Conductivity Control of Al-doped ZnO Thin Films Deposited by Radio Frequency Sputtering

Abstract

Films made up of Al-doped ZnO (AZO) are the promising transparent conductive oxides. Hall measurements were used to investigate the effects of varying the sputtering parameters on the electrical resistivity, electron concentration and electron mobility of a series of AZO films produced by radio frequency (RF) sputtering. Increases in plasma power, chamber pressure, argon (Ar) flow rate and decreases in substrate temperature lead to the higher electrical resistance. However, all the samples exhibit a pattern in which electrical resistivities decrease with increasing annealing temperature (below 200-400 ºC) and increase (above 200-400 ºC). As the number of electrons increases, the electrical resistance decreases and vice-versa. The carrier compensation effect or excess carrier compensation due to the formation or annihilation of conductive defects is responsible for these shifts in the electrical characteristics. It was also found that the conductivities of the AZO films formed via RF-sputtering dependent on imperfections in structure such as ionized impurities and grain boundaries, as electron mobility is shown to be proportional to the electron concentration.