Contacts on n-type germanium using variably doped zinc oxide and highly doped indium tin oxide interfacial layers

The impact of varying interfacial layer (IL) doping on the performance of Ti/IL/n-Ge contacts is demonstrated using undoped ZnO, aluminumdoped ZnO (AZO), and O-vacancy-doped n(+)-ZnO ILs having similar conduction band offsets Delta E-c with respect to Ti and Ge. Diode and transfer length method measurements show Fermi-level unpinning for all the ILs; however, the contact resistance and its dependence on the IL thickness decrease with increasing IL doping owing to the reduction in the tunneling resistance. The contact resistivity depends on the IL doping (N-IL) as rho(c-n+)-ZnO < rho(c-AZO) < rho(c-ZnO) for Nn+-ZnO > N-Lambda ZO > N-ZnO. Contacts using a highly doped, low Delta E-c tin-doped In2O3 IL exhibit the lowest value, 1.4 x 10(-7) Omega.cm(2). (C) 2015 The Japan Society of Applied Physics