Stark shift of the absorption spectra in Ge/Ge_(1-x)Sn_x/Ge type-Ⅰ single QW cell for mid-wavelength infra-red modulators

摘要

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 (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 Schroedinger 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.