Atomic layer deposition of undoped and Al-doped ZnO thin films using the Zn alkoxide precursor methylzinc isopropoxide.

Undoped and Al-doped ZnO thin films have been prepared by atomic layer deposition (ALD) using the Zn precursor methylzinc isopropoxide [MZI, (CH3)Zn(OCH(CH3)2)] with water (H2O). Dimethylaluminum isopropoxide (DMAI) was used as an Al precursor. The self-limiting ALD process via alternate surface reactions of MZI and H2O was confirmed by thickness measurements of the ZnO films with varying MZI supply time and numbers of MZI-H2O ALD cycles. Under optimal reaction conditions, the growth rate of the ZnO films was 1.9 to approximately 2.0 A/cycle in the substrate temperature range of 160 to approximately 200 degrees C and the maximum growth rate reached about 2.58 A/cycle at 240 degrees C. Room temperature photoluminescence (PL) measurements revealed a strong free excitonic peak at 3.27 eV with almost negligible deep level emission. Resistivities of ZnO films were measured to be 5 x 10(-3) to approximately 3.2 x 10(-3) omega cm depending on the substrate temperature. By Al-doping, the resistivity was minimized to approximately 1.35 x 10(-4) cm.