Patterned backgating using single-sided mask aligners: application to density-matched electron-hole bilayers

TL;DR

This paper demonstrates a method for fabricating patterned backgates on thin semiconductor samples using single-sided mask aligners, and applies it to create tunable electron-hole bilayer devices with matched densities.

Contribution

It introduces a novel fabrication technique for patterned backgates on thin samples and a mathematical model for analyzing electrochemical potential variations.

Findings

Successful fabrication of patterned backgates on thin semiconductor samples.

Ability to independently contact and tune densities of electron-hole bilayers.

Matching electron and hole densities using bias voltages in bilayer devices.

Abstract

We report our work on fabricating lithographically aligned patterned backgates on thin (50-60$\mu$m) \Roman{roman3}-\Roman{roman5} semiconductor samples using {\it single sided mask aligners only}. Along with this we also present a way to photograph both sides of a thin patterned chip using inexpensive infra-red light emitting diodes (LED) and an inexpensive (consumer) digital camera. A robust method of contacting both sides of a sample using an ultrasonic bonder is described. In addition we present a mathematical model to analyse the variation of the electrochemical potential through the doped layers and heterojunctions that are normally present in most GaAs based devices. We utilise the technique and the estimates from our model to fabricate an electron-hole bilayer device in which each layer is separately contacted and has tunable densities. The electron and hole layers are separated by barriers either 25 or 15nm wide. In both cases, the densities can be matched by using appropriate bias voltages.