Copper light-induced-degradation (LID)

Light-induced degradation of copper-contaminated Si was first observed in early experiments performed by Henley et al. [1] and Tarasov et al. [2] in 1998, who observed a degradation of minority carrier diffusion length in 9-20 Ωcm p-type Cz-Si (see Figure 1 for an example of copper LID). Similar observations in B-doped FZ-Si, n-type Si and Ga-doped Si confirmed the occurrence of such degradation regardless of boron or oxygen concentration [3-5]. The existence of LID in intentionally Cu-contaminated Ga-doped Si (i.e. – absent of any BO-LID effects) confirmed the role of Cu in this degradation, leading to the definition of this mechanism as Cu-related light-induced degradation (Cu-LID).

Cu-LID has been shown to rely on the presence of interstitial Cu (Cui) in the bulk prior to illumination [6]. The degradation rate of Cu-LID has since been observed to increase with increasing temperature [7], illumination intensity [8], interstitial Cu concentration [9] and oxygen/BMD concentration [10]. Conversely, the degradation rate decreases with increasing doping concentration [7]. Unlike BO-LID, only partial recovery of Cu-LID has been observed in Cz-Si and FZ-Si after annealing at 200 °C, and only if the concentration of Cui is below 1014 cm-3 [11], whilst no recovery has been observed in Si with higher Cui concentrations. However, high-temperature rapid-thermal-annealing (800-900 °C) has resulted in full defect dissociation [12].

Recent analysis of Cu-LID defects in Si by Inglese et al. using lifetime spectroscopy indicated that the most likely source of Cu-LID is a silicide-based precipitate of Cu [13]. The Cu-LID defect recombination parameters identified by Inglese et al. also correspond with the recombination parameters determined for thermally-generated Cu precipitates as identified by Macdonald et al. [14], thus strengthening the hypothesis of Cu precipitates as the defect responsible for Cu-LID in Si.

Cu-LID curve.png
Figure 1: Effective minority lifetime of a copper-contaminated c-Si sample as a function of illumination time.

[1] – Henley, W.B., D.A. Ramappa, and L. Jastrezbski, Detection of copper contamination in silicon by surface photovoltage diffusion length measurements. Applied Physics Letters, 1999. 74(2): p. 278-280.

[2] – Tarasov, I. and O. Ostapenko. Light induced defect reactions in boron-doped silicon: Cu vs Fe. 1998. Copper Mountain, CO, USA.

[3] – Lindroos, J., et al., Light-induced degradation in copper-contaminated gallium-doped silicon. physica status solidi (RRL) – Rapid Research Letters, 2013. 7(4): p. 262-264.

[4] – Ramappa, D.A., Surface photovoltage analysis of phase transformation of copper in p-type silicon. Applied Physics Letters, 2000. 76(25): p. 3756-3756.

[5] – Savin, H., M. Yli-Koski, and A. Haarahiltunen, Role of copper in light induced minority-carrier lifetime degradation of silicon. Applied Physics Letters, 2009. 95(15).

[6] – Belayachi, A., et al., Influence of light on interstitial copper in p-type silicon. Applied Physics A: Materials Science and Processing, 2005. 80(2): p. 201-204.

[7] – Lindroos, J. and H. Savin, Formation kinetics of copper-related light-induced degradation in crystalline silicon. Journal of Applied Physics, 2014. 116(23).

[8] – Väinölä, H., et al., Sensitive Copper Detection in P-type CZ Silicon using μPCD. Journal of The Electrochemical Society, 2003. 150(12): p. G790-G790.

[9] – Väinölä, H., et al., Quantitative copper measurement in oxidized p-type silicon wafers using microwave photoconductivity decay. Applied Physics Letters, 2005. 87(3).

[10] – Yli-koski, M., Optical Activation of Copper in Silicon Studied By Carrier Lifetime Measurements. 2004. 88-88.

[11] – Inglese, A., J. Lindroos, and H. Savin, Accelerated light-induced degradation for detecting copper contamination in <i>p</i> -type silicon. Applied Physics Letters, 2015. 107(5): p. 052101-052101.

[12] – Nampalli, N., et al., Rapid thermal anneal activates light induced degradation due to copper redistribution. Applied Physics Letters, 2018. 113(3): p. 032104-032104.

[12] – Inglese, A., et al., Recombination activity of light-activated copper defects in p-type silicon studied by injection- and temperature-dependent lifetime spectroscopy. Journal of Applied Physics, 2016. 120(12): p. 125703.

[13] – Macdonald, D., et al., Temperature- and injection-dependent lifetime spectroscopy of copper-related defects in silicon. Proceedings of 3rd World Conference on Photovoltaic Energy Conversion, 2003. 1: p. 87-90.