Infrared Ellipsometry Investigation of Hydrogenated Amorphous Silicon
- PDF / 242,084 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 89 Downloads / 239 Views
1153-A16-03
Infrared Ellipsometry Investigation of Hydrogenated Amorphous Silicon Franco Gaspari1*, Anatoli Shkrebtii1, Tom Tiwald2, Andrea Fuchser2, Shafiq Mohammed1, Tome Kosteski3, Keith Leong3 and Nazir Kherani3 1 Faculty of Science, University of Ontario Institute of Technology 2000 Simcoe Street North, Oshawa, ON, Canada L1H 7K4. 2 J.A. Woollam Co., Inc. 645 M Street, Suite 102, Lincoln, NE 68508, USA 3 Dept. of Electrical & Computer Engineering, University of Toronto, Toronto, ON, Canada M5S 1A4. ABSTRACT Hydrogenated amorphous silicon (a-Si:H) has been extensively investigated experimentally in the infrared spectral region via techniques such as Fourier Transform Infrared (FTIR) and Raman spectroscopy. Although spectroscopic ellipsometry has been proven to be an important tool for the determination of several parameters of a-Si:H films, including dielectric constant, surface roughness, doping concentration and layer thickness, the spectral range used in these studies has rarely covered the infrared region below 0.6 eV, and never over the complete spectral region of interest (0.04 – 0.3 eV), which contains atomic vibration frequencies. We have measured for the first time the dielectric function of a-Si:H films grown by the saddle field glow discharge technique by spectroscopic ellipsometry in the energy range from 0.04 eV to 6.5 eV, thus extending the analysis into the far infrared region. The a-Si:H films were deposited on germanium substrates for the ellipsometry studies, and on crystalline silicon substrates for the comparative FTIR analysis. Preparation parameters were chosen to obtain films with different hydrogen content. In this paper, we present the results of the ellipsometry analysis, evaluate different fitting techniques, and compare the results with the corresponding FTIR spectra. The similarities and differences between the spectra are discussed in terms of the a-Si:H properties. INTRODUCTION Hydrogenated amorphous silicon (a-Si:H) has been the subject of numerous theoretical studies and experimental characterizations over the past 40 years; yet, quite a few issues still remain to be clarified [1-2]. The authors have initiated a systematic study of a-Si:H based on abinitio molecular dynamics simulations [3,4]. The initial results have shown that vibrational spectroscopy data, in particular Fourier Transform Infrared Transmission Spectroscopy (FTIR), provide a good basis for validation of models. IR spectroscopic ellipsometry has also been used in the past by, among others, Drevillon [5] and Darwich [6]. However, these investigations have usually been limited to exploring the stretching modes (at about 2000 cm-1). To better understand the nature of vibrational absorption in a-Si:H, we have investigated the results obtained from IR spectroscopic ellipsometry, extending the range of the investigation into all the relevant wavenumbers for amorphous silicon, i.e., from 400 cm-1 and up. This allows for comparison of the FTIR data with the ellipsometry data in the specific regions of the hydrogen stret
Data Loading...
