Antidot superlattices in two-dimensional hole gases confined in strained germanium layers

Antidot superlattices with a period of a=500 nm and different etch depths were fabricated in two-dimensional hole gases confined in surface-side as well as in substrate-side modulation-doped Ge/SiGe heterostructures by holographic lithography and reactive ion etching and were then studied by magnetotransport at T=4.2 K. Even though the elastic mean free paths are smaller than or comparable to the superlattice period, typical features of locally ballistic transport around groups of antidots, such as commensurability oscillations and additional, non-quantized Hall plateaus, are observed in both types of samples at sufficient etch depth. These geometry-related effects are found to be rather robust against inhomogeneities and defects brought about by imperfect fabrication.