Photoellipsometry Analysis of n-AlGaAs/GaAs Heterojunction Structures

Abstract

Photoellipsometry, a new contactless spectroscopic method, was applied to n-AlGaAs/GaAs heterojunction structures. Two samples were measured and analyzed, each having an epitaxially grown AlGaAs layer of a thickness of about 100 nm, with a different Al composition and a different doping density, on top of an undoped GaAs substrate. The objective of this research 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 nonuniform 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.