Optical control of conductivity type and valley polarization via persistent photoconductivity in (Pb,Sn)Se quantum wells

TL;DR

This study demonstrates that persistent photoconductivity in (Pb,Sn)Se quantum wells allows optical tuning of carrier density, conductivity type, and valley polarization, enabling reconfigurable valleytronic devices at cryogenic temperatures.

Contribution

It introduces persistent photoconductivity as an optical gating method to control electronic and valley properties in IV-VI quantum wells, with detailed experimental and theoretical validation.

Findings

PPC induces Fermi level shifts converting hole gas to electron gas.

Sign inversion of Hall slope confirms conductivity type change.

Quantum Hall measurements reveal valley polarization control.

Abstract

The ability to tune the Fermi level of semiconductors is at the heart of modern electronics. Here, we demonstrate that persistent photoconductivity (PPC) enables tuning of carrier density, conductivity type, and, consequently, the valley polarization in (Pb,Sn)Se/(Pb,Eu)Se quantum wells. Illumination of these samples induces Fermi level shifts that convert the system from a threefold-degenerate $\bar{M}$-valley two-dimensional hole gas to a single $\bar{\Gamma}$-valley-polarized electron gas with similar values of mobility. The optically induced state persists for more than $10^{3}$ minutes at cryogenic temperatures and enables stepwise optical gating without the need for device processing. These transitions are confirmed by the sign inversion of the Hall slope and the modification of quantum Hall plateau degeneracies measured in magnetic fields up to 35 T. Landau level $k\cdot p$ model calculations quantitatively reproduce the experimental data. Furthermore, studies of weak-field magnetoresistance demonstrate the significance of quantum localization phenomena at the transition between the weakly and strongly localized regimes in compensated narrow-gap semiconductors. Spectral studies allow us to identify the critical role of the barrier material and determine the photon energies that can reverse the PPC effect. The persistent light-induced upward shift of the Fermi level in the $p$-type quantum well is explained in terms of specific energy positions of donor and acceptor defect states in the studied system. Our results demonstrate that PPC is a powerful optical gating tool for the IV-VI quantum wells, a versatile platform for reconfigurable valleytronic architectures.