Effect of the proximity of an ex situ patterned interface on the quality of two-dimensional electron gases at GaAs/AlGaAs heterojunctions

Abstract

High-quality two-dimensional electron gases (2DEGs) were regrown onto ex situ patterned substrates and the effect of the distance between the 2DEG and the contaminated regrowth interface was investigated. At a separation of 220 nm mobilities of 7.1×105 cm2 V−1 s−1 in the dark and 1.3×106 cm2 V−1 s−1 after illumination with a red light-emitting diode (LED) were measured with corresponding carrier concentrations of 2.4×1011 and 4.3×1011 cm−2. The quality of this 2DEG was equivalent to that attained in conventionally grown 2DEGs at the time, indicating that the 2DEG was not affected by presence of the regrowth interface in this case. For smaller separations a degradation in the 2DEG quality was observed. Thus, at a separation of only 60 nm, a mobility of 4.1×105 cm2 V−1 s−1 at a carrier concentration of 4.2×1011 cm−2 was measured after illumination. The use of an independently contacted n+ layer in the patterned substrate as a backgate was also demonstrated.