Optical characterization of tensile-strained a p-type Ge layer on a Si (100) substrate

A boron doped p-type Ge layer has been grown on an n-type Si (100) wafer (8 inch in diameter, resistivity = 5 ∼ 15 Ω · cm) by using. The top surface roughness and the thickness of the p-type Ge layer grown on the Si (100) substrate are smooth and ∼1.8 µm. From the high-resolution X-ray diffraction, the in-plane lattice constant is evaluated to be 0.5664 nm, corresponding to an in-plane tensile strain of ∼0.49%. The Ge peak in the Raman shift for each location indicates a tensile strain from the Ge wafer. We estimate the in-plane strain as the tensile strain of ∼0.50%, in excellent agreement with the X-ray analysis. Moreover, initial photocurrent spectrum experiments on this sample confirm the valence band splitting of the direct gap induced by the tensile strain. The temperature dependence of the direct band-gap energy E Γ1 of Ge can be described by using Varshni’s empirical expression: E Γ1 ( T ) = 0.85 - 5.82 × 10 -4 T 2 /( T + 296).