Transport properties of epitaxial lift-off films

Transport properties of epitaxially lifted-off (ELO) films were characterized using conductivity, Hall, and Shubnikov-de Haas measurements. A 10%-15% increase in the two-dimensional electron gas concentration was observed in these films as compared with adjacent conventional samples. We believe this result to be caused by a backgating effect produced by a charge buildup at the interface of the ELO film and the quartz substrate. This increase results in a significant decrease in the quantum lifetime in the ELO samples, by 17%-30%, but without a degradation in carrier mobility. Under persistent photoconductivity, only one subband was populated in the conventional structure, while in the ELO films the population of the second subband was clearly visible. However, the increase of the second subband concentration with increasing excitation is substantially smaller than anticipated due to screening of the backgating effect.