The influences of sputtered AlN buffer layer on AlInGaN based blue and near‐ultraviolet light emitting diodes

Abstract

Instead of conventional GaN buffer layer, a sputtered AlN buffer layer is utilized on the patterned sapphire substrate in AlInGaN based 450‐nm blue and 380‐nm near‐ultraviolet light emitting diodes (LEDs). As a result, the full‐width at half maximum (FWHM) of GaN (002) and (102) X‐ray diffraction rocking curve decrease from 220 to 135 arcsec and from 245 to 172 arcsec, respectively. Consequently, peak external quantum efficiency (EQE) of 380‐nm LED is enhanced by 18–66%, while the EQE of the 450‐nm one shows inconspicuous improvement. This phenomenon implies that the radiative recombination efficiency is more sensitive to dislocation density in 380‐nm LED. Fitting results of temperature‐dependent photoluminescence spectra indicate that the carrier localization effect is weakened as indium composition decreases in the active region, which is regarded as one ordinary explanation. Moreover, carrier lifetimes in 450‐ and 380‐nm LEDs are also measured. The shorter carrier lifetime in 380‐nm LED is considered as another key factor.