Papers by Author: S.K. Ray

Abstract: The set of quantum confinement levels in SiGe quantum wells (QW) was observed in the temperature range from 80 to 300 K by means of charge deep-level transient spectroscopy (Q-DLTS) and transport measurements. These observations proved possible due to a passivation of structure surface with organic monolayer deposition. Si/SiGe/Si structures with different Ge contents in SiGe layer were studied. The confined levels in passivated structures became apparent through DLTS measurements as various activation energies in temperature dependence of the rate of carrier emission from QW. It was found that the recharging of SiGe QWs and carrier emission accomplish due to thermo-stimulated tunneling. The steps in the current-voltage characteristics originated from direct tunneling via the confined states were found to determine the current flow at high fields.

Abstract: Nickel silicide Schottky contacts were formed on 4H-SiC by consecutive deposition of a titanium adhesion layer, 4 nm thick, and nickel, 100 nm thick, followed by annealing at temperatures from 600 to 750 °C. It was found that contacts with barrier heights of 1.45 eV, consisting mainly of NiSi phase, formed in the 600-660 °C temperature range, while annealing at around 750 °C led to the formation of Ni2Si phase with barrier heights of 1.1 eV. Annealing at intermediate temperatures resulted in the nucleation of Ni2Si grains embedded in the NiSi film which were directly observed by micro-Raman mapping. It was concluded that the thermodynamically unfavourable NiSi phase appeared in the 600-660 °C temperature range due to the fact that the solid state chemical reaction between Ni and SiC at these temperatures is controlled by nickel diffusion through the titanium barrier.

Abstract: We report the self-assembled growth of Ge islands of different shapes and sizes on p-Si (001) by r.f. magnetron sputtering by varying the r.f. power, growth temperature and postdeposition annealing condition. The well known Stranski-Krastanov growth mechanism due to lattice mismatch between Si & Ge leads to the formation of Ge islands, similar to a more sophisticated MBE growth, albeit at a much higher pressure in our study. Ge nanocrystals embedded in SiO2 matrix have also been grown. Optical properties of nanocrystals exhibiting visible luminescence at room temperature are presented.