Abstract:
In this work, the energy and flux of high energetic ions were controlled by RF superimposed DC sputtering
process to increase the grain size and suppress grain boundary potential with minimum residual stress
in Al doped ZnO (AZO) thin film. AZO thin films were deposited at different RF/(RF + DC) ratios by keeping
total power same and were investigated for their electrical, optical, structural and nanoscale grain
boundaries potential. All AZO thin film showed high crystallinity and orientation along (002) with peak
shift as RF/(RF + DC) ratio increased from 0.0, pure DC, to 1.0, pure RF. This peak shift was correlated with
high residual stress in as-grown thin film. AZO thin film grown at mixed RF/(RF + DC) of 0.75 showed high
electron mobility, low residual stress and large crystallite size in comparison to other AZO thin films. The
nanoscale grain boundary potential was mapped using Kelvin Probe Force Microscopy in all AZO thin film
and it was observed that carrier mobility is controlled not only by grains size but also by grain boundary
potential. The XPS analysis confirms the variation in oxygen vacancies and zinc interstitials which explain
the origin of low grain boundaries potential and high carrier mobility in AZO thin film deposited at 0.75
RF/(RF + DC) ratio. This study proposes a new way to control the grain size and grain boundary potential
to further tune the optoelectronic-mechanical properties of AZO thin films for next generation flexible
and optoelectronic devices.
