Fabrication of closely spaced, independently contacted Electron-Hole bilayers in GaAs-AlGaAs heterostructures

TL;DR

This paper presents a new fabrication technique for closely spaced, independently contacted electron-hole bilayers in GaAs-AlGaAs heterostructures, enabling advanced transport and interaction studies at low temperatures.

Contribution

A novel method for making shallow, annealing-free contacts to low-density 2DEGs in GaAs-AlGaAs heterostructures, allowing four-terminal measurements on bilayers 25nm apart.

Findings

High hole mobility >10^5 cm^2/Vs at 1.5K

High electron mobility >10^6 cm^2/Vs at 1.5K

Enhanced Coulomb interactions observed at low temperatures

Abstract

We describe a technique to fabricate closely spaced electron-hole bilayers in GaAs-AlGaAs heterostructures. Our technique incorporates a novel method for making shallow contacts to a low density ($<10^{11}cm^{-2}$) 2-dimensional electron gas (2DEG) that do not require annealing. Four terminal measurements on both layers (25nm apart) are possible. Measurements show a hole mobility $\mu_{h}>10^{5}{\rm cm}^{2}{\rm V}^{-1}{\rm s}^{-1}$ and an electron mobility $\mu_{e}>10^{6}{\rm cm}^{2}{\rm V}^{-1}{\rm s}^{-1}$ at 1.5K. Preliminary drag measurements made down to T=300mK indicate an enhancement of coulomb interaction over the values obtained from a static Random Phase Approximation (RPA) calculation.