Plasma-aided hydrogenation and Al-doping: Increasing the conductivity and optical transparency of ZnO transparent conducting oxide

Plasma-assisted magnetron sputtering with varying ambient conditions has been utilised to deposit Al-doped ZnO (AZO) transparent conductive thin films directly onto a glass substrate at a low substrate temperature of 400 °C. The effects of hydrogen addition on electrical, optical and structural properties of the deposited AZO films have been investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM), Hall effect measurements and UV-vis optical transmission spectroscopy. The results indicate that hydrogen addition has a remarkable effect on the film transparency and conductivity with the greatest effects observed with a hydrogen flux of approximately 3 sccm. It has been demonstrated that the conductivity and the average transmittance in the visible range can increase simultaneously contrary to the effects observed by other authors. In addition, hydrogen incorporation further leads to the absorption edge shifting to a shorter wavelength due to the Burstein-Moss effect. These results are of particular relevance to the development of the next generation of optoelectronic and photovoltaic devices based on highly transparent conducting oxides with controllable electronic and optical properties.

▶ The application of a plasma allows growth at a low substrate temperature (400 °C). ▶ The addition of hydrogen to the plasma strongly influences the properties of the ZnO films. ▶ The electronic, optical and structural properties of the film can be tuned by modifying the flow rate of hydrogen. ▶ The flow rate can be optimized and to achieve the best values of optical transmittance and resistivity. ▶ The adsorption edge is shifted to a shorter wavelength as the H2 flow rate increases.