Issues in developing ohmic contacts to GaN

Approaches to achieve low resistivity ohmic contacts to GaN with planar and abrupt interfaces are discussed. Three types of thermally stable metallizations were studied: Ti/TiN for n-GaN, Ni/Si for p- and n-GaN, and ZrN/ZrB/sub 2/ for p-GaN. Although all these systems enable formation of ohmic contacts, it is suggested that the underlying mechanism, as investigated by a number of analytical methods, is different in each case.