Inhomogeneous exciton broadening and mean free path in In/sub 1-x/Ga/sub x/As/sub y/P/sub 1-y/-InP heterostructures

Absorption and electroabsorption spectra are investigated at low temperature to derive broadening parameters of excitonic absorption edges in the alloy crystals. A strong increase of the inhomogeneous linewidth of excitons is observed for quaternary material which exceeds significantly the width expected from compositional fluctuations. The linewidth decreases again for phosphorous rich samples. Franz-Keldysh oscillations above the absorption edge contain information on the coherence length of band states. They show a corresponding decrease of the mean free path from 150 nm for ternary material to 70 nm for quaternary material.