Revisiting the interface sensitive selective crystallization in HWCVD a-Si:H/Al bilayer system

In the kinetics of Aluminum Induced Crystallization (AIC) process, the sequence of deposition plays a significant role; specifically, for the hydrogenated amorphous silicon (a-Si:H) films deposited by Hot Wire Chemical Vapour Deposition (HWCVD). We show that while the layer sequence of substrate/a-Si:H/Al crystallizes at a relatively lower temperature of 300 degrees C in 5 min (relatively faster rate), the layer sequence of substrate/Al/a-Si:H takes about 1 h at 450 degrees C for crystallization. We have carried out extensive Raman spectroscopy, X-ray diffraction, focused ion beam (FIB) imaging, field emission scanning electron microscopy (FESEM) and glow discharge optical emission spectroscopy (GDOES) to first establish the difference in the kinetics of crystallization in these two layer sequences and then to explain the reasons for the same. We put forward a hypothesis followed by a supportive experimental evidence, using FTIR spectroscopy as a tool, that the high hydrogen concentration at the a-Si:H/Al interface slows down the kinetics in AIC.