Mitin, V., Antipov, A., Sergeev, A., Vagidov, N., Eason, D., & Strasser, G. (2011). Quantum Dot Infrared Photodetectors: Photoresponse Enhancement Due to Potential Barriers. Nanoscale res lett, 6(1), 6.
Abstract: Potential barriers around quantum dots (QDs) play a key role in kinetics of photoelectrons. These barriers are always created, when electrons from dopants outside QDs fill the dots. Potential barriers suppress the capture processes of photoelectrons and increase the photoresponse. To directly investigate the effect of potential barriers on photoelectron kinetics, we fabricated several QD structures with different positions of dopants and various levels of doping. The potential barriers as a function of doping and dopant positions have been determined using nextnano3 software. We experimentally investigated the photoresponse to IR radiation as a function of the radiation frequency and voltage bias. We also measured the dark current in these QD structures. Our investigations show that the photoresponse increases ~30 times as the height of potential barriers changes from 30 to 130 meV.
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Семенов, А. В., Девятов, И. А., Рябчун, С. А., Масленников, С. Н., Масленникова, А. С., Ларионов, П. А., et al. (2011). Поглощение терагерцового электромагнитного излучения в “грязной” сверхпроводниковой пленке при произвольном виде спектральных функций. Ж. Радиоэлектрон., 10, 7.
Abstract: A problem of absorption of high-frequency electromagnetic field in dirty superconductor is treated within Keldysh technic. Expression for the source term in the kinetic equation for quasiparticle distribution function is derived. The result is significant for deriving a consistent microscopic theory of superconducting detectors for terahertz frequency range, perspective detectors on kinetic inductance of current-biased superconducting strip and on Josephson inductance of tunnel.
В технике Келдыша рассмотрена задача о поглощении мощности высокочастотного электромагнитного поля в сверхпроводнике, удовлетворяющем условию грязного предела. Получено выражение для члена источника в кинетическом уравнении для функции распределения квазичастиц, справедливое при произвольном виде спектральных функций. Этот результат имеет значение для развития последовательной микроскопической теории сверхпроводниковых детекторов излучения терагерцового диапазона, в частности, перспективных детекторов на кинетической индуктивности смещённой током сверхпроводниковой полоски и джозефсоновской индуктивности туннельного контакта.
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González, F. J., & Boreman, G. D. (2005). Comparison of dipole, bowtie, spiral and log-periodic IR antennas. Inf Phys & Technol, 46(5), 418–428.
Abstract: Antenna-coupled microbolometers use planar lithographic antennas to couple infrared radiation into a bolometer with sub-micron dimensions. In this paper four different types of infrared antennas were fabricated on thin grounded-substrates and coupled to microbolometers. Dipole, bowtie, spiral and log-periodic IR antenna-coupled detectors were measured at 10.6 μm and their performance compared. A new method to calculate the radiation efficiency based on the spatial and angular response of infrared antennas is presented and used to evaluate their performance. The calculated radiation efficiency for the dipole, bowtie, spiral and log-periodic IR antennas was 20%, 37%, 25% and 46% respectively. A dipole-length study was performed and shows that the quasistatic value of the effective permittivity accurately describes the incident wavelength in the substrate at infrared frequencies for antennas on a thin substrate.
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Il'in, K. S., Lindgren, M., Currie, M. A., Semenov, D., Gol'tsman, G. N., Sobolewski, R., et al. (2000). Picosecond hot-electron energy relaxation in NbN superconducting photodetectors. Appl. Phys. Lett., 76(19), 2752–2754.
Abstract: We report time-resolved characterization of superconducting NbN hot-electron photodetectors using an electro-optic sampling method. Our samples were patterned into micron-size microbridges from 3.5-nm-thick NbN films deposited on sapphire substrates. The devices were illuminated with 100 fs optical pulses, and the photoresponse was measured in the ambient temperature range between 2.15 and 10.6 K (superconducting temperature transition TC). The experimental data agreed very well with the nonequilibrium hot-electron, two-temperature model. The quasiparticle thermalization time was ambient temperature independent and was measured to be 6.5 ps. The inelastic electron–phonon scattering time Ï„e–ph tended to decrease with the temperature increase, although its change remained within the experimental error, while the phonon escape time Ï„es decreased almost by a factor of two when the sample was put in direct contact with superfluid helium. Specifically, Ï„e–ph and Ï„es, fitted by the two-temperature model, were equal to 11.6 and 21 ps at 2.15 K, and 10(±2) and 38 ps at 10.5 K, respectively. The obtained value of Ï„e–ph shows that the maximum intermediate frequency bandwidth of NbN hot-electron phonon-cooled mixers operating at TC can reach 16(+4/–3) GHz if one eliminates the bolometric phonon-heating effect.
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D. Henrich, L. R. S. D., M. Hofherr, K. Il'in, A. Semenov, and M. Siegel. (2012). Detection efficiency of a spiral-nanowire superconducting single-photon detector. arXiv:1210.3988.
Abstract: We investigate the detection efficiency of a spiral layout of a Superconducting Nanowire Single-Photon Detector (SNSPD). The design is less susceptible to the critical current reduction in sharp turns of the nanowire than the conventional meander design. Detector samples with different nanowire width from 300 to 100 nm are patterned from a 4 nm thick NbN film deposited on sapphire substrates. The critical current IC at 4.2 K for spiral, meander, and simple bridge structures is measured and compared. On the 100 nm wide samples, the detection efficiency is measured in the wavelength range 400-1700 nm and the cut-off wavelength of the hot-spot plateau is determined. In the optical range, the spiral detector reaches a detection efficiency of 27.6%, which is ~1.5 times the value of the meander. In the infrared range the detection efficiency is more than doubled.
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