Tensile strained epitaxial Ge films on Si(100) substrates with potential application in L-band telecommunications

Abstract

Tensile strained epitaxialGefilms were grown on Si(100) substrates by ultra-high vacuum chemical vapor deposition. The tensile strain was induced by the thermal expansion coefficient mismatch between Si and Ge during the cooling process from elevated growth temperatures, which induces narrowing of the Ge direct band gap, E g Γ , and pushes the absorptionspectrum of Ge toward longer wavelengths. The E g Γ versus strain relation was measured experimentally by photoreflectance and x-ray diffraction, and the result agrees well with calculations by deformation potential theory. With an in-plane tensile strain of 0.21%, the E g Γ of the Gefilmgrown at 800 °C decreased from 32 meV to 0.768 eV compared with 0.80 for bulk Ge, and corresponded to an absorption edge at 1610 nm. The broadened absorptionspectrum of tensile strained Ge makes it promising as a Si-compatible photodector material for L -band (1560–1620 nm) optical communications.