Field effect on optical recombination in Si/SiGe quantum heterostructures having U, W and M type II potential designs

We report on optoelectronic properties of devices based on Si/Si1−xGex systems. To limit the inherent problems of the type II character and the indirect nature of the bandgap, we propose Si/Si1−xGex strained QWs embedded in relaxed Si1−yGey barriers. The conduction and the valence band present a W-, Usami- or M-like potential profile with a quasi-type I heterostructures. Based on Schrödinger equation, a theoretical analysis is made to calculate electric field dependent interband transitions in the three above-mentioned structures. The thickness and compositions (x > y) of these heterostructures are computed in order to get: (i) the optimum quantum confinement of electrons and heavy-holes levels; (ii) the optimum out of plane oscillator strength and wave functions overlap; (iii) to satisfy a fundamental emission at a key 1.55 μm wavelength below the absorption gap of the three designed structures. The effect of the applied electric field on quantum levels and oscillator strength is discussed.