferably, the antenna 120 can be manufactured so that an area of the antenna 120 is larger than a cross sectional area of the nanowire 110. By this it is safeguarded that the antenna 120 absorbs the majority of the photons impinging the device 100. Preferably, the antenna 120 has an extension being at least half of the target wavelength.

[0050] The device 100 further comprises a first electrode 140 and a second electrode 130. A current will be generated from charge carriers induced from radiation absorption in the antenna, the induced charge carries being injected into the nanowire 110. More on the absorption of the incident radiation in the antenna 120 and injection of the charge carries will be discussed below.

[0051] The generated current may be read out from the first and second electrodes 140, 130. The first electrode 140 is arranged in contact with a first end 111 of the nanowire 110. The first end 111 of the nanowire 110 is forming part of the first doped portion 112 of the nanowire 110. The second electrode 130 is arranged in contact with a second end 113 of the nanowire 110. The second end 113 of the nanowire 110 is forming part of the second doped portion 114 of the nanowire 110.

[0052] At least one of the first electrode 140 and the second electrode 130 is structured and arranged as to substantially not obscure incoming photons in the MWIR band. This may be for example be achieved by using thin electrode. One such example of a thin electrode is a lOnm thin electrode made of TiN. Such an electrode 10 transmits ~80% of incoming radiation in the MWIR range. Alternatively, or in combination, the electrode may be patterned with a pattern having a pitch smaller than the wavelength of the incoming radiation, i.e. a pitch smaller than 2 pm. This will allow for further reduction in interaction with the incoming radiation and allow the incoming radiation to pass through the electrode.

[0053] The antenna 120 and the nanowire 110 are at least partly enclosed in a dielectric material body 160. The antenna 120 and the nanowire 110 may be fully enclosed in the dielectric material body 160. The dielectric material body 160 is made from a dielectric material chosen so that it is transparent to photons in the MWIR band. The dielectric material may be selected form one or 20 more of SisIX , SiCh, SiOC, SiC, SiOF or SiCN. All these materials are researched for low-k value dielectrics in Si CMOS technology. Any of these would work here. SisIX and SiO2 are the most established dielectrics for which deposition techniques for high-quality films exist. SisIX etches very slowly in HF (1-4 nm / min), which is a benefit compared to SiO2 which etches much faster (60-200 nm / min).

[0054] The device structure proposed herein can achieve high-performance MWIR detection at room temperature due to a combination a nanowire 110 having an nBn (or pBp) heterostructure together with an antenna 120 configured to absorb MWIR radiation with energy down to half the bandgap of the semiconductor into the vicinity of the nanowire 110 and inject generated carriers into it.

[0055] The function of an nBn heterostructure will now be described in connection with Fig. 3a. The nBn heterostructure consists of an n-type semiconductor with a conduction band barrier inserted next to a contact layer. By avoiding the conventional p-n junction structure usually found in photovoltaic detectors, Schottky-Read-Hall carrier generation is effectively suppressed and the barrier blocks majority charge carriers, leading to very low currents under dark conditions compared to p-n junctions. Importantly, the temperature dependence of the dark current in this device is stronger than from depending on a factor of half the semiconductor band gap (Eg / 2) to instead having a stronger dependency of the full band gap (Eg). Photodetectors based on nBn can thus be operated at significantly higher temperature, and detectivities of ~101:LJones at 4 pm have been reached at 150K.

[0056] Further, the present device 100 rely on radiation absorption in metal of the antenna 120 at an interface to the semiconductor of the nanowire 110, this is illustrated in connection with Fig. 3b. This will generate short-lived hot electrons and holes in the metal which will be injected into the semiconductor, resulting in a process referred to as "hot carrier injection" in the literature. As both hot holes and electrons gain the energy of the incident photons, Ep, and end up at double that energy distance in the metal, injection of the carriers can occur into semiconductor with up to twice the Eg of the incident radiation. Thus, we can extend the sensitivity of the device 100 to twice the wavelength of the incoming radiation while maintaining a low dark current. In other words, for a given target wavelength we can use a semiconductor material with twice the band gap, thus with significantly lower dark current. The n-doping in the first doped portion 112 is preferably low enough so that the Fermi level resides close to the center of the band gap, and the work function of the metal is preferably aligned to this Fermi level to achieve sensitivity extension close to half the bandgap, Eg.

[0057] Furthermore, the dark current is directly proportional to the volume of the active semiconductor. As we use a nanowire as the active region the dark current is kept very small. According to one example, the nanowire may have a volume of: Ti * (50 nm)2* 300 nm = 0.0023 / zm3.

[0058] This is 1000-2000x smaller than a conventional pixel size: for detection at 4 pm wavelength. The dark current is expected to scale similarly with the reduction in volume, hence being 1000-2000x smaller than the dark current of a conventional pixel for detection at 4 pm. Hence, a small volume of the nanowire 110 will reduce the dark current as compared with conventional pixel for detection. Dimensions of the different portions of the nanowire 110 will be further elaborated on below.

