Photoellipsometry characterization of AlGaAs/GaAs heterojunctions for solar cells

Photoellipsometry, a new contactless optical method, was applied to n-AlGaAs/GaAs heterojunctions used for solar cells. Two samples were studied each having an MOCVD-grown AlGaAs layer of thickness of ~100 nm, with a different Al composition and a different doping density, on top of an undoped GaAs substrate. The authors´ main objective was to determine surface built-in electric field strength, depletion width, broadening, and critical point energies of AlGaAs for each given sample. The measured spectra were analyzed using the Franz-Keldysh theory with the inclusion of field inhomogeneity and broadening effects. Good agreement between the measured and calculated spectra indicates that theories and models used were appropriate for the samples investigated and that the calculated results were reliable