Observation of Superconductivity in Self-Assembled Indium Island Epitaxially Grown on top of III-V Semiconductors

Abstract

Molecular beam epitaxy (MBE) is used to grow indium islands on top of semiconductor structures. Electrical contacts to a single indium island are fabricated. Superconductivity is observed by a drop in the resistance at 3.33K. The field of hybrid superconductor-semiconductor structures has recently taken off with the first signs of Majorana fermions detected in InSb nano-wires coupled to superconducting aluminum [1]. The proximity effect/Andreev reflection, essential for the semiconductor to inherit superconducting properties, strongly depends on the quality of the interface between the semiconductor and superconductor. Clearly the best interfaces can be obtained by using MBE to grow high purity metals immediately following the growth of the semiconductor. MBE has been used before to deposit aluminum on InAs nanowires [2]. Here we'll present data on indium islands grown on a GaAs buffer, a ndoped GaAs buffer and on a thin (~3Å) InAs layer. The indium forms self-assembled islands, with size and density controlled through the deposition rate and time [3]. For the largest of these islands (~2.3 μm), we performed electron beam lithography to precisely fabricate gold contacts to a single island. The resistance of the island was measured as the sample was cooled in a He3 cryostat. Clear signs of superconductivity were observed as the temperature of the sample dropped below a transition temperature of 3.33K compared to bulk indium with a transition at 3.4K. Differential resistance measurements reveal the critical current of the indium island. This observation opens the possibility of using indium islands on top of a InAs nano-structure as an ideal system for studying Majorana fermions, Andreev reflection as well as photon emission from a hybrid superconductor-semiconductor system [4].[1] V.