Semiconducting superlattice as a solid-state terahertz local oscillator for NbN hot-electron bolometer mixers

Abstract

The terahertz frequency range comprises a consid erable part of the electromagnetic spectrum between the microwave and infra red ranges. However, explo ration of this frequency region began fairly recently owing to lack of powerful terahertz sources and receiv ers capable of detecting terahertz radiation.The problem with building efficient terahertz sources which would cover a wide frequency range is that the existing technology for generating radiation of neighbouring regions does not work quite as well at terahertz frequencies. At the high frequency end of the terahertz region it is difficult to achieve stable inverse population of energy levels with a sufficiently long lifetime, as in lasers. That is the reason why, for example, quantum cascade lasers (QCL) have to be cooled down to nitrogen temperatures or below in order to generate terahertz radiation. At the low fre quency end, the maximum frequency is determined by the electron travel time in the device, as in backward wave oscillators (BWO). In consequence, high electric and magnetic fields are required to produce terahertz radiation.Solid state radiation sources, such as avalanche diodes and quantum wells, are rather attractive owing to their small size, possibility of frequency remote control in a wide range, low weight and low energy consumption. However, these sources have certain limitations posed by influence of spurious parameters that grows with frequency and results in mismatch and decreased power output. The easiest and well known way to produce terahertz radiation is to multiply the frequency of an external generator with varactor mul tiplier diodes-doublers, triplers and arrays of such diodes. Although certain progress has been made in this direction, operation in the sub millimetre range requires high power reference generators and high efficiency multipliers. In this respect, semiconducting GaAs/AlAs superlattice (SSL) nanostructures look rather promising as candidates for frequency multipli cation because of their high efficiency, and so can potentially be used as terahertz LOs. The reason for this is that SSL's current voltage (IV) curve has a region with a negative differential resistance which continues up to terahertz frequencies [1].It has been shown that SSLs can be employed in high resolution spectroscopy measurements at tera hertz frequencies [2], in phase lock loops [3], as LOs of hot electron bolometer (HEB) receivers, and as a signal source in spectroscopy systems up to 3.2 THz [4,5]. As demonstrated in [6], SSLs can operate in a wide tem perature range of 4.2-300 K, and their efficiency is increased by an order of magnitude at helium temper atures (4.2 K).In this paper we present our results of studying the output power of an SSL operated at 4.2 K, and its per formance as an LO of a terahertz NbN HEB receiver. The authors of paper [7] have shown that the optimal LO power level for quasioptical and waveguide NbN HEB receivers does not exceed 100-200 nW at tera hertz frequencies. Our HEB mixers were fabricated at MSPU from superco...

Current state and prospects of detectors in the terahertz range. Part 2. Heterodyne detection of terahertz radiation

“…Сверхпроводящие HEB-детекторы характеризуются хорошими темновыми характеристиками, ГГц-скоростью счета и они также перспективны как счетчики отдельных фотонов в широком ИК спектральном диапазоне. Сомнительно, что сверхпроводящие HEBs, действующие при высоких температурах, достигнут чувствительности низкотемпературных сверхпроводящих HEBs из-за избыточного шума, но вследствие короткого времени электрон-фононной релаксации эти материалы являются перспективными для широкополосных приборов [24][25][26].…”