Mechanism of the enhancement of electrical conductivity of nanocrystalline silicon due to hydrogen plasma treatment.
The mechanism of electrical charge transport in hydrogenated nanocrystalline silicon (nc-Si:H) and the enhancement in electrical conductivity by hydrogen plasma exposure has been studied. Nanoscale electrical conduction measurements (laterally on the surface) suggested that the dominant charge transport in nc-Si:H occurs through the crystalline grain interiors while grain boundaries are highly resistive. Room temperature low-power/short-duration (10 W, 10 s) surface hydrogen plasma treatment enhanced the local surface and bulk electrical conductivity of nc-Si:H films which was attributed to improved passivation of surface and bulk dangling bonds, increase in crystalline fraction and decrease in grain boundary (GB) fraction. However, the improvement in electrical conductivity due to high-power/long-duration (50 W, 10 min) hydrogen plasma exposure was not as pronounced as low-power/short-duration exposure. Temperature-dependent dark conductivity measurements showed dual activation-energy behavior; increase in activation energy in the high-temperature regime (400-585 K) was attributed to the temperature dependence of tunneling probability of carriers and explained using a heteroquantum dots model. A decrease in activation energy with plasma exposure was observed which was explained using the framework of a three-phase model of nc-Si:H where GB width and barrier potential played a critical role in determining the relative contribution of tunneling and thermally activated carrier transport.
Department of Electrical Engineering, South Dakota State University, Brookings, SD 57007, USA.
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Dutta
Mukesh
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Kumar
Monika
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Rathi
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Ahrenkiel
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Paul
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Galipeau
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Bommisetty