Physical model of depletion and accumulation in quantum-wellinfrared photodetectors

摘要

Numerical work has shown that, at low operating temperatures ornlarge incident photon fluxes, carriers deplete from the quantum wellsnnear the emitter contact in a quantum-well infrared photodetectorn(QWIP). A physical model is developed in this work to describe, withnclosed-form analytical expressions, the accumulation and depletion ofncarriers in QWIPs. In QWIPs having the same growth sequence (layernwidths and compositions) in each period, carrier depletion is found tonoccur only in one or two QWs near the emitter contact at the smallnapplied biases for which the electron drift velocity is linear in thenelectric field. At intermediate applied biases for which the electronndrift velocity is saturated, carrier depiction is found to be partial,nuniform (throughout the depletion region), and abrupt, with the totalncharge in the depletion region fixed and with the depletion widthnincreasing linearly with applied bias. At a large applied bias, carriersnare found to be uniformly accumulated in the device. Carrier depletionnor accumulation in QWIPs arises from the different dependences on thenlocal electric field of the different physical mechanisms which arenresponsible for the carrier injection from the contacts (via thermionicnemission or thermionic field assisted tunneling) and for thenphotoconduction process (via drift)