Interband characterization and electronic transport control of nanoscaled GeTe/Sb$_2$Te$_3$ superlattices

TL;DR

This study investigates the electronic and optical properties of nanoscaled GeTe/Sb$_2$Te$_3$ superlattices, revealing how layer composition and thickness influence free electron density and transport, with implications for phase-change memory devices.

Contribution

It introduces a model for controlling electronic transport in GeTe/Sb$_2$Te$_3$ superlattices by adjusting layer thickness and composition, advancing nanoscale phase-change material design.

Findings

Free electron density decreases with more GeTe content below 3 nm layers.

Layer mixing forms a GeSbTe alloy buffer layer.

Transport properties can be tuned via deposition parameters.

Abstract

The extraordinary electronic and optical properties of the crystal-to-amorphous transition in phase-change materials led to important developments in memory applications. A promising outlook is offered by nanoscaling such phase-change structures. Following this research line, we study the interband optical transmission spectra of nanoscaled GeTe/Sb$_2$Te$_3$ chalcogenide superlattice films. We determine, for films with varying stacking sequence and growth methods, the density and scattering time of the free electrons, and the characteristics of the valence-to-conduction transition. It is found that the free electron density decreases with increasing GeTe content, for sub-layer thickness below $\sim$3 nm. A simple band model analysis suggests that GeTe and Sb$_2$Te$_3$ layers mix, forming a standard GeSbTe alloy buffer layer. We show that it is possible to control the electronic transport properties of the films by properly choosing the deposition layer thickness and we derive a model for arbitrary film stacks.