Defects and Impurities in 4H- and 6H-SiC Homoepitaxial Layers: Identification, Origin, Effect on Properties of Ohmic Contacts and Insulating Layers and Reduction.

A chemical vapor deposition system has been designed and is being constructed for the purpose of depositing 4H- and 6H-SiC and AlN thin films. The design incorporates a separate load lock from which the growth chamber and a RHEED chamber are attached. Comparisons between the wetting characteristics of 6H-SiC0001Si and Si111 surfaces in various acids and bases were conducted. The 101 HF dipped Si111 surfaces were hydrophobic the 0001Si 6H-SiC surfaces were hydrophilic. The 6H-SiC0001Si surfaces capped with a 20A Si layer, however, were hydrophobic after HF dipping and exhibited outgassing levels on annealing which were several orders of magnitude lower than SiC wafers dipped in HF without the capping layer. Annealing the Si capped 0001Si 6H-SiC surfaces in UHV at 1100 deg C for 5 min. caused thermal desorption of the Si capping layer and the formation of a 3x3 Si rich, oxygen free 0001Si 6H-SiC surface. As-deposited at RTNiAl, Au, and Ni contacts were rectifying on p-type 6H-SiC 0001 with very low leakage current densities approx. 1x10exp. -8 Asq cm at 10 V. The Schottky barrier heights showed a reduced dependence on the metal work functions, a result which is in agreement with those for n-type SiC. NiNiAl contacts on p 1x10exp. -19cu cm SiC were ohmic after annealing for 10-80 s at 1000 deg C in a N2 ambient. The estimated specific contact resistivity was 2-3x10exp. -2W.sq cm.