Carbon-Incorporated Alloys (SI_1-x C _x , SI_1-x-y GE _x C _y , etc.)

Abstract

The group-IV alloy semiconductors, including C, Si, Ge, and Sn, have been actively investigated for use in heterojunction devices compatible with Si circuit technology [1,2]. For a variety of technical reasons, in particular to adjust the strain in the het-eroepitaxial layers, it is desirable to adjust the stain in the group-IV materials and form alloys (e.g., Si_1-x C _x , and Si_1-x-y Ge _x C _y ). For the Si-Ge system, the bond-length mismatch is only 4%, whereas it is about 40% for the Si-C system. Due to the small covalent radius of the C atom, the incorporation of C in substitutional sites can lead to the strain relaxation of compressively strained Si-Ge alloy. According to Vegard’s law, the lattice-matching condition for Si_1-x-y Ge _x C _y on Si is x=8.2y (Si_1-9.2yGe_8i2yC_y) [2]. It must be noted, however, that the solid solubilities of C in these constituents are extremely low (∼3×10¹⁸ cm^-3 for Si and ∼5×10¹⁸ cm^-3 for Ge at the melting points [3]). Growth under nonequilibrium conditions at relatively low growth temperatures enables us to obtain alloys with significant C fractions. Indeed, Si_1-x C _x alloys with C fractions as high as x∼0.2 have been prepared by MBE, and Si_1-x-y Ge _x C _y alloys with y≤0.1 have been achieved by CVD (see Ref. [4]).