Fabrication and Characterization of Nanostructured Cadmium Oxide Thin Films Doped with Indium by Sol–Gel Spin-Coating for CdO (n)/Si (p) Heterojunction Photodiode Applications

Abstract

In this study, nanostructured thin films based on cadmium oxide doped with Indium (CdO:In) were fabricated by sol–gel spin-coating technique on p-type monocrystalline silicon (c-Si) for the integration in n-p heterojunction photodiode applications. A comprehensive analysis of structural, morphological, compositional, optical and electrical properties of the surface of undoped CdO and CdO:In films on silicon substrates was conducted. The doping of CdO films with Indium by incorporating In³⁺ ions maintained a nanocrystalline network in a cubic structure with reduced average grain size and smooth heterointerface with the c-Si substrate. The anti-reflection role of undoped CdO and doped CdO:In was validated through lower optical reflectance compared to the bare Si substrate, especially in short wavelength range. The electrical current–voltage I-V characteristics, measured in the dark and under illumination, were used to determine the main diode parameters of different CdO (n)/ c-Si (p) heterojunction structures. Compared to undoped CdO thin films, In-doping of CdO lead to higher ideality factor and reverse saturation current, but lower potential barrier and series resistance. Higher photogenerated current at the Si region with more light sensitivity was obtained in the CdO:In/Si diode owing to better transparency and wider bandgap than the undoped CdO film.Whereas, lower conduction band offset at the CdO:In/Si heterojunction enabled an improvement in charge carrier transport in the CdO:In/Si diode compared to the CdO/Si diode. Our results demonstrate the effective integration of nanostructured In-doped CdO thin films in CdO/Si n-p heterojunction photodiode applications.