Growth, optimization and high-temperature performance of GeO2/Ga2O3 MOSCAPs

Abstract

In this study, GeO₂ thin films were grown by pulsed laser deposition (PLD) on β-Ga₂O₃, ($-201$) single crystal substrates to fabricate metal-oxide-semiconductor capacitors (MOSCAPs) to investigate their properties using current-voltage (I-V) and capacitance-voltage (C-V) measurements at elevated temperatures. The amorphous nature, an ultrawide bandgap of ∼5.11 eV and the elemental compositions with their corresponding chemical states of the GeO₂ thin films were confirmed by X-ray diffraction (XRD), UV–Vis spectrometery and the x-ray photoelectron spectroscopy (XPS), respectively. The Ge-3d deconvoluted peak at 32.4 eV confirms the elemental bonding in GeO₂, with an additional peak found at 30.9 eV that can be attributed to a small portion of GeO_2-x. The Au/GeO₂/Ga₂O₃ MOSCAPs were fabricated to study its high-temperature performance from room temperature (RT) to 300 °C. The reverse leakage current was increased from 1.19 × 10⁻⁷ A to 3.66 × 10⁻⁴ A (nearly four orders of magnitude) as the temperature rises from RT to 300 °C. Due to the presence of oxygen vacancy in GeO_2-x, the Poole-Frenkel current conduction mechanism was utilized to determine a trap level of 0.8 V (below the conduction band of GeO₂) with an activation energy of 0.55 eV. The C–V measurements also show a significant contribution from defects in the flat-band voltage shift and the changes of the slopes indicates an increase in the oxide and interface-trapped charges. The density of oxide-trapped charges increased from 3.9 × 10¹² cm⁻² to 1.3 × 10¹³ cm⁻², as the temperature reached 300 °C. Similarly, the density of interface-trapped charges increased from 3.4 × 10¹² cm⁻² at RT to 1.1 × 10¹³ cm⁻² at 300 °C. The flat-band voltage shift and density of interface-trapped charges of GeO₂/Ga₂O₃ MOSCAPs exhibit exciting materials characteristics for next-generation high-power and high-temperature electronic devices.