A Brief Introduction to Band Structure in Three Dimensions

TL;DR

This paper introduces methods to model and understand three-dimensional band structures in crystalline materials, connecting quantum mechanics principles to practical semiconductor properties.

Contribution

It extends one-dimensional quantum models to three dimensions and demonstrates how to approximate real semiconductor band structures, like silicon.

Findings

Construction of 3D periodic potentials

Observation of band gaps and level splitting

Agreement with silicon band diagram

Abstract

Without our ability to model and manipulate the band structure of semiconducting materials, the modern digital computer would be impractically large, hot, and expensive. In the undergraduate QM curriculum, we studied the effect of spatially periodic potentials on the spectrum of a charged particle in one dimension. We would like to understand how to extend these methods to model actual crystalline materials. Along the way, we will explore the construction of periodic potentials in three dimensions, and we use this framework to relate the single-particle Hamiltonian to the potential contribution from each atom. We then construct a crude model system analogous to the semiconductor silicon, and demonstrate the appearance of level splitting and band gaps as the strength of the potential is varied, in accordance with our intuition from the one-dimensional case. We discuss refinements of the model to include many-particle effects, and finally we show how a careful choice of the potential function leads to good agreement with the correct band diagram for silicon.