Determination of surface morphology and electrical properties of MoO₃ layer deposited on GaAs substrate with RF magnetron sputtering

Abstract

We report the effects of the substrate temperature on the surface morphology of Molybdenum tri-oxide (MoO₃) thin films and the electrically detailed examination of Au/MoO₃/n–GaAs MOS heterojunction structure with the best homogeneity. MoO₃ thin film was deposited both on soda–lime silicate glass as a thin film and n-type and (100) oriented GaAs substrates using RF magnetron sputtering method at substrate temperatures of room temperature, 100 °C, 200 °C and 300 °C. Surface morphology of the MoO₃ thin films were investigated by utilizing atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements. AFM and SEM results have shown that MoO₃ thin film with substrate temperature of 200 °C has the lowest surface roughness and the homogeneity of the film structures significantly enhances with increasing substrate temperature up to 200 °C. An inclement in roughness of thin film structure was detected at higher temperature than 200 °C due to the deterioration of homogeneity. Therefore, we primarily focused on the MoO₃ thin films produced at the substrate temperature of 200 °C to examine the electrical properties of Au/MoO₃/n–GaAs MOS heterojunction device. In order to determine the electrical properties, temperature dependent $I-V$ measurements were performed in between 200 and 400 K by steps of 25 K. The fundamental electrical parameters such as saturation current (${I}_{0}$), ideality factor ($n$), and barrier height (${\phi }_{0}$) were calculated by analyzing the forward bias $I{-}V$ curves at different temperatures. The series resistance (${R}_{s}$) values of the device were also determined using the plot of structure resistance (${R}_{\text{i}}$) vs applied bias voltage (${V}_{i}$), Thermionic Emission Theory and Cheung and Cheung methods. The ${R}_{s}$ value of Au/MoO₃/n–GaAs MOS heterojunction device shows an abnormal behavior of up to 350 K, which is the critical temperature value and tends to increase with increasing temperature. Above the critical temperature value, it exhibits ideal behavior.