PHOTOELLIPSOMETRIC DETERMINATION OF BUILT-IN ELECTRIC-FIELD IN DELTA-DOPED GAAS

In this study, photoellipsometry, a contactless optical method sensitive to surface and interface built-in electric fields in semiconductor structures, was employed to study delta-doped GaAs. Three delta-doped samples, each containing an undoped GaAs cap layer of different thickness, were measured. The objective was to determine the built-in field strength in the cap layer of each chosen sample. Data analysis was performed using the Franz-Keldysh theory, in which the effect of broadening and the contributions from both heavy and light holes were included. Good agreement was found between the measured and calculated spectra for all the samples studied, indicating that the model calculations were adequate. In addition, the Linear relationship observed between the build-in field and the reciprocal of the cap layer thickness suggests that the surface Fermi level was pinned at a fixed position for the samples measured.