Characteristics of long wavelength infrared detectors using p-Si/sub 1-x/Ge/sub x//Si multiple quantum wells

We report the first systematic study of p-Si,-,Ge,/Si quantum well infrared photodetectors (QWIPs) grown by low pressure vapour phase epitaxy, including detailed structural, electrical and opticaI characterisation. The growth method is compatible with industrial production, and the devices are potentially suitable as photoconductive detectors operating in normal incidence in large 2-D thermal imaging arrays. Structures have been grown with different numbers of periods and different QW widths, Si,-,Ge, compositions and doping levels. The Si barrier layers are typically 50nm thick and the p-Si contacts are ohmic. Representative characteristics for a 200pm diameter, mesa-isolated, 50 period device under 2V bias are a peak (7.2pm) quantum efficiency of 1 % for a single optical pass, differential resistances of 16MQ at 56K and 170kQ at 75K, and a 1OkHz noise current of 6.5E-13 A/*z at 77K.