First-principles predictions of band alignment in strained Si/Si1-xGex and Ge/Si1-xGex heterostructures

TL;DR

This study uses first-principles density functional theory to accurately predict band offsets in strained Si/Si1-xGex and Ge/Si1-xGex heterostructures across all compositions, aiding quantum device design.

Contribution

It provides the first comprehensive first-principles calculations of band offsets across the full composition range, including nonlinear effects and refined conduction-band edges.

Findings

Offsets show pronounced composition nonlinearity.

Results agree with experimental benchmarks.

Provides analytic expressions for practical use.

Abstract

Accurate band offsets are essential for predictive continuum modeling of nanostructures such as quantum wells and quantum dots formed in strained Si/Si1-xGex and Ge/Si1-xGex heterostructures. Experimental offset data for these systems remain sparse away from endpoint compositions, making composition-dependent design difficult. We use atomistic first-principles density functional theory to compute valence- and conduction-band offsets across the full range 0 <= x <= 1. Random alloying is treated with special quasirandom structures, interface lineup terms are extracted from macroscopically averaged local Kohn-Sham potentials in thick periodic superlattices, valence-band spin-orbit coupling is included through species-resolved Mulliken weights, and conduction-band edges are refined using the screened hybrid Heyd-Scuseria-Ernzerhof functional. The resulting offsets show pronounced composition nonlinearity beyond the linear models explored in previous works, agree with experimental benchmarks, and reproduce the high-Ge slope change in the relaxed-alloy band gap. Analytic fitting expressions are provided for direct use in simulations, facilitating practical design of modern quantum technology devices.