This Small Business Technology Transfer (STTR) Phase I project will develop nonpolar gallium nitride (GaN)-based light emitting diodes (LEDs) with high energy efficiency and output power. Nonpolar GaN-based LEDs will find immediate application in demanding next-generation solid-state lighting applications. Recently there has been significant improvement in the performance of light emitting diodes (LEDs) utilizing gallium nitride (GaN) semiconductors. However, key limitations in the growth and fabrication of these conventional LEDs will ultimately prevent their adoption for the most demanding lighting applications. Commercial GaN-based LEDs are fabricated on ill-matched substrates including sapphire and silicon carbide. The resulting GaN device films contain high dislocation densities (> 109 /cm2) and/or crack densities, often requiring complicated device processing. Additionally, nearly all GaN-based LEDs have been fabricated from polar c-plane GaN thin films. Such devices suffer from built-in polarization fields that reduce carrier recombination efficiency and thus limit light output. Research groups have fabricated nonpolar GaN-based LEDs, which have no built-in polarization fields. They have inherently higher internal quantum efficiency and thus higher output power than conventional c-plane LEDs. The company proposes a research effort to grow and fabricate high-brightness nonpolar (m-plane and a-plane) blue and green GaN-based LEDs on nonpolar GaN films with uniformly low extended defect density. The company team will grow high-quality nonpolar GaN 'template' layers, while the research team will perform LED growth, fabrication, and testing. Commercially, the largest future application for nonpolar GaN-based LEDs is replacement of conventional white light sources such as fluorescent bulbs. Solid-state white lighting may be achieved via combinations of discrete red, green, and blue LEDs; alternately, short-wavelength (e.g. blue, ultraviolet) nitride LEDs can excite phosphor mixtures. In either case, the LEDs must have sufficiently low cost and high output power to justify replacement of conventional lamps. Nonpolar GaN-based LEDs will meet the most demanding lighting requirements, whereas conventional polar GaN-based LEDs cannot. Additionally, since nonpolar GaN-based LEDs emit polarized light, applications such as liquid crystal display backlighting will greatly benefit from their adoption.
