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Oxygen‐Related Defect Centers in Solar‐Grade, Multicrystalline Silicon. A Reservoir of Lifetime Killers
Author(s) -
Karg D.,
Pensl G.,
Schulz M.,
Hässler C.,
Koch W.
Publication year - 2000
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/1521-3951(200011)222:1<379::aid-pssb379>3.0.co;2-2
Subject(s) - ingot , wafer , materials science , carrier lifetime , silicon , solar cell , impurity , metallurgy , oxygen , doping , getter , vanadium , thermal , optoelectronics , chemistry , physics , organic chemistry , alloy , meteorology
The effective lifetime of charge carriers τ eff in multicrystalline silicon (mc‐Si) Baysix ® wafers (in our case: Bridgman‐type) cut from areas close above the ingot bottom is reduced ( τ eff < 1 μs). However, the efficiency of solar cells processed on such bottom‐near Baysix ® wafers is comparable to that one of solar cells processed on Baysix ® wafers taken from the middle of the ingot. In order to clarify this unusual behavior, specially casted, low‐doped n‐ and p‐type mc‐Si ingots, respectively, were fabricated by Bayer AG and were studied by optical and electrical characterization techniques. It is demonstrated that the decrease of the effective lifetime τ eff in as‐grown wafers originating from a region directly above the ingot bottom is caused by oxygen‐related Thermal Donors (TDs), Shallow Thermal Donors (STDs) and O1‐/O2‐defects as well as by low concentrations (≤1.5 × 10 12 cm —3 ) of vanadium and chromium impurities. Most of the oxygen‐related defect centers are thermally dissociated by the solar cell process resulting in comparable efficiencies as obtained for wafers taken from the middle of the ingot.