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

• Published in: Journal of alloys and compounds 2021-07, Vol.868, p.159178, Article 159178
• Main Authors: Dalal, Avijit, Dhar Dwivedi, Shyam Murli Manohar, Ghosh, Chiranjib, Lahiri, Rini, Henini, Mohamed, Mondal, Aniruddha
• Format: Article
• Language: English
• Subjects: Absorption spectra; Atomic force microscopes; Atomic force microscopy; Capacitive memory; Delta depletion model; Depletion; Devices; Electric potential; Electron beams; Energy gap; Field emission microscopy; High k dielectric; Lattice parameters; Leakage current; Mg:TiO2 alloy; Optical absorption; Substrates; Thin films; Titanium dioxide; Transition probabilities; Urbach model; Voltage
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.159178

•Precise and control incorporation of Mg has been done to prepare MgxTi1−xO2 (x = 0.1, 0.2).•Modified Urbach model has been developed to simulate absorption spectrum.•Mg incorporation enhanced the band gap and dielectric constant of the TiO2 TF gradually.•The density of interface states increases due to incorporation of Mg into TiO2 TF.•Enhanced capacitive memory has been recorded for Mg:TiO2 TF devices. [Display omitted] 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 conce