Equivalent circuit analysis of Al/rGO-TiO2 metal-semiconductor interface via impedance spectroscopy: Graphene induced improvement in carrier mobility and lifetime

A metal-semiconductor (MS) contact often gives rise to a Schottky barrier junction and is immensely important in electronic devices. Recently, graphene and its nanocomposites have attracted interest for their tremendous potential in schottky barrier diodes (SBDs). To realize a high performance SBD, detail characterization of the MS interface is of utmost importance. In this regard, here we employ impedance spectroscopy (IS) as a simple yet powerful technique for the equivalent circuit analysis and characterization of Al/reduced graphene oxide(rGO)-TiO2 interface. Al/rGO-TiO2 SBDs are fabricated with different weight ratios of rGO (rGO:TiO2 = 0, 1:50, 1: 30, 1:15) in the composite and IS analysis is performed for all the SBDs. Built-in potential, charge carrier density, depletion layer width and barrier height of the diodes are extracted from capacitance-voltage measurements. Moreover, we obtain the charge career lifetime, mobility and diffusion length based on the equivalent circuit model. Current-voltage measurement is also performed and mobility values from IS are further verified by space charge limited current (SCLC) measurements. The best device performance and charge transport properties was exhibited by rGO:TiO2 = 1:15. The carrier mobility increased by almost 2.6 times compared to pure TiO2, while the lifetime and diffusion length improved by 113% and 130% respectively. In short, we demonstrate the equivalent circuit analysis for the investigation of Al/rGO-TiO2 MS interface and successfully implement the IS model to determine charge transport parameters. This study reveals the beneficial impact of graphene on device performance and establish the huge potential of IS technique for characterization of MS devices.