INFLUENCE OF GRAIN-BOUNDARIES ON HYDROGEN TRANSPORT IN POLYCRYSTALLINE SILICON

The effect of the microscopic structure of polycrystalline silicon on hydrogen transport was investigated by H and D diffusion experiments. Poly-Si composed of columnar grains and grown by low pressure chemical vapor deposition (LPCVD-grown) exhibits enhanced diffusion compared t o solid-state crystallized (SSC) poly-Si. The data can be explained by a two-level model used to explain diffusion in amorphous silicon. Cle ar evidence for deep H traps was only found for SSC poly-Si. LPCVD-gro wn poly-Si exhibited little evidence of deep trapping. Shallow transpo rt traps were found to be about 0.5 eV and similar to 1.6 eV below the transport level, respectively. The H chemical potential changes about 0.2 eV in response to an increase of the H concentration from mid-10( 18) to approximate to 10(20) cm(-3). (C) 1998 Elsevier Science B.V. Al l rights reserved.