Quantum-confined direct band transitions in tensile strained Ge/SiGe quantum wells onsilicon substrates

Abstract

We directly demonstrate quantum-confined direct band transitions in the tensile strainedGe/SiGe multiple quantum wells grown on silicon substrates by room temperaturephotoluminescence. The tensile strained Ge/SiGe multiple quantum wells withvarious thicknesses of Ge well layers are grown on silicon substrates with a lowtemperature Ge buffer layer by ultrahigh vacuum chemical vapor deposition.The strain status, crystallographic, and surface morphology are systematicallycharacterized by high-resolution transmission electron microscopy, atomic forcemicroscopy, x-ray diffraction, and Raman spectroscopy. It is indicated that thephotoluminescence peak energy of the tensile strained Ge/SiGe quantum wellsshifts to higher energy with the reduction in thickness of Ge well layers. Thisblue shift of the luminescence peak energy can be quantitatively explained bythe direct band transitions due to the quantum confinement effect at theΓ point of the conduction band.