A DEVICE FOR OPERATING WITH THZ AND/OR IR AND/OR MW RADIATION

Abstract

The present invention relates to a device for operating with THz and/or IR and/or MW radiation, comprising:—an antenna having one or more antenna branches (A1; A1, A2) and adapted to operate in the THz and/or IR and/or MW frequency range; and—a structure made of at least one photoactive material defining a photo-active area (Ga) arranged to absorb light radiation impinging thereon. The focus area of the at least one antenna branch (A1; A1, A2) is dimensionally equal or smaller than the photo-active area (Ga).

Claims

1. The device according to claim 29, wherein said photothermal effect is a photo-thermoelectric effect.

2. The device according to claim 1, wherein said dimension of the photo-active area measured in parallel to said first direction and transversally to said interface across said adjacent regions is 2L.sub.cool, where L.sub.cool is the cooling length of hot carriers on both adjacent regions.

3. The device according to claim 1, wherein another dimension of the photo-active area is defined by the width of the structure made of at least one photoactive material.

4. The device according to claim 1, wherein said antenna has at least two antenna branches that are separated by a distance, measured along a separation direction, which is equal or smaller than the dimension of said photo-active area measured along a direction that is parallel to said separation direction.

5. The device according to claim 1, further comprising a split-gate comprising first and second gate sections separated by a gap and capacitively coupled to said structure to create said two sections when a voltage differential is applied to the split-gate, wherein at least one of said focus area of the at least one antenna branch and said distance separating said at least two antenna branches is dimensionally equal or smaller than a separation distance defined by said gap separating the first and second gate sections and being measured along a direction that is parallel to at least one of said first direction and said separation direction.

6. The device according to claim 5, wherein said antenna has at least two antenna branches that are separated by a distance, measured along a separation direction, which is equal or smaller than the dimension of said photo-active area measured along a direction that is parallel to said separation direction, and wherein said antenna and said split-gate are the same element, each of said at least two antenna branches being a respective of said first and second gate sections.

7. The device according to claim 1, further comprising a bottom dielectric layer and an active layer made of said photoactive material arranged on top of said bottom dielectric layer.

8. The device according to claim 7, further comprising a top dielectric layer, wherein said active layer is arranged between said top and said bottom dielectric layers.

9. The device according to claim 1, further comprising one or more active layers made of at least one of the following photoactive materials: graphene, black phosphorus, Bi.sub.2Te.sub.3 or other topological insulator.

10. The device according to claim 8, wherein said structure comprises an encapsulated graphene structure having, as said active layer, at least a graphene layer arranged between said top and said bottom dielectric layers.

11. The device according to claim 7, wherein said antenna has at least two antenna branches that are separated by a distance, measured along a separation direction, which is equal or smaller than the dimension of said photo-active area measured along a direction that is parallel to said separation direction, and wherein said bottom dielectric layer is arranged over the antenna bridging a gap between the two antenna branches so that said interface between the two sections of the structure is arranged over said antenna branches gap.

12-14. (canceled)

15. The device according to claim 1, constituting a detector of at least one of THz, IR, and MW radiation, wherein the antenna is configured and arranged to focus and confine at least one of THz, IR, and MW radiation in the focus area of the at least one antenna branch, to concentrate said radiation at said photo-active area, which is arranged to absorb at least one of THz, IR, and MW light radiation, and the device further comprises at least first and second electrical contacts electrically connected to distanced regions of the structure to measure photo-induced current flowing between said first and second electrical contacts, through the structure, when at least one of THz, IR, and MW light radiation impinges on the photo-active area.

16-17. (canceled)

18. The device according to claim 1, constituting an emitter of at least one of THz, IR, and MW radiation, wherein said photo-active area is arranged to absorb light radiation from femtosecond light pulses shined thereon, wherein the device further comprises a controlled light source adapted and arranged to generate and emit controlled femtosecond light pulses on said photo-active area, so that a photothermoelectrically induced local photovoltage is created at the structure by ultrafast charge separation which leads to the generation of at least one of THz, IR, and MW radiation, and wherein the antenna is configured and arranged to emit said generated at least one THz, IR, and MW radiation to far field regions around the device.

19. The device according to claim 18, further comprising: a split-gate comprising first and second gate sections separated by a gap and capacitively coupled to said structure to create said two sections when a voltage differential is applied to the split-gate, wherein at least one of said focus area of the at least one antenna branch and said distance separating said at least two antenna branches is dimensionally equal or smaller than a separation distance defined by said gap separating the first and second gate sections and being measured along a direction that is parallel to at least one of said first direction and said separation direction; and a first voltage source connected to the first gate section and a second voltage source connected to the second gate section, to generate and apply said voltage differential to the split-gate; wherein the first and second voltage sources are adapted to generate and apply said voltage differential to the split-gate to electrostatically control the generation and emission of said at least one THz, IR, and MW radiation.

