Controlling In–Ga–Zn–O thin films transport properties through density changes

• Magnetron cathode current (IC) controls the transport properties of In–Ga–Zn–O (IGZO).
• Low IC results in IGZO films with nanocrystalline inclusions in amorphous matrix.
• High IC reduces the number of trap states in depletion region of Schottky contacts.

In the following study we investigate the effect of the magnetron cathode current (Ic) during reactive sputtering of In–Ga–Zn–O (a-IGZO) on thin-films nanostructure and transport properties. All fabricated films are amorphous, according to X-ray diffraction measurements. However, High Resolution Transmission Electron Microscopy revealed the a-IGZO fabricated at IC = 70 mA to contain randomly-oriented nanocrystals dispersed in amorphous matrix, which disappear in films deposited at higher cathode current. These nanocrystals have the same composition as the amorphous matrix. One can observe that, while IC is increased from 70 to 150 mA, the carrier mobility improves from μHall = 6.9 cm2/Vs to μHall = 9.1 cm2/Vs. Additionally, the increase of IC caused a reduction of the depletion region trap states density of the Ru–Si–O/In–Ga–Zn–O Schottky barrier. This enhancement in transport properties is attributed to the greater overlapping of s-orbitals of the film-forming cations caused by increased density, evidenced by X-ray reflectivity, at a fixed chemical composition, regardless nanostructure of thin films.