[0059] By using InAs nanowires Eg= 0.36 eV) we therefore will be able to detect radiation up to Eg / 2, or 6.9 pm, covering the whole MWIR band. This while minimizing the dark currents by the large £gand minimal volume of the semiconductor. The present device therefore provides to radically reduce the thermal noise in an optical detector for MWIR radiation.

[0060] The nanowire 110 may have a radius in the range of 10-100nm. A length of the nanowire 110 along its longitudinal direction reaching from the first electrode 140 to the second electrode 130 may be in the range of 100-400nm, wherein the lower portion of this range for the longitudinal direction of the nanowire 110 apply for the lower portion of the range for the radius of the nanowirellO.

[0061] The first doped portion 112 of the nanowire 110 may have a length of as short as lOOnm. This in order to minimize the time it takes for carriers injected into the nanowire 110 to travel to the first and second electrodes 140, 130. Further, as the absorption of the MWIR radiation is meant to occur in the antenna 120, close to the nanowire 110, there is no gain in having a too long first doped portion 112 of the nanowire 110.

[0062] A length of the barrier portion 116 needs to be long enough to avoid quantum tunneling through the barrier portion 116 but still short enough to make sure it is fully depleted (carriers would "fall" into the more narrow band gap material). A suitable length is therefore 20-50 nm.

[0063] The second doped portion 114 is present to ensure a good electrical contact with the second electrode 130. Further, the second doped portion 114 is present to secure that there is no influence of the second electrode 130 on electrostatic potential in the barrier portion 116. Otherwise the second doped portion 114 is preferably made as short as possible. Hence, the second doped portion 114 is only meant to be a "contacting" portion. In the end, the second doped portion 114 ensures that the nBn band structure (or the pBp structure) is unaffected by potential Schottky barriers at the second electrode 130. A length of 20-50 nm is suitable for the second doped portion 114.

[0064] In the end the spacing between the first and second electrodes 140, 130 also matters for the absorption resonance of the device 100. Thus, the considerations of the design of the antenna 120 may impact the size of the rest of the device 100.

[0065] In connection with Figs. 4 and 5 a method 500 of manufacturing the device 100 will be discussed. The method comprising a number of steps.

[0066] The method comprises providing S502 a dielectric material body 160 enclosing an antenna metal layer 124 and a bottom electrode 132. The antenna metal layer 124 may have a thickness of 10-50 nm. The antenna metal layer 124 is configured to form the antenna 120 after the manufacturing being completed. For details on the antenna 120 reference is made to the above.

[0067] The method further comprises forming S504 a cavity 170 in the dielectric material body 160. The cavity is formed from a top 162 of the dielectric material body 160 down to the bottom electrode 132. The cavity 170 is formed such that it intersects the antenna metal layer 124. Especially, the cavity 170 is formed such that a hole is etched through the antenna metal layer 124. The forming S504 of the cavity 170 may be made by dry etching using a mask layer 180. A diameter, d, of the cavity may be in the range of 10-100nm.

[0068] According to the present method of manufacturing the device 100 the antenna metal layer 124 is reasonably formed prior to the step of forming S504 the cavity 170 so that a hole is etched through the antenna metal layer 124. A shape of the antenna metal layer 124 may be made during a process of building up a layer stack comprising the bottom electrode 132, the antenna metal layer 124 and the dielectric material body 160.

[0069] The method further comprises growing S506 a nanowire 110 in the cavity 170. The growing may be made by a selective metalorganic vapor phase epitaxy, MOVPE, process. The nanowire 110 being grown such that the nanowire 110 comprises a first doped portion 112 and a second doped portion 114 separated by a barrier portion 116. Both of the first doped portion 112 and the second doped portion 114 are either n- doped or p-doped. Hence, the nanowire is forming a nBn or pBp structure. For details on the nanowire 110 reference is made to the above. Further, the nanowire 110 being grown such that the nanowire 110 integrates with the antenna metal layer 124, thereby forming a antenna 120 integrated with the nanowire 110. Further, the nanowire 110 being grown such that a bottom end of the nanowire 110 is arranged in contact with the bottom electrode 132. The bottom electrode 132 may, as in the in Fig. 4 illustrated example, form the second electrode 130. However, the bottom electrode may as well form the first electrode 140. All depending on how the first and second doped portions 112, 114 of the nanowire 110 are arranged. The method further comprises arranging S508 a top electrode at a top end of the nanowire 110. The top electrode may form the first electrode 140. However, the top electrode may as well form the second electrode 130. All depending on how the first and second doped portions 112, 114 of the nanowire 110 are arranged.

[0070] With reference to Figs 6a-c preliminary results demonstrating the feasibility of the present invention will be discussed. Fig. 6a displays an example of an InAs nanowire grown on W within a hole in Si3N4 using the method discussed in connection with Figs 4 and 5. Electron backscatter diffraction, EBSD, analysis prove that the nanowires are single crystalline, Fig. 6b, and we have confirmed high electrical quality. Thus, the foundations for fabrication of the device are already in place, demonstrating its feasibility. Fig. 6 illustrates a design and simulation of the device using a bow-tie shaped antenna. With the simulated design it is illustrated that efficient focusing of the electromagnetic field to the metal-lnAs interface with more than 70% absorption efficiency at 4.7 pm wavelength can be achieved. Importantly, the indicated dimensions are feasible for fabrication using available nanofabrication infrastructure.

