The growth and measurement of terahertz quantum cascade lasers

Results are presented for two GaAs/AlGaAs quantum cascade laser (QCL) structures that emit at frequencies of 2.59 and 2.75 THz. Both structures have a nominally identical, bound-to-continuum active region design, and the difference between their emission frequencies is interpreted as resulting from small differences in the gallium and aluminium growth rates, which were measured both before and after laser growth using a pyrometric spectrometry technique. The same technique allows the QCL growth itself to be monitored real-time, and drifts in growth rates identified.