M. Lastapis, D. Riedel, A. Mayne, K. Bobrov, and G. Dujardin, Low temperature electron transport on semiconductor surfaces, Low Temp. Phys. 29, (2003) [Fiz. Nizk. Temp. 29, 263-269, (2003)] DOI: https://doi.org/10.1063/1.1542440.