[0071] The person skilled in the art realizes that the present invention by no means is limited to what is explicitly described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

[0072] For example, in the in Fig. 2 illustrated example, the second doped portion 114 is illustrated as being closest to the substrate 130. However, it is realized that the device 100 can be made the other way around as well having the first doped portion 112 arranged closest to the substrate 150.

[0073] Moreover, above the device 100 has been illustrated as comprising one nanowire 110, it is however to be understood that a plurality of parallel nanowires 110 may be used in the device 100. This for example in case the antenna 120 is designed to deliver field strength in more than one point.

[0074] Additionally, variations can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

Claims

CLAIMS1. A device for detecting radiation at a target wavelength within the mid-wavelength infrared, MWIR, band, the device comprising: a nanowire (110) made of semiconductor material, wherein the nanowire (110) comprises a first doped portion (112) and a second doped portion (114) separated by a barrier portion (116), wherein both the first doped portion (112) and the second doped portion (114) are either n-doped or p-doped forming a nBn or pBp-structure of the nanowire (110), wherein the semiconductor material of the nanowire (110) is selected such that it has virtually no absorption of photons at the target wavelength; an antenna (120) connected with the first doped portion (112) of the nanowire (110), wherein the antenna (120) is arranged to absorb photons at the target wavelength; a first electrode (140) arranged in contact with a first end (111) of the nanowire (110); and a second electrode (130) arranged in contact with a second end (113) of the nanowire (110), wherein the antenna (120) and the nanowire (110) are at least partly enclosed in a dielectric material body (160).

2. The device according to claim 1, wherein the dielectric material body (160) is transparent to photons in the MWIR band.

3. The device according to claim 1 or 2, wherein the dielectric material body (160) is made from a material selected form one or more of SisIX , SiC>2, SiOC, SiC, SiOF or SiCN.

4. The device according to any of the claims 1-3, wherein at least one of the first electrode (140) and the second electrode (130) is structured and arranged as to substantially not obscure incoming photons in the MWIR band.

5. The device according to claim 4, wherein the at least one of the first electrode (140) and the second electrode (130) is a thin electrode made of TiN.

6. The device according to claim 4 or 5, wherein the at least one of the first electrode (140) and the second electrode (130) is patterned with a pattern having a pitch smaller than the wavelength of the incoming radiation.

7. The device according to any of the claims 1-6, wherein the semiconductor material has a bandgap which is up to twice of the energy corresponding to the target wavelength.

8. The device according to any of the claims 1-7, wherein the first and second doped portions (112, 114) consists of one or more of InAs, InSb and InAsSb, and wherein the barrier portion (116) consists of one or more of InGaAs, AlAsSb and GaAsSb.

9. The device according to any of the claims 1-8, wherein the antenna (120) is comprised of a plurality of antenna portions (122a, 122b), wherein each antenna portion (122a, 122b) is connected to the first doped portion (112) of the nanowire (110).

10. The device according to any of the claims 1-9, wherein the nanowire is singlecrystalline.

11. The device according to any of the claims 1-10, wherein the antenna (120) is oriented perpendicularly to the nanowire (110).

12. The device according to any of the claims 1-11, wherein the antenna (120) is a bow-tie antenna where the nanowire (110) is placed in the center of the bow-tie.

13. The device according to any of the claims 1-12, wherein the antenna (120) ismade from a material absorbing more than 50% of photons at the target wavelength.

14. The device according to any of the claims 1-13, wherein an area of the antenna (120) is larger than a cross sectional area of the nanowire (110), and wherein the antenna (120) has an extension being at least half of the target wavelength.

15. The device according to any of the claims 1-14, wherein the first doped portion (112) has a length of > 100 nm, wherein the barrier portion (116) has a length of 20- 50 nm, and wherein the second doped portion (114) has a length of 20-50 nm.

16. The device according to any of the claims 1-15, wherein the antenna (120) has a thickness of 10-50 nm.

17. A method of manufacturing the device according to any one of claims 1-16, the method comprising: providing (S502) a dielectric material body (160) enclosing an antenna metal layer (124) and a bottom electrode (132); forming (S504), from a top (162) of the dielectric material body (160) down to the bottom electrode, a cavity (170) in the dielectric material body (160), the cavity (170) intersecting the antenna metal layer (124); growing (S506) a nanowire (110) in the cavity (170), the nanowire (110) being grown such that: the nanowire (110) comprises a first doped portion (112) and a second doped portion (114) separated by a barrier portion (116), wherein both of the first doped portion (112) and the second doped portion (114) are either n- doped or p-doped, the nanowire (110) integrates with the antenna metal layer (124), thereby forming an antenna (120) integrated with the nanowire (110), and a bottom end of the nanowire (110) is arranged in contact with the bottom electrode (132); andarranging (S508) a top electrode at a top end of the nanowire (110).

18. An IR camera comprising an array of devices according to any one of claims 1-16.

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