Low-resistance Ti/Al ohmic contact on undoped ZnO

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 × 10^?7 ωcm², was obtained from the Ti (300 Å)/Al (3,000 Å) contact annealed at 300°C. It was found that TiO was produced, and the atomic ratio of Zn/O was dramatically increased after annealing at 300°C. 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.