Contents lists available at ScienceDirect Materials Science in Semiconductor Processing journal homepage: www.elsevier.com/locate/mssp Equivalent circuit analysis of Al/rGO-TiO 2 metal-semiconductor interface via impedance spectroscopy: Graphene induced improvement in carrier mobility and lifetime Mrinmay Das, Joydeep Datta, Sayantan Sil, Arka Dey, Rajkumar Jana, Soumi Halder, Partha Pratim Ray ⁎ Department of Physics, Jadavpur University, Kolkata 700 032, India ARTICLE INFO Keywords: Metal-semiconductor Schottky barrier diode Reduced graphene oxide-TiO 2 Impedance spectroscopy Equivalent circuit model Carrier lifetime Carrier mobility ABSTRACT 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)- TiO 2 interface. Al/rGO-TiO 2 SBDs are fabricated with different weight ratios of rGO (rGO:TiO 2 = 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:TiO 2 = 1:15. The carrier mobility increased by almost 2.6 times compared to pure TiO 2 , 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-TiO 2 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. 1. Introduction Metal-semiconductor (MS) interfaces occur frequently in numerous semiconductor devices and integrated circuits [1]. It is seen that, the interface quality plays a decisive part in determining the performance of these devices [1]. Depending upon the work function of the mate- rials, the MS contacts often gives rise to either Ohmic or rectifying behaviour, which are useful for a diverse range of applications [1]. Recently, impedance spectroscopy (IS) has been proved to be a simple yet powerful technique for the characterizations of the MS interfaces and can also be used to analyze the dynamics of bound or mobile charge in the interfacial region of solid or liquid materials [1,2]. Particularly, the IS technique can be used to develop an appropriate equivalent circuit model for the MS interface, which can be employed to analyze the electrical characteristics and the conduction mechanism of various thin film devices [3–9]. For thin film devices, a clear insight on the carrier lifetime and mobility of the materials is very important. A ple- thora of techniques to measure these parameters, such as transient photovoltage [10–13] for carrier lifetime and time-of flight [14], field- effect-transistor (FET) [15,16], and space charge limited current (SCLC) [17–20] methods for carrier mobility measurements, have been de- ployed. But, the IS technique has relatively been underused over the years. However, of late it has attracted renewed interest from re- searchers for being able to provide us with many important electronic parameters from just a single set of experiments [1,2,18]. In the last few years, the novel 2D materials have generated a lot of attention from numerous research groups [21–28]. Among them, gra- phene, the atomic thin material composed of sp 2 hybridized carbon atoms, has become the frontrunner for next generation technology, due to its extraordinary and unique properties [20,29,30]. Moreover, its composites have seen a meteoric rise for device applications such as Schottky diodes, solar cells, LEDs, transistors and also storage https://doi.org/10.1016/j.mssp.2018.03.039 Received 14 February 2018; Received in revised form 25 March 2018; Accepted 29 March 2018 ⁎ Corresponding author. E-mail address: partha@phys.jdvu.ac.in (P.P. Ray). Materials Science in Semiconductor Processing 82 (2018) 104–111 1369-8001/ © 2018 Elsevier Ltd. All rights reserved. T