Sucheta Juneja

Effect of power on growth of nanocrystalline silicon films deposited by VHF PECVD technique for solar cell applications

An investigation of the effect of power on the deposition of nanocrystalline silicon thin films were carried out using a gaseous mixture of silane and hydrogen in the 60MHz assisted VHF plasma enhanced chemical vapor deposition (PECVD) technique. The power was varied from 10 to 50 watt maintaining all other parameters constant. Corresponding layer properties w.r.t. material microstructure, optical, hydrogen content and electrical transport are studied in detail. The structural properties have been studied by Raman spectroscopy and x-ray diffraction (XRD). The presence of nano-sized crystals and their morphology have been investigated using atomic force microscopy (AFM). The role of bonded hydrogen content in the films have been studied from the results of Fourier transform infrared spectroscopy. It was observed from the results that with increase in power, crystalline volume fraction increases and crystallite size changes from 4 to 9 nm. The optical band gap varies from 1.7 to 2.1eV due to quantum confine...

Nanocrystalline silicon thin films and grating structures for solar cells

Enhancement of optical absorption for achieving high efficiencies in thin film silicon solar cells is a challenge task. Herein, we present the use of grating structure for the enhancement of optical absorption. We have made grating structures and same can be integrated in hydrogenated micro/nanocrystalline silicon (μc/nc-Si: H) thin films based p-i-n solar cells. μc/nc-Si: H thin films were grown using plasma enhanced chemical vapor deposition method. Grating structures integrated with μc/nc-Si: H thin film solar cells may enhance the optical path length and reduce the reflection losses and its characteristics can be probed by spectroscopic and microscopic technique with control design and experiment.

Design and fabrication of a 1-DOF drive mode and 2-DOF sense mode micro-gyroscope using SU-8 based UV-LIGA process

This paper presents design and fabrication of a 1-DOF (degree-of-freedom) drive mode and 2-DOF sense mode micro-gyroscope. It is an inherently robust structure and offers a high sense frequency bandwidth. The proposed design utilizes resonance of the1-DOF drive mode oscillator and employs dynamic amplification concept in sense modes to increase the sensitivity while maintaining robustness. The 2-DOF in the sense direction renders the device immune to process imperfections and environmental effects. The design is simulated using FEA software (CoventorWare®). The device is designed considering process compatibility with SU-8 based UV-LIGA process, which is an economical fabrication technique. The complete fabrication process is presented along with SEM images of the fabricated device. The device has 9 µm thick Nickel as the key structural layer with an overall reduced key structure size of 2.2 mm by 2.1 mm.

Reactive ion etching of indium-tin oxide films by CCl4-based Inductivity Coupled Plasma

Indium tin oxide (ITO) films have been a subject of extensive studies in fabrication of micro-electronic devices for opto-electronic applications ranging from anti-reflection coatings to transparent contacts in photovoltaic devices. In this paper, a new and effective way of reactive ion etching of a conducting indium-tin oxide (ITO) film with Carbon tetrachloride (CCl4) has been investigated. CCl4 plasma containing an addition of gases mixture of dissociated argon and oxygen were used. Oxygen is added to increase the etchant percentage whereas argon was used for stabilization of plasma. The etching characteristics obtained with these gaseous mixtures were explained based on plasma etch chemistry and etching regime of ITO films. An etch rate as high as ~20 nm/min can be achieved with a controlled process parameter such as power density, total flow rate, composition of reactive gases gas and pressure. Our Investigation represents some of the extensive work in this area.

Role of Plane and Textured TCO Surfaces in Enhancing the Efficiency of Thin Film Amorphous Silicon Solar cell: A Theoretical Approach

In the present work, comparison is made between ITO indium tin oxide) and ZnO (zinc oxide) as TCO layer for the amorphous silicon (a-Si:H) solar cell applications using AFORS-HET simulation software. In order to improve the efficiency of a-Si:H solar cell optimization of band gap of p layer was done along with suggesting the effective light trapping measures which can be adopted in this regard. The optimized value of band gap for p layer 2.1 eV was found for obtaining maximum efficiencies of 14.91 % with ITO and 17.02 % with ZnO as front contact. The further study explored the use of textured TCO surfaces instead of the plane surfaces. The use of textured surfaces of ITO and ZnO enhanced the efficiencies to 15.85 % and 18.10 % respectively at optimized values of the band gap of p, i, and n layers. Hence the overall investigation of a-Si:H solar cells with the idea of maximizing the light trapping using plane as well as textured surfaces of TCO coatings suggests the possibilities for fabrication of efficient a-Si:H solar cells. Our simulation results reveals ZnO as suitable TCO material in order to enhance the efficiencies of solar cell compared to ITO.

Study of light-induced structural changes associated with Staebler-Wronski Photo-degradation in micro-crystalline silicon thin films

Hydrogenated amorphous silicon based devices lacks behind in their fruitful applications as it suffers from major drawback i.e. light induced degradation or S–W effect. Various theories or literature have been discussed so far, but exact mechanism is still an open challenge in research community. We report on light-induced structural changes in amorphous and micro/nano crystalline silicon by performing light soaking experiments for nearly 8 h. Under vacuum accompanied with the effect of annealing on these films. The electrical, structural and optical properties were analyzed with the use of dark and photo conductivity measurements, Raman spectroscopy, Scanning electron microscopy (SEM) and Photoluminescence studies. Using Raman spectroscopy, we estimated the bond distortion w.r.t degradation percentage in samples. We observed that crystallinity as well as particle size are responsible for increase or decrease in degradation of photoconductivity. Having 72.25 % crystallinity highly stable microcrystalline silicon films showed 1.44 % photo-degradation.