New Directions in GaN Research at Yale University

So far the impact and promise of GaN devices are focused mainly on optoelectronic and microelectronic devices. The blue LEDs and their inventors have been recognized with Nobel prizes, and GaN power transistors are positioned to play a key role in compact energy efficient power electronics.The ability to grow single-crystalline semiconductor material on amorphous surfaces present a unique challenge using traditional growth techniques. We have recently demonstrated single crystal GaN growth by employing the general phenomenon in film deposition of evolutionary selection. In the concept that has been proposed and demonstrated, evolutionary selection (ES) was employed in first a vertical, then in a lateral direction, allowing a final single crystal of GaN to be formed. This was implemented by deposition of an (0001) oriented AlN layer on a SiO2/Si(100) substrate. A SiO2 confined mask structure is then formed, and subsequent lateral selective area growth of GaN by MOCVD using AlN as a seed, produced site-selected placement of GaN and eliminated the in-plane misalignment.In the 2nd half of the presentation we will talk about new development in GaN photonics. The exploration of GaN in photonic devices and structures, which seeks to manipulate optical density of states and propagation properties through linear and non-linear optical index engineering, has received much less attention. In this talk we will summarize our effort in making GaN resonators in one, two, and three dimensions. We will review the performance and challenges associated with different fabrication pathways. With the use of a novel electrochemical process, we are able to selectively porosify or electro-polish GaN. The electrochemical process enables unprecedented tuning in the index of refraction, making it possible to create optical confined structures and laser diodes.The research is supported by US Department of Energy, National Science Foundation, and DARPA.