Shortwave limit of infrared intersubband quantum cascade lasers

The feasibility and fundamental difficulty in developing the infrared intersubband quantum cascade lasers in shorter wavelength range were discussed. theoretically. The band offsets of InAs/AlSb on GaSb substrate, InAs/Al0.6Ga0.4Sb on GaSb substrate, and In0.53Ga0.47As/In0. 52Al0. 48As on InP substrate, and the confined states of their quantum wells with and without an applied electric field were analyzed and calculated by using the fundamental assumption of model-solid theory, strained band structure theory, empirical-two-band model for non-parabolic band, and methods of propagation matrix and laminar approach. It was found that the greatest energy difference between subband edges can not exceed 56 similar to 62% of the conduction band offset, and will be decreased further by the indirect valley. A designed structure of intersubband quantum cascade laser consisting of 250 coupled quantum wells in 25 periods under electric field 100kV/cm for emitting the shortest wavelength 2. 88 mum was proposed.