Dharam Pal Gosain

Nonvolatile memory based on reversible phase transition phenomena in telluride glasses

The phase transitions from amorphous to crystalline states, and vice versa, by applying electrical pulses were studied for sandwich structures of metal/GexTe100-x thin film/metal. A systematic study of the crystallization temperature in GexT100-x(5leqslant x leqslant 30) thin films has been carried out. In some compositions, more than 104 repetitions of amorphous to crystalline states, and vice versa, were attained by the application of electric pulses. A model is proposed to explain the results observed.

High Mobility Thin Film Transistors Fabricated on a Plastic Substrate at a Processing Temperature of 110°C

We present results from excimer laser processed poly-silicon thin film transistors fabricated on a plastic substrate. Except for the temperature rise during excimer laser irradiation for crystallization, the highest processing temperature that the substrate was subjected to was 110°C. Transistor field-effect mobility of 250 cm2/Vs and sub-threshold swing of 0.16 V/decade were measured in these devices. These are the best characteristics reported to date for a thin film transistor (TFT) on a plastic substrate. The performance is attributed to our optimized laser crystallization process of helium sputtered Si films, laser-assisted low-temperature doping processes, and transient annealing.

Some properties of Sb2Te3−xSex for nonvolatile memory based on phase transition

Composition dependence of properties of Sb2Te3−xSex in the range 0⩽x<3 were studied using differential thermal analysis and X-ray diffraction. Sb2Te3−xSex form solid solution for 0<x⩽1.25 and 2.75⩽x<3. A systematic study of crystallization temperature in Sb2Te3−xSex (0⩽x⩽2.75) thin films prepared by flash evaporation was carried out. In preliminary experiments for some compositions, more than 103 repetitions between amorphous and crystalline states were attained by the application of electric pulses.

Control of the Size and Position of Silicon Nanowires Grown via the Vapor-Liquid-Solid Technique

The diameter and position of vapor-liquid-solid (VLS) grown Si nanowires can be controlled by exploiting the difference in Au condensation coefficient on Si and SiO2 surfaces at elevated temperature. For low Au fluxes in the temperature range 520–700° C, Au condensation is completely selective to Si. Holes are etched through the surface oxide layer of a thermally oxidized Si(111) wafer to expose the Si. When Au is then evaporated onto the surface, the Au atoms condense selectively in the holes and form liquid Au/Si alloy balls. If the holes contain a small Si island protrusion formed by etching this acts as an alloy nucleation center and the alloy can agglomerate to form a single ball, the diameter of which is determined by the diameter of the hole and the total dose of Au. When silane gas is then introduced into the chamber as the Si source gas in the VLS reaction each alloy ball grows to form a Si wire of controlled diameter and position.

Formation of (100)-Textured Si Film Using an Excimer Laser on a Glass Substrate.

We investigated the texture of excimer-laser crystallized Si film. For the first time, Si thin films with more than 96% (100) texture have been produced using excimer-laser crystallization of a-Si on a glass substrate. The (100) textured film has rectangular grains with edges parallel to the (110) direction. Results of scanning electron microscopy (SEM), electron backscatter diffraction patterns (EBSP), X-ray diffraction and transmission electron microscopy (TEM) are presented. The results are interpreted on the basis of Si/SiO2 interface energy and a new grain-selection model.

Instability of Amorphous Indium Gallium Zinc Oxide Thin Film Transistors under Light Illumination

The electrical and optical properties of amorphous indium gallium zinc oxide (a-IGZO) thin films and thin film transistors (TFTs) were investigated for their applications in flat panel displays (FPD). The device characteristics were found to be sensitive to gate dielectric and interlayer film material. TFTs using SiO2 as a gate dielectric and passivation showed very good characteristics when measured in the dark, with mobility above 10 cm2 V-1 s-1, on/off ratio of ≈108, sub-threshold swing less than 0.2 V/decade and the threshold voltage (Vth) 0.9 V. However when exposed to light of wavelength below 420 nm Vth shifted markedly. The shift in Vth increased with increasing power density, irradiation time, and decreasing wavelength. The shift is attributed to trapping of photogenerated holes in the light induced traps in SiO2 close to the IGZO interface. It is postulated that these traps are created due to the unstable IGZO surface. Shielding TFTs from light stabilizes the characteristics, however, stabilization of the IGZO surface is required to realize stability for practical applications.

High Performance Bottom Gate TFTs by Excimer Laser Crystallization and Post Hydrogenation

Small grain poly-Si has defects of the order of 10 18 to 10 19 spins/cm 3 . Hydrogen is generally used to terminate these defects, which is introduced from a hydrogen plasma. Damage caused by UV emitted from the plasma glow discharge was identified as one of the causes limiting the quality of the bottom gate thin film transistor (TFT) devices. The effect of UV on the TFT transfer characteristics was studied. ESR was used to measure the change in the poly-Si dangling bond density as a result of UV irradiation. It was confirmed that plasma UV creates damage in the poly-Si. A combination of plasma hydrogenation and SiN x :H passivation and thermal annealing was found to be particularly effective in reducing the defect density by reconstruction of dangling bonds and redistribution of hydrogen without hydrogen loss. The excellent characteristics obtained using this hydrogenation method are presented

Effects of preparation conditions of the bulk and source temperature on the composition of As2Se3 films

Abstract The composition of evaporated films of the Asue5f8Se system depends strongly on the preparation conditions of the bulk and the evaporation conditions. The best conditions for obtaining stoichiometric As 2 Se 3 films are reported. The results are explained on the basis of chemical order and polymerization in Asue5f8Se bulk glasses.