Caracterização óptica e elétrica de filmes finos de GaAs dopados com mg crescidos pela técnica de MBE

Abstract

Magnesium doped GaAs thin films grown in (100) and (111)B Semi-Insulating GaAs substrates by MBE weren't deeply investigated until today. Mg is a promising option (non-carcinogenic and non-toxic) to replace Beryllium as a p-type dopant in III -V materials, such as GaAs, GaN and alloys[1-3]. Mg forms a shallow defect in the GaAs electronic structure, being incorporated in a Ga site (substitucional defect MgGa) [1, 4]. As far as we know, no report was made concerning the electrical and optical properties of thin films of Mg doped GaAs grown in GaAs substrates with crystal orientation (111)B by the MBE technique. For this purpose several GaAs:Mg samples were grown, with different growth conditions using two substrate crystalline orientations. The transport properties were investigated by the standard Hall measurements techniques, by the four point probe Van der Pauw method. This measurements were carried out at room temperature for samples with Hall carrier concentrations ranging from 1016cm-3 to 1019cm-3. The activation energy for the Mg desorption process from the GaAs surface was found to be different for the two substrate orientations. The activation energy Ea= 1,5 eV, found for the (100) orientation confirms already reported values for samples grown in the (100) orientation. For the (111)B substrate orientation Ea=2,5eV, a result that confirm s the suggestion of Makoto et al.[5], which expected that the available site for the Mg incorporation in this substrate orientation is more stable than the one in the (100) orientation. The thin films optical properties were investigated by photoluminescence at several temperatures. The photoluminescence peak position of the e-A transition was used to find the activation energy of the defect in the GaAs electronic band. The results have shown an activation energy of Ea100= 27meV for the (100) samples Ea111b= 33meV and for the (111)B samples. The temperature dependent PL spectrum was investigated in order to understand the role of the nonradiative recombination mechanisms.