An application of a pulsed, solid-state laser with a Gaussian and flat-top beam profiles is considered for annealing and nano-texturing of amorphous-silicon (a-Si) films. Investigations are performed with the third harmonics (355 nm) Nd3+:YAG laser. To crystallize and subsequently induce texture, a-Si films are treated by spatial-overlapping of the laser spots on the surface by 90% of its size. The generation of texturization mechanism in laser assisted annealing and texturing is theoretically investigated and experimentally analyzed. ©2010 IEEE.

Nilesh Jayanthilal Vasa

Department of Engineering Design

G. Rajiv

Makaram Singaperumal

A-SI FILMS

FLAT TOP BEAM

Gaussians

Laser annealing

LASER SPOTS

LASER TEXTURING

LASER-ASSISTED

NANOTEXTURING

PHOTOVOLATAIC APPLICTAIONS

POLYCRYTSALLINE SILICON

TEXTURIZATION

Third harmonic

YAG LASER

ACOUSTOOPTICAL EFFECTS

Amorphous films

Annealing

Gaussian beams

Lasers

Neodymium

Pulsed lasers

Amorphous silicon

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Annealing and texturing of a-Si film using Nd 3+ :YAG laser with Gaussian and flat-top beam profiles

IEEE Region 10 Annual International Conference, Proceedings/TENCON

Influence of wavelengths and beam profiles of a pulsed Nd3+:YAG laser on the formation of a polycrystalline-silicon (poly-Si) on a-Si thin film is investigated. Two sets of samples of amorphous-Silicon (a-Si) thin films deposited on glass (a-Si/glass) and crystalline Si (a-Si/c-Si) substrates were treated with different laser-fluence values. After the laser treatment, the films were analyzed by a scanning electron microscope, the Raman spectroscopy technique and the resistance-measurement technique. In the case of the third harmonics (355 nm) of the Nd3+:YAG laser, poly-Si films were obtained with laser-fluence values ranging from 260 mJ/cm2 to 560 mJ/cm2, where as in the case of the second harmonics (532 nm), the process window for the formation of poly-Si films, in terms of the laser fluence, was ranging from 300 mJ/cm2 to 480 mJ/cm2. On the other hand, in the case of samples treated with the fundamental wavelength (1064 nm), a narrow process window with higher laser-fluence values around 1100 mJ/cm2 was observed. Further, the substrate was also affected because of the higher laser-fluence value. It has also been observed that the crystallization characteristics of poly-Si films improved with the flat-top intensity distribution as compared to the Gaussian intensity distribution of the Nd3+:YAG laser beam. A theoretical simulation based on thermal modeling was performed to understand the mechanism of crystallization. © 2009 Elsevier B.V. All rights reserved.

Thin Solid Films

Influence of laser wavelength and beam profile on Nd3+:YAG laser assisted formation of polycrystalline-Si films

Development of textured crystalline silicon from amorphous silicon film using a pulsed Nd3+:YAG laser is reported. The technique involved is laser annealing and subsequent laser nano texturing by over lapping the laser spot by 50% and 90% of the diameter. Experimental investigations were performed using third (355 nm), second (532 nm) and fundamental harmonics (1064 nm) of the pulsed Nd3+:YAG laser. To investigate the texturization AFM measurement was performed. Absorbance and photoconductivity measurements were performed to analyze the photovoltaic properties of thin films. The process was theoretically analyzed using a 3-D heat transformation model in FEMLAB software. 355 nm laser assisted nano-texturing with 90% overlap showed an improvement in crystalline property and improved textured surface with a higher absorbance as compared to that of 50% overlap.

Fulltext

Journal of Laser Micro Nanoengineering

Investigation on laser-annealing and subsequent laser-nanotexturing of amorphous silicon (a-Si) films for photovoltaic application

In the present research, an approach of converting amorphous-silicon (a-Si) thin films into polycrystalline thin films using the third harmonics of an all-solid-state pulsed Nd3+:YAG laser (355 nm) is studied. Two different samples of a-Si thin films on alkali-free glass (a-Si/glass) substrates and a-Si thin film on crystalline-Si substrates (a-Si/c-Si) are laser treated at different laser fluences ranging from 170 to 960 mJ/cm2. The amount of heat incident on the surface has been analyzed theoretically by solving the one-dimensional heat-equation model. The ablation threshold, the region of crystallization and the depth of crystallization have been investigated theoretically. The influence of laser irradiation, ablation and crystallinity has been experimentally analyzed through in-situ reflectivity measurements, scanning electron microscopy (SEM) and Raman spectroscopy studies. In the case of a-Si/c-Si, the extent of crystallinity and the influence of structural characteristics on electronic properties are studied using the Hall-effect technique. The ablation threshold and the range of crystallization regime are in good agreement with the theoretical results. Laser fluence between 300 and 500 mJ/cm2 is required for crystallization and the ablation threshold is estimated to be above 500 mJ/cm2 for a-Si thin film with a thickness up to 400 nm. © 2009 Elsevier Ltd. All rights reserved.

Materials Science in Semiconductor Processing

Crystallization and ablation in annealing of amorphous-Si thin film on glass and crystalline-Si substrates irradiated by third harmonics of Nd3+:YAG laser

Annealing and texturing of a-Si film using Nd3+:YAG laser with Gaussian and flat-top beam profiles

Journal	IEEE Region 10 Annual International Conference, Proceedings/TENCON
Open Access	No