Low-resistance Ti/Al ohmic contact on undoped ZnO

Abstract

We report a low-resistance ohmic contact on undoped ZnO using a promising contact scheme of Ti/Al. Specific-contact resistivity, as low as 9.0 x 10(-7) Omegacm(2), was obtained from the Ti(300 Angstrom)/Al(3,000 Angstrom) contact annealed at 300degreesC. It was found that TiO was produced, and the atomic ratio of Zn/O was dramatically increased after annealing at 300degreesC. This provides the evidence that a number of oxygen vacancies, acting as donors for electrons, were produced below the contact. This leads to the increase of electron concentration via the reduction of contact resistivity.