Mg-Doping of (111)B GaAs Thin Films Grown by Molecular Beam Epitaxy

Abstract

In this work, the influence of the growth conditions in the incorporation of Mg p-type dopant atoms in epitaxial GaAs(100) and (111)B thin films was investigated. Hall effect measurements and photoluminescence spectroscopy were used to investigate the electrical and optical properties of the films, respectively. The doping level varied between 1016 and 1019 cm–3 and increased with the inverse of the growth temperature and with the temperature of the Mg evaporation cell, with similar behavior in both crystal orientations. The analysis of the Mg incorporation at several growth temperatures and Mg arrival rates established a value of Ed(111)B = 1.6 ± 0.1 eV for the thermal desorption activation energy of Mg in the GaAs(111)B, a value 33% higher than for the (100) case. However, when a more realistic incomplete ionization model for the acceptors is considered, the value of the thermal activation energy for desorption of Mg adatoms increases to 2.7 ± 0.8 eV and equals the value for the (100) surface. Two very close broad bands were observed in the PL emission of the samples: free electron-to-Mg acceptor level (e–A) transition, at approximately 1.49 eV, and the donor-to-Mg acceptor (D–A) transition, at approximately 1.48 eV. However, a relative small red shift and broadening of these optical transitions for the (111)B samples suggest that this orientation is less susceptible to many-body interaction as the doping level increases, and Mg acceptors get close enough to interact. The small increase of the full width at half-maximum with the doping level for both transitions also indicates that the crystalline quality of the GaAs(111)B thin films was not severely perturbed by the high doping levels studied in this work.