Measurements of breakdown voltage in p-i-n diodes with thin i regions are compared with local and non-local theoretical calculations. It is found that overshoot effects compensate for the dead space at high fields close to breakdown but that non-local aspects become stronger at lower fields.

Gain and geometric magnetoresistance electron mobility measurements are presented for quantum-well infrared photoconductors. The electron mobility is found to be identical for both the photocurrent and the dark current and has a value of 2.6×103 cm2 V−1 s−1 in devices made from GaAs/AlxGa1−xAs and 9.4×103 cm2 V−1 s−1 in the InxGa1−xAs/GaAs devices at 77 K. This difference in mobility is associated with the purity of the barrier material which is much greater in GaAs than in AlxGa1−xAs. The photoelectron lifetime before recapture can be deduced from the combination of the gain and mobility measurements. This lifetime is found to be 7.2 ps in the AlxGa1−xAs/GaAs detectors and 5.5 ps in the InxGa1−xAs/GaAs devices.

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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.