20. The device according to claim 9, further comprising a mechanism for enhancing the photoresponse of the device, by exploiting graphene plasmons of the graphene layer.

21. (canceled)

22. The device according to claim 1, wherein the device is configured and arranged to operate: as a detector of at least one of THz, IR, and MW radiation, wherein the antenna is configured and arranged to focus and confine at least one of THz, IR, and MW radiation in the focus area of the at least one antenna branch, to concentrate said radiation at said photo-active area, which is arranged to absorb at least one of THz, IR, and MW light radiation, and the device further comprises at least first and second electrical contacts electrically connected to distanced regions of the structure to measure photo-induced current flowing between said first and second electrical contacts, through the structure, when at least one of THz, IR, and MW light radiation impinges on the photo-active area, and as an emitter of at least one of THz, IR, and MW radiation, wherein said photo-active area is arranged to absorb light radiation from femtosecond light pulses shined thereon, wherein the device further comprises a controlled light source adapted and arranged to generate and emit controlled femtosecond light pulses on said photo-active area, so that a photothermoelectrically induced local photovoltage is created at the structure by ultrafast charge separation which leads to the generation of at least one of THz, IR, and MW radiation, and wherein the antenna is configured and arranged to emit said generated at least one THz, IR, and MW radiation to far field regions around the device.

23. An apparatus, comprising: a detector of at least one of THz, IR, and MW radiation, comprising: an antenna having at least one antenna branch and adapted to operate in at least one of the THz, IR, and MW frequency range; and a structure made of at least one photoactive material defining a photo-active area arranged to absorb light radiation impinging thereon; wherein said at least one antenna branch has a focus area which is dimensionally equal or smaller than said photo-active area, wherein said structure is made of a photoactive material with high Seebeck coefficient and comprises two sections with different Seebeck coefficients, such that said photo-active area, within an active channel having a Seebeck gradient and arranged to absorb light radiation impinging thereon, is defined at the interface between said two sections and through adjacent regions thereof at both sides of the interface, and wherein said focus area is dimensionally equal or smaller, according to a first direction, than the dimension of the photo-active area measured in parallel to said first direction and transversally to said interface across said adjacent regions, wherein the detector is optimized for a photoresponse based on the photo-thermal effect, where a photoresponse is generated through light-induced charge carrier heating, in combination with the presence of said Seebeck gradient; and wherein the antenna is configured and arranged to focus and confine at least one of THz, IR, and MW radiation in the focus area of the at least one antenna branch, to concentrate said radiation at said photo-active area, which is arranged to absorb at least one of THz, IR, and MW radiation, and the detector further comprises at least first and second electrical contacts electrically connected to distanced regions of the structure to measure photo-induced current flowing between said first and second electrical contacts, through the structure, when at least one of THz, IR, and MW radiation impinges on the photo-active area; and an emitter of at least one of THz, IR, and MW radiation.

24. The apparatus according to claim 23, wherein said emitter is constituted by one of: a device comprising: an antenna having at least one antenna branch and adapted to operate in at least one of the THz, IR, and MW frequency range; and a structure made of at least one photoactive material defining a photo-active area arranged to absorb light radiation impinging thereon; wherein said at least one antenna branch has a focus area which is dimensionally equal or smaller than said photo-active area, wherein said structure is made of a photoactive material with high Seebeck coefficient and comprises two sections with different Seebeck coefficients, such that said photo-active area, within an active channel having a Seebeck gradient and arranged to absorb light radiation impinging thereon, is defined at the interface between said two sections and through adjacent regions thereof at both sides of the interface, and wherein said focus area is dimensionally equal or smaller, according to a first direction, than the dimension of the photo-active area measured in parallel to said first direction and transversally to said interface across said adjacent regions, wherein the device is optimized for a photoresponse based on the photo-thermal effect, where a photoresponse is generated through light-induced charge carrier heating, in combination with the presence of said Seebeck gradient and a THz laser source, in which case the detector is a THz radiation detector.

