Recently doping of isovalent substitutional impurities (Group-IV) into semiconductors have been attracted keen interests. Such impurities have almost no effects electrically but have unique interactions with harmful defects to improve the device yield and output through the local strain compensation. Particularly, Ge is effective to suppress formation of vacancy-oxygen clusters in electron-irradiated Si crystals [1]. In comparison with Ge, information on Sn is rather limited except some studies for lack of suitable crystals. These isovalent impurities are expected to affect local vibration of interstitially dissolved O_i and substitutional C_s in Si as known in SiGe alloys [2]. Here, we report the Czochralski-growth of Si crystals heavily doped with Sn and to discuss compositional variation along the growth direction of the crystals. Also, doping effects on infrared absorption spectra of O_i and C_s due to the dopant-induced elastic strain are shown.

Si single crystals heavily doped with Sn were grown by the Czochralski method with a constant pulling rate in a flowing Ar gas atmosphere. Certain amount of high purity Sn pellets was added as a dopant. [111]- or [001]-oriented Si seeds were used.

A full single crystal, as large as around 20 mm in diameter and 40 mm in length, was obtained under a pulling rate of 8 mm/h. The Sn concentration at the top part of the crystal was 1.5 x 10¹⁹ cm^-3, determined by ICP-OES and WDX, then increased along the growth direction, and reached to 4 x 10¹⁹ cm^-3, close to the solubility limit in a literature [3]. The variation of the Sn concentration well followed to a normal segregation with a coefficient 0.016 [3]. From the optical absorption peak at 1106 cm^-1 of O_imeasured by FT-IR, the Oi concentrations in the crystals were around 8 x 10¹⁷ cm^-3. The absorption peak shifted to the low wave number side with an increase in [Sn] along the growth direction, possibly due to the expansion of Si–Si bonds.

[1] C. A. Londos et al., J. Appl. Phys. 112, 123517 (2012).

[2] I. Yonenaga et al., Physica B 308-310, 539 (2001).

[3] F. A. Trumbore, Bell Syst. Techn. J. 39, 205 (1960).

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