Intervalley coupling for interface-bound electrons in silicon: An effective mass study

TL;DR

This study investigates how intervalley coupling at silicon interfaces affects electron energy levels, using an effective mass model to understand the physical mechanisms and compare different theoretical approaches.

Contribution

It provides a comprehensive effective mass analysis of intervalley coupling at Si interfaces, including full Bloch function expansions and comparison with other models.

Findings

Intervalley coupling causes level splitting that varies significantly across samples.

The effective mass approach with full Bloch expansion offers clear physical insights.

Different approximations have varying applicability depending on the physical scenario.

Abstract

Orbital degeneracy of the electronic conduction band edge in silicon is a potential roadblock to the storage and manipulation of quantum information involving the electronic spin degree of freedom in this host material. This difficulty may be mitigated near an interface between Si and a barrier material, where intervalley scattering may couple states in the conduction ground state, leading to nondegenerate orbital ground and first excited states. The level splitting is experimentally found to have a strong sample dependence, varying by orders of magnitude for different interfaces and samples. The basic physical mechanisms leading to such coupling in different systems are addressed. We expand our recent study based on an effective mass approach, incorporating the full plane-wave expansions of the Bloch functions at the conduction band minima. Physical insights emerge naturally from a simple Si/barrier model. In particular, we present a clear comparison between ours and different approximations and formalisms adopted in the literature and establish the applicability of these approximations in different physical scenarios.