Influence of Impact Ionization of Shallow Donors on Luminescence in GaAs
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Luminescence spectra of n-type molecular beam epitaxial layer and semi-insulating liquid encapsulated Czochralski grown bulk GaAs were measured at liquid helium temperature for zero electric field and for fields which caused impact ionization of shallow donors. Application of the electric field caused a decrease in the luminescence intensity and a broadening of all observed structures. It was found that the electric field changed the luminescence spectrum of the n-type material in a different way than it did in the case of the semi-insulating one. For the n-type sample, an intensity of excitonic lines decreased much more than that of donor-acceptor lines when the electric field grew. A contrary was observed for the semi-insulating sample. An explanation of the result is proposed which takes into account an influence of ionised impurity scattering and localization in fluctuations of the electrostatic potential on the luminescence process.
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