Current-voltage (I-V) characteristics of Au/n-Ge heterostructure based on cobalt phthalocyanine (CoPc) interlayer

The influence of cobalt phthalocyanine (CoPc) interlayer on the I-V measurements of Au/n-Ge (pristine) contacts is investigated. I-V characteristics reveals the decrease in the reverse leakage current of CoPc interlayer contacts than compared to contacts without interlayer. The Schottky barrier parameters were described using forward I-V measurements by assuming standard thermionic emission mechanism. The barrier height (BH) of the contact with CoPc interlayer is significantly improved than compared to pristine contact. The observed BHs of pristine and CoPc interlayer contacts are found to be 0.63 eV and 0.67 eV respectively. Reduced interface state density and altered space charges on the n-Ge surface reduces tunneling resistance, may account for the larger BH observed in contacts with CoPc interlayer than pristine contacts. The series resistance evaluated for the contacts using Cheung's method shows its consistency with Norde method. The observed series resistance value of the Au/CoPc/n-Ge contacts found to be significantly smaller in magnitude than Au/n-Ge contacts. The current conduction mechanism of pristine contact and contact with interlayer was evaluated using double logarithmic I-V plot in the forward bias region. Three regions of conduction mechanisms are observed for Au/CoPc/n-Ge contacts. It is evident that the CoPc interfacial layer considerably changes the conduction mechanism from ohmic conduction to trap charge limited current (TCLC) mechanism at moderately high voltages. The associated transition in the conduction mechanism might be due to the presence of shallow traps (low energy traps) with exponential distribution at the CoPc/n-Ge interface.