Simulation and design of GaAs/A1[subscript]xGa₁₋[subscript]xAs Multiple-Quantum-Well Fabry-Perot optical modulators

Abstract

A systematic study of the GaAs/A1[subscript]xGa₁-[subscript]xAs Multiple-Quantum-Well (MQW) normal-incident modulators, including the theoretical calculations of the absorption coefficient and refractive index of GaAs/A1[subscript]xGa₁₋[subscript]xAs quantum wells (QWs) and bulk A1[subscript]xGa₁₋[subscript]xAs is presented. For bulk GaAs, the discrepancy between the calculated refractive index and the experimental data is about 0.003 at 1.8 eV, and is about 0.012 at 1.2 eV. For all the other bulk A1[subscript]xGa₁-[subscript]xAs, the calculated optical properties are in satisfactory agreement with the experimental data for photon energies from 1.2 to 6 eV. The calculated absorption coefficients of the GaAs/A1[subscript]xGa₁₋[subscript]xAs QWs as a function of electric field have been compated with the experimental data, and achieved very good of electric field have been compared with the experimental data, and achieved very good agreement with the experimental data without any adjustment in the parameters used in the calcuations. The accuracy of the calculated refractive indices of the GaAs/A1[subscript]xGa₁₋[subscript]xAs QWs as a function of electric field has been indirectly verified by comparing the calculated reflectance spectra of a reported normally-off GaAs/A1₀.₂Ga₀.₈As MQW reflection modulator with the experimental data. Using the optical transfer matrices, and including the absorption of the GaAs/A1[subscript]xGa₁₋[subscript]xAs QWs in the MQW active region and the GaAs substrate, the operations of a GaAs/A1[subscript]xGa₁₋[subscript]xAs MQW normal-incident modulator are well simulated. Our calculations suggest that a normally-off refractive GaAs/A1₀.₂Ga₀.₈As MQW reflection modulator with an ON/OFF reflectance change of 42.9% and ON/OFF contrast ratio of 1539 for an operating voltage of only 2.33 V can be fabricated by MBE, which is better than any normally-off modulators so far reported in the literature.