Electronic and optical properties of GaSb:N from first principles

TL;DR

This study uses first-principles density functional theory with hybrid functionals to analyze the electronic and optical properties of GaSb doped with nitrogen, revealing unique band structure features and emphasizing the importance of orbital analysis.

Contribution

It provides the first detailed theoretical analysis of GaSb:N using hybrid functional methods, highlighting differences from GaAs:N and proposing a new approach to modeling dilute-nitrides.

Findings

GaSb:N has a smaller band gap than GaAs:N.

The lowest conduction band is quasi-delocalized with significant N-3s character.

High N concentrations lead to a dispersive N-derived band influencing properties.

Abstract

GaSb:N displays promise towards realization of optoelectronic devices accessing the mid-infrared wavelength regime. Theoretical and experimental results on its electronic and optical properties are however few. To address this, we present a first principles, density functional theory study using the hybrid HSE06 exchange-correlation functional of GaSb doped with 1.6$\%$ nitrogen. To study dilute-nitrides with small band gaps, the local density approximation (LDA) is insufficient and more accurate techniques such as HSE06 are needed. We conduct a comparative study on GaAs:N, also with 1.6$\%$ nitrogen mole fraction, and find that GaSb:N has a smaller band gap and displays more band gap bowing than GaAs:N. In addition we examine the orbital character of the bands, finding the lowest conduction band to be quasi-delocalized, with a large N-$3s$ contribution. At high concentrations, the N atoms interact via the host matrix, forming a dispersive band of their own which governs optoelectronic properties and dominates band gap bowing. While this band drives the optical and electronic properties of GaSb:N, its physics is not captured by traditional models for dilute-nitrides. We thus propose that a complete theory of dilute-nitrides should incorporate orbital character examination, especially at high N concentrations.