C.M.S. Rauthan

Realization of different carbon nanostructures by a microwave plasma enhanced chemical vapor deposition technique

Various process conditions are summarized that allows one to grow carbon nanostructures (carbon nanotubes and nanodiamonds) and diamond-like carbon (DLC) films at room temperature by exciting C 2 H 2 + Ar plasma in a microwave plasma enhanced chemical vapor deposition (PECVD) system. These nanostructures are formed at some specific but different parameter space. The films were characterized by atomic force microscopy, cathodoluminescence (CL), Raman spectroscopy, transmission electron microscopy and glancing angle X-ray diffraction (XRD) techniques. DLC films were deposited with different applications in mind. The films were ultra smooth with RMS roughness <0.07 nm and found to show CL when excited with an electron beam. Carbon nanotubes and nanodiamond structures were obtained simply by varying the applied RF bias at an optimized microwave power of 25 W. Again, the nanodiamond films were found to be ultra smooth (RMS roughness <0.06 nm) with 60-100 nm grain size nanocrystallites. The Raman and glancing angle XRD analysis suggests hexagonal polymorph structure for nanodiamond crystallites. Carbon nanotubes grown on ophthalmic glass substrates at room temperature, without any preconditioning and intentional heating of substrate, were found to be multiwalled with their diameters varying from 23-30 nm at optimized parameters.

Effect of power on the growth of nanocrystalline silicon films

Nanocrystalline silicon thin films were grown using a gaseous mixture of silane, hydrogen and argon in a plasma-enhanced chemical vapor deposition system. These films were deposited away from the conventional low power regime normally used for the deposition of device quality hydrogenated amorphous silicon films. It was observed that, with the increase of applied power, there is a change in nanocrystalline phases which were embedded in the amorphous matrix of silicon. Atomic force microscopy micrographs show that these films contain nanocrystallite of 20–100 nm size. Laser Raman and photoluminescence peaks have been observed at 514 cm−1 and 2.18 eV, respectively, and particle sizes were estimated using the same as 8.24 nm and 3.26 nm, respectively. It has also been observed that nanocrystallites in these films enhanced the optical bandgap and electrical conductivity.

Crystalline silicon surface passivation by thermal ALD deposited Al doped ZnO thin films

The evidence of good quality silicon surface passivation using thermal ALD deposited Al doped zinc oxide (AZO) thin films is demonstrated. AZO films are prepared by introducing aluminium precursor in between zinc and oxygen precursors during the deposition. The formation of AZO is confirmed by ellipsometry, XRD and Hall measurements. Effective minority carrier lifetime (τeff) greater than 1.5ms at intermediate bulk injection levels is realized for symmetrically passivated p-type silicon surfaces under optimised annealing conditions of temperature and time in hydrogen ambient. The best results are realised at 450°C annealing for >15min. Such a layer may lead to implied open circuit voltage gain of 80mV.

Aperiodic Silicon Nanowire Arrays: Fabrication, Light Trapping Properties and Solar Cell Applications

Solar photovoltaic (SPV) is capable of providing the most feasible carbon-free route to the worldwide traditional power consumption. During the last decade, there has been tremendous development in silicon wafer based photovoltaic (PV) cells technology and today commercial silicon PV cells over 20 % efficiencies have been achieved. However, large-scale implementation of silicon wafer PV is currently not economical because of their high cost as compared to traditional power sources. One of the primary cost components for silicon PV cells is the starting silicon wafer, which requires extensive purification to maintain reasonable performance. Therefore, development of efficient and low cost PV devices is extremely important. Silicon nanowires (SiNWs) are a very promising candidate for next generation PV. The SiNW arrays exhibit low reflection, strong broadband light absorption and may be used as antireflection surface in solar cells. In addition to enhanced optical properties, nanowire arrays also have the potential for efficient charge carrier collection across the nanowire diameter for radial junction (homo/hetro p-n junctions) solar cells and therefore may relax high quality material requirement, enabling lower-cost PV cells. In the chapter, a short review of aperiodic SiNW arrays fabrication by silver assisted wet chemical etching method, their light trapping properties and PV applications with emphasis on SiNW arrays based solar cells would be presented. Finally, challenges in effective use of SiNW arrays in PV devices and future perspective would also be briefly discussed.

Structural and nano-mechanical properties of nanostructured diamond-like carbon thin films

The effect of self bias on structural and nano-mechanical properties of nanostructured diamond-like carbon (ns-DLC) thin films is explored. These films are grown at different negative self biases ranging from −100 V to −200 V using radio frequency (13.56 MHz) plasma enhanced chemical vapor deposition technique. The generation of nanostructured morphology at room temperature in these films is confirmed by scanning electron microscopy, whereas change in microstructure produced by varying the self biases is confirmed by Raman analysis. These ns-DLC films exhibit very high hardness, which varied from 16 GPa to 31 GPa. With the help of load versus displacement curves, various other important nano-mechanical parameters such as elastic modulus, elastic recovery etc are also estimated. The nano-mechanical properties are further correlated with the Raman and SEM analyses. Owing to their versatile nano-mechanical properties, these ns-DLC films may find application as hard and protective coatings.

Effect of metallic interfacial layers on the properties of diamond-like carbon thin films

Diamond like carbon (DLC) thin films with metallic interfacial layers of aluminum and nickel-chromium (Al and Ni-Cr) were grown using a low cost hybrid technique involving a resistive heating thermal evaporator and radio frequency plasma enhanced chemical vapor deposition techniques. Stress, hardness, elastic modulus, bonding, phase, and electrical conductivity of these films were investigated. Introduction of interfacial Al and Ni-Cr layers in DLC led to drastic improvement of its conductivity along with a significant reduction in residual stress but with some reduction of hardness and the elastic modulus. The structural and surface properties of thin films were studied using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy techniques.

Effect of ethylene glycol doping on performance of PEDOT:PSS/µT-n-Si heterojunction solar cell

This study reports effect of co-solvent doping in poly (3, 4-ethyelenedioxythiophene):poly(dimethyl sulfoxide) (PEDOT:PSS) over the performance of Ag/PEDOT:PSS/µT-n-Si/In:Ga architecture based solar cell. PEDOT:PSS polymer is doped with varying concentration of ethylene glycol (EG). At 10% (volume) concentration performance of the device is highest with 4.69% power conversion efficiency. At higher or lower concentrations of ethylene glycol device performance deteriorates with sharp decline in short-circuit current density. Improvement in conductivity of the PEDOT:PSS polymer due to addition of co-solvent is the reason behind improvement in the performance of the device efficiency.