Modeling of intersubband transitions in quantum well infrared photodetectors with complex well-barrier structures

The subband dispersions and optical intersubband transitions in n-type quantum well infrared photodetectors (QWIPs) with complex well-barrier structures are calculated using 8-band k(.)p model combined with the envelope-function Fourier expansion method. It is shown that the method presented here is very effective for simulating numerically quantum well structures with complex potential profile. The relaxation of quantum confinement in the growth direction has been taken into consideration in detail. The calculation results for the voltage-tunable InGaAs/AlGaAs QWIP with linear-graded barrier for broadband photodetection under different applied bias conditions are consistent with experimental observations very well. It has also been indicated that the selection rules were broken in the asymmetrical quantum well structures, resulting in great changes of intersubband transitions. This work is helpful for analysis and design of QWIPs with various complex well-barrier structures working under various applied bias.