Kinetics of quantum states in quantum cascade lasers: device design principles and fabrication

Quantum cascade lasers are based on radiative transition between quasi-boun d states formed by superlattices in the presence of high electric field. In order to understand the device principle so that we can explain and predic t which structures perform better, it is necessary to develop a microscopic model for carrier and current distribution among these quasi-bound states. A mathematical model and simulation results for the kinetics of these quan tum states in quantum cascade lasers are presented in comparison with our e xperimental results. The role of the ratio between inter- and intrasubband scattering rates, and the presence of non-equilibrium phonons are identifie d with explicit calculation. Our preliminary experimental results and calcu lation show that the lasers can have very high T-0 up to 210 K and very low threshold current density of J(th) = 3.4 kA/cm(2) at 300 K with the curren t design. However, it is emphasized that in order to further improve the de vice performance at high temperature, it is very important to devise a stru cture that can dissipate the generated phonons much more efficiently. (C) 1 999 Elsevier Science Ltd. All rights reserved.