Structural, electrical and optical characterization of Ti-doped ZnO films grown by atomic layer deposition

Thin films of Ti-doped ZnO (TZO) have been deposited using Atomic Layer Deposition (ALD) achieving highly conductive materials with resistivities down to 1.8 × 10−3 Ω cm at 1.7 cat% Ti doping, with a maximum dopant efficiency of 31%. The high conductivity and doping efficiency suggests a good distribution of dopants, otherwise a common challenge for doping by ALD. The charge mobility for Ti concentrations below 1.2 cat% was higher than for pure ZnO. The texture of the films changed from a predominantly c-axis to a-axis orientation with increasing Ti concentration, while the lattice parameters remained unaltered. The TZO films were highly transparent with an absorbance in the visible range of less than 2% for 200 nm films. The band gap increased with Ti content from 3.28 eV for pure ZnO to 3.67 eV for 5.9 cat% Ti, attributed to the Burstein Moss effect. The index of refraction varied with the Ti content showing a minimum of 1.90 for 1.7 cat% Ti.