ABSTRACT
A demonstration of 2D hole gases in GeSn/Ge heterostructures with a mobility as high as 20 000 cm2 V-1 s-1 is given. Both the Shubnikov-de Haas oscillations and integer quantum Hall effect are observed, indicating high sample quality. The Rashba spin-orbit coupling (SOC) is investigated via magneto-transport. Further, a transition from weak localization to weak anti-localization is observed, which shows the tunability of the SOC strength by gating. The magneto-transport data are fitted to the Hikami-Larkin-Nagaoka formula. The phase-coherence and spin-relaxation times, as well as spin-splitting energy and Rashba coefficient of the k-cubic term, are extracted. The analysis reveals that the effects of strain and confinement potential at a high fraction of Sn suppress the Rashba SOC caused by the GeSn/Ge heterostructures.
ABSTRACT
We convert calculations of the bound-to-continuum absorption in type-II semiconductor quantum wells into an equivalent source-radiation problem under the effective-mass approximation with band mixing. Perfectly matched layers corresponding to the eight-band Luttinger-Kohn Hamiltonian are introduced to incorporate the effect of quasi-bound states in open regions. In this way, the interplay between quantum tunneling and optical transitions is fully taken into account. From resulted lineshapes of the Fano resonance, we can evaluate tunneling rates of these metastable states and related absorption strengths relative to those of the continuum. The approach here is useful in estimations of carrier extraction rates from type-II nanostructures for photovoltaic applications.
