Gallium oxide thin films deposited by spray pyrolysis with low contact resistance towards indium-tin oxide and their implementation in heterojunctions with nickel oxide

Gallium oxide (Ga₂O₃) is gaining significant attention as an ultrawide band gap semiconductor, offering promising potential for high-power and high-voltage electronic applications. Its band gap of approximately 4.8 eV allows devices to operate efficiently under extreme conditions, such as high electric fields and temperatures. This makes it ideal for use in power electronics, including diodes and transistors for electric grids and electric vehicles. However, the process of creating effective electrical contacts with Ga₂O₃ is particularly challenging. The material's wide band gap complicates the formation of low-resistance ohmic contacts, often necessitating the development of specialized metallization techniques and surface treatments.
This contribution uses spray pyrolysis to deposit gallium oxide thin films onto Indium-Tin-Oxide (ITO), which formed in-situ a low-ohmic contact by interdiffusion between the two layers. The deposition takes place at 380°C and uses gallium acetylacetonate as precursor substance dissolved in an acetic acid/water mixture. Special care is taken with regard to solution chemistry in order to keep the precursor species volatile during the solvent evaporation, which guarantees CVD-like growth leading to uniform coverage of rough substrates.
Single layers and n/p heterojunctions with NiO deposited by RF-sputtering were fabricated in order to extract the electronic properties with X-ray photoelectron spectroscopy (XPS), Kelvin probe and ambient pressure photoemission spectroscopy (APS). Extracted properties were band gap, work function, ionization energy, electron affinity and charge carrier density.
The junction properties of the NiO/Ga2O3 heterojunctions were further explored with respect to the of the thickness of the layers. For this, a combinatorial approach was used, where the Ga2O3 layer thickness was varied per substrate by using a dedicated spraying pattern. The IV-characteristics of these gradient samples were then recorded with a home-made measurement setup, allowing the high-throughput characterization of up to 64 pixels per 1 sqin substrate.