LOW-ENERGY NITROGEN ION DOPING INTO GAAS USING COMBINED ION-BEAM AND MOLECULAR-BEAM EPITAXY METHOD

Low energy nitrogen (N) ions were irradiated during the epitaxial grow th of GaAs using combined ion beam and molecular beam epitaxy (CIBMBE) method as a function of N+ ion acceleration energy (E(a)) and N+ ion beam current density (I-N). E(a) was varied from 70 to 170 eV and I-N from 900 pA/cm(2) to 75 nA/cm(2). GaAs growth rate was fixed to 1 mu m /h. In 2 K photoluminescence (PL) spectra of the samples with I-N = 3 nA/cm(2) and E(a) = 70-100 eV, two sharp emissions at 1.508 eV (X(1)) and 1.495 eV (X(2)), which have been attributed to the emissions of ex citons bound to isolated N atoms, and another one at 1.443 eV (X(5)) w ere observed. These results show that nitrogen (N) atom in GaAs become s optically active as an isoelectronic impurity at least in as-grown c ondition. For N+ ion-irradiated samples with rather high I-N, e.g., wi th I-N = 75 nA/cm(2) and E(a) = 100 eV