Yellow Luminescence and Optical Quenching of Photoconductivity in Ultrathin Suspended GaN Membranes Produced by Surface Charge Lithography

Spatial and spectral distribution of cathodoluminescence as well-as photoelectrical properties under excitation with two beams of monochromatic radiation of various wavelengths are investigated in ultrathin suspended GaN membranes produced by surface charge lithography as compared to bulk GaN layers. GaN membranes are designed by focused ion beam treatment of GaN epilayer surfaces with subsequent photoelectrochemical etching. The analysis of the spatial and spectral distribution of microcathodoluminescence demonstrates that the membranes exhibit mainly yellow luminescence (YL). In investigating photoelectrical properties, the first beam of radiation induces photoconductivity, while the second beam is used for the investigation of optical quenching (OQ) effects. It was found that the second beam of radiation produces OQ of photoconductivity, but not quenching of the persistent photoconductivity (PPC), in bulk layers. In contrast to this, OQ of both photoconductivity and PPC occurs in ultrathin GaN membranes. We suggest that the enhancement of YL and the OQ of PPC in ultrathin membranes involved are related to each other, and both phenomena can be attributed to the same point defects which are most likely gallium vacancies.