With the interest in the terahertz region of the spectrum (0.1-3.0 Hz) for applications in imaging, communication, security and defense, there is an increasing need for terahertz detectors exhibiting low dark current and operating at high temperatures. One major challenge is the reduction of the dark current (due to thermal excitations) associated with the terahertz detection mechanisms. Since quantum dot (QD) based detectors inherently show low dark currents, a QD based structure is a suitable choice for terahertz detectors. The work described here demonstrates a terahertz tunneling quantum dot infrared photodetector (T-QDIP) operating up to 150 K. In the T-QDIP structure grown by molecular beam epitaxy (MBE), a QD (InGaAs or AlGaAs) is placed in a well (GaAs/AlGaAs) followed by a double barrier (AlGaAs/InGaAs/AlGaAs) next to the well. The photocurrent generated by a transition from the ground state in the QD to a state in the well coupled with the double barrier (resonant state) can be selectively collected by resonant tunneling, while the double-barrier blocks the majority of the carriers contributing to the dark current (carriers excited to any other state in the well). Two important properties of the T-QDIP detectors are the tunability of the operating wavelength and the multi-color (band) nature of the photoresponse based on different transitions in the structure. Successful results on a two-color T-QDIP with photoresponse peaks at ~6 μm and ~17 μm operating at room temperature, and a terahertz T-QDIP responding at 6 THz (50 μm) at 150 K is presented. Furthermore, the wavelength bands in a dual-band T-QDIP resulting in transitions from the QD ground state to two states in the well coupled with double-barrier states (i.e. two resonant states) can be tuned by the bias. This is due to the dependence of resonance conditions for each resonant state on the applied bias. This would allow the separation of photocurrent due to two response bands without using external filters. This multi-band nature of T-QDIP detectors would be useful for applications such as mine detection, where scanning in two different wavelength bands greatly enhances detection capabilities and reduces false positives.

This work is done jointly with Prof. P. Bhattacharya’s group at University of Michigan, Ann Arbor, under NSF grants, ECCS: 0620688 and ECCS: 0553051.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/9682 must be provided.