Doping and its effect on ZnO properties

Abstract

ZnO samples used in this thesis were fabricated by solution method using water bath (WB) and microwave heating (MVH) and by pulsed laser deposition (PLD). The PLD ZnO samples were n-type doped with Ga and the electron effective mass was measured for the first time as a function of doping concentration by combining THz-TDS and Hall measurement. It is also noticed that the electron mobility determined by THz-TDS can be 7 times greater than that obtained by Hall due to carrier localization. Comparison of ZnO grown by WB and MVH shows that MVH synthesized ZnO has less intrinsic doping/defects and more uniform distribution. It is found that to obtain reliable p-type doping with potassium (K), the amount of K interstitial, Ki and KZn-Ki complexes must be minimized by annealing above 700oC for 30 minutes to break down the complexes and drive out Ki and Hi which compensate the p-conductivity.