High-frequency modulation without the relaxation oscillation resonance in quantum cascade lasers

Quantum cascade (QC) lasers, based on intersubband transitions in semiconductor quantum wells, are characterized by ultrafast (picosecond) carrier lifetimes. An important consequence of this unique property is the expected absence of relaxation oscillations in the transient response of these devices. Here, we discuss and experimentally verify this prediction by measuring the modulation response of several 8-mum-QC lasers, properly processed and packaged for high-speed operation, up to 10 GHz. (C) 2001 American Institute of Physics.