MICROSTRUCTURE OF TI AL OHMIC CONTACTS FOR N-ALGAN/

Transmission electron microscopy was employed to evaluate the microstr ucture of Al/Ti ohmic contacts to AlGaN/GaN heterostructure field-effe ct transistor structures. Contact resistance was found to depend on th e structure and composition of the metal and AlGaN layers, and on atom ic structure of the interface. A 15-25-nm-thick interfacial AlTi2N lay er was observed at the contact-AlGaN interface. Formation of such nitr ogen-containing layers appears to be essential for ohmic behavior on n -type III-nitride materials suggesting a tunneling contact mechanism. Contact resistivity was found to increase with Al fraction in the AlGa N layer. (C) 1998 American Institute of Physics. [S0003-6951(98)01244- 3].