Confinement effects in bulk samples derived from the Franz-Keldysh effect

Differential electroabsorption spectra of thick ${\mathrm{Ga}}_{0.47}{\mathrm{In}}_{0.53}\mathrm{As}$ epilayers demonstrate a significant distortion of the Franz-Keldysh effect if the sample is thinner than the mean free path. Such confinement effects are clearly visible in 100-nm-thick samples, where they reduce the range and amplitudes of Franz-Keldysh oscillations. Further oscillations appear well above the gap which are related to quantum-confined states. Additional sharp spectral features are observed near the gap which are related to field-induced interface states. The spectra are compared with calculations based on the envelope approximation.