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Title:
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The interface of a-SiNx:H and Si: Linking the nano-scale structure to passivation quality
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Author(s):
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Lamers, M.W.P.E.; Hintzsche, L.E.; Butler, K.T.; Vullum, P.E.; Fang, C.M.; Marsman, M.; Jordan, G.; Harding, J.H.; Kresse, G.; Weeber, A.W.
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Published by:
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Publication date:
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ECN
Solar Energy
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28-5-2013
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ECN report number:
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Document type:
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ECN-W--13-018
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Article (scientific)
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Number of pages:
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6
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Published in: Solar Energy Materials & Solar Cells (Elsevier), , 2014, Vol.120, p.311-316.
Abstract:
Surface passivation by hydrogenated amorphous silicon nitride (a-SiNx:H)is determined by the combined effect of two mechanisms: so-called chemical passivation by reducing the density of
interface states (Dit) and ?eld-effect passivation as a result of the number of ?xed charges Qf)at the interface with Si. These are related to the K defect center: *Si-N3. Defects near the
interface (in both Si as in a-SiNx:H), modeled by force ?eld Molecular Dynamics MD)and ab
initio Density Functional Theory (DFT), can be related to Qf and Dit measured experimentally
using CV-MIS (Capacitance–Voltage Metal–Insulator– Semiconductor). The compositional build up
at the interface as is determined by HRTEM High Resolution Transmission Electron Microscopy) and modeled by MD corresponds to each other; a gradual change from Si to the bulk a-SiNx:H composition in the ?rst 2 nm of the a-SiNx:H layer. At the c-Si side a highly distorted
layer (about 1–3 nm) caused by the insertion of N and/or H is found. The insertion and
adhesion of N into and at the Si surface is called nitridation and can be altered by using a NH3 plasma prior to a-SiNx:H deposition. HRTEM image analysis shows that by varying the nitridation of the Si surface the amount and penetration depth of N inside the Si surface is altered. Using MD modeling, it is shown that this process changes the amount of K-centers at the surface, which explains the variation in Qf and Dit that is found experimentally. Ab initio DFT studies of a-SiNx:H (x ¼ 1.17) show that K-centers and Si atoms in distorted con?guration, are the dominating defects resulting in a higher Dit. For lower x (x ¼ 1) the Dit caused by K-centers increases, which is observed experimentally too.
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