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

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.

Full text

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.