Modeling of spectral broadening and photoresponse in III-V infrared sensors incorporating low dimensional quantum confined systems

Abstract

Infrared (2􀀀10 m) is an extremely useful region of the electromagnetic spectrum for trace gas analysis in environmental or medical monitoring applications, since a large number of strong fundamental vibrational molecular transition spectral lines fall in this range. Present work explores the mid-IR photodetection mechanism in III-V quantum con ned system in twofold ways. Firstly, it models the extent of spectral linewidth broadening of photo-detector. Secondly, it investigates whether a strong perturbation of light can modulate the electronic bandstructure and thus add non-linearity to the opto-electronic behavior of the device. Electronphoton interaction in the device is modeled in Non-equillibrium Green's Function( NEGF) formalism. Photo-absorption mechanism in the detector is correlated to reduced carrier lifetime in ground state which leads to uncertainty in energy levels and homogeneous spectral widening- which is calculated here. Besides homogeneous broadening in photo-current spectrum, inhomogeneous broadening in quantum dot-in-a-well infrared photo-detector(DWELL-IP) is also taken care of. Inhomogeneous broadening is attributed to the non-uniform size and composition of quantum dots in a self-grown assembly. Individual contribution of these factors towards spectral broadening is modeled in order to get the envelop of photocurrent spectrum. The model generates photocurrent spectrum with 1:4 m broadening centered at 3:5 m at 77K for a DWELL-IP, which agrees with the experimental result. The calculated photocurrent spectral width of 1:3 m for GaAs=AlGaAs Quantum Well(QW) centered at 8:31 m at 77K also supports experimental data. In addition to photocurrent peak at mid-IR, the calculation reveals the emergence of a second resonant peak in the spectrum of QW-IP in far infrared region (20 􀀀 50 m) as the photon volume density increases upto 0:1% of carrier density inside the active region. At such high density of photon, perturbation theory falls short of explaining the system behavior. To account for the creation of far-IR resonant photocurrent peak, a hybrid density-of-states for strongly coupled electronphoton system is introduced here. The mid-IR photocurrent peak is found to shift upto 2 m towards the red end as the photon volume density reaches from 0:1% to 1:0% of carrier density, while the far-IR peak experiences pronounced blue-shift.