High quality relaxed germanium layers grown on (110) and (111) silicon substrates with reduced stacking fault formation

Abstract

Epitaxial growth of Ge on Si has been investigated in order to produce high quality Ge layers on (110)- and (111)-orientated Si substrates, which are of considerable interest for their predicted superior electronic properties compared to (100) orientation. Using the low temperature/high temperature growth technique in reduced pressure chemical vapour deposition, high quality (111) Ge layers have been demonstrated almost entirely suppressing the formation of stacking faults (< 10⁷ cm⁻²) with a very low rms roughness of less than 2 nm and a reduction in threading dislocation density (TDD) (∼ 3 × 10⁸ cm⁻²). The leading factor in improving the buffer quality was use of a thin, partially relaxed Ge seed layer, where the residual compressive strain promotes an intermediate islanding step between the low temperature and high temperature growth phases. (110)-oriented layers were also examined and found to have similar low rms roughness (1.6 nm) and TDD below 10⁸ cm⁻², although use of a thin seed layer did not offer the same relative improvement seen for (111).