AVS 52nd International Symposium
    Thin Films Wednesday Sessions
       Session TF+EM-WeM

Invited Paper TF+EM-WeM5
In-Situ Real Time Spectroscopic Ellipsometry Studies of the Growth of Amorphous and Epitaxial Silicon for Photovoltaic Applications

Wednesday, November 2, 2005, 9:40 am, Room 310

Session: In-Situ/ Ex-Situ & Real- Time Monitoring
Presenter: D.H. Levi, National Renewable Energy Laboratory
Authors: D.H. Levi, National Renewable Energy Laboratory
C.W. Teplin, National Renewable Energy Laboratory
E. Iwaniczko, National Renewable Energy Laboratory
Y. Yan, National Renewable Energy Laboratory
T.H. Wang, National Renewable Energy Laboratory
H.M. Branz, National Renewable Energy Laboratory
Correspondent: Click to Email
In-situ monitoring of material properties during thin film deposition provides researchers with a valuable tool for maximizing solar cell performance, while also enabling efficient exploration of deposition parameter space. In this presentation I will describe how our research team at NREL has utilized in-situ real time spectroscopic ellipsometry (RTSE) to maximize our productivity in two related projects. We are using hot wire chemical vapor deposition (HWCVD) for low-temperature (90 to 350@super o@C) deposition of very thin films of amorphous hydrogenated silicon (a-Si:H) for a-Si / crystal-Si (c-Si) heterojunction (SHJ) solar cells. We are also using HWCVD for low temperature (200 to 440@super o@C) deposition of epitaxial films of silicon (epi-Si) on c-Si substrates. We utilize RTSE as both an in-situ diagnostic and a post-growth analysis tool for SHJ solar cells and epi-Si films grown by HWCVD. RTSE enables precise thickness control of the 3 to 10 nm thick layers used in the SHJ devices, as well as monitoring crystallinity and surface roughness in real time. Post-growth analysis of the RTSE data has enabled us to determine the optical, electronic, and structural properties of the thin films used in the SHJ devices, as well as crystallinity vs. thickness in the epi-Si layers. This information has been used to fine-tune the deposition parameters to optimize device performance and epi-Si thickness. Using input from RTSE analysis we have achieved a photovoltaic energy conversion efficiency of 17% on an Al-backed p-type float-zone c-Si wafer. Epi-Si films have been grown as thick as 500 nm utilizing parameter optimization based on RTSE analysis.