Photovoltaic-Quality Silicon Epitaxy by Hot-Wire CVD at Glass-Compatible Temperatures

Epitaxial crystal silicon films 2 to 10-microns thick on high-quality seed layers have the potential to approach wafer silicon photovoltaic efficiencies at thin-film area costs. Using hot-wire chemical vapor deposition (HWCVD) from silane precursor gas, we have grown epitaxial layers up to 40-microns thick with defect densities of about 2 x 10⁵ cm^-2, corresponding to defects separated by more than 20 μm. This should be adequate for film-silicon photovoltaic applications. Films are grown at rates above 100 nm/min, at about 680°C, a temperature compatible with relatively inexpensive substrates such as display glass. We have also grown both n- and p-type epitaxial layers with mobilities close to those of wafers and achieved epitaxy at a growth rate of 300 nm/min. We have not yet reached a fundamental limit to the deposition rate.