In situ preparation of the semiconductor–superconductor interface: Nb contacts on InAs quantum wells

Abstract

In this article we describe an in situ, low damage, process sequence designed to provide a more reliable, higher quality metal (superconductor)–semiconductor interface. We produce discrete Nb contacts on an InAs quantum well (125 A) that is embedded within thick (∼3000 A) Al0.5Ga0.5Sb barrier layers by utilizing a multichamber ultrahigh vacuum system, in which two Varian GenII, Molecular Beam Epitaxy chambers are directly connected to a high vacuum etch station. The principal process steps include (1) a short, “selective” thermal Cl2 etch of the top barrier layer to expose and define the InAs contact region, (2) a post-etch anneal (under As2 flux) to desorb residual etch products (i.e., InCl3) and restore a clean and well-ordered InAs (2×4) surface, (3) a Sb capping/passivation layer on the treated surface, (4) atmospheric transfer of the capped sample to a remote Nb deposition chamber, and (5) a post-anneal (in vacuum) to desorb the Sb cap immediately followed by Nb deposition. The priority throughout is...