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

TL;DR

This paper demonstrates a high-mobility hole bilayer in a strained germanium double quantum well, with detailed characterization of its electronic properties and subband interactions.

Contribution

It introduces a novel germanium-based hole bilayer system with high mobility and low percolation density, including experimental and theoretical analysis of its subband structure.

Findings

High combined mobility of 3.34×10^5 cm^2/Vs

Low percolation density of 2.38×10^10 cm^-2

Observation of anti-crossing of bilayer subbands at a specific density

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 Schr\"odinger-Poisson simulations.