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/Ge 1− x Sn x /Ge a type-I single quantum wells (SQW) partially strain compensated on Ge 1− y Sn y relaxed layers grown onto (0 0 1)-oriented Ge substrate. Such elementary cells with W -like potential profiles of conduction and valence bands have been modeled by solving the one-dimensional Schrodinger equation under an applied external electrical field. First, strain effects on electrons, heavy holes (hh) and light holes (lh) energy bands for strained/relaxed Ge 1− x Sn x /Ge 1− y Sn y 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, Ge 1− y Sn y /Ge/Ge 0.80 Sn 0.20 /Ge/Ge 1− y Sn y cells are computed as a function of the Ge 0.80 Sn 0.20 well width for three compositions of the Ge 1− y Sn y 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 × 10 3  cm −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 0.38 eV (i.e., λ  = 3.26–2.70 μm) at large external fields (50 kV/cm). These characteristics are attractive for the design of MWIR optical modulators.