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Investigation of post-annealing effect on efficient ohmic contact to ZnO thin film using Ti/Al metallization strategy



Ohmic and Schottky contacts are playing a major role in the field of ZnO based electronics device fabrication. It is seen that several works have been reported on metallization scheme, contacts with this semiconducting material. But, the thickness of semiconducting material and the choosing of substrate still remain imperfect and inefficient for advanced IC technology. To estimate contact resistance, the transmission line method (TLM) is found to be more complex. So, Schottky barrier height (SBH) model is considered to obtain at most accuracy to find Ohmic contact parameters. Herein, the investigation of parameters like barrier height, ideality factor and saturation current at room temperature of very low specific resistance Ohmic contact to ZnO using Ti/Al metallization scheme are performed. The thermal evaporation technique is performed for the deposition of ZnO thin film of 200 nm and Ti (100nm) /Al (100nm). Further, using a vacuum furnace, post-annealing treatment is also done at different temperatures (Four samples of 3000C, 4500C, 6000C and 7000C at a time period of 20 minutes for each temperature). Characterization of the contacts are done through current-voltage (I –V) using a semiconductor parameter analyzer. The parameters like barrier height, ideality factor and saturation current of this metallization scheme are extracted from the current-voltage plot. It is considered that the theory of thermionic emission is the fundamental phenomenon behind carrier transport at the interface. After post annealing, a comparative analysis is done and the deviations in the parameters are analyzed from semi-log current versus voltage plot and Richardson plot.