Comparative study of nc-Si: H deposited by reactive sputtering using crystalline and polycrystalline silicon targets

Nanocrystalline silicon (nc-Si:H) is an important material for solar cell applications. Thin films of nc-Si:H can be deposited cost-effectively using chemical vapor deposition (CVD) and sputter deposition. While CVD method offer higher deposition rate and is commonly used in PV industry, microstructural properties (such as hydrogen incorporation, crystallinity, surface morphology, dopant incorporation) can be efficiently controlled using sputter deposition. While all the previous studies on sputter deposited nc-Si used crystalline Si (c-Si) sputter target, the current study compares the properties of nc:Si-H films using single and polycrystalline Si (p-Si) targets. P-Si is relatively inexpensive and easy to fabricate in bulk quantities. Several sets of nc-Si:H films were deposited using both c-Si and p-Si targets under similar conditions on glass substrates and characterized using TEM, XRD, AFM, UV-VIS spectroscopy and DC conductivity. Results indicate that surface morphology, size of nanocrystals, crystalline fraction, optical bandgap, coefficient of optical absorption and activation energy of samples were independent of sputter target used. Preferred orientation of nanocrystallites for all the films was along (111) direction with a crystallite size of 4-10 nm. All the samples have wide optical band gap ranging between 2 and 2.1 eV. Comparable activation energies at low (≪370K) and high temperature (≫370K) regions was obtained and was attributed to carrier transport through nanocrystalline and amorphous phase of the films. These results indicate that nc-Si:H thin films for solar cell applications can deposited using low-cost p-Si targets in-lieu of conventional c-Si targets.