Laser crystallization of hydrogenated amorphous silicon

Abstract

Doped and undoped hydrogenated amorphous silicon films were crystallized employing a step-by-step laser crystallization method. The influence of laser crystallization on structural properties and hydrogen bonding in polycrystalline silicon was investigated using Raman backscattering spectrometry, electron paramagnetic resonance, and hydrogen effusion measurements. At low laser fluences, EL, a two-layer system is created. With increasing EL the spin density of undoped poly-Si increase and saturates at a value of about 5.2 × 1018 cm−3. With increasing boron and phosphorous concentration the LO-TO phonon line shifts to smaller wave numbers and broadens asymmetrically due to a resonant interaction between optical phonons and direct intraband transitions known as a Fano resonance. From H effusion spectra the hydrogen density-of-states distribution is derived. Laser crystallization results in an increase of the H bonding energy by about 0.3 eV. Interestingly, H bonding is also affected by the deposition temperature of the amorphous starting material. In completely crystallized poly-Si a residual H concentration of up to 17 at.% can be observed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)