Probing the infrared properties of a p-doped Ge\(_{0.938}\)Sn\(_{0.062}\) thin film via polarization-dependent FTIR spectroscopy

The complex relative permittivity of doped Ge₁₋ₓSnₓ thin films (realized using state-of-the-art growth techniques) are obtained by devising a methodology based upon polarization-dependent reflection measurements along with multi-layer Fresnel reflection equations. The developed approach is implemented to acquire the complex relative permittivity of a 170-nm-thick Ge₁₋ₓSnₓ film exhibiting a hole carrier concentration of 3.3 × 10¹⁹ cm⁻³ and x = 6.2%, with this Sn composition suggesting the film is on the cusp of exhibiting a direct bandgap. The investigation conducted on this thin film as well as the developed methodology are expected to further establish Ge₁₋ₓSnₓ as the primary semiconductor for on-chip light emission and sensing devices.