Stark shift of the absorption spectra in Ge/Ge1−xSnx/Ge type-I single QW cell for mid-wavelength infra-red modulators

Abstract

For mid-wavelength infra-red (MWIR) modulation or detection applications, we propose α-Sn rich Ge/Ge1−xSnx/Ge a type-I single quantum wells (SQW) partially strain compensated on Ge1−ySny relaxed layers grown onto (001)-oriented Ge substrate. Such elementary cells with W-like potential profiles of conduction and valence bands have been modeled by solving the one-dimensional Schrödinger equation under an applied external electrical field. First, strain effects on electrons, heavy holes (hh) and light holes (lh) energy bands for strained/relaxed Ge1−xSnx/Ge1−ySny heterointerfaces are investigated using the model-solid theory in the whole ranges (0⩽x, y⩽1) of Sn compositions. From the obtained band-discontinuities, band gaps and effective masses, Ge1−ySny/Ge/Ge0.80Sn0.20/Ge/Ge1−ySny cells are computed as a function of the Ge0.80Sn0.20 well width for three compositions of the Ge1−ySny buffer layer (y=0.05, 0.07 and 0.09) in order to get the optimum quantum confinement of electrons and holes levels while keeping a reasonable amount of averaged strain in the cell. The electric field effect on the absorption spectra is given. An absorption coefficient in the 6× to 3×103cm−1 range is reasonably obtained for a SQW at room temperature with a rather large Stark shift of the direct transition between 0.46 and 0.38eV (i.e., λ=3.26–2.70μm) at large external fields (50kV/cm). These characteristics are attractive for the design of MWIR optical modulators.