Spatial distribution of composition and strain in multicrystalline SiGe bulk crystal and their impact on solar cell applications

We report on microscopic structural characterizations of multicrystalline SiGe (mc-SiGe) bulk crystal, which contains microscopic compositional distribution, and discuss possible influence on solar cell applications. By combining microscopic Raman spectroscopy and energy-dispersive X-ray analysis, the existence of built-in strain and its spatial distribution were experimentally obtained. By a simple calculation assuming ellipsoidal SiGe inclusion coherently embedded in Si-matrix, effect of the built-in strain on the band gap is quantitatively estimated. For example, an ellipsoidal Si/sub 0.5/Ge/sub 0.5/ inclusion with an aspect ratio less than 0.10 is predicted to have the similar band gap with unstrained Ge. Therefore, to utilize strain is concluded to be important to realize spectroscopic response in the near infrared regime with minimizing incorporation of Ge.