Atomic Layer Deposition of Undoped and Al-Doped ZnO Thin Films Using the Zn Alkoxide Precursor Methylzinc lsopropoxide

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). Dimethyl-aluminum isopropoxide (DMAI) was used as an AI 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 similar to 2.0 angstrom/cycle in the substrate temperature range of 160 similar to 200 degrees C and the maximum growth rate reached about 2.58 angstrom/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)similar to 3.2 x 10(-3) Omega cm depending on the substrate temperature. By Al-doping, the resistivity was minimized to similar to 1.35 x 10(-4) Omega cm.