GaN light-emitting diodes on glass substrates with enhanced electroluminescence

We report the enhanced electroluminescence (EL) of GaN light-emitting diodes (LEDs) on glass substrates by controlling GaN crystal morphology, crystallinity, and device fabrication. Depending on the degree of epitaxy, we studied three different GaN morphologies; randomly oriented GaN polycrystals, nearly single-crystalline pyramid arrays, and fully single-crystalline pyramid arrays, which were fabricated by controlling the epitaxial relationship with the substrates. At proper growth temperature, GaN crystallinity was improved with increasing GaN crystal size irrespective of the GaN crystallographic orientation, as determined by spatially resolved cathodoluminescent spectroscopy. All the different GaN morphologies were further fabricated into LEDs to investigate their EL characteristics. The optimized GaN LEDs on glass composed of the nearly single-crystalline GaN pyramid arrays exhibited excellent microscopic EL uniformity and luminance values of about 2700 and 1150 cd m(-2) at peak wavelengths of 537 and 480 nm, respectively.