Blue luminescence and Schottky diode applications of monoclinic HfO2 nanostructures

Abstract

Schottky diodes based on metal–semiconductor (MS) and metal–insulator–semiconductor (MIS) configurations are nowadays widely regarded as key components for the realization of a number of improved electronic and optoelectronic functions. In this regard, hafnium dioxide (HfO₂) nanostructures were processed through a facile chemical route for application in MIS Schottky diodes. Their monoclinic phase and micro-structural characteristics were studied in detail using the X-ray diffraction, Raman and electron microscopic measurements. The nanostructures were studied to evolve in form of particulate structures at an average scale of 8–10 nm. The low-temperature photoluminescence measurements revealed the optical activity of HfO₂ to spread across the blue region of electromagnetic spectrum. And their origin has been related to the transitions taking place across the intermediary energy levels established by the oxygen related vacancies. The power of incident laser irradiation was also noted to have a significant influence on the surface-state related defect emissions. The electrical properties of HfO₂ were studied using the Bode, Nyquist and Mott–Schottky type plots extracted from the impedance spectroscopic measurements. MIS Schottky diode architectures were finally fabricated using the HfO₂ thin films that were spin cast on n-Si. A significant improvement in the diode characteristics were noted for the heat treated devices, suggesting the improved tunnelling and limiting of charge leakages across the integrated heterojunctions.