Deposition of Optimal a-Si:H and a-SiGe:H by HWCVD Using the Same Filament Temperature and Substrate Temperature

Abstract

ABSTRACTThe incorporation of high Ge content a-SiGe:H into a low bandgap solar cell device commonly involves the use of bandgap (Ge) profiling. In previous work using the hot wire (HWCVD) technique, device quality low bandgap (ETauc= 1.25eV) a-SiGe:H films were deposited at low Tsub(∼200-250°C) filament operating at Tfil∼ 1750-1800°C. However, higher bandgap films containing little or no Ge and deposited under the same low temperature (Tsub,Tfil) conditions were of decidedly inferior quality to those deposited using higher temperatures (Tfil∼2000°C,Tsub∼360°C) solar cell with an efficiency ∼ 5.85% was fabricated using these materials, it was clear that our best ‘end point’ materials alloying at this low Tfilseverely limits film reproducibility and filament lifetime. This work explores deposition of device quality low bandgap a-SiGe:H and (high bandgap) a-Si:H, both at the same low Tsub, using a tantalum (Ta) filament operating at low Tfil. Film material properties are presented.