Improvement of electron diffusion lengths in polycrystalline silicon wafers by aluminium

In order to improve the electron diffusion lengths Ln in P-type large grained polycrystalline silicon wafers, an aluminium layer was deposited on the back surface. The structure is then annealed at 450 °C during 2h. It was found that Ln is increased, provided the initial value was smaller than 50 µm, and tht the mean density of dislocations is larger than 5 x 104 cm-2. Backside gettering appears to be the most likely mechanism to explain the results and it is assumed that dissolved oxygen may be involved.