Abstract
This study reports the structural properties of zinc oxide thin films co-doped with aluminum and nitrogen (ZnO:Al-N) grown by RF magnetron sputtering from an AZO (ZnO with 2 wt% Al2O3) target under nitrogen (N2) atmosphere at room temperature (RT). Nitrogen partial pressures of 0.00, 0.10, 0.25 and 1.00 mTorr were used. The film thickness was around 270 nm. Ultraviolet-Vis-NIR transmittance (T) spectra of the films revealed T values of 80 to 85% in the 400 to 700 nm wavelength range. XRD results indicated that the films had a hexagonal wurtzite structure and were preferentially oriented in the (002) plane. Analyses by EDS indicated that the N atoms tend to be incorporated into the ZnO matrix at the expense of oxygen atoms. The ideal [N]/[Al] was obtained at a N2 partial pressure of 0.25 mTorr, producing a p-type film. For a [N]/[Al] of 1.53, the film also exhibited p-type conduction with an electrical resistivity of 31.92 Ω cm, mobility of 18.65 cm2/V s and carrier density of 1.22 x 1016 cm-3. The low carrier density is attributed to the energetically favorable formation of inactive nitrogen phases instead of acceptor-receiver-acceptor complexes, even at the ideal [N]/[Al].
Highlights
Zinc oxide (ZnO) is biodegradable, non-toxic, and composed of elements abundant in the Earth’s crust (Zn – 132 ppm in the Earth’s crust, O – 49,4%), making it important for large-scale applications
Following the success of GaN as a blue light emitter, efforts have been remade to obtain p-type doped ZnO, which would permit the fabrication of LEDs, for example
Comparing the composition of the AZO target with that of the ZnO:Al film, there is a reduction in Zn concentration while the concentration of Al does not change significantly
Summary
Zinc oxide (ZnO) is biodegradable, non-toxic, and composed of elements abundant in the Earth’s crust (Zn – 132 ppm in the Earth’s crust, O – 49,4%), making it important for large-scale applications. ZnO is widely used industrially as an additive for rubber, paints, cosmetics and medicines, amongst others[1]. Since it is a semiconductor with a wide direct bandgap of 3.3 eV and high binding energy excitons (60 meV), it is a strong candidate in new generations of optoelectronic devices, including semiconductors, light-emitting-diodes (LEDs) and lasers[1,2]. Following the success of GaN as a blue light emitter, efforts have been remade to obtain p-type doped ZnO, which would permit the fabrication of LEDs, for example. The following strategies have been used to produce p-type doping of ZnO: (i) group VA element atoms substitute oxygen atoms; (ii) group IA element atoms substitute Zn atoms; (iii) co-doping with donors and acceptors[4]
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