Propriedades opticas de camadas epitaxiais de semicondutores III-V com gas bi-dimensional de eletrons

AUTOR(ES)
DATA DE PUBLICAÇÃO

1990

RESUMO

In this work we present a detailed study of photoreflectance measurements on silicon d-doped GaAs samples. These samples were grown by molecular-beam epitaxy technique. With different silicon concentration and cap layer thickness. The features, observed in the photoreflectance spectra above the GaAs fundamental energy gap, are attributed to transitions involving 3D continuous states at the valence band and 2D quantum-confined states at the conduction band. We performed a systematic self-consistent calculation, in the Hartree approximation of the subband energies and its occupancies, in the delta potential well, as a function of silicon concentration and residual acceptor concentration, spreading of dopants and temperature. The observed inter-band transitions, in the samples grown with different dopant concentration, are in qualitative agreement with the calculated ones. The temperature has a strong effect in the d-doping system, modifying the electrostatic confinement potential well and, consequently, the subband energies. Photoreflectance spectra taken at increasing temperatures show an abrupt change in the position of the above band gap features. This can be well explained by a theoretical model, being associated with the shift of the absorption main peak to the lower subband, due to the crossing of the Fermi level. The photoreflectance spectra of several samples presented oscillatory structures in the above band gap region. Due to the Franz-Keldysh effect. The period of these oscillations depends strongly on the cap layer thickness, where the built in electric field depends on the conditions of the samples surface and on the d-doping potential well. The temperature dependence of these oscillations, in some cases, are very different from that observed in bulk of GaAs, suggesting a possible relation between the observed Franz-Keldysh oscillations and the d-doping structure. We also investigated the photoreflectance spectra of a periodically d-doping GaAs sample. Differently, with the single d-doping, the observed transitions above the gap involve continuos states in the conduction band and quantum-confined states in the valence band

ASSUNTO(S)

semicondutores

ACESSO AO ARTIGO

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