On the Field-induced Refractive Index Change Considering Valence Band Nonparabolicity in Quantum Well Structures

Abstract

We investigate the effect of valence subband dispersion on predicting the field-induced change in the refractive index in a lattice-matched InAlGaAs/InAlAs quantum well (QW). Emphasis is on the second-lowest valence subband dispersion having heavy-hole nature at the Brillouin zone center, which displays negative hole effective masses due to the presense of the valence subband nonparabolicity. Realistic electroabsorption (EA) spectra calculated taking the nonparabolicity, are compared with approximated EA spectra assuming parabolic valence subbands. It is shown that the nonparabolicity makes the transition from the second heavy-hole subband contribute more to the EA change than the transition from the first light-hole subband. Only the nonparabolic EA spectra is found to be essential to the nearly quadratic dependence of the increase in the refractive index change with electric field strength, which we expect in the electro-optic modulation due to the quantum-confined Stark effect.