Eigenstates and absorption spectra of interdiffused AlGaAs-GaAs multiple-quantum-well structures

We present a comprehensive analysis of the inter-well coupled eigenstates in interdiffused AlGaAs-GaAs multiple quantum-well structures. A full numerical calculation is considered without any approximation or presumption of the eigenstates. During the initial interdiffusion in the quantum-well structure with well and barrier thickness equaling 100 Å, the wavefunctions behave as in the case of a single quantum well with almost no well-to-well coupling of the states. However, as interdiffusion proceeds, the eigenstate in each subband forms minibands, as in the case of superlattice. Distortion of the coupled wavefunctions can also be observed as a consequence of the nonuniformity of the confined wells at the far sides of the multiquantum-well core. The polarized absorption coefficients, including valence band-mixing, are also calculated. Results show that the blue shift of the absorption edge is greater in the range of 10 Å⩽L _d⩽30 Å. The two-dimensional quantum-well properties are at its strongest in the beginning of interdiffusion. An estimation of the modulator performance also shows an improvement of the contrast ratio and lower absorption loss during the initial stage of interdiffusion. This predicts wavelength tuning range of almost 60 nm