25-28. (canceled)

29. A device for operating with at least one of THz, IR, and MW radiation, comprising: an antenna having at least one antenna branch and adapted to operate in at least one of the THz, IR, and MW frequency range; and a structure made of at least one photoactive material defining a photo-active area arranged to absorb light radiation impinging thereon; wherein said at least one antenna branch has a focus area which is dimensionally equal or smaller than said photo-active area, wherein said structure is made of a photoactive material with high Seebeck coefficient and comprises two sections with different Seebeck coefficients, such that said photo-active area, within an active channel having a Seebeck gradient and arranged to absorb light radiation impinging thereon, is defined at the interface between said two sections and through adjacent regions thereof at both sides of the interface, and wherein said focus area is dimensionally equal or smaller, according to a first direction, than the dimension of the photo-active area measured in parallel to said first direction and transversally to said interface across said adjacent regions, and wherein the device is optimized for a photoresponse based on the photo-thermal effect, where a photoresponse is generated through light-induced charge carrier heating, in combination with the presence of said Seebeck gradient.

30. The device according to claim 29, wherein said photothermal effect is a photo-thermomagnetic effect.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0084] In the following some preferred embodiments of the invention will be described with reference to the enclosed figures. They are provided only for illustration purposes without however limiting the scope of the invention.

[0085] FIG. 1 is a schematic perspective view of one embodiment of the device of the present invention, where the antenna branches and gate segments are separate elements.

[0086] FIG. 2 is a schematic perspective view of another embodiment of the device of the present invention, where the antenna branches and gate segments are the same elements.

[0087] FIG. 3 is a schematic perspective view of another embodiment of the device of the present invention, highlighting some crucial dimensions thereof.

[0088] FIG. 4 is a perspective view, also schematic, which shows the device of the present invention, for an embodiment for which the device constitutes a THz and/or IR radiation detector;

[0089] FIG. 5 is another schematic perspective view, which shows the device of the present invention, for an embodiment for which the device constitutes a THz emitter;

[0090] FIG. 6 shows experimental results with the photoresponse of a working prototype: photocurrent as a function of gate voltage.

[0091] FIG. 7 shows a schematic perspective view, of one embodiment of the present invention, where the antenna consists of a single branch.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

[0092] As depicted in the attached drawings, the device of the present invention comprises, for the illustrated embodiments: [0093] an antenna having two antenna branches A1 and A2, and adapted to operate as an antenna in the THz and/or IR and/or MW frequency range; [0094] a structure, made of a photoactive material with high Seebeck coefficient, such as graphene arranged on top of a bottom dielectric layer Bd (for example made of hBN), wherein said structure comprises two sections G1, G2 with different Seebeck coefficients, such that a photo-active area Ga (identified in FIG. 3, represented schematically by a solid-line rectangle), within an active channel having a Seebeck gradient and arranged to absorb light radiation impinging thereon, is defined at the interface between the two sections G1, G2 and through adjacent regions thereof at both sides of the interface, particularly along the cooling length L.sub.cool at each side of the interface, and with a width Wg (as shown in FIG. 3) defined by the width of the photo-active channel defined by the structure.

[0095] For the embodiment shown in FIG. 3, the device of the present invention only includes one dielectric layer, particularly bottom dielectric layer Bd, while for the embodiments of FIGS. 1-4 and 7 the device also includes a top dielectric layer Td arranged on top of the photoactive material with high Seebeck coefficient (such as graphene).

[0096] Although the photo-active area Ga is only represented in FIG. 3, the embodiments of FIGS. 1 to 3 and 5 also include such a photo-active area Ga with the same dimensions (Wg and 2L.sub.cool). Therefore, for all of said embodiments (as shown in FIG. 3), the two antenna branches A1, A2 are separated by a distance D′ which is smaller (although it could be equal) than the dimension of the photo-active area Ga measured transversally to said interface across said adjacent regions, i.e. smaller than 2L.sub.cool. Therefore, the focus area of the antenna is also smaller than 2L.sub.cool.

[0097] For the illustrated embodiments, the device of the present invention also comprises a split gate having two gate segments/sections Sg1 and Sg2, adapted to create the above mentioned two regions G1, G2 in the photoactive structure, with the aim of generating a Seebeck gradient in between said two regions G1, G2. As stated in a previous section of this document, alternatively, other kind of mechanisms could be used for creating regions G1, G2, instead of the mentioned split gate.

[0098] The first Sg1 and second Sg2 gate sections of the split gate are separated by a gap D and capacitively coupled to said structure to create, when a voltage differential is applied to the split-gate, the two sections G1, G2 with independently tuneable Fermi energy therein when a voltage differential is applied to the split-gate, wherein the width of the photo-active channel Wg and the cooling length L.sub.cool define the photo-active area Ga, wherein the distance D′ separating the at two antenna branches A1, A2 is equal or smaller than a separation distance defined by said gap D separating the first Sg1 and second Sg2 gate sections.

