Photoluminescence from structural defects in GaN

We studied optical manifestation of structural defects in unintentionally doped GaN. A series of sharp peaks (labeled as Yi with i=1,2,y,11) was observed in the low-temperature photoluminescence spectrum in the photon energy range between 2.6 and 3.46 eV. We attribute the majority of these peaks to excitons bound to yet unidentified structural defects. A preliminary transmission electron microscopy study in one of the samples exhibiting strong Yi lines revealed numerous inclusions, presumably inversion domains, which may be responsible for at least some of the Yi lines

Scanning tunnelling luminescence studies of nitride semiconductor thin films under ambient conditions

We have investigated the properties of a commercial light-emitting diode (LED) structure containing an InGaN single quantum well (SQW) by scanning tunneling luminescence (STL). Data was acquired under ambient conditions, i.e., in air and at room temperature, using our unique STL microscope with a novel light collection geometry. Scanning tunneling microscopy (STM) images revealed the presence of hexagonal pits in the structure, with STL images showing strong luminescence from these pits. The variation of STL intensity with bias voltage shows the STL threshold at --2.1 V is numerically similar to the peak position of the SQW luminescence band. A slight shoulder at --2.8V corresponds to the plateau of the delocalised absorption profile, observed in macroscopic measurements. The peak observed at --3.2 V is close to the observed GaN band edge emission