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Coupled used of SKP and C-V measurements to highlight the charge distribution and behavior in the Si/SiO2/Al2O3 stack for silicon solar cells surface passivation

Authors:

Abstract

To reduce the material cost, solar cells tend to be thinner, increasing the surface defects impact on the solar cell efficiency. Then a suitable surface passivation is all the more needed to reduce this impact and preserve the efficiency or even to improve it. So far, a few nanometer thick layer of Al2O3 coated by PE-ALD (Plasma Enhanced Atomic Layer Deposition) gives the bests results on p-type silicon. Reasons of this high level passivation are a good chemical passivation, ensuring a very low density of interface defects (Dit), in addition with a suitable field effect passivation thanks to a high density of effective charges. In this study, chemical surface analyses such as XPS (X-Ray Photoelectron Spectroscopy) and SIMS (Secondary Ion Mass Spectrometry) have been made on passivated samples to understand the origin of the charges. They highlight the presence of a few nanometer thick silicon oxide at the interface. Then an original complementary use of electrical measurements using SKP (Scanning Kelvin Probe) performed in darkness and C-V (Capacitance-Voltage) characteristics based on MOS structures is completed. These two techniques, applied on different alumina film thicknesses, give the charge distribution through the Si/SiO2/Al2O3 stack. It appears that the silicon oxide induced by PE-ALD is the keystone of a good surface passivation. An explanation of the chemical behavior of the structure during the deposition process and after annealing treatments is also given.
Symposium N : Synthesis, processing and characterization of nanoscale multi functional
oxide films
Coupled used of SKP and C-V measurements to highlight the charge distribution and
behavior in the Si/SiO2/Al2O3 stack for silicon solar cells surface passivation
Authors : M. Pawlik, F. Morini, C. Sion, D. Aureau, A. Etcheberry, E. Dubois, J-P. Vilcot
Affiliations : Institut d’Electronique, de Microélectronique et de Nanotechnologie (IEMN)
UMR 8520 Université Lille1 Sciences et Technologies, Ecole Centrale de Lille, Institut
Lavoisier de Versailles Université de Versailles-St-Quentin en Yvelines
Abstract
To reduce the material cost, solar cells tend to be thinner, increasing the surface defects impact
on the solar cell efficiency. Then a suitable surface passivation is all the more needed to reduce
this impact and preserve the efficiency or even to improve it. So far, a few nanometer thick
layer of Al2O3 coated by PE-ALD (Plasma Enhanced Atomic Layer Deposition) gives the bests
results on p-type silicon. Reasons of this high level passivation are a good chemical passivation,
ensuring a very low density of interface defects (Dit), in addition with a suitable field effect
passivation thanks to a high density of effective charges. In this study, chemical surface
analyses such as XPS (X-Ray Photoelectron Spectroscopy) and SIMS (Secondary Ion Mass
Spectrometry) have been made on passivated samples to understand the origin of the charges.
They highlight the presence of a few nanometer thick silicon oxide at the interface. Then an
original complementary use of electrical measurements using SKP (Scanning Kelvin Probe)
performed in darkness and C-V (Capacitance-Voltage) characteristics based on MOS structures
is completed. These two techniques, applied on different alumina film thicknesses, give the
charge distribution through the Si/SiO2/Al2O3 stack. It appears that the silicon oxide induced
by PE-ALD is the keystone of a good surface passivation. An explanation of the chemical
behavior of the structure during the deposition process and after annealing treatments is also
given.
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