Speaker:Holger T. Grahn received the diploma in physics from the Kiel University, Germany, in 1983 and his Ph. D. from Brown University in Providence, Rhode Island, USA, in 1987. From 1988 to 1992, has worked as a postdoctoral research associate at the Max Planck Institute for Solid State Research in Stuttgart, Germany. In 1992 he moved to the Paul Drude Institute for Solid State Electronics in Berlin, Germany, where he has been department head for Analytics (until 1996) and Semiconductor Spectroscopy (since 1997). In 2001, he was appointed Adjunct Professor in Physics at the Technical University Berlin, Germany. His research interests include optical and electronic properties of semiconductor hetero- and nanostructures, ultrafast spectroscopy, quantum-cascade lasers, and group-III nitrides. He co-authored more than 370 publications and holds several patents.
The 187th:Terahertz Quantum-Cascade Lasers
Date:
From:9:00am, Mrch 11, 2013
Title:Terahertz Quantum-Cascade Lasers
Speaker:Prof. Holger T. Grahn （Paul Drude Institute for Solid State Electronics, Berlin, Germany）
Time:9:00am, Mrch 11, 2013
Venue:Salon Meeting Room, Institute of Semiconductors, CAS
Abstract:Quantum-cascade lasers (QCLs) are unipolar devices, where the lasing transition occurs between subbands within either the conduction or the valence band. From the structural point of view, QCLs are semiconductor superlattices with a rather complex unit cell. The emission energy can be engineered by design. The population inversion for the gain is provided by tunneling of carriers from an injector into the upper laser level so that the optical and transport properties depend critically on the balance between the intersubband transition rates and the carrier distribution. For the terahertz (THz) spectral range, the materials system of choice is GaAs for the quantum well and (Al,Ga)As for the barrier. THz QCLs ranging from 1 to 5 THz are promising light sources for a variety of applications such as THz imaging as well as absorption spectroscopy and are used as local oscillators in heterodyne receivers.Important device parameters are the threshold current density, minimum operating voltage, maximum slope efficiency, and maximum operating temperature. These quantities can be optimized using different designs of the unit cell, which are determined by the number of quantum wells, the layer thicknesses, the barrier height, and the doping profile. Recent developments with respect to these device parameters will be discussed.