The Refractive Index of Gallium Antimonide

TL;DR

This paper provides highly accurate measurements of the complex refractive index of gallium antimonide (GaSb) in the near- to mid-infrared range, crucial for improving photonic device design and simulation.

Contribution

It introduces a precise measurement method for GaSb's refractive index with quantified uncertainties, enhancing reliability over previous theoretical or less accurate experimental data.

Findings

Measured $n_{GaSb}$ with <7.8e-5 relative uncertainty

Measured $k_{GaSb}$ with <2.0e-3 relative uncertainty

Reported $n_{AlAsSb}$ with <3.9e-4 relative uncertainty

Abstract

Gallium antimonide (GaSb) is a key material for near- and mid-infrared photonics, enabling high-performance laser architectures and detectors. Design and simulation of such devices depend on accurate optical material data, especially the complex refractive index $n^*_{\text{GaSb}} = n_{\text{GaSb}} +ik_{\text{GaSb}}$, consisting of the real part $n_{\text{GaSb}}$ (refractive index) and the imaginary part $k_{\text{GaSb}}$ (extinction coefficient). However, GaSb refractive index values are based either on theoretical models, typically informed by legacy experimental data, or on experimental measurements without quantified uncertainties. This limits their reliability for state-of-the-art devices. Here, we present measurement results of $n^*_{\text{GaSb}}$ in the near- to mid-infrared range from \SIrange{1}{3.1}{\micro \metre} with a relative uncertainty <\num{7.8e-5} for $n_{\text{GaSb}}$, and <\num{2.0e-3} for $k_{\text{GaSb}}$. As a side result of our method, we also report $n_{\text{AlAsSb}}$ for aluminium arsenide antimonide ($\mathrm{AlAs_{0.08}Sb_{0.92}}$) with a relative uncertainty <\num{3.9e-4}. Our results are based on two complementary measurements on a GaSb/AlAsSb-based heteroepitaxial structure under controlled environmental conditions: photometric transmission and layer-thickness analysis by cross-sectional scanning electron microscopy. We simultaneously retrieve the refractive indices of the two materials by fitting a Sellmeier equation and a theoretical dispersion model by Djuri\v{s}i\'c \textit{et al.}~\cite{djurisic_modeling_2000}. The uncertainties of $n^*_{\text{GaSb}}$ and $n_{\text{AlAsSb}}$ are quantified using a Monte Carlo-based approach. Our results provide accurate complex refractive index values for GaSb, which are vital to advance photonics-related technologies in the near- and mid infrared spectral region.