The donor impurity distribution in a GaN epitaxial layer was studied using Raman imaging. The A1(LO) Raman line at 735 cm−1 is found to be inversely correlated to the presence of silicon in GaN due to phonon interaction with the free carrier plasma associated with donor impurities in the material. The spatial variation of the A1(LO) signal was imaged directly using newly developed instrumentation. Features with dimension of about 0.5 μm are observed in faceted GaN crystallites. This variation in free carrier concentration is attributed to preferential donor impurity incorporation during growth.
Results are presented of high-resolution luminescence studies from individual dislocations and related defects in ZnSe and InP performed in a transmission electron microscope. In the case of ZnSe unusual luminescence bands (Y at 2.60 eV and S at 2.52 eV) originally observed in photoluminescence studies are attributed to dislocations. In some instances, complete quenching of the excitonic transitions was observed to correlate with the presence of Y emission from complex dislocation tangles. In the case of individual screw dislocations this quenching of the exciton luminescence was found to be variable; for example reduction of the exciton signal was not always observed. For InP, donor-exciton-related transitions were quenched at individual screw dislocations. Donor-acceptor pair/free-to-bound and deep level (band C) transitions were unaffected. For the case of InP, unlike ZnSe, no dislocation-related luminescence was observed within the system detection limit (0.7-4.0 eV).
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