9522756 Abernathy In electronics applications, narrow budget and/or high doping levels are usually needed in order to minimize the resistances arising from Ohmic contacts. Similar contact schemes must be developed for nitride-based p-n junction devices. In addition to a low contact resistance it is especially important that the contracts be thermally stable as the devices will often have to operate in a high temperature environment. The first objective of this proposal is to fabricate stable non-alloyed Ohmic contacts on both n-type GaN and graded n-InxGa1-xN/n-GaN layers to determine the contact resistance as deposited over a wide range of measurement temperatures and drive current densities. Next, Ohmic contacts on structures containing an additional graded layer of InASyN1-y on top of the graded InxGa1-x N will be fabricated to determine what improvement if any these contacts show at room and elevated temperatures. Contact resistances as a function of measurement temperature for Ti/Pt/Au, Pd/Ge or Si sometimes deposited as a single crystal/Ti/Pt, W, and possibly other metallization schemes will be measured using the transmission line method (TLM) over the range of 230C to 5000C at current densities ranging from 103 A.cm-2. For all of these structures, extensive characterization of the metal-semiconductor interface will be carried out using Auger Electron Spectroscopy (AES) to determine the degree of interdiffusion and transmission electron microscopy (TEM) to evaluate the structural integrity of the semiconductor/contact. This information will be used to determine the failure models of these structures to provide insight into methods for improvement and a more in depth understanding of how Ohmic contact is formed. Contacts to p-type GaN will be investigated as well. Using non-alloyed contacts to p-GaN as a baseline, structures containing heavily carbon doped GaASyN1-y contact layers will be fabricated and compared. As discussed above, contact performance and integrity will be measured over a wide range of ambient temperatures. In this program, the University of Florida will supply the epitaxial used for Ohmic contact information, while EPSD will provide contact processing and testing. ***
