Shortwave limit of infrared intersubband quantum cascade lasers

The feasibility and fundamental difficulty in developing the infrared inter subband quantum cascade lasers in shorter wavelength range were discussed. theoretically. The band offsets of InAs/AlSb on GaSb substrate, InAs/Al0.6G a0.4Sb on GaSb substrate, and In0.53Ga0.47As/In0. 52Al0. 48As on InP substr ate, and the confined states of their quantum wells with and without an app lied electric field were analyzed and calculated by using the fundamental a ssumption of model-solid theory, strained band structure theory, empirical- two-band model for non-parabolic band, and methods of propagation matrix an d laminar approach. It was found that the greatest energy difference betwee n subband edges can not exceed 56 similar to 62% of the conduction band off set, and will be decreased further by the indirect valley. A designed struc ture of intersubband quantum cascade laser consisting of 250 coupled quantu m wells in 25 periods under electric field 100kV/cm for emitting the shorte st wavelength 2. 88 mum was proposed.