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.