Photoconductivity of a degenerate electron-hole plasma in GaInAs/AlInAs MQW structures

Abstract

Degenerate electron-hole plasmas have been produced in the quantum wells of GaInAs/AlInAs MQW systems using 100 ps pulses from a Q-switched, mode-locked Nd-YAG laser. Photoconductivity parallel to the layers showed band-filling effects, and good exponential decays were observed over several orders of magnitude of carrier density. For a 50 well system with 50 AA wells and 100 AA barriers the recombination time constant was 3.6+or-0.2 ns between 300 K and 150 K, rising to 7 ns at 40 K. There was no indication of Auger processes, implying that the Auger coefficient was less than 10-30 cm6 s-1, which is much smaller than the reported values. The intensity of light at the onset of band filling reduced linearly with reducing temperature between 300 K and 150 K following a trend expected from the temperature dependence of the band gap. The initial well photoconductivity produced by a given light intensity reduced with reducing temperature. The electron mobility in the electron-hole plasma was about 400 cm2 V-1 s-1. No change with carrier density was observed. Below 40 K short time constant components tend to dominate the decay and the photoconductivity becomes noisy. In the case of a 20 well sample the signal was heavily influenced by photoconductivity in the semi-insulating InP substrate. It is pointed out that band filling allows a distinction to be made between well and substrate/cladding photoconductivities.