The Refractive Index of Gallium Antimonide
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 Djurišić \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.