Low resistance nonalloyed Al-based ohmic contacts on n-ZnO:Al

We have investigated the electrical properties of nonalloyed Al, Al/Au, and Al/Pt ohmic contacts on n-type ZnO:Al (2×1018 cm−3). All Al-based nonalloyed ohmic contacts on the n-ZnO:Al reveal linear current–voltage behavior with low specific contact resistivity of 8.5×10−4 (Al), 8.0×10−5 (Al/Au) and 1.2×10−5 Ω cm2 (Al/Pt), respectively. Using secondary ion mass spectroscopy (SIMS) and x-ray photoelectron spectroscopy (XPS) depth profiles, it was found that the O atoms in the ZnO:Al layer outdiffused to Al metal layer while the Al atoms indiffused to the surface region of ZnO:Al. This interdiffusion between Al and O atoms at room temperature results in an increase of doping concentration in the surface region of the ZnO:Al and reduces a specific contact resistivity of the Al-based ohmic contacts without thermal annealing process.