A p-i-n structure with near-UV(n-UV) emitting InGaN/GaN multiple quantum well(MQW) structure stacked on a green unipolar InGaN/GaN MQW was epitaxially grown at the same sapphire substrate. Photon recycling green light-emitting diodes(LEDs) with vertical-conduction feature on silicon substrates were then fabricated by wafer bonding and laser lift-off techniques. The green InGaN/GaN QWs were pumped with n-UV light to reemit low-energy photons when the LEDs were electrically driven with a forward current. Efficiency droop is potentially insignificant compared with the direct green LEDs due to the increase of effective volume of active layer in the optically pumped green LEDs, i.e., light emitting no longer limited in the QWs nearest to the p-type region to cause severe Auger recombination and carrier overflow losses.

This study demonstrates that selective-area Si implantation performed on the GaN templates instead of conventional dielectric layers, such as SiO2 or SiNx, serves as the mask layer for the epitaxial lateral overgrowth (ELOG) process. Although the substantial mask layer is absent on the templates, selective growth initially occurs on the implantation-free area and then evolves a lateral overgrowth on the Si-implanted area during the regrowth process. This selective growth is attributed to that the crystal structure of the Si-implanted area subjected to the high doses of ion bombardment produces an amorphous surface layer, thereby leading to a lattice mismatch to the regrown GaN layer. Microstructural analyses reveal that the density of the threading dislocations above the Si-implanted regions is markedly lower than the GaN layer in the implantation-free regions. Consequentially, UV LEDs fabricated on the Si-implanted GaN templates exhibit relatively higher light output and lower leakage current compared with those of LEDs grown on ELOG-free GaN templates.

AlGaN/GaN strained layer superlattice (SLS) structures were prepared by metalorganic vapor deposition (MOCVD) under various growth conditions. It was found that the surface morphology and V-shaped pits were determined by growth temperature. Two different types of pit were observed namely, minute pits and open V-shape pits, in scanning electronic microscopy (SEM) and atomic force microscopy (AFM) images. The density of minute pits of AlGaN/GaN SLS decreased with increasing growth temperature. It was also found that the groovelike and striplike shapes of the surface morphology of the samples prepared at 800 C revealed a preferred orientation at about 30 angle to the flat side of the substrate, but this preferred orientation was disrupted at a higher growth temperature. The samples prepared at 850 and 900 C exhibited a higher PL intensity with a peak wavelength of about 363 nm because of the improvement in the crystal quality of AlGaN/GaN SLS.