Infrared optical and electronic properties in low tellurium doped GaSb substrates for SLS FPA applications

Abstract

Epi-ready GaSb wafers with low absorption coefficients are of a special interest as substrates for molecular beam epitaxy (MBE) growth of material for IR focal plane arrays that operate under back-side illumination configuration, when the substrate is not completely removed. While low absorption coefficient across a broad IR spectral range (~2um-20um) is achievable in GaSb crystals with low Te doping, the control of the doping distribution across the wafers is especially challenging in the mass-production of optically transparent, high-resistivity Te-doped GaSb wafers. In this work, we examine data from the n-type and p-type Te-doped GaSb samples with doping concentration below 1e18 cm-3. The carrier concentration measured by the Hall and the transmission data measured by FTIR spectroscopy are correlated. We perform a rigorous analysis of the absorption coefficient based on the free-carrier absorption mechanism that is dominant for the n-type GaSb and the inter-valence band absorption due to the transitions from the light-hole to the heavy-hole band that is the dominant absorption mechanism for the p-type GaSb. Based on the correlation between the Hall and the FTIR data, carrier concentration profile can be estimated from the non-destructive FTIR transmission mapping of the wafer.