Vinod Kumar Paliwal

Ageing effect of Sb2Te3 thin films

Abstract Post deposition variation in film resistance of Sb 2 Te 3 films deposited on glass substrates at room temperature and an elevated temperature (110°C) are investigated. The resistance of films grown at room temperature shows a non-linear decrease with time which is thickness dependent as opposed to the increasing resistance of film grown at elevated temperature. The decreasing resistance with time can be attributed to the transformation of an amorphous phase of the as-grown film to a micro-crystalline phase as revealed by X-ray diffraction. The increasing resistance was found to be due to the surface oxidation (Sb 2 O 3 ) and a diffusion as a function of time. However, the underneath layer of Sb 2 Te 3 below the top Sb 2 O 3 layer remains amorphous even after 2 years from the date of fabrication.

Sb induced (7 × 7) to (1 × 1) surface phase transformation of the Si(111) surface

Abstract Adsorption of Sb at a very low flux rate results in an epitaxial layer-by-layer growth on Si(111) surface held at room-temperature. Band-bending is not observed for submonolayer Sb coverages while sharp changes in the photoemission features are observed for 1.0 monolayer (ML) Sb adsorption. Changes in the core level binding energy and width in X-ray photoelectron spectroscopy, surface related feature in Electron energy loss spectroscopy and spot intensity ratios in Low energy electron diffraction studies suggest a surface phase transition upon adsorption of 1.0 monolayer of Sb. A plausible model is proposed to explain the abrupt metal–semiconductor transformation at this critical coverage of 1.0 ML.

Formation of interfacial phases in the epitaxial growth of Sb on Si(111)-7 ¥ 7 reconstructed surface

Understanding the evolution of the Sb/Si(111) interface is of great interest in the formation of devices of nanodimensions. We have undertaken in situ (∼10-11 torr) studies of Sb adsorption (at room temperature) and its desorption on the 7 X 7 reconstructed Si(111) surface, by complementary techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and electron energy loss spectroscopy (EELS). For room-temperature (RT) Sb adsorption, the overlayer grows in the Frank van der Merwe mode, forming an interface state of δ(7 X 7) in the submonolayer Sb coverage regime. Adsorption of 1.0 monolayer (ML) Sb at RT shows an abrupt shift of 0.8 eV in the peak position of the Sb 3d5/2 transition owing to band-bending caused by a metallic (7 X 7) to a semiconducting (1 X 1) surface phase transformation. Changes observed in full width at half-maximum (fwhm) and Sb 3d3/2 and 3d5/2 branching ratio are discussed. Thermal annealing experiments provide evidence for agglomeration of Sb islands, before the multilayer and monolayer desorption. During this desorption process, we have observed two novel surface phases of (5 X 5) at 0.4 ML and (5√3 X 5√3R30°) at 0.2 ML, stable at higher temperatures.