Mg:TiO2 alloy thin films based MOS capacitors grown on GaAs substrates

Dalal, Avijit; Murli Manohar Dhar Dwivedi, Shyam; Ghosh, Chiranjib; Lahiri, Rini; Henini, Mohamed; Mondal, Aniruddha

Abstract

Electron beam evaporation technique is employed to synthesise TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 thin films (TFs) grown on (100) n-type GaAs substrates. Field emission gun-scanning electron microscope (FEG-SEM) results show that the TFs have a thickness of ~ 225 nm. The non- contact atomic force microscopy (NC-AFM) images shows the pore volume of the TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 TFs enhanced gradually. UV-Vis absorption measurements are performed on the samples to determine the main bandgap and defect level transition of the material. A unique modified Urbach theoretical model has been introduced to simulate the experimental absorption spectrum. The main bandgap energy of the TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 samples are calculated to be ~ 3.45 eV, 3.85 eV and 4.30 eV respectively. A gradual enhancement in main bandgap transition probability and decrease in defect level transition of the material has been observed with enhanced incorporation of Mg into the TiO2 host material. X-ray diffraction (XRD) is performed, which shows a continuous change in lattice constant of TiO2 with Mg. Current (I)-voltage (V) characteristics of the TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 Schottky devices revealed that the leakage current at -1 V was 1.28×10-6 A, 1.46×10-9 A and 2.44×10-10 A respectively. Capacitance (C) – voltage (V) measurements are performed on the devices at different frequencies. A theoretical simulation has been adopted by amending the delta depletion model at 1 MHz. The dielectric constant and the flat band voltage of the TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 devices are found to be 100, 120 and 160 and 16.1 V, 14.7 V and 9.7 V respectively. Hill-Coleman’s method shows a gradual enhancement of the density of interface states (Dit) with Mg concentration. The calculated Dit value of the TiO2, Mg0.1Ti0.9O2 and Mg0.2Ti0.8O2 TF devices are ~ 6.16×1010 eV-1 cm-2, 6.44×1010 eV-1 cm-2 and 1.11×1011 eV-1 cm-2 respectively. The observed C-V hysteresis confirms an enhancement in the charge retention into the film with increasing Mg concentration, which in turn improves the memory window (MW) from ~ 0.36 V (at ±7 V) to ~ 0.67 V (at ±7 V) and ~ 0.87 V (at ±10 V) to ~ 1.0 V (at ±10 V) with sweeping voltage.

Citation

Dalal, A., Murli Manohar Dhar Dwivedi, S., Ghosh, C., Lahiri, R., Henini, M., & Mondal, A. (2021). Mg:TiO2 alloy thin films based MOS capacitors grown on GaAs substrates. Journal of Alloys and Compounds, 868, Article 159178. https://doi.org/10.1016/j.jallcom.2021.159178

• Journal Article Type: Article
• Acceptance Date: Feb 9, 2021
• Online Publication Date: Feb 13, 2021
• Publication Date: Jul 5, 2021
• Deposit Date: Feb 19, 2021
• Publicly Available Date: Feb 14, 2022
• Journal: Journal of Alloys and Compounds
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 868
• Article Number: 159178
• DOI: https://doi.org/10.1016/j.jallcom.2021.159178
• Public URL: https://nottingham-repository.worktribe.com/output/5333913
• Publisher URL: https://www.sciencedirect.com/science/article/abs/pii/S0925838821005867