Al$_x$Ga$_{1-x}$As crystals with direct 2 eV band gaps from computational alchemy

TL;DR

This paper introduces a computational alchemy approach using alchemical derivatives to efficiently predict band structures, enabling rapid discovery of AlGaAs alloys with large direct band gaps for semiconductor applications.

Contribution

It presents a novel application of alchemical derivatives combined with genetic algorithms to accelerate the design of semiconductor alloys with targeted electronic properties.

Findings

Identified dozens of crystal polymorphs with >2 eV direct band gaps for x>2/3

Achieved convergence after ~800 candidate evaluations from a single DFT calculation

Demonstrated broad applicability of alchemical gradients to various crystal types and properties

Abstract

We use alchemical first order derivatives for the rapid yet robust prediction of band structures. The power of the approach is demonstrated for the design challenge of finding Al$_x$Ga$_{1-x}$As semiconductor alloys with large direct band gap using computational alchemy within a genetic algorithm. Dozens of crystal polymorphs are identified for $x>\frac{2}{3}$ with direct band gaps larger than 2\:eV according to HSE approximated density functional theory. Based on a single generalized gradient approximated density functional theory band structure calculation of pure GaAs we observe convergence after visiting only $\sim$800 crystal candidates. The general applicability of alchemical gradients is demonstrated for band structure estimates in III-V and IV-IV crystals as well as for H$_2$ uptake in Sr and Ca-alanate crystals.