AlAs/GaAs quantum cascade lasers based on large direct conduction band discontinuity

The design and operation of quantum cascade (QC) lasers using AlAs/GaAs cou pled quantum wells are reported. In this material system, the conduction ba nd offset at the Gamma point (similar to 1 eV) is much higher than in previ ously reported QC lasers. The use of high band discontinuity allows us to i ncrease the energy separation among the subbands, thus suppressing thermall y activated processes which limit device performance at high temperature. T he measured thermal characteristics of these promising devices are strongly improved from previously reported GaAs-based QC lasers: The temperature de pendence of the threshold current density is described by a very large T-0 (320 K) and the laser slope efficiency does not vary for increasing heat si nk temperatures. The maximum operating temperature is 230 K, limited by neg ative differential resistance effects that occur when the applied bias reac hes 8 V. (C) 2000 American Institute of Physics. [S0003-6951(00)01530-8].