Gul, Yilmaz; Holmes, Stuart Nicholas; Cho, Chang-Woo; Piot, Benjamin A; Myronov, Maksym; Pepper, Michael; (2022) Two-dimensional localization in GeSn. Journal of Physics: Condensed Matter , 34 (48) , Article 485301. 10.1088/1361-648X/ac9814.

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Abstract

Localization behaviour is a characteristic feature of the p-type GeSn quantum well system in a Metal-Insulator-Semiconductor device. The transition to strongly localized behaviour is abrupt with thermally activated conductivity and a high temperature intercept of 0.12×e^{2}/ħ^{-1} at a hole carrier density 1.55×10^{11} cm^{-2}. The activation energy for the conductivity in the localized state is 0.40±0.05 meV compared to an activation energy of ~ 0.1 meV for conductivity activation to a mobility edge at carrier densities > 1.55×10^{11} cm^{-2}. Insulating behaviour can occur from a system that behaves as though it is in a minimum metallic state, albeit at high temperature, or from a conductivity greater than a minimum metallic state behaviour showing that local disorder conditions with local differences in the density of states are important for the onset of localization. In the presence of a high magnetic field, thermally activated conductivity is present down to Landau level filling factor < ½ but without a magnetic-field-dependent carrier density or a Variable Range Hopping transport behaviour developing even with conductivity << e^{2}/h^{-1}. In the localized transport regime in p-type doped Ge_{0.92}Sn_{0.08} quantum wells the Variable Range Hopping mechanism is suppressed at temperatures > 100 mK and this makes this two-dimensional system ideal for future Many Body Localization studies in disordered hole gases that can be thermally isolated from a temperature reservoir.

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