Electronic properties of Hydrogenated nanocrystalline Silicon for Photovoltaic Applications Authors : Daniela Cavalcoli and Anna Cavallini Department of Physics, University of Bologna, viale C. Berti-Pichat 6/II, 40127 Bologna, Italy. Resume : Hydrogenated nanocrystalline silicon (nc-Si:H) is a promising material for photovoltaic applications, mainly due to its higher stability with respect to amorphous silicon, nevertheless its physical characterization has been carried out only recently, and several material properties are still not clearly understood. The present contribution deals with the study of electrical conductivity and below band gap spectroscopy in intrinsic and doped nc-Si:H films grown by LEPECVD (Low Energy Plasma Enhanced Chemical Vapor Deposition). The films have been deposited using SiH4 and H2 precursor gases, at temperatures ranging from 200 to 400°C, SiH4 dilution ratios from 1% to 50%, on several substrates: crystalline Si, glass, glass covered with ITO or ZnO. The crystal fraction ranged from 25 to 75%, p-type and n-type doped layers were obtained by adding to the precursor gases B2H6 and PH3, respectively. Sub-micron resolution current maps have been obtained by conductive atomic force microscopy (C-AFM) applying a fixed voltage to a conductive tip. The maps of the intrinsic films present a clear evidence of enhanced conduction in the nanocrystals, while the disordered tissue surrounding the nano-grains is mostly nonconductive. In doped films the maps show a quite similar behavior, but the spatial distribution of conductive nanocrystals differs from the one of the intrinsic films. Surface photovoltage spectroscopy (SPS) has been applied to intrinsic nc-Si:H films. The spectra have allowed for the determination of defect states, energy gap and Urbach tails in the films. Several characteristics of the films were obtained: slight n-type conductivity, optical gap around 1.5 eV, Urbach tails around 50meV and the presence of intra-gap transitions relevant to defective states.
Electronic properties of Hydrogenated nanocrystalline Silicon for Photovoltaic Applications
CAVALCOLI, DANIELA;CAVALLINI, ANNA
2010
Abstract
Electronic properties of Hydrogenated nanocrystalline Silicon for Photovoltaic Applications Authors : Daniela Cavalcoli and Anna Cavallini Department of Physics, University of Bologna, viale C. Berti-Pichat 6/II, 40127 Bologna, Italy. Resume : Hydrogenated nanocrystalline silicon (nc-Si:H) is a promising material for photovoltaic applications, mainly due to its higher stability with respect to amorphous silicon, nevertheless its physical characterization has been carried out only recently, and several material properties are still not clearly understood. The present contribution deals with the study of electrical conductivity and below band gap spectroscopy in intrinsic and doped nc-Si:H films grown by LEPECVD (Low Energy Plasma Enhanced Chemical Vapor Deposition). The films have been deposited using SiH4 and H2 precursor gases, at temperatures ranging from 200 to 400°C, SiH4 dilution ratios from 1% to 50%, on several substrates: crystalline Si, glass, glass covered with ITO or ZnO. The crystal fraction ranged from 25 to 75%, p-type and n-type doped layers were obtained by adding to the precursor gases B2H6 and PH3, respectively. Sub-micron resolution current maps have been obtained by conductive atomic force microscopy (C-AFM) applying a fixed voltage to a conductive tip. The maps of the intrinsic films present a clear evidence of enhanced conduction in the nanocrystals, while the disordered tissue surrounding the nano-grains is mostly nonconductive. In doped films the maps show a quite similar behavior, but the spatial distribution of conductive nanocrystals differs from the one of the intrinsic films. Surface photovoltage spectroscopy (SPS) has been applied to intrinsic nc-Si:H films. The spectra have allowed for the determination of defect states, energy gap and Urbach tails in the films. Several characteristics of the films were obtained: slight n-type conductivity, optical gap around 1.5 eV, Urbach tails around 50meV and the presence of intra-gap transitions relevant to defective states.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
