Thermally Induced Nano-Structural and Optical Changes of nc-Si:H Deposited by Hot-Wire CVD
1 CSIR National Centre for Nano-Structured Materials, P.O. Box 395, Pretoria, 0001, South Africa
2 Department of Physics, University of the Western Cape, Private Bag X17, Bellville, 7535, South Africa
3 School of Physics, University of the Witwatersrand, Private Bag 3, P.O. Wits, Johannesburg, 2050, South Africa
4 Department of Physics, University of Malawi, The Polytechnic, Private Bag 303, Blantyre, Malawi
Nanoscale Research Letters 2009, 4:307-312 doi:10.1007/s11671-008-9243-0Published: 21 January 2009
We report on the thermally induced changes of the nano-structural and optical properties of hydrogenated nanocrystalline silicon in the temperature range 200–700 °C. The as-deposited sample has a high crystalline volume fraction of 53% with an average crystallite size of ~3.9 nm, where 66% of the total hydrogen is bonded as ≡Si–H monohydrides on the nano-crystallite surface. A growth in the native crystallite size and crystalline volume fraction occurs at annealing temperatures ≥400 °C, where hydrogen is initially removed from the crystallite grain boundaries followed by its removal from the amorphous network. The nucleation of smaller nano-crystallites at higher temperatures accounts for the enhanced porous structure and the increase in the optical band gap and average gap.