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

Abstract

The design and operation of quantum cascade (QC) lasers using AlAs/GaAs coupled quantum wells are reported. In this material system, the conduction band offset at the Γ point (∼1 eV) is much higher than in previously reported QC lasers. The use of high band discontinuity allows us to increase the energy separation among the subbands, thus suppressing thermally activated processes which limit device performance at high temperature. The measured thermal characteristics of these promising devices are strongly improved from previously reported GaAs-based QC lasers: The temperature dependence of the threshold current density is described by a very large T0 (320 K) and the laser slope efficiency does not vary for increasing heat sink temperatures. The maximum operating temperature is 230 K, limited by negative differential resistance effects that occur when the applied bias reaches 8 V.