Optical studies of Group III-nitride semiconductor

In this thesis I will discuss the results of optical spectroscopy measurements inrelation to the study of quantum well and multiple quantum well structures made upof group III-nitride semiconductors. This will include the results of photoluminesence(PL), reflectance, and time resolved photoluminesence spectroscopy experiments aswell as the results of time correlated single photon counting (TCSPC) experiments.I have investigated the droop in efficiency observed in InGaN/GaN quantum wellsas the current density or excitation power density is increased. I will show that atthe onset of the efficiency droop a simultaneous reduction in the S-shape temperaturedependence of the peak emission energy shift is observed. These results suggest thatone of the mechanisms behind the efficiency droop is the saturation of localised statesas the density of carriers is increased.I also discuss the carrier dynamics in non-polar GaN/AlGaN quantum wells inter-sected by basal plane stacking faults (BSF)s. In order to describe the form of the resultsof TCSPC results I put forward a model for the transfer of carriers from the quantumwell into the regions of the quantum well intersected by BSFs.Finally I show the results of an investigation into the features observed in photolu-minesence excitation measurements by N Hylton et al [1, 2] near the GaN band gap.These features are caused by a red shift in the peak emission energy using the resultsof PL measurements made as a function of excitation photon energy it is possible toresolve the lowest energy feature observed by Hylton et al into two features. Two pos-sible mechanisms are then discussed for how the excitation of carriers at set energiesabove the GaN band gap results in a change to the peak energy of the quantum wellemission.