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

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/[Formula: see text]-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/[Formula: see text]-V characteristics exhibited clear dependence on frequency and voltage, emphasizing the significant influence of series resistance ([Formula: see text] and interface state density ([Formula: see text] on the electrical properties of the device. Notably, anomalous peaks were observed in the C-V characteristics within the voltage range of [Formula: see text]1.5–0[Formula: see text]V, which were attributed to the combined effects of [Formula: see text] and [Formula: see text]. Most strikingly, negative capacitance (NC) was detected in the forward bias region at frequencies above 300[Formula: see text]kHz, suggesting complex interfacial dynamics and a distinctive charge redistribution mechanism. Key electrical parameters — such as built-in potential ([Formula: see text], diffusion potential ([Formula: see text], doping concentration ([Formula: see text], barrier height ([Formula: see text], Fermi level ([Formula: see text], and depletion layer width ([Formula: see text] — were derived from C[Formula: see text]-V measurements at 1 MHz. These values obtained were [Formula: see text] [Formula: see text]V, [Formula: see text] [Formula: see text]eV, [Formula: see text] [Formula: see text]cm[Formula: see text], [Formula: see text] [Formula: see text]eV, [Formula: see text] [Formula: see text]eV, and [Formula: see text] [Formula: see text]nm. Additionally, the study examined the frequency and bias voltage dependence of the [Formula: see text], which was found to decrease as frequency increased. The [Formula: see text], estimated using the conductance method, was approximately 10[Formula: see text] [Formula: see text]eV[Formula: see text] [Formula: see text]cm[Formula: see text] at 1[Formula: see text]MHz. 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.