Analysis of negative capacitance and interface states in MoOx-based n-Ge devices

Abstract

This study investigates the electrical properties of MoOx hole-selective contacts deposited on an n-type crystalline germanium (n-Ge) substrate via thermal evaporation at room temperature (RT) using frequency-dependent capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements to analyze the Ag/MoOx/n-Ge heterostructure. X-ray diffraction (XRD) pattern confirmed the amorphous nature of the MoOx thin film. The C-V and G/omega-V characteristics exhibited clear dependence on frequency and voltage, emphasizing the significant influence of series resistance (RS) and interface state density (Dit) on the electrical properties of the device. Notably, anomalous peaks were observed in the C-V characteristics within the voltage range of -1.5-0V, which were attributed to the combined effects of RS and Dit. Most strikingly, negative capacitance (NC) was detected in the forward bias region at frequencies above 300kHz, suggesting complex interfacial dynamics and a distinctive charge redistribution mechanism. Key electrical parameters - such as built-in potential (V0), diffusion potential (VD), doping concentration (ND), barrier height (Phi B), Fermi level (EF), and depletion layer width (WD) - were derived from C-2-V measurements at 1 MHz. These values obtained were V0=0.267 V, VD=0.241 eV, ND=6.67x1015 cm-3, Phi B=0.35 eV, EF=0.589 eV, and WD=266 nm. Additionally, the study examined the frequency and bias voltage dependence of the RS, which was found to decrease as frequency increased. The Dit, estimated using the conductance method, was approximately 1012 eV-1 cm-2 at 1MHz. These findings provide valuable insights into the behavior of MoOx/n-Ge heterostructures, focusing on interfacial phenomena, and offer guidance for optimizing these materials for future applications.