Real-time control and characterization of a-Si:H growth in a-Si:H/c-Si heterojunction solar cells by spectroscopic ellipsometry and infrared spectroscopy

We have performed real-time process control and characterization of hydrogenated amorphous silicon (a-Si:H) growth on crystalline silicon (c-Si) in a-Si:H/c-Si heterojunction solar cells. By applying real-time spectroscopic ellipsometry, thickness control of a-Si:H layers with a precision better than ±1 Å has been demonstrated during a-Si:H p-i layer growth on the n-type c-Si substrate by conventional plasma-enhanced chemical vapor deposition. A heterojunction solar cell fabricated by this process shows a relatively high conversion efficiency of 14.5%. At the amorphous/crystalline interface, however, infrared attenuated total reflection spectroscopy (ATR) revealed the formation of a porous a-Si:H layer with a large SiH₂-hydrogen content of 27 at.%. From SE and ATR, we have investigated the growth processes and structures of a-Si:H in heterojunction solar cells.