Indium‐Doped Silicon for Solar Cells—Light‐Induced Degradation and Deep‐Level Traps

Abstract

Indium‐doped silicon is considered a possible p‐type material for solar cells to avoid light‐induced degradation (LID), which occurs in cells made from boron‐doped Czochralski (Cz) silicon. Herein, the defect reactions associated with indium‐related LID are examined and a deep donor is detected, which is attributed to a negative‐U defect believed to be InsO2. In the presence of minority carriers or above bandgap light, the deep donor transforms to a shallow acceptor. An analogous transformation in boron‐doped material is related to the BsO2 defect that is a precursor of the center responsible for BO LID. The electronic properties of InsO2 are determined and compared to those of the BsO2 defect. Structures of the BsO2 and InsO2 defects in different charges states are found using first‐principles modeling. The results of the modeling can explain both the similarities and the differences between the BsO2 and InsO2 properties.

Acceptor-oxygen defects in silicon: The electronic properties of centers formed by boron, gallium, indium, and aluminum interactions with the oxygen dimer

“…In the conventional DLTS spectra recorded on all diodes (Schottky and n + -p junctions) from all the p-type Cz-Si crystals (doped with either B, Al, Ga, or In impurities) studied in this work, a hole-emission-related peak with its maximum at about 390 K for the emission rate window of 10 s −1 was detected. This peak has been observed earlier in B-and In-doped samples [4][5][6][7] and will be referred to as H 390 K hole emission signal in the following. The concentrations of the defect(s), which gives rise to the H 390 K emission signal, vary from sample to sample and are found to be in the range of a few times of 10 13 cm −3 in the majority of as-received samples.…”

“…2 are described well by a mono-exponential-growth equation and resemble those observed earlier for Cz-Si samples doped with either B or In. 4,5,7 The characteristic features of the ΔC(t p ) dependencies in all the samples are as follows: (i) the capture rates, C p , 11 are temperature dependent and (ii) the maximum values of the emission signal, ΔC max , reachable at long filling pulses, are temperature dependent. The ΔC max value is a measure of equilibrium occupancy of a defect with charge carriers.…”

“…4,5 Further, a defect with very similar electronic properties to those for the B s O 2 defect has been detected in Czochralski-grown silicon crystals doped with indium. 7 It has been argued that the defect in In-doped Cz-Si is a complex consisting of a substitutional indium (In s ) atom and the oxygen dimer, and its negative-U electronic properties are related to the "square"-staggered configuration transformations of O 2 in the vicinity of an In s atom. 7 First-principles modeling results suggest that at equilibrium conditions in p-type Si (in the absence of minority carriers), the ground state of InO 2 is positively charged, comprising close In-and O 2 -square units with the formation of In-O bonds.…”

“…7 It has been argued that the defect in In-doped Cz-Si is a complex consisting of a substitutional indium (In s ) atom and the oxygen dimer, and its negative-U electronic properties are related to the "square"-staggered configuration transformations of O 2 in the vicinity of an In s atom. 7 First-principles modeling results suggest that at equilibrium conditions in p-type Si (in the absence of minority carriers), the ground state of InO 2 is positively charged, comprising close In-and O 2 -square units with the formation of In-O bonds. 7 On the other hand, the location of the occupancy (À/þ) level was better described by the model assuming that the dimer breaks away from the acceptor and adopts a staggered O 2 configuration in the neutral charge state.…”

“…7 First-principles modeling results suggest that at equilibrium conditions in p-type Si (in the absence of minority carriers), the ground state of InO 2 is positively charged, comprising close In-and O 2 -square units with the formation of In-O bonds. 7 On the other hand, the location of the occupancy (À/þ) level was better described by the model assuming that the dimer breaks away from the acceptor and adopts a staggered O 2 configuration in the neutral charge state.…”