IMPROVEMENT IN ELECTROABSORPTION AND THE EFFECTS OF PARAMETER VARIATIONS IN THE 3-STEP ASYMMETRIC COUPLED QUANTUM-WELL

Exciton binding energies, radiuses, emission energies, and oscillator strengths in a three-step asymmetric coupled quantum well (QW) are numerically analyzed as a function of electric field. This analysis predicts that the change in the absorption coefficient for an n = 1 heavy-hole exciton can be made larger and on-state transmission loss can be lowered by reducing oscillator strength at zero bias and increasing it at operating voltages. The Stark shifts also can be increased, thus allowing lower operating voltages. Estimation of influences of alloy composition and thickness variations on electroabsorption reveals that the thickness of epitaxial layers must be controlled to within one monoatomic layer and that variations in alloy composition must be controlled to within +/- 4%. An analysis of exciton peak shifts caused by one-monolayer change in the QW layer thicknesses predicts that interface roughness broadening may be small when the electric field is increased, in contrast to the case of conventional square-potential QWs. The influence of the broadening of the exciton spectra on the proposed improvements is also examined.