Comparative studies of structural and electrical properties of doped microcrystalline silicon thin films deposited by hot-wire chemical vapor deposition

This work reports the investigation of p- and n-doped microcrystalline silicon layers deposited by hot-wire chemical vapor deposition (HWCVD). Trimethylboron (TMB) and boron trifluoride (BF3) are used as p-type doping gases and phosphine (PH3) as the n-type doping gas. The structural and electrical properties of doped layers depend strongly on the type of doping gas used. As long as the structure of the films is microcrystalline their dark conductivity strongly increases with the incorporation of dopant atoms, as expected. It is found that the incorporation probability of dopant atoms in solid phase is very different for the doping gases used. The doping efficiencies estimated for the TMB and BF3 doped p-μc-Si and PH3 doped n-μc-Si films, however, are independent on the doping gas and is about 20%, which is of course much higher compared to that of amorphous silicon (a-Si:H). Doped silicon films with crystalline fraction greater than 50% exhibit a dark conductivity in the range of 0.1 – 1 S/cm.