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Yang, Z. Q., Hajenius, M., Baselmans, J. J. A., Gao, J. R., Klapwijk, T. M., Voronov, B., et al. (2005). Improved sensitivity of NbN hot electron bolometer mixers by vacuum baking. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 222–225).
Abstract: We find that the sensitivity of heterodyne receivers based on superconducting hot-electron bolometer (HEB) in- creases by 25 − 30% after baking at 85 o C and in a high vacuum. The devices studied are twin-slot antenna coupled HEB mixers with a small NbN bridge of 1×0.15 μm 2 . The mixer noise temperature, gain, and resistance versus temperature curve of a HEB before and after baking are compared and analyzed. We show that baking reduces the intrinsic noise of the mixer by 37 % and makes the superconducting transition of the bridge and the contacts sharper. We argue that the reduction of the noise is due to the improvement of the transparency of the contact/film interface. The lowest receiver noise temperature of 700 K is measured at a local oscillator frequency of 1.63 THz and a bath temperature of 4.3 K.
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Budyanskij, M. Y., Sejdman, L. A., Voronov, B. M., & Gubkina, T. O. (1992). Increase of reproducibility in production of superconducting thin films of niobium nitride. Sverkhprovodimost': Fizika, Khimiya, Tekhnika, 5(10), 1950–1954.
Abstract: Technique to control the composition of gas medium in the reactive magnetron discharge and the composition of the deposited films of niobium nitride using electrical parameters of discharge only, in particular, by δU = Up – Uar value at contant stabilized discharge current is described. Technique to select optimal condition for deposition of niobium nitride films when the films have composition meeting chemical formula, is suggested. Thin films of niobium nitride with up to 7 nm thickness and with rather high temperature of transition into superconducting state Tk > 10 K) and with low width of transition (δ < 0.6 K), are obtained. It is determined, that substrate material and dielectric sublayer do not affect. Tk value, while difference in coefficients of thermal expansion of substrate and of film affects δTk value.
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Hajenius, M., Baselmans, J. J. A., Gao, J. R., Klapwijk, T. M., de Korte 2, P. A. J., Voronov, B., et al. (2004). Increased bandwidth of NbN phonon cooled hot electron bolometer mixers. In Proc. 15th Int. Symp. Space Terahertz Technol. (pp. 381–386).
Abstract: We study experimentally the IF gain bandwidth of NbN phonon-cooled hot-electron-bolometer (HEB) mixers for a set of devices with different contact structures but an identical NbN film. We observe that the IF bandwidth depends strongly on the exact contact structure and find an IF gain bandwidth of 6 GHz for a device with an additional superconducting layer (NbTiN) in between the active NbN film and the gold contact to the antenna. These results contradict the common opinion that the IF bandwidth is determined by the phonon-escape time between the NbN film and the substrate. Hence we calculate the IF gain bandwidth of a superconducting film using a two-temperature model. We find that the bandwidth increases strongly with operating temperature and is not limited by the phonon escape time. This is because of strong temperature dependence of the phonon specific heat in the NbN film.
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Rosfjord, K. M., Yang, J. K. W., Dauler, E. A., Anant, V., Berggren, K. K., Kerman, A. J., et al. (2006). Increased detection efficiencies of nanowire single-photon detectors by integration of an optical cavity and anti-reflection coating. In CLEO/QELS (JTuF2 (1 to 2)).
Abstract: We fabricate and test superconducting NbN-nanowire single-photon detectors with an integrated optical cavity and anti-reflection coating. We design the cavity and coating such as to maximize absorption in the NbN film of the detector.
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Emelianov, A. V., Nekrasov, N. P., Moskotin, M. V., Fedorov, G. E., Otero, N., Romero, P. M., et al. (2021). Individual SWCNT transistor with photosensitive planar junction induced by two‐photon oxidation. Adv. Electron. Mater., 7(3), 2000872.
Abstract: The fabrication of planar junctions in carbon nanomaterials is a promising way to increase the optical sensitivity of optoelectronic nanometer-scale devices in photonic connections, sensors, and photovoltaics. Utilizing a unique lithography approach based on direct femtosecond laser processing, a fast and easy technique for modification of single-walled carbon nanotube (SWCNT) optoelectronic properties through localized two-photon oxidation is developed. It results in a novel approach of quasimetallic to semiconducting nanotube conversion so that metal/semiconductor planar junction is formed via local laser patterning. The fabricated planar junction in the field-effect transistors based on individual SWCNT drastically increases the photoresponse of such devices. The broadband photoresponsivity of the two-photon oxidized structures reaches the value of 2 × 107 A W−1 per single SWCNT at 1 V bias voltage. The SWCNT-based transistors with induced metal/semiconductor planar junction can be applied to detect extremely small light intensities with high spatial resolution in photovoltaics, integrated circuits, and telecommunication applications.
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