Si1-xGex/Si multiquantum well IR detectors grown by low pressure vapour phase epitaxy

The authors report measurements on Si_1-xGe_x/Si MQW IR detectors grown by low-pressure vapour phase epitaxy (LP-VPE). Device characteristics such as the temperature-dependent IV curves, IR photoresponse and photoconductive gain are presented. It has been shown that the tunnelling component of the low temperature dark current in Si_1-xGe_x/Si MQWs is very sensitive to B doping level in QWs for sample growth at 640°C, low silane flow, and with doping across the full width of the QWs. For samples lightly doped in only the central 2/3 of each QW and grown at 610°C and higher silane flow, low tunnelling currents were obtained. A photoresponse has been measured for the lightly doped structures in the 5-14 μm range. A small peak at 11.5 μm with a sharp cut-off at increasing wavelength is probably due to a QW transition because of its close agreement with E_a for the sample. The photoconductive gain derived from noise measurements shows no bias dependence for biases up to 0.1 V per period for both the 10 and 50 MQW period devices, suggesting that the hole mean free path remains constant. The gain shows the expected variation with the number of QWs