Photoluminescence and free carrier interactions in erbium-doped GaAs

The photoluminescence properties of GaAs:Er doped with a new pyrazole and pyridine-based Er source, tris(3,5-di-tert-butylpyrazolato)bis(4-tert-butylpyridine)erbium(III), were investigated. These samples showed significantly stronger and sharper 1.54 μm Er3+ luminescence than in GaAs:Er samples doped with cyclopentadienyl-based Er sources. The efficient luminescence was associated with the Er–2O center, formed with unintentional oxygen impurities. The Er3+ emission was greatly reduced in n-type samples, whereas the emission remained strong in p-type samples. This trend suggests that either the free hole concentration is very important to the Er3+ excitation efficiency, and/or there is a strong Auger quenching mechanism which involves free electrons. A model based on the results of a two-beam experiment indicates the presence of strong Auger energy transfer from the Er-bound exciton to a free electron. Auger energy transfer from the excited Er3+ ion to a free electron was found to be much less important. The temperature dependence of the Er3+ emission was also examined. A decrease in intensity was observed at the lowest temperatures. This effect was attributed to the freeze-out of carriers onto a relatively shallow trap which could be related to either Er or shallow acceptors.