Defect Luminescence at n-GaN Electrodes

Abstract

Luminescence measurements in aqueous solutions were performed upon n-GaN layers grown on sapphire substrates and on Si substrates. Photoluminescence ͑PL͒ measurements at n-GaN/sapphire and n-GaN/Si electrodes show an identical emission band centered at 2.20 eV ͑the well-known yellow luminescence band͒, showing that the same deep acceptor level is present in both materials. Additional reddish luminescence is observed when the holes are injected from the solution ͓electroluminescence ͑EL͔͒, which may be ascribed to the occurrence of radiative ͑near͒ surface recombination. From an analysis of the potential dependence of both the PL and EL intensity of the 2.20-eV band, it may be concluded that this band possesses a significant contribution from the ͑near͒ surface.

Solution-based growth of ZnO nanorods for light-emitting devices: hydrothermal vs. electrodeposition

“…However, it should be noted that GaN also exhibits defect emissions (yellow and red) in a similar spectral range [32,33]. Yellow defect emission in GaN has been attributed to transitions from conduction band or a shallow donor to a deep acceptor [32,33]. In this case as well the exact identity of the acceptor has not been conclusively established, but there is evidence indicating that this acceptor defect is likely a gallium vacancy [33].…”

“…Explanations proposed to explain orange luminescence also include oxygen interstitials, since this emission is reduced by annealing in vacuum or hydrogen/argon gas mixture [28]. However, it should be noted that GaN also exhibits defect emissions (yellow and red) in a similar spectral range [32,33]. Yellow defect emission in GaN has been attributed to transitions from conduction band or a shallow donor to a deep acceptor [32,33].…”

“…In heavily Mg doped pGaN, red emission band can occur due to deep donor-deep acceptor transition [33]. It was also proposed that red emission bands originate from near-surface region, and that the yellow band is also enhanced near the surface compared to the bulk [32].…”

“…Considering the fact that yellow emission under reverse bias was also observed in devices which exhibited green defect emission PL from ZnO [23], it is possible that yellow emission indeed originates either from GaN or the interface between GaN and ZnO. Since the yellow emission in GaN exhibits higher intensity in near-surface region [32], the interface between the two materials is expected to have higher defect concentration. The origin of the violet emission centered around 400 nm is less clear since there are no corresponding peaks in the PL spectra of both p-GaN and ZnO.…”