Aluminum Zinc Oxide Films and Precursors

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Aluminum zinc oxide (AZO) is a promising earth abundant alternative to Sn-doped In2O3 (ITO) as an n-type transparent conductor for electronic and photovoltaic applications. The deposition of AZO films with an optimal aluminium-doping level exhibiting high electrical conductivity remains challenging. Various methods have been employed to dope AZO, including plasma nitriding and high pressure chemical vapour deposition (HPCVD). The use of a suitable precursor is important in determining the final morphology, composition, and optical properties of the deposited film. A recent study investigated the influence of different solvents and deposition temperatures on the structural, crystalline structure, and functional properties of AZO thin films doped with varying levels of aluminium by atomic layer deposition (ALD) [Reference Tynell and Karppinen]. A typical process involves alternating pulses of trimethylaluminum (TMA) and diethylzinc (DEZ) with inert gas purge steps.

The results show that the morphology of AZO films doped with 0 at. %-5 at. % aluminium is highly (002)-oriented with large crystallites. The optical transmission spectra of the films demonstrate that the spectral gap of the wurtzite structure decreases with increasing doping level. The relative intensity of the (hkl) peaks, which corresponds to the proportion of crystallites oriented in the desired direction, also increases with the doping level.

The work functions of AZO thin films prepared by an Al-terminated and ZnO-terminated ALD recipe were measured using a scanning Kelvin probe, and a consistent trend was observed as the aluminium concentration increased. The result suggests that the optimum aluminium-doping level of a AZO film can be adjusted by changing the precursor composition and adjusting the deposition conditions.

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