[0099] For the embodiment of FIG. 1, the antenna branches A1, A2 and gate segments Sg1, Sg2 are separate elements, and as shown therein D′<D, while for the embodiments of FIGS. 2 to 5, they are the same elements, so D′=D.

[0100] As shown especially in FIGS. 1 to 5, the bottom dielectric layer Bd is arranged over the antenna bridging gap D′ so that the interface between the two sections G1, G2 is arranged over gap D′, i.e. over the focus area of the antenna.

[0101] Although not shown in the drawings, the device of the present invention comprises a first voltage source connected to the gate section Sg1 and a second voltage source connected to the gate section Sg2, to generate and apply the above mentioned voltage differential to the split-gate.

[0102] The following different dimensions (some of which are indicated in FIG. 3) refer to respective embodiments of the device of the present invention, including those shown in FIGS. 1-5 and 7, with values included in those ranges already indicated in a previous section, and which for a working prototype are the ones indicated below: [0103] Wg: Width of photo-active channel (i.e. of photo-active area Ga), with a value from 0.1 μm up to 5 μm. [0104] Wa: Width of each antenna branch/gate section A1/Sg1, A2/Sg2, with a value of 2 μm. [0105] Lg: Length of the photo-active structure formed by sections G1 and G2, with a value from 0.2 μm up to 5 μm, always larger than 2*cooling length. [0106] La: Length of each antenna branch/gate section A1/Sg1, A2/Sg2, from a few microns up to a few hundred microns. [0107] Ta: Thickness of each antenna branch/gate section A1/Sg1, A2/Sg2, with a value of 30 nm. [0108] h1 (only for the embodiments of FIGS. 1, 2, 4, 5, and 7): Thickness of the top dielectric layer Td, with a value between 0.5 nm and 50 μm. [0109] h2: Thickness of the bottom dielectric layer Bd, with a value between 0.5 nm and 50 μm. [0110] Lc: Length of each of the electrical contacts E1-E2, with a value just enough to allow access thereto. For example, a value of 10 μm is appropriate for to wirebonding to them, although for other kind of connection, a value of just 2 μm would do. [0111] W.sub.c: Width of electrical contacts E1-E4, with a value of 200 nm. [0112] hc: thickness of the electrical contacts E1-E4, with a value of 30 nm.

[0113] Although not shown in the attached Figures, note that a substrate is generally included in the device of the present invention to support the rest of elements arranged there on or there under.

[0114] Electrical contacts E1 and E2 are not necessary for the embodiments for which the device constitutes a THz and/or IR and/or MW radiation emitter, but only for implementing a THz and/or IR and/or MW detector, while electrical contacts E3 and E4 (see FIG. 3) are not essential for any embodiment, but only included in case a wirebonding to the antenna branches/gate sections A1/Sg1, A2/Sg2 is required.

[0115] As already stated in a previous section, the device of the present invention can be used as a THz and/or IR and/or MW detector, as shown in FIG. 4, and as a THz and/or IR and/or MW emitter, as shown in FIG. 5. For both of the embodiments illustrated in FIGS. 4 and 5, the device can be operated under zero bias voltage, which provides a minimal dark current (limited by Johnson noise) and lower power consumption, although it can also be operated with an applied bias voltage.

[0116] Specifically, for the embodiment of FIG. 4, the device of the present invention constitutes a THz and/or IR and/or MW radiation detector, wherein the antenna is configured and arranged to focus and confine THz and/or IR and/or MW radiation in between the two antenna branches A1, A2 (i.e., in the focus area), to concentrate it at the photo-active area Ga, which is arranged to absorb THz and/or IR and/or MW light radiation, and the device further comprises first E1 and second E2 electrical contacts electrically connected to distanced regions of the graphene layer G to measure photo-induced current flowing between the first E1 and second E2 electrical contacts (i.e. by means of a photoresponse measuring element as depicted in FIG. 4), through the photo-active layer, when THz and/or IR and/or MW light radiation impinges on the photo-active area.

[0117] The operation details for a working prototype of the embodiment of FIG. 4 is described below.

[0118] A voltage V1 is applied to gate segment Sg1, and a voltage V2 to gate segment Sg2, where V1 and V2 are voltages on the order of 1 V. The voltage differential creates the above mentioned Seebeck gradient in the photo-active channel defining the photo-active area Ga, for example a pn-junction if the photo-active material is encapsulated graphene directly above the split-gate interface, with a distance corresponding to the cooling length on both sides of the interface defining one dimension of the photo-active area where the photoresponse is generated, the other dimension being the width of the photo-active channel. For optimal device operation, incident THz and/or IR and/or MW light needs to overlap with the photo-active area Ga of the photodetector. That's exactly what the antenna of the device of the present invention does: it focuses the THz and/or IR and/or MW light in between the two antenna branches A1 and A2.

