Abstract
It is well established that boron reacts with two oxygen atoms in Czochralski-grown silicon (Cz-Si) to form a defect, which is responsible for the dominant light-induced degradation (LID) in solar cells made from Cz-Si:B material. The detrimental effect of LID has stimulated a move by solar cell manufacturers to the use of silicon with other group-III dopants, particularly with gallium. Cz-Si:Ga is immune to the BO-type LID. The information available in the literature on the interactions of oxygen with either Al, Ga, or In impurities in Si is limited. We use ab initio modeling and junction spectroscopy techniques to study a family of defects with unusual electronic properties, which have been detected in Cz-Si samples doped with different shallow acceptor species. We have carried out detailed measurements of the temperature dependencies of hole emission rate, equilibrium occupancy, and hole capture kinetics for the traps observed in differently doped p-type Cz-Si samples. It is found from the analysis of the changes in magnitude of the deep-level-transient signals with temperature that the equilibrium occupancy function of the traps is characteristic for a defect with negative-U properties in all the samples. The positions of the E(−/+) occupancy level of the defects are very close in differently doped samples, E(−/+) = Ev + (0.31 ± 0.01) eV. It is argued that the oxygen dimer interacts with group-III atoms in silicon and these interactions result in the formation of AsO2 complexes (A is either B, Al, Ga, or In atom) with very similar electronic properties.
Highlights
A defect with negative electron correlation energy, U, in a semiconductor is a center, which can emit or capture at least two charge carriers, and for which the ionization energy of the first charge carrier (I1) exceeds the ionization energy of the second carrier (I2): U = I2 − I1 < 0.1–3 In other words, a negative-U defect has an inverted order of energy levels in the gap
It is well established that boron reacts with two oxygen atoms in Czochralski-grown silicon (Cz-Si) to form a defect, which is responsible for the dominant light-induced degradation (LID) in solar cells made from Cz-Si:B material
It has been shown recently that a complex consisting of a substitutional boron atom and two oxygen atoms (BsO2) is a center with negative-U properties, and it is responsible for minority carrier trapping effects, persistent photoconductivity, and lightinduced degradation (LID) of minority carrier lifetime in Czochralski-grown silicon (Cz-Si) crystals doped with boron
Summary
From an analysis of temperature dependencies of rates of carrier emission and capture by the BsO2 defect in Cz-Si:B samples with different hole concentrations, electronic characteristics of the defect have been determined and its configuration coordinate diagram constructed.. It has been argued that the defect in In-doped Cz-Si is a complex consisting of a substitutional indium (Ins) atom and the oxygen dimer, and its negative-U electronic properties are related to the “square”-staggered configuration transformations of O2 in the vicinity of an Ins atom.. We have carried out detailed measurements of temperature dependencies of hole emission rate, equilibrium occupancy, and hole capture kinetics for the detected traps and determined their electronic characteristics in the Cz-Si samples doped with different acceptor impurities. The calculations show that like BO2, { Al, Ga, In} O2 are negative-U complexes and suggest that the complexes that are detected by junction spectroscopy do not involve the formation of direct A–O bonds
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