A high-mobility hole bilayer in a germanium double quantum well

Abstract

We design, fabricate, and study a hole bilayer in a strained germanium double quantum well. Magnetotransport characterisation of double quantum well field-effect transistors as a function of gate voltage reveals the population of two hole channels with a high combined mobility of 3.34$\times$10${}^5$ cm${}^2$/Vs and a low percolation density of 2.38$\times$10${}^{10}$ cm${}^{-2}$. We resolve the individual population of the channels from the interference patterns of the Landau fan diagram. At a density of 2.0$\times$10${}^{11}$ cm${}^{-2}$ the system is in resonance and we observe an anti-crossing of the first two bilayer subbands characterized by a symmetric-antisymmetric gap of $\sim$0.69 meV, in agreement with Schrödinger-Poisson simulations.