Surface mechanics of GaAsP/GaAs epilayers for non-linear optical devices

We report on nanoindentation measurements of hydride vapor phase epitaxy (HVPE) grown Gallium Arsenide Phosphide (GaAs 1-x P x ) epilayers, of interest for generation of mid-infrared wavelengths via frequency conversion. Our results indicate a linear trend in Young's modulus with increasing phosphorus content (P-content), in keeping with Vegard’s Law for ternary compounds. The corresponding data for hardness demonstrate significant bowing with a peak of 10.7 GPa occurring at 78% P-content. Some epilayers exhibit non-negligible spatial variation in their mechanical properties, which is investigated with complementary measurements. Photoluminescence measurements indicate high composition uniformity, while atomic force microscopy reveals a direct correlation between surface roughness and mechanical variability. Preliminary laser-induced damage threshold (LIDT) results are reported, and the implications for material optimization are discussed. With a 1070-nm continuous wave laser, GaAs 0.75 P 0.25 and GaAs 0.52 P 0.48 epilayers demonstrated LID thresholds of 600 kW/cm 2 and 300 kW/cm 2 , respectively. • Nanoindentation of GaAs 1-x P x films reveals a nonlinear trend in alloy hardness. • Young’s Modulus follows a linear trend consistent with Vegard’s Law. • AFM data confirms a link between surface roughness and local mechanical variance. • Hardness alone cannot predict laser-induced damage threshold for GaAs 1-x P x films.