Photoreflection spectrum on Si-surface-delta-doped GaAs

In this paper we present the observation of the interband transition in the GaAs (100) surface Si-delta-doping potential. Samples with different surface doping concentrations (Ns equals undoped, 3.0 X 1012, 6.3 X 1013, 2.4 X 1014 and 3.6 X 104 cm-2) have been studied at room temperature in the MBE high vacuum chamber using modulated photo-reflection (PR) spectroscopy technique. The MBE chamber guarantees that all the sample surfaces are free of oxidation or uncontrollable contamination. The optical transition of at GaAs bandedge around 1.41 eV is strong and is almost independent of Ns. A relatively weak feature above 1.42 eV has been observed which is clearly enhanced and blue-shifted following the increase of Ns. The experimental results have been analyzed and well explained based on the self-consistent Schrodinger-Poisson equations. The theoretical analysis indicates that it is not proper to attribute the PR spectral peak of 1.42 eV simply to be certain subband-related optical transition. The observed spectral peak of 1.42 eV is more likely to be related to the high-index confined-levels in the half-V-shape conduction band at the sample surface.

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