Effect of HVPE GaN Substrate Condition on the Characteristics and Performance of 405 nm LEDs

Abstract

AbstractThis article reports on the effects of HVPE GaN substrate condition on the performance of 405 nm LEDs grown by MOCVD. Three 1 cm2 HVPE GaN substrates were received from a commercially available source and characterized for the substrate condition. AFM and optical microscope were used to characterize the surface morphology and this was found to vary from a “moonscaped” morphology to a smooth surface. The presence of nanoscale pits and substrate bowing were also found. XRD measurements showed a variation in crystalline quality of the substrates with the FWHM of the (0002) rocking curve varying from 87 arcsec to 192 arcsec with some substrates showing multiple peaks in the rocking curve. Photoluminescence was used to measure the optical quality of the substrates and both band edge luminescence and yellow luminescence were found to vary greatly within one substrate as well as from substrate to substrate. After characterization of each individual substrate a 405 nm LED structure was grown using identical growth conditions on each substrate, in separate growth runs. A GaN template was included in each growth for consistency. The surface morphology and crystalline quality of the device structures were then measured. Following this devices were fabricated and tested for electroluminescence optical output power and current-voltage characteristics. The device characteristics and performance as related to starting substrate quality will be presented with respect to substrate surface morphology and crystalline structure.