• ONKAR MANGLA

Articles written in Bulletin of Materials Science

• A study on defect annealing in GaAs nanostructures by ion beam irradiation

In this study, annealing of deep level (EL2) defect in gallium arsenide (GaAs) nanostructures by argon ion beam irradiation has been reported. GaAs nanodots of diameter ranging from 15 to 22 nm were deposited on silicon substratesusing the ions of GaAs generated by hot, dense and extremely non-equilibrium argon plasma in a modified dense plasma focus device. GaAs nanodots thus obtained were irradiated by Ar$^{2+}$ ion beam of energy 200 keV with varying ion fluences from $1 \times 10^{13}$ to $5 \times 10^{15}$ ions cm$^{−2}$ in the low energy ion-beam facility. The ion-beam irradiation transformed the as deposited GaAs nanodots into uniform GaAs nanostructured films of thickness $\sim$30 nm. The obtained nanostructured films are polycrystalline with paucity of arsenic antisite (EL2) deep level defect. The excess arsenic present in the as-deposited GaAs nanodots is the main cause of EL2 defect. Raman and photoluminescence measurements of GaAs nanostructured films indicates removal of excess arsenic, which was present in as-deposited GaAs nanodots, thereby suggesting annealing of EL2 defect from the ion-irradiated GaAs nanostructured films. The change in conductivity type from n- to p-type obtainedfrom Hall measurement further confirms annealing of EL2 defects. The ion-irradiated GaAs nanostructured films have low leakage current due to removal of defects as obtained in current–voltage study, which corroborate the annealing of EL2 defect. The defect-free GaAs nanostructured films thus obtained have potential applications in fabrication of highly efficient optoelectronic and electronic devices.

• Synthesis of nano-diamond-like carbon for protective optical window coating applications

This study reports the fabrication of carbon using ions of carbon generated by high temperature, high density and extremely non-equilibrium argon plasma produced in modified dense plasma focus device. Carbon is deposited using two bursts of focussed plasma on n-type silicon substrates kept at a temperature of 20 (room temperature) and 130°C. The formation of nano-diamond-like carbon (nano-DLC) is observed at substrate temperature of 130°C. The samplesdeposited at different substrate temperatures are found to have amorphous in nature as observed from X-ray diffraction studies. These amorphous samples of carbon and nano-DLC possess nanostructures of average size ${\sim}$27 and ${\sim}$10 nm for 20 and 130°C substrate temperature, respectively, as obtained from atomic force microscopy and scanning electron microscopy studies. The possibility of formation of nano-DLC was analysed using Raman measurements. Peaks related toD and G band of graphitic carbon are observed in Raman spectra of both the samples. However, the samples grown at substrate temperature of 130°C show peaks related to nano-grain of diamond in Raman spectra, indicating high sp$^3$ content, thereby confirming the formation of nano-DLC. The hardness measurement reveals the maximum value of hardness ${\sim}$45.5 GPa for nano-DLC sample, which reconfirms that sample is of nano-DLC nature. The nano-DLC arefound to have band gap of ${\sim}$2.45 eV, which makes the nano-DLC a potential candidate for applications in protective optical window coating.

• # Bulletin of Materials Science

Volume 45, 2022
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020