Computation of the electronic structure and direct-gap absorption spectra in Ge-rich Si1−x Gex/Ge/Si1−xGex type-I quantum wells

This paper presents the results of conduction band discontinuities calculation for strained/relaxed Si1−x Ge x /Si1−y Ge y heterointerfaces in Γ 15C , Γ 2′C and L upper bands minima, as well as the room-temperature strained (vs. relaxed) band gaps deduced from the classical model-solid theory. Based upon the obtained data, we propose a type-I W-like Si1−y Ge y /Si1−x Ge x /Ge/Si1−x Ge x /Si1−y Ge y quantum wells heterostructure optimized in terms of compositions and thicknesses. Electronic states and wave functions are found by solving Schrodinger equation without and under applied bias voltage. An accurate investigation of the optical properties of this heterostructure is done by calculating the energies of the interband transitions and their oscillator strengths. Moreover, a detailed computation of the bias-voltage evolution of the absorption spectra is presented. These calculations prove the existence of type-I band alignment at Γ 2′C point in compressively strained Ge quantum wells grown on relaxed Ge-rich Si1−y Ge y buffers. The strong absorption coefficient (> 8 × 103 cm-1) and the large Stark effect (0.1 eV @ 2 V) of the Γ 2′C transitions thresholds open up perspectives for application of these heterostructures for near-infrared optical modulators.