InGaN Light-Emitting Diode with a Photochemically Oxidized GaN Nanorod Structure

Abstract

InGaN light-emitting diodes (LEDs) embedded with air voids and a gallium oxide (Ga 2 O 3 ) layer were fabricated through a photoelectrochemical (PEC) oxidation process. The epitaxial lateral overgrowth process occurred at the PEC oxidized nanorods to form the air-voids structure. The light output power of the treated LED with the air-voids structure had a 70% enhancement compared with a non-treated LED at a 20 mA operation current. High internal quantum efficiency and low piezoelectric field were measured in the treated LED structure through a bias-dependent micro-photoluminescence measurement. The strain-induced piezoelectric field in InGaN active layer was partially reduced by forming the Ga 2 O 3 layer and the air-voids structure.Gallium nitride materials have attracted considerable interest in the development of optoelectronic devices such as white light-emitting diodes (LEDs) 1 for indoor lighting sources and blue/green laser diodes for laser micro-projector applications. The large lattice mismatch at a GaN/sapphire interface and an InGaN/GaN interface caused the compress strain induced piezoelectric field in the InGaN active layer that had the quantum confined Stark effect. 2 A large piezoelectric field in the InGaN active layer resulted in a spatial separation of electrons and holes, which led to the reduction of the radiative recombination efficiency. Hence, many researchers have proposed various methods to reduce the piezoelectric fields in the InGaN/GaN MQW structures by using an InGaN pre-strained layer, 3 the epitaxial lateral overgrowth processes, 4,5 and the surface roughening techniques of p-GaN layer. 6,7 Photoelectrochemical (PEC) gallium oxide layer had been reported for the dielectric layer in the metal-oxide-semiconductor structures, 8,9 the ultraviolet photodetectors, 10 and the LED structure. 11 Soh et al. 12 reported the high optical performance of amber-emitting quantum dots incorporated in an InGaN LED structure regrown on UV-enhanced electrochemically etched nanoporous GaN structure. Lee et al. 13 reported the effect of gallium oxide hydroxide (GaOOH) nanorod arrays on the light extraction of InGaN LEDs.In this paper, an InGaN LED structure embedded with an air void structure and a photoelectrochemical (PEC) gallium oxide layer were fabricated. The InGaN LED epitaxial layers were regrown on a PEC oxidized GaN nanorod structure to form the air-voids structure. High light extraction efficiency and high internal quantum efficiency were observed in the regrown LED structure by forming the air-voids under the InGaN active layers. ExperimentalThe InGaN-based LED structures were grown on c-face (0001) 2 in. diameter patterned-sapphire substrate through a metallorganic chemical vapor deposition (MOCVD) system. During the epitaxial growth process, trimethylgallium (TMGa), trimethylindium (TMIn), and ammonia (NH 3 ) were used as gallium, indium, and nitrogen sources, respectively. Silane (SiH 4 ) and biscyclopentadienyl magnesium (CP 2 Mg) were used as the n-type doping and p-type doping source, r...