Confined states in multiple quantum well structures of Si$_{n}$Ge$_{n}$ nanowire superlattices

TL;DR

This study investigates the mechanical and electronic properties of SiGe nanowire superlattices, revealing quantum confinement effects and potential for novel quantum well devices based on their band structure and passivation.

Contribution

It provides first-principles analysis of the atomic, mechanical, and electronic structures of SiGe nanowire superlattices, highlighting quantum confinement and tunable electronic properties.

Findings

Si nanowires are stiffer than Ge nanowires.

Hydrogen passivation increases nanowire stiffness.

Superlattice electronic states form subbands and quantum wells.

Abstract

Mechanical properties, atomic and energy band structures of bare and hydrogen passivated Si$_{n}$Ge$_{n}$ nanowire superlattices have been investigated by using first-principles pseudopotential plane wave method. Undoped, tetrahedral Si and Ge nanowire segments join pseudomorphically and can form superlattice with atomically sharp interface. We found that Si$_{n}$ nanowires are stiffer than Ge$_{n}$ nanowires. Hydrogen passivation makes these nanowires and Si$_{n}$Ge$_{n}$ nanowire superlattice even more stiff. Upon heterostructure formation, superlattice electronic states form subbands in momentum space. Band lineups of Si and Ge zones result in multiple quantum wells, where specific states at the band edges and in band continua are confined. The electronic structure of the nanowire superlattice depends on the length and cross section geometry of constituent Si and Ge segments. Since bare Si and Ge nanowires are metallic and the band gaps of hydrogenated ones varies with the diameter, Si$_{n}$Ge$_{n}$ superlattices offer numerous alternatives for multiple quantum well devices with their leads made from the constituent metallic nanowires.