Highly tunable electrical properties in undoped ZnO grown by plasma enhanced thermal-atomic layer deposition.

Undoped ZnO thin films with highly tunable physical properties have been achieved by a new plasma enhanced thermal atomic layer deposition. This innovative yet straightforward approach has not been reported before but is demonstrated to be capable of controlling material properties in a wide range. The structural, electrical, and optical properties of the ZnO films were investigated by various characterization techniques. The growth mechanisms are discussed in terms of the chemistry of the additional O2 plasma on ZnO formation. Without extrinsic doping, the resistivity and carrier concentration of the ZnO films can be controlled up to seven and five orders of magnitude, respectively, by simply adjusting the plasma conditions. The electrical properties of the ZnO films were also found to correlate with significant changes in their optical properties. This extreme control and tunability of material properties is rarely achievable for undoped and even doped ZnO and should enhance the viability of ZnO in advanced device applications.