Optical characterisation of quantum well infra-red detector structures

Optical characterisation of GaAs/AlGaAs quantum well infra-red photodetecto r (QWIP) structures by interband photoluminescence (PL) spectroscopy has be en performed. The effect on the low temperature PL spectrum of both the dop ing concentration in the wells and the presence of thin lateral barriers is analysed. In addition to the main peak (e1-hh1), a second peak at lower en ergy is observed in doped structures and attributed to a donor-to-acceptor transition. The broadening of the e1-hh1 peak when the doping in the wells is increased is interpreted in terms of the bandfilling effect in the wells . An additional broadening appears when thin lateral barriers with higher c ontent are introduced in the structure. Responsivities as high as 0.5 A/W w ithout external coupling mechanisms of the incident light have been measure d in samples showing the above-mentioned features in the PL spectra.