Continuous wave and ultra-fast reflectivity studies for the determination of GaN excitonic oscillator strengths as a function of the in-plane biaxial strain

Up to now, many works have been dedicated to the study of the excitonic parameters of GaN by analyzing cw-spectroscopy results. In this work, time-resolved reflectivity experiments are carried out to record the impulse response of excitons at the femtosecond scale. By combining the analysis of continuous wave and time-resolved reflectivity spectra recorded on high quality GaN samples, the excitonic parameters are determined with accuracy. The oscillator strength evolutions of A, B and C free excitons are analysed versus the in-plane biaxial stress and compared with theoretical predictions.