InP based, terahertz quantum cascade lasers with 4 quantum well active region design

The quantum cascade laser (QCL) is a semiconductor laser that employs radiative transitions of an electron between the bounded states in a superlattice (SL) and phenomenon of resonant tunnelling. Here we present a QCL that operates in the terahertz (THz) spectral region at wavelength of 95 mum.The presented device is based on four quantum well design with spatially diagonal radiative transition and longitudinal-phonon scattering assisted depopulation of lower lasing state. Diagonal nature of the transition with dipole matrix element z=5.2nm leads to favourable lifetime ratio of upper and lower lasing states with better high temperature operation. Maximum operating temperature and output power was improved to and is comparable to the GaAs counterparts.