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Title: Experimental evidence on removing copper and light-induced degradation from silicon by negative charge

Abstract

In addition to boron and oxygen, copper is also known to cause light-induced degradation (LID) in silicon. We have demonstrated previously that LID can be prevented by depositing negative corona charge onto the wafer surfaces. Positively charged interstitial copper ions are proposed to diffuse to the negatively charged surface and consequently empty the bulk of copper. In this study, copper out-diffusion was confirmed by chemical analysis of the near surface region of negatively/positively charged silicon wafer. Furthermore, LID was permanently removed by etching the copper-rich surface layer after negative charge deposition. These results demonstrate that (i) copper can be effectively removed from the bulk by negative charge, (ii) under illumination copper forms a recombination active defect in the bulk of the wafer causing severe light induced degradation.

Authors:
; ; ;  [1]; ;  [2]
  1. Department of Micro and Nanosciences, Aalto University, Tietotie 3, 02150 Espoo (Finland)
  2. SolarWorld Innovations GmbH, Berthelsdorfer Str. 111A, 09599 Freiberg (Germany)
Publication Date:
OSTI Identifier:
22391905
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 105; Journal Issue: 18; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; BORON; CHEMICAL ANALYSIS; COPPER; COPPER IONS; CRYSTAL DEFECTS; DEFECTS; ETCHING; OXYGEN; SILICON; SURFACES

Citation Formats

Boulfrad, Yacine, E-mail: yacine.boulfrad@crystals.no, Lindroos, Jeanette, Yli-Koski, Marko, Savin, Hele, Wagner, Matthias, and Wolny, Franziska. Experimental evidence on removing copper and light-induced degradation from silicon by negative charge. United States: N. p., 2014. Web. doi:10.1063/1.4901533.
Boulfrad, Yacine, E-mail: yacine.boulfrad@crystals.no, Lindroos, Jeanette, Yli-Koski, Marko, Savin, Hele, Wagner, Matthias, & Wolny, Franziska. Experimental evidence on removing copper and light-induced degradation from silicon by negative charge. United States. doi:10.1063/1.4901533.
Boulfrad, Yacine, E-mail: yacine.boulfrad@crystals.no, Lindroos, Jeanette, Yli-Koski, Marko, Savin, Hele, Wagner, Matthias, and Wolny, Franziska. 2014. "Experimental evidence on removing copper and light-induced degradation from silicon by negative charge". United States. doi:10.1063/1.4901533.
@article{osti_22391905,
title = {Experimental evidence on removing copper and light-induced degradation from silicon by negative charge},
author = {Boulfrad, Yacine, E-mail: yacine.boulfrad@crystals.no and Lindroos, Jeanette and Yli-Koski, Marko and Savin, Hele and Wagner, Matthias and Wolny, Franziska},
abstractNote = {In addition to boron and oxygen, copper is also known to cause light-induced degradation (LID) in silicon. We have demonstrated previously that LID can be prevented by depositing negative corona charge onto the wafer surfaces. Positively charged interstitial copper ions are proposed to diffuse to the negatively charged surface and consequently empty the bulk of copper. In this study, copper out-diffusion was confirmed by chemical analysis of the near surface region of negatively/positively charged silicon wafer. Furthermore, LID was permanently removed by etching the copper-rich surface layer after negative charge deposition. These results demonstrate that (i) copper can be effectively removed from the bulk by negative charge, (ii) under illumination copper forms a recombination active defect in the bulk of the wafer causing severe light induced degradation.},
doi = {10.1063/1.4901533},
journal = {Applied Physics Letters},
number = 18,
volume = 105,
place = {United States},
year = 2014,
month =
}
  • Light-induced degradation (LID) is a deleterious effect in crystalline silicon, which is considered to originate from recombination-active boron-oxygen complexes and/or copper-related defects. Although LID in both cases appears as a fast initial decay followed by a second slower degradation, we show that the time constant of copper-related degradation increases with increasing boron concentration in contrast to boron-oxygen LID. Temperature-dependent analysis reveals that the defect formation is limited by copper diffusion. Finally, interface defect density measurements confirm that copper-related LID is dominated by recombination in the wafer bulk.
  • Copper is a harmful metal impurity that significantly impacts the performance of silicon-based devices if present in active regions. In this contribution, we propose a fast method consisting of simultaneous illumination and annealing for the detection of copper contamination in p-type silicon. Our results show that, within minutes, such method is capable of producing a significant reduction of the minority carrier lifetime. A spatial distribution map of copper contamination can then be obtained through the lifetime values measured before and after degradation. In order to separate the effect of the light-activated copper defects from the other metastable complexes in lowmore » resistivity Cz-silicon, we carried out a dark anneal at 200 °C, which is known to fully recover the boron-oxygen defect. Similar to the boron-oxygen behavior, we show that the dark anneal also recovers the copper defects. However, the recovery is only partial and it can be used to identify the possible presence of copper contamination.« less
  • We investigate the impact of copper on the light induced minority-carrier lifetime degradation in various crystalline silicon materials. We demonstrate here that the presence of neither boron nor oxygen is necessary for the degradation effect. In addition, our experiments reveal that copper contamination alone can cause the light induced minority-carrier lifetime degradation.
  • The calculation of the space-charge density under illumination from surface photovoltage measurements has been adapted to analyze light-soaking experiments in intrinsic hydrogenated amorphous silicon (a-Si:H). We find that the positive space-charge densities increase and the space-charge widths decrease with light exposure while very little change occurs in the hole diffusion length. These results indicate that changes in electric field distribution with light soaking are important causes of degradation of amorphous silicon solar cells, rather than changes which may ocur in the hole diffusion length. We also review and discuss results of others regarding application of the surface photovoltage (SPV) tomore » study light-induced phenomena, evidence of two different types of light-induced defects, and potential limitations of SPV in a-Si:H.« less