Effect of electron irradiation on optical properties of gallium nitride

The effect of electron irradiation on the optical properties of GaN epilaye rs is studied in detail by photoluminescence (PL) spectroscopy. The most co mmon types of GaN material are used, i.e. strained heteroepitaxial layers g rown on 6H SiC or Al2O3 substrates, and thick bulk-like layers with the con ductivity varying from n-type to semi-insulating and p-type. The main effec ts of electron irradiation on all investigated samples are found to be as f ollows: (i) a radiation-induced quenching of excitonic emissions in the nea r band gap region; (ii) an appearance of broad overlapping PL emissions wit hin the spectral range 0.7-1.1 eV and (iii) the appearance of a PL band wit h a sharp no-phonon (NP) line at around 0.88 eV followed by a rich phonon a ssisted sideband. The 0.88 eV band is shown to originate from an internal t ransition of a deep defect. With increasing temperature a hot PL line can b e observed at about 2-4 meV above the NP line, originating from higher lyin g excited states of the defect. The electronic structure of the 0.88 eV def ect is shown to be very sensitive to the internal strain held in the GaN ep ilayers.