Nitrogen plasma-assisted codoped P-type (In, N):SnO₂ ultra-fine thin films and N-ZnO/p-In:SnO₂ core-shell heterojunction diodes fabricated by an ultrasonic spray pyrolysis method

In this study, tin oxide (SnO₂) solution mixtures containing indium (In) of 0%, 3%, 7%, 15%, and 30% were used to fabricate In- and N-codoped SnO₂ films on glass at 400 °C using an ultrasonic spray pyrolysis method combined with thermal annealing at 600 °C and post nitrogen plasma treatment. X-ray diffraction analysis demonstrated that the incorporation of elemental In in the SnO₂ film primarily induces the evolution of crystalline phases from In-doped SnO₂ to Sn-doped In₂O₃, depending on the doping concentration. Upon exposure to N plasma, the dark current dramatically increases in proportion to the treatment duration (5-40 min); the dark current can be enhanced for the 3% and 7%-doped samples by as much as 3 orders of magnitude compared to the untreated samples. Hall measurements confirmed that hole carriers could dominate the SnO₂ host matrix to promote p-type properties at a low In content (3% and 7%) with an increase in resistance compared to undoped samples. However, samples with higher In content (15% and 30%) showed the opposite trend, due to the formation of a secondary phase of n-type In₂O ₃. X-ray photoelectron spectroscopy was used to probe the incorporation and dissociation of chemical bonds between the doped In and N atoms in the SnO₂. Moreover, depth profile measurements showed a correlation between the elemental compositions and elemental distributions of the codoped SnO₂ film. Current-voltage (I-V) characterization revealed the improved behavior of heterojunction diodes consisting of a p-type (In, N)-doped SnO₂ thin film deposited on n-type ZnO nanorod arrays.