Boron Doped Polycrystalline Silicon Produced By Step-by-Step XeCl Excimer Laser Crystallization
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0910-A23-02
Boron Doped Polycrystalline Silicon Produced By Step-by-Step XeCl Excimer Laser Crystallization Rosari Saleh1, and Norbert H Nickel2 1 Jurusan Fisika FMIPA, Universitas Indonesia, Kampus Baru Universitas Indonesia Depok, Depok, 16424, Indonesia 2 Hahn Meitner Institute, Kekulestr.5, Berlin, 12489, Germany ABSTRACT A series of boron doped polycrystalline silicon were produced using step-by-step laser crystallization process from amorphous silicon. The influence of doping concentrations on laserinduced dehydrogenation and crystallization of amorphous silicon and on hydrogen bonding have been investigated employing Raman spectroscopy and hydrogen effusion measurements. From hydrogen effusion spectra the hydrogen chemical potential is determined as a function of hydrogen concentration, which can be related to the hydrogen density-of-states distribution. The results from hydrogen effusion are consistent with the results obtained from Raman spectroscopy.
INTRODUCTION Polycrystalline silicon (poly-Si) films are viewed as a very attractive material for thin film electronic devices. Poly-Si produced by laser crystallization of amorphous silicon (a-Si) is gaining increasing importance in the fabrication of large-grained poly-Si thin-films on low-cost glass substrate without introducing thermal damage. Usually a-Si with a low hydrogen content is used as a starting material since otherwise the laser-induced rapid annealing of the specimens can lead to ablation of the film. However, employing a step-by-step crystallization procedure hydrogenated amorphous silicon (a-Si:H) can be used [1]. This technique takes advantage of the fact that the amount of hydrogen evolving from the specimens increases with increasing laser fluence. In this paper, we present results obtained on laser crystallized boron doped poly-Si. The specimens were crystallized using the laser dehydrogenation and crystallization technique. Our results show that in the first step of the laser crystallization procedure a structural transformation takes place. Initially, the sequential crystallization process leads to the formation of a two-layer system. The Raman spectra of completely crystallized heavily doped films are distorted. This is due to a resonant interaction between optical phonons and direct intraband transitions that is well known as a Fano resonance [2]. The structural change is accompanied by a significant change in Si-H bonding and a decrease of the total hydrogen concentration in specimens. The hydrogen bonding is influenced by the presence of dopant. Samples crystallized with a laser fluence of EL ≥ 300 mJ/cm2 can no longer be characterized by Raman spectroscopy. This drawback can be overcome by hydrogen effusion measurements. From this measurement, the hydrogen density-of-states distribution can be derived. The results of Raman spectroscopy are consistent with the results obtained from hydrogen diffusion measurements.
EXPERIMENTAL DETAILS The samples used in this study were prepared by the following procedure. Hydrogenated amorphous
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