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Determination of Defect Densities in Thin (i) a‐Si:H Used as the Passivation Layer in a‐Si:H/c‐Si Heterojunction Solar Cells from Static Planar Conductance Measurements
Author(s) -
Levtchenko Alexandra,
Le Gall Sylvain,
Brüggemann Rudolf,
Kleider Jean-Paul
Publication year - 2019
Publication title -
physica status solidi (rrl) – rapid research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.786
H-Index - 68
eISSN - 1862-6270
pISSN - 1862-6254
DOI - 10.1002/pssr.201900411
Subject(s) - heterojunction , materials science , band bending , passivation , silicon , fermi level , conductance , dangling bond , condensed matter physics , band gap , annealing (glass) , layer (electronics) , analytical chemistry (journal) , optoelectronics , chemistry , nanotechnology , electron , composite material , physics , quantum mechanics , chromatography
A set of (p) a‐Si:H/(i) a‐Si:H/(n) c‐Si heterostructures is investigated by coplanar conductance measurements. The thickness of the (i) a‐Si:H buffer layer is varied between 2 and 50 nm, well beyond the values used in heterojunction solar cells. The change in this thickness plays a role on band bending at the heterointerface and therefore impacts the level of inversion of carrier population at the c‐Si surface. Measurements are compared with 1D analytical calculations and 2D electrical modeling. It is demonstrated that the deep defect density, related to silicon dangling bonds, in the (i) a‐Si:H layer strongly increases from 1 × 10 17 to 4 × 10 18 cm −3 when the (i) a‐Si:H layer thickness is decreased from 50 to 2 nm. This result is interpreted in terms of defect formation and dependence of the defect density upon the position of the Fermi level with respect to the valence band edge. Quantitative analysis in the framework of the defect‐pool model demonstrates that the strong increase of defect density is also promoted by an increase in the width of the valence band tail in the thin (i) a‐Si:H layer, suggesting that a very thin layer also suffers from increased disorder.