Temperature dependence of responsivity in quantum dot infrared photodetectors

Photoconductive spectra of InAs quantum dots embedded within InAlAs barriers show several peaks, ranging from 4 to 12 μm. The nature of these peaks differs, as indicated by their dependence on bias and on temperature. The long wavelength peak drops rapidly with temperature, while the first peak hardly changes up to 60 K. While the wide peak around 4 μm depends linearly on bias, indicating a direct excitation into the quasi-continuum, the peak at 12 μm increases super-linearly since the photocarriers are generated by a two-step process, excitation into a bound level followed by tunneling to the continuum. This explains the drop with temperature, since as the temperature increases more carriers relax from the excited state back to the ground level rather than tunneling into the continuum.