[0119] FIG. 6 shows experimental results with the photoresponse of said working prototype, particularly in the form of photocurrent as a function of gate voltage.

[0120] From measurement made with the above described working prototype, it has been checked that the detector is relatively broadband (defined by the antenna) and can reach a Noise-equivalent power (NEP) of −160 pW/Hz.sup.1/2 and a Detectivity (D*) of −0.6 10{circumflex over ( )}8 Jones, together with a response time of a few picoseconds. Also, there is no need for cooling the detector and the material and fabrication processes are cheap.

[0121] For the embodiment of FIG. 5, the device of the present invention constitutes a THz and/or IR and/or MW radiation emitter, wherein the photo-active area Ga is arranged to absorb light radiation from femtosecond light pulses shined thereon with a controlled light source F of the device, which is adapted and arranged to generate and emit controlled femtosecond light radiation, so that a photothermoelectrically induced local photovoltage is created at the graphene structure by ultrafast charge separation which leads to the generation of THz and/or IR and/or MW radiation, and wherein the antenna is configured and arranged to emit said generated THz and/or IR and/or MW radiation to far field regions around the device.

[0122] First and second voltage sources (not shown) are respectively connected to the antenna branch/gate section A1/Sg1 and the antenna branch/gate section A2/Sg2, and adapted to generate and apply a voltage differential to the split-gate to electrostatically control the generation and emission of said THz and/or IR and/or MW radiation.

[0123] The operation details for a working prototype of the embodiment of FIG. 5 is described more specifically below.

[0124] A voltage V1 is applied to A1/Sg1, and a voltage V2 to A2/Sg2, where V1 and V2 are voltages on the order of 1 V. The voltage differential creates the above mentioned Seebeck gradient, for example a pn-junction, in the structure including sections G1, G2, (formed, for example, by encapsulated graphene) directly above the split-gate interface, with the photo-active area Ga where the photoresponse is generated defined in one dimension by the cooling length of hot carriers on both sides of the Seebeck gradient (2×Lcool) and in the other dimension by the width of the photo-active channel Wg. As explained above, Femtosecond light pulses (of basically any wavelength) are shined on the photo-active area Ga, and the antenna will emit THz and/or IR and/or MW radiation due to ultrafast generation of a PTE (photo-thermoelectric) photovoltage. In contrast to other known emitters of the state of the art [5], the device of the present invention includes an antenna for better out-coupling if the light and provides an electrostatic control of the generation and emission of the THz and/or IR and/or MW radiation through the voltages applied on the split-gate.

[0125] It must be noted that, for non-illustrated embodiments, the antenna of the device of the present invention is different to the one depicted in FIGS. 1-5, both regarding the type of antenna, which could be spiral antennas, a bowtie antennas (triangles), patch antennas, etc., and also regarding their dimensions.

[0126] As stated in a previous section, non-illustrated embodiments similar to the ones described with reference to the attached drawings, but for which other kind of photo-active areas not including two sections with different Seebeck coefficients are included, are also covered by the present invention.

[0127] Finally, FIG. 7 shows a schematic perspective view of a further embodiment of the device of the present invention, where the antenna consists of a single branch Al that has a focus area which is dimensionally equal or smaller than the photo-active area Ga. Said focus area is located at the extremity of the antenna branch Al that occupies a volume which is located below (or above, for a non-illustrated embodiment) part of the photoactive area Ga (which, although not identified in FIG. 7, is defined and dimensioned as that of FIG. 3).

[0128] FIGS. 8a and 8b show two respective embodiments of the apparatus of the present invention, for which the apparatus comprises a laser source L, preferably a THz QCL, and the THz and/or IR and/or MW radiation detector is a THz radiation detector D.

[0129] For the embodiment of FIG. 8a the THz detector D is integrated into the QCL, i.e. within the same box, where the THz detector is preferably positioned close to the cooling unit that is present in the QCL, i.e. close to the QCL stack.

[0130] However, for the embodiment of FIG. 8b the THz detector D is not integrated into the QCL but just combined therewith, i.e. placed in a separate box, but part of the same equipment.

[0131] For both embodiments, an arrangement for a TOF application is shown, in order to measure a distance to an object O.

[0132] A person skilled in the art could introduce changes and modifications in the embodiments described without departing from the scope of the invention as it is defined in the attached claims.