Bandgap energy tuning of electrochemically grown ZnO thin films by thickness and electrodeposition potential

ZnO thin films were electrochemically deposited onto opaque and transparent substrates (copper and ITO). The electrolyte consisted of a 0.1 M Zn(NO3)2 solution with the initial pH adjusted to 6.0, different electrodeposition potentials from E=−700 to −1200 mV (saturated calomel electrode, SCE). The resulting samples have the structural, chemical and morphological properties of hexagonal ZnO, with thickness varying from less than 1 μm to almost 30 μm. The bandgap energy varies inversely with film thickness, ranging from less than 3.1 to 3.4 eV. The bandgap also depends on the electrodeposition potential. This result allows to adjust the desired absorption edge within a 30 nm wide region in the UV.