In situ Al-doped ZnO films by atomic layer deposition with an interrupted flow

In situ aluminum-doped ZnO (AZO) films were grown on glass substrates by atomic layer deposition (ALD) with an interrupted flow at temperatures in range 200-280 C; the optimal temperature, 260 C, depended on the electrical properties. To assess the effect of the ratio of pulses of diethylzinc (DEZn) and trimethylaluminium (TMA) on the structural, optical and electrical properties, we grew AZO films with various pulse ratios of DEZn:TMA in a range from 3:1 to 10:1 at 260 C. These properties and the content of Al were investigated with X-ray diffraction, X-ray reflectivity (XRR), a high-resolution transmission electron microscope (HRTEM), a secondary-ion mass spectrometer (SIMS), transmission spectra, Hall measurements and X-ray photoelectron spectra (XPS). The electrical resistivity was least, 5.7 × 10^-4 Ω cm, for ALD-AZO films with pulse ratio 6:1; the carrier mobility was 8.80 cm² V^-1 s^-1 and optical transmittance up to 94%. The epitaxial AZO films grown in situ also on m-plane sapphire exhibited the two-fold symmetry of ZnO (110) in the orthorhombic crystal system. All results show that a novel in situ doping method with an interrupted flow controls the Al content of AZO films more easily, and is more usefully applicable for a structure with a large aspect ratio for an advanced photoelectric device.