High-Frequency Negative Capacitance in Graphene Quantum Dots/Lanthanum(III) Hydroxide-based MIS Heterostructure

Lanthanides have significant potential for electronic technologies based on graphene quantum dots (GQDs), as they have unique electronic configurations characterized by 4f electrons. In this context, lanthanum(III) hydroxide nanoparticles (La(OH)₃NPs) are used as dopants for polyethyleneimine (PEI)-doped nitrogen (N)-doped graphene quantum dots(^PEIGQDs^N) in this study. Using a novel green method, the La(OH)₃NPs-doped ^PEIGQDs^N nanocomposites are prepared from La(NO)₃ in a single step and exploited as an interlayer in a metal/interlayer/semiconductor (MIS) heterojunction with Au and n-Si. Capacitance & conductance-voltage (C-V & G/ω-V) characteristics of the Au/La(OH)₃NPs doped ^PEIGQDs^N/n-Si MIS heterojunction have been investigated as a function of frequency in the wide 500 Hz to 3 MHz range from −3 V to 5 V, at 300 K. It has been observed that the structure is highly sensitive to the frequency. In particular, at high frequencies, above 1.5 MHz, the positive capacitance (PC) transforms into a negative capacitance (NC) in forward bias. In addition, impedance measurements at high frequencies were carried out after the measurements in the dark, while the surface of the structure was illuminated at 100 mW/cm². At the frequencies of 2 MHz and 3 MHz, where inductive behavior was observed, the light refilled the depleted trap levels, catalyzing the transition from NC to PC in forward bias. These findings suggest that the capacitance and conductance of the heterojunction have a remarkable frequency sensitivity, particularly evident at higher frequencies. The outcomes of this study are poised to significantly influence the comprehension of carbon-lanthanides-based electronic technology, and enable the creation of new hybrid functional materials for use in electronic or optoelectronic applications.