Showing papers by "Somnath Ghosh published in 2006"

Study of process induced variation in the minority carrier lifetime of silicon during solar cells fabrication

Abstract: A systematic study of the variation in the minority carrier effective lifetime in silicon associated with the different solar cell processing steps in a conventional industrial production line has been carried out using the microwave photoconductive decay (μ-PCD) technique. The solar grade silicon wafers used for this study presented bulk carrier lifetime of ∼10 μs and resistivity 0.5–3 Ω cm. Alkali texturing, phosphorus diffusion using POCl3, thermal oxide growth for surface passivation, plasma etching for edge isolation, and APCVD of TiO2 for surface passivation and antireflection coating were the major steps taken into consideration. The results clearly showed that the lifetime increased as the fabrication process proceeds from the bare wafer with the exception of the step associated to plasma edge isolation. The effective lifetime of the bare wafer was 4.04 μs, which increased to 16.67 μs after the antireflection coating and surface passivation with TiO2. The results of a systematic study of the effective minority carrier lifetime of silicon due to different surface passivation processes are also reported. The results obtained are useful for the design and implementation of proper measures for minority carrier lifetime enhancement during silicon solar cell fabrication at the industrial scale.

Formation of nanoscale metallic structures on cupric nitride thin film surface by the impact of 200 MeV Au15+ ions

Abstract: Cupric nitride films deposited on borosilicate glass and Si substrates by RF reactive sputtering are irradiated by 200 MeV Au 15+ ions from Pelletron accelerator. On-line elastic recoil detection analysis (ERDA) technique shows a large depletion of N (∼75% depletion) from the films due to electronic sputtering effect of heavy ion whereas the copper content remains unchanged. This observation is associated with a sharp rise in sample ladder current signifying an enhancement of electron emission from the film during irradiation. The surface of the as deposited film studied by atomic force microscope (AFM) shows nanodimensional grain formation. Conducting AFM (CAFM) measurements show that at certain regions (10–30 nm) of the irradiated film surface a rapid rise of current (∼9000 pA) takes place. Enhancement of electron emission together with conducting AFM measurements lead us to conclude that conductivity of the surface enhances due to formation of nanodimensional metallic zones under Au ion impact. The entire process is understood on the basis of thermal spike model of ion–solid interaction.

Heavy ion elastic recoil detection analysis set up for electronic sputtering studies

Abstract: Heavy ion elastic recoil detection analysis (ERDA) set up with a large solid angle (∼4.8 msr) Δ E−E position-sensitive telescope detector is developed at Inter University Accelerator Centre as a dedicated facility for the study of electronic sputtering of thin films under swift heavy ion (SHI) irradiation. The detector consists of a gas ionization chamber (Δ E) and a solid-state surface barrier detector (E) housed in a same assembly. The electronic sputtering yield (atoms/ion) is determined by analyzing on-line fluence-dependent ERDA data obtained from a variety of thin films. Large erosion (>105 atoms/ion) of carbon from a-C:H by 150 MeV Ag13+ ions, evolution of nitrogen (∼880 atoms/ion) from copper nitride and depletion of oxygen (∼1000 atoms/ion) from copper oxide film under 200 MeV Au15+ ion impact are studied and reported in this work. The electronic sputtering of these materials is discussed on the basis of the thermal spike model of SHI and solid interaction.

Study of High-Density Helicon-Plasma Generation and Measurement of the Plasma Parameters by Using a Frequency-Compensated Langmuir Probe

Abstract: Institute for Plasma Research, Bhat, Gandhinagar, India 382-428(Received 13 September 2005, in final form 6 March 2006)The present work is an experimental study of the various parameters of a high density plasmaproduced by using helicon waves in a toroidal structure using ordinary Langmuir probe and anRF compensated Langmuir probe. Helicon breakdown and the parameters were investigated in thetoroidal vessel was observed with a right helical antenna (m = +1) at a frequency of 32 MHz. Duringthe experiment, transition from a capacitive mode to a helicon mode of discharge was observed.This work also takes a step toward a realization of the necessity for a compensated Langmuir probein the study of an RF plasma, especially in the frequency range of tens of MHz. A toroidal magneticfield of 600G (max) is applied at the central axis of a toroidal vessel with an aspect ratio equal to3. The plasma is generated by using a helical antenna to form and sustain a plasma using hydrogengas. The power is delivered from an RF generator at 32 MHz via an L-Type matching network.A comparative study has been done using compensated and uncompensated Langmuir probes tomeasure various plasma parameters. A nonlinear increase in the plasma density with input RFpower and with the magnetic field is observed.

Metastable surface modification processes for corrosion and oxidation control

Abstract: This technical note discusses recent advances in the field of high energy surface alloying with particular reference to their non-stoichiometric solid state interaction and their corrosion resistance behaviour by electrochemical techniques. High energy treated surfaces undergo solid state interaction like diffusion, unconventional miscibility, solid solubility and nonstoichiometric compositions which impose a certain degree of metastability on the surface, which alters the electrode surfaces significantly. By introducing a high degree of surface metastability, it is possible to create scope for the physical and chemical properties of the electrodes. This transition of the interface from the metastable state to a stable state is normally accompanied by the formation of a stress free stable thin adherent and protective surface oxide layer. All these aspects are discussed in the present paper in the context of their corrosion resistance industrial usage, in particular to chloroalkali industrial applications. A generalised mechanism of protection of these high energy treated surfaces, is proposed based on surface metastability induced on the surface, as a result of the non-stoichiometry of solid state processing and its electrochemical interactions.