Improved light-emitting diode performance by conformal overgrowth of multiple quantum wells and fully coalesced p-type GaN on GaN nanowires

Abstract

We demonstrate a light-emitting diode (LED) structure with multiple quantum wells (MQWs) conformally grown on semipolar and nonpolar plane facets of n-GaN nanowires (NWs), followed by deposition of fully coalesced p-GaN on these nanowires. Overgrowth on the nanowires’ tips results in inclusion of high density voids, about one micron in height, in the GaN film. The light output intensity of NWs LEDs is more than three times higher than corresponding c-plane LEDs grown simultaneously. We believe this results from a reduced defect density, increased effective area of conformally grown MQWs, absence of polar plane orientation, and improved light extraction.

Enhanced radiative recombination and suppressed Auger process in semipolar and nonpolar InGaN/GaN quantum wells grown over GaN nanowires

“…The room temperature PL intensity of the NW-MQWs integrated over its emission band is nearly 10 times that of the c-MQWs, representing the evident improvement of light emission properties of NW-MQWs over conventional c-MQWs. It is noteworthy that the observed enhancement is substantially greater than that measured in the previous EL study of NW-MQWs embedded in p-n junction LEDs [9], wherein the light output power was found to be more than 3 times larger in NWs LEDs than the c-plane LEDs. This difference is postulated to arise from the participation of the radiation process by the MQWs on the nonpolar m-and α-planes that are located at the lower part of the NWs.…”

“…A significant enhancement in electroluminescence (EL) output was obtained for the MQW LEDs grown on NWs' nonpolar/semipolar facets over those 2D c-plane MQW LEDs [9]. The improved EL output was ascribed to a joint effect of four unique structural features of the MQW LEDs grown on NWs, i.e., reduced defect density, increased effective area of conformally grown MQW LEDs, absence of polar plane orientation, and embedded voids for light guiding.…”

“…Recently, Frajtag et al reported an alternative approach to conformally grow multiple quantum wells (MQWs) on semipolar and nonpolar plane facets of n-GaN NWs using the embedded void structure [8,9]. A significant enhancement in electroluminescence (EL) output was obtained for the MQW LEDs grown on NWs' nonpolar/semipolar facets over those 2D c-plane MQW LEDs [9].…”

“…Details of the growth conditions and processes have been reported elsewhere [8,9]. The EVA starts with a bulk n-type GaN film grown by the metal organic chemical vapor deposition (MOCVD) technique on a sapphire substrate.…”

“…The carrier density in c-MQWs was calculated to be ∼7.7 × 10 17 cm −3 . For NW-MQWs, the MQWs on the semipolar planes will have an effective area larger than that of the c-plane by 1.05-2.12 [9]. When the effective area of nonpolar MQWs is approximated to be comparable to that of semipolar MQWs, the carrier density in NW-MQWs is roughly estimated to be in the range of ∼4.3 × 10 17 − 8.5 × 10 17 cm −3 , which is close to that in c-MQWs.…”