Impurity-induced resonant Raman scattering in GaAs below the band gap at low temperature

by Qing Huang
Doctoral thesis
Date of Examination:2000-06-21
Date of issue:2001-11-07
Advisor:Prof. Dr. Rainer G. Ulbrich
Referee:Prof. Dr. Wolfgang Felsch
Persistent Address: http://dx.doi.org/10.53846/goediss-4233

 

 

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Abstract

English

Acceptor-induced resonance Raman scattering (RRS) below the band gap in lightly doped p-type GaAs is investigated at 2 K. The Raman scattering intensities are measured and analyzed. Both impurity-induced one-phonon Raman scattering and multi-phonon scattering are verified and studied. For the one-phonon acceptor-induced Raman scattering, the resonances occur at the threshold of (e, Ao) and (Ao, X). The Raman scattering intensities are large though the impurity concentration is relatively low. Both Fröhlich-induced LO-scattering and deformation potential-induced TO-scattering are observed and interpreted. The breakdown of selection rules is explained as due to q-relaxation in the scattering and the large Raman intensities are ascribed to the large oscillator strengths of the impurity-related interband transitions. For the multi-phonon scattering, the additional scattering line shows the dispersion behavior, whose Stokes shift increases with the incident light energy. This is due to additional acoustic phonon scattering besides the one LO-phonon scattering. It is proved that when the excitation energy is above the (e, Ao) theshold, the mixed-processes occur with one, two, or more LA phonons contributing to the scattering. The impurity-induced resonant Raman scattering signals overlap the impurity-related luminescence strongly at low temperature, thus it is necessary to analyze the influence of luminescence on the intensity and profile of the Raman scattering line. It is confirmed that the luminescence may stem from up-converted luminescence, selective luminescence and donor-pair luminescence.
 
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