Lifetime and DLTS studies of interstitial Fe in p-type Si
Syre, M.
,
Monakov, E.
,
Holt, A.
,
Svensson, B.G
Physica status solidi (C): Current topics in solid state physics, Vol. 8, no. 3 (2011), 721-724.
- Utg. år
- 2011
- Publ. type
- article
- Sammendrag
- Fe is one of the most prominent metallic impurities in solar-grade Si. In this work we have investigated the kinetics of in-diffusion and formation of the interstitial fraction (Fei). P-type Cz-Si with a resistivity of 10 Ω-cm has been intentionally contaminated with Fe by in-diffusion from a surface layer of FeCl3 at 700 °C followed by cooling with a rate of ∼ 3.3 K/s. The concentration of Fei has been measured both by microwave photo conductance decay (μ-PCD) and deep level transient spectroscopy (DLTS). In the μ-PCD measurements, the Fei concentration has been determined using the ef- fect of light-induced splitting of the iron-boron pairs (FeB), while in the DLTS measurements Fei has been monitored by the donor electronic state at 0.43 eV above the valence band. We have observed a linear dependence between the minority carrier lifetime (τ) and the inverse Fei concentration. This confirms Fei as the dominating recombination centre. In the present investigations we use a material relevant for solar cells with a resistivity of 10 Ω-cm. We have found that the concentration of interstitial iron decreases with increasing time for in-diffusion of Fe, provided identical cooling condition. This decreasing con- centration of Fei is believed to be due to formation of more iron precipitates that serve as sinks for fast diffusing Fei. A high temperature anneal at 1000 °C for 1 minute followed by fast cooling (∼ 33 K/s) results in dissolution of the precipitates and freezing Fe into interstitial positions, where the concentration of Fei increases with increasing in-diffusion time.
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