Showing papers by "Suzanne E. Mohney published in 1996"

Estimated phase equilibria in the transition metal-Ga-N systems: consequences for electrical contacts to GaN

Abstract: High quality electrical contacts to GaN are required for the advancement of electronic and optoelectronic devices based on the III-V nitrides. In this study, the metallurgy of contacts to GaN and the implications for the design of electrical contacts are considered. First, phase diagrams are estimated for the transition metal-Ga-N systems. The diagrams are then used as an aid in predicting the reaction products of annealed metal/GaN contacts, to suggest materials that may be useful as thermally stable electrical contacts and to explore the role of the partial pressure of N2 in the annealing environment on the reactions in metal/GaN contacts. It is believed that this information will be particularly useful to researchers during the early stages of contact development since very little experimental information is currently available on the GaN contact metallurgy.

Investigation of Aluminum and Titanium/Aluminum Contacts to n-Type Gallium Nitride

Abstract: We report on a study of Al and Ti/Al contacts to n-type GaN. Al contacts on n-GaN (7 x l017cm-3) annealed in forming gas at 600°C reached a minimum contact resistivity of 8x10~6Qcm2 and had much better thermal stability than reported by previous researchers. Ti/Al (35nm/l 15nm) contacts on n-GaN (5xl0I7cm~3) had resistivities of 7 x l0"6Qcm2 and 5xl0"6Qcm2 after annealing in Ar at 400°C for 5min and 600°C for 15sec, respectively. Depth profiles of Ti/Al contacts annealed at 400°C showed that low contact resistance was only achieved after Al diffused to the GaN interface. We propose that the mechanism for ohmic contact formation in Ti/Al contacts annealed in the 400-600°C range includes reduction of the native oxide on GaN by Ti and formation of an Al-Ti intermetallic phase in intimate contact with the GaN. Contacts with different Ti/Al layer thicknesses were investigated and those with 50nm/100nm layers had the same low resistance and better stability than 25nm/125nm contacts.

Approaches to High Temperature Contacts to Silicon Carbide

Abstract: Metallurgical reactions between contacts and SiC can alter the electrical characteristics of the contacts, either beneficially or detrimentally. Simultaneously, consumption of the underlying SiC epilayer takes place. During prolonged operation at elevated temperature, contacts that are not in thermodynamic equilibrium with SiC may continue to react with it. For this reason, interest in thermally stable carbide and silicide contacts to SiC has been growing. To select appropriate carbides or silicides for further study, however, knowledge of the transition metal-silicon-carbon (TM-Si-C) phase equilibria is required. A significant body of literature on the TM-Si-C systems exists and should therefore be examined in the context of electronic applications. In this paper, phase equilibria for representative TM-Si-C systems are presented, trends in these systems with respect to temperature and position of the metal in the periodic table are discussed, and attractive carbide and silicide contacts and processing schemes for thermally stable contacts are highlighted.