A superconductor single photon detector based on NbN nanowire was fabricated using electron beam lithography (EBL) and reactive ion etching (RIE) for infrared photon detection. When biased well below its critical current at 4.2 K, NbN nanowire is very sensitive to the incident photons. Typical telecommunication photons with a wavelength of 1550 nm were detected by this detector. Data analysis indicates the repeating rate of the device with 200 nm NbN nanowire may be up to 100 MHz, and the quantum efficiency is about 0.01% when biased at 0.95Ic.
ZHANG LaBao ZHONG YangYin KANG Lin CHEN Jian JI ZhengMing XU WeiWei CAO ChunHai
Using YBa2Cu3O7-δ/MgO bicrystal Josephson junction,we have developed a setup for spectrum analyses of terahertz signals,up to 2.5 THz,with a frequency resolution of 3 GHz.The junction works at liquid nitrogen temperature when the signal frequencies are low while for signals at 1.6 THz and 2.5 THz the junction is cooled to 6 K.Digital signal processing(DSP) chips are made use of to build a data acquisition and processing system so that it can be compact,fast,and intelligent.With the completion of the relevant hardwares and softwares,the measurements are now automated.
XU WeiWei,CHEN Jian,KANG Lin & WU PeiHeng Department of Electronic Science & Engineering,Nanjing University,Nanjing 210093,China
This paper describes the design and fabrication of superconducting hot electron bolometer (HEB) mixer based on ultra-thin superconducting NbN films. The high quality films were epitaxially grown on high resistance Si substrates. The device was fabricated by magnetron sputtering, electron beam lithography (EBL), reactive ion etching (RIE), lithography, and so on. The device's resistance-tempera-ture (R-T) curves and current-voltage (I-V) curves were studied. The results of THz response of the device are presented. Y-factor technique was used to measure the device's noise temperature. When the device was irradiated with a laser radiation of 2.5 THz, the obtained lowest noise temperature of the device was 2213 K.
WANG JinPing LI YangBin KANG Lin WANG Yu ZHONG YangYin LIANG Min CHEN Jian CAO ChunHai XU WeiWei WU PeiHeng
A simple Fourier transform spectrometer was designed and constructed for the measurement of detectors,sources,passive devices and materials in the terahertz(THz) range.It can be operated at frequencies between 0.3 and 1.5 THz,using a 50-μm-thick Mylar-film beam splitter.The spectral range can be changed by altering the thickness of the beam splitter.The highest frequency resolution is 750 MHz.We studied the properties of heterodyne detectors including superconductor mixers and semiconductor harmonic mixers,direct detectors including an InSb semiconductor bolometer,superconducting tunnel junctions and the Golay cell,and sources including Gunn oscillators and a microwave source with its multipliers,as well as various materials and passive devices including Si wafers and metal mesh filters.
Voltage responsivity of bolometer will benefit from high temperature coefficient of resistance (TCR) of the material. The Nb5N6 thin solid films we proposed in this paper have high TCR, compared with the commonly-used materials such as Nb and Bi. The films were sputtered on Si(100), SiO2/Si(100), SiO2 substrates by using radio frequency (rf) magnetron sputtering. The deposition conditions have been optimized to get high TCR. The highest TCR is over 0.91% K-1 at 300 K and up to 4.5% K -1―7% K-1 at 78 K, which is good enough to be used in terahertz detection and thermometer fabrication in the range from 78 K to 300 K.
LU XueHui HE Ning KANG Lin CHEN Jian JIN BiaoBing WU PeiHeng
