International Journal of Terahertz Science and Technology
Vol.1, No.4, December 2008. PP.190-236 (4)
date2008-12-22 14:25:58 Click No.6267

TST, Vol. 1, No. 4, PP. 190-206

Invited Talk in SICAST2007

(Invited Talk in SICAST2007) Superconducting THz Detectors and Their Applications in Radio Astronomy

Sheng-Cai SHI *
Purple Mountain Observatory, National Astronomical Observatories, Chinese
Academy of Sciences, Nanjing 210008, China
* scshi@pmo.ac.cn

1. Introduction
It is common knowledge now that the THz region, loosely defined from 0.1THz to 10THz, is rich in scientific and technological opportunities. For example, THz astronomical observations may help answer key questions in the field of astronomy and cosmology. In fact, an entirely new class of galaxy, formed at a very early stage in the universe, has recently been discovered through THz observations [1]. The THz region, however, is to be fully explored as technologies available for this frequency regime are still rather limited. One of significant technical challenges is the development of THz detectors of high sensitivity and large array sizes.

As is well known, detectors can be classified into two categories: incoherent detectors (namely direct detectors, e.g., bolometer) and coherent detectors (e.g., heterodyne mixers). The former is typically of large bandwidth and low or moderate spectral resolution mainly characterizing thermal emissions, while the latter of small bandwidth and high spectral resolution mainly characterizing molecular and atomic spectral lines. On the other hand, superconducting detectors, based essentially on the mechanism of Cooper-pair breaking, have very high sensitivity and can be developed for large arrays (multiple pixels) through lithographic fabrication. They are finding widely used in the fields ranging from astronomy to biology and medicine [2-3].

doi: 10.11906/TST.190-206.2008.12.16

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TST, Vol. 1, No. 4, PP. 207-220

Received Date:20081009

Terahertz band-gap in InAs/GaSb type II superlattices

L.L. Li 1, W. Xu 1,3, Z. Zeng 1, and Y.L. Shi 2
1 Key Laboratory of Materials Physics, Institute of Solid State Physics,
Chinese Academy of Sciences, Hefei 230031, China
2 Kunming Institute of Physics, Kunming, China and
3 Terahertz Research Center,
University of Electronic Science and Technology, Chengdu 610054, China

Abstract: We demonstrate theoretically that it is possible to realize terahertz (THz) fundamental band-gap between the electron mini-band in the InAs layer and the heavy-hole mini-band in the GaSb layer in InAs/GaSb based type II superlattices (SLs). The THz band-gap can be tuned by varying the sample growth parameters such as the well widths of the InAs and/or GaSb layers. The presence of such band-gap can result in a strong cut-off of optical absorption at THz frequencies. For typical sample structures, the THz cut-off of the optical absorption depends strongly on temperature and a sharper cut-off can be observed at relatively high-temperatures. This study is pertinent to the application of InAs/GaSb type II SLs as THz photodetectors. PACS numbers: 72.80.Cw, 72.20.Dp, 73.61.Cw

Keywords: THz band-gap, InAs/GaSb, typesuperlattices(SLÅs) , THz photodetectors

doi: 10.11906/TST.207-220.2008.12.17

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TST, Vol. 1, No. 4, PP. 221-229

Received Date:20080925

(2008-09-25) Improvement of Grating for Smith-Purcell Device

D.Li *, K. Imasaki
Institute for Laser Technology, Osaka 565-0871, Japan
* Email:
dazhi_li@hotmail.com
X. Gao, J. Hou, Z.Yang
University of Electronic and Science Technology, Chengdu 610054, China Gun-Sik Park
Seoul National University, Seoul 151-747, Korea

Abstract: It is known that a grating plays a vital role in the development of a terahertz Smith-Purcell device. The transverse diffusion of optical mode in a general grating is regarded to weaken the beam-wave interaction. In this paper, a sidewall grating for the Smith-Purcell device is proposed. The optical beam can be confined between the side walls to avoid transverse diffusion, so it is possible to enhance the coupling of the optical mode with the electron beam. With the help of three-dimensional particle-in-cell simulations, it has been shown that, comparing with the general grating, the usage of a sidewall grating improves the growth rate and dramatically shortens the time for the device to reach saturation. It is also found that the sidewall grating holds the potential to reduce the start current for the operation of a Smith-Purcell device. We also simulated an ongoing experiment, and predicted the radiation characteristics and the current threshold for the device to start oscillation. This is not only an improvement of grating, but also helpful for further understanding the transverse effect of the grating optical mode.

Keywords: terahertz radiation, sidewall grating, Smith-Purcell radiation, three-dimensional simulation

doi: 10.11906/TST.221-229.2008.12.18

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TST, Vol. 1, No. 4, PP. 230-236

Monte Carlo Simulation of Terahertz Quantum-Cascade Lasers

H. Li and J. C. Cao *
State Key Laboratory of Functional Materials for Informatics,
Shanghai Institute of Microsystem and Information Technology,
Chinese Academy of Sciences,
865 Changning Road, Shanghai 200050, China
* Email:
jccao@mail.sim.ac.cn

Abstract: An ensemble Monte Carlo model is used to evaluate the bias and temperature dependent performance of a 4.1-THz quantum cascade laser with four-well resonant-phonon design. Carrier transport and gain characteristics are investigated. A buleshift in lasing frequency with increasing temperature is clearly observed. Because the broadening effect of temperature dependent gain profile is excluded in the model, our calculations overestimate the peak gain and subsequently overrate the maximum operating temperature. Under a linear approximation condition, the deduced maximum operating temperature is in good agreement with experiment. The simulation also shows that the lasing frequency is insensitive to temperature.

Key words: terahertz, quantum cascade laser, Monte Carlo

doi: 10.11906/TST.230-236.2008.12.19

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