Formation of ohmic contacts to p-type ZnO

Formation of ohmic contacts to p-type zinc oxide (ZnO) was studied. The p-type ZnO samples were grown by metalorganic molecular-beam epitaxy with diethylzinc, deionized water vapor and monomethylhidrazine and were annealed under oxygen gas ambient at 650 °C or 700 °C for 20 min to activate doped nitrogen acceptors. Although the current-voltage characteristics measured through gold p-contacts were not perfectly ohmic, they showed perfectly ohmic properties after rapid thermal annealing (RTA) in the temperature range of 300 to 520 °C for 2 min. The ohmic contact resistivity was measured with the transmission-line measurement method and it was decreased to approximately 1/64 with increasing the RTA temperature. The minimum contact resistivity of 3.15 × 10 -3 Ωcm 2 was observed with RTA at 520 °C for 2 min.