Post dry etching treatment of nanopillar GaN/InGaN multi-quantum-wells

Time-resolved photoluminescence (PL), current-voltage characteristics and deep trap spectra of nanopillar GaN/InGaN multi-quantum-well (MQW) light emitting diodes (LEDs) prepared by reactive ion etching (RIE) from planar samples were studied as a function of post-RIE surface treatment. Immediately after RIE, we observe a sharp drop of intensity of the 460 nm MQW PL band and a strong increase of intensity of the defect-related 600 nm MQW band similar to the yellow band in n-GaN. KOH etching and (NH₄)₂S sulfur passivation treatments increased the MQW PL band intensity above the level of the planar structure and decreased the intensity of the defect 600 nm PL band, but was not effective in decreasing the RIE-induced excessive leakage current of the LEDs. Only annealing at ≥ 700 °C following RIE was able to strongly suppress the excessive leakage. Deep trap spectra suggest that the RIE-induced drop of the 460 nm PL intensity and increase of the 600 nm PL intensity are accompanied by the increase of the Ec-0.7 eV electron trap density and of Ev+0.8 eV hole trap density in the quantum wells. The first of these defects is attributed to nitrogen interstitial acceptors believed to be effective nonradiative recombination centers, while the hole traps are attributed to gallium vacancy acceptor complexes with shallow donors. Both types of defects are produced on the sidewalls of nanopillars by RIE and can be largely annealed at 700 °C, although higher annealing temperatures are needed to fully suppress their negative impact. These results are also relevant to curing the effects of dry-etch damage for micro-LEDs with small chip dimensions, a serious problem in the micro-LED field.