Towards quantum transport in single-crystalline PbTe nanowire MOSFET devices

Abstract

PbTe is a narrow band gap semiconductor with a remarkably high Lande g-factor and spin-orbit interaction. This ´ makes it a very interesting possible candidate for Majorana devices. Therefore the MBE growth of low-defect single-crystalline PbTe nanowires has been developed. This research aimed to develop a fabrication recipe for reliable fabrication of nanowire MOSFET devices. And to use these to characterise the electronic transport properties of these nanowires.

However, Schottky barriers were formed between the nanowire and the Ti/Au source and drain contacts, partially due both the material choice and the fabrication procedure. The Schottky barriers have been characterised based by fitting the measured transport data with a thermionic emission model. This established thermionic emission as the dominant transport mechanism, and allowed for the determination of the Schottky barrier height (Φeff = 0.55 ± 0.25V). Despite the Schottky barriers, an attempt has been made to extract the carrier mobility and density from the transport data. Carrier densities in the order of ∼ 10^18cm−3 have been obtained. This seems a plausible value compared to the carrier densities of other narrow band gap semiconductors (InAs, InSb). The obtained mobilities (µe = 0.02−0.12cm^2 /Vs) are two orders of magnitude lower than in other semiconductors. However, it was to be expected that the mobility of the device was heavily impacted by the presence of barriers at the contact interface. PbTe nanowires grown in Eindhoven have been fabricated into similar devices in the Frolov group at the University of Pittsburgh. There cryogenic transport measurements were performed on the devices. The barriers at the metal/semiconductor interface, though much less pronounced, turned the nanowires into nanowire quantum dots. Some curious signatures were observed in the transport characteristics of these dots. Some of these features can be explained to be signatures of Wigner localisation of electrons in the dot. Steps have been made in the full quantum-mechanical modelling of this system, but still a lot of time has to be invested to completely reproduce the experimental results.