In an earlier paper [P.J. Wellmann, A. Albrecht, U. Künecke, B. Birkmann, G. Mueller, M. Jurisch, Eur. Phys. J. Appl. Phys. 27, 357 (2004)] an optical method based on whole wafer absorption
measurements was presented to determine the charge carrier concentration and
its lateral distribution in n-type (Si/Te) doped GaAs. The submitted results
for Si-doped GaAs gave rise to questions concerning the interpretation of
absorption mappings in wafers with high dislocation densities. GaAs
substrates for optoelectronic devices are strongly affected by
dislocations. Therefore further studies were conducted: absorption and
Hall measurements were performed on GaAs:Si wafers with high and low
dislocation densities.
Absorption in Si-doped GaAs is far more complex than in Te-doped GaAs. It
shows a co-dependency on charge carrier concentration and dislocation
content which causes complications in the quantitative optical determination
of the charge carrier concentration. Qualitatively, absorption mappings
depict dislocations and variations of charge carrier concentration very
well.