Abstract
Quantum cascade lasers (QCLs) are semiconductor lasers based on intersubband transitions in semiconductor
quantum wells. We discuss the temperature dependences of laser performances for QCLs emitting
in the mid-infrared region. The device characteristics of QCLs depend on transition strength, the lifetime
of each energy level, and the coupling strength among energy levels. Temperature-insensitive QCLs have
been successfully implemented by employing deep quantum wells and high barriers within the active region.
In addition, QCLs based on anti-crossed dual-upper-state designs are a promising candidate for
many spectroscopic applications, because of their broad bandwidth and high device performances. The
lasers characterized by strong, super-linear, current-light output curves possess an exceptionally elevated
characteristic temperature that ranges from T0 = 400 ~ 1085 K. The slope efficiency rises with temperature,
as shown by a negative value of T1. The distinct features are due to optical-absorption quenching in
the injector and reduced carrier leakage in the active region.
