Reappearance of linear hole transport in an ambipolar undoped GaAs/AlGaAs quantum well

Deepyanti Taneja,Ian Farrer,David Ritchie,Issai Shlimak,Vijay Narayan,Moshe Kaveh

doi:10.1088/1361-648x/aa6529

Abstract

We report the results of an investigation of ambipolar transport in a quantum well of 15 nm width in an undoped GaAs/AlGaAs structure, which was populated either by electrons or holes using positive or negative gate voltage Vtg, respectively. More attention was focussed on the low concentration of electrons n and holes p near the metal–insulator transition (MIT). It is shown that the electron mobility increases almost linearly with increase of n and is independent of temperature T in the interval 0.3 K–1.4 K, while the hole mobility depends non-monotonically on p and T. This difference is explained on the basis of the different effective masses of electrons and holes in GaAs. Intriguingly, we observe that at low p the source–drain current (ISD)–voltage (V) characteristics, which become non-linear beyond a certain ISD, exhibit a re-entrant linear regime at even higher ISD. We find, remarkably, that the departure and reappearance of linear behaviour are not due to non-linear response of the system, but due to an intrinsic mechanism by which there is a reduction in the net number of mobile carriers. This effect is interpreted as evidence of inhomogeneity of the conductive 2D layer in the vicinity of MIT and trapping of holes in ‘dead ends’ of insulating islands. Our results provide insights into transport mechanisms as well as the spatial structure of the 2D conducting medium near the 2D MIT.

Highlights

Ambipolar transport, or the ability to switch between electrons and holes in the same device, has strong implications towards the implementation of functional devices: for instance, creating gate-defined n- and p-type conducting channels in the same device can be exploited in thermoelectric
Be of much interest to contrast these behaviours in the vicinity of the so-called 2D metal–insulator transition (MIT) where localisation and interaction effects [3,4,5,6] might be more prominent
In this article we report measurements of ambipolar transport in an undoped quantum wells (QWs) device of width d = 15 nm in the T interval from 3 K down to 0.3 K in parallel magnetic fields B of up to 10 T, with particular emphasis on the low carrier concentration regime

Summary

Introduction

The ability to switch between electrons and holes in the same device, has strong implications towards the implementation of functional devices: for instance, creating gate-defined n- and p-type conducting channels in the same device can be exploited in thermoelectric. In this article we report measurements of ambipolar transport in an undoped QW device of width d = 15 nm in the T interval from 3 K down to 0.3 K in parallel magnetic fields B of up to 10 T, with particular emphasis on the low carrier concentration regime.

Results

Conclusion