Band edge optical transitions in dilute-nitride GaNSb

Dilute-nitride GaNSb bulk materials with up to 1.4% nitrogen were grown by molecular beam epitaxy on GaSb substrates. Hall measurements indicate residual hole concentrations of nearly 1019 cm−3 at room temperature, but a decrease to below 1016 cm−3 and a hole mobility of 1300 cm2/V s at 4.5 K for a sample with 0.6% nitrogen. Photoluminescence (PL) and optical absorption measurements demonstrate a bandgap reduction by up to 300 meV with increasing nitrogen incorporation. The experimental absorption spectra are well fit by a functional dependence corresponding to direct allowed optical transitions, and the PL spectra are also consistent with that interpretation. Room temperature carrier relaxation times in the picosecond range are measured using an ultrafast PL upconversion technique.