Gallium nitride optoelectronic devices are amongst the fastest expanding fields and are being extensively used in solid-state lighting, optical imaging, scanners, power amplifiers and switches for interfacing renewable energy with the electric grid. Therefore, their importance is of the utmost concern. Efforts to successfully improve the material's quality will enhance device performance and impact several industrial and consumer products.
TECHNICAL DETAILS: III-Nitride compounds are the material of choice in several optical and electronic devices. High defect densities (approximately 10exp9 to 10exp10 /cm2) are currently present in III-Nitride compounds due to the lack of both lattice matched substrates and lattice matched multilayers made from binary and ternary compounds. These defects act as non-radiative recombination and scattering centers that, for example, impact minority carrier lifetime and reduce thermal conductivity. These high defect densities limit the performance and reliability of several optoelectronic devices such as ultraviolet (UV) light-emitting diodes (LEDs), laser diodes as well as power devices and switches. Previous efforts to reduce these defects have had limited success. The objective of this project is to achieve films in III-nitride compounds with defect densities lower than 10exp7/cm2 over the entire wafer. The overall approach is involves overgrow from nanostructured GaN templates by using an innovative approach. It begins with a mask-less fabrication of nanowires with conical tips to facilitate the growth and coalescence of the overgrown GaN film. GaN three-dimensional growth on different crystallographic facets in early overgrowth stages on nanowire structures plays a key role in the remaining dislocation interactions (since the likelihood for dislocation annihilation and formation of dislocation loops are greatly increased). Subsequently a network of embedded voids in the epitaxial films are generated that act as dislocation sinks. Studies are underway to determine the dominant mechanism in the defects reduction. During the course of this project, both undergraduate and graduate students are engaged in the research. As well, the outreach program includes undergraduates, minority students, and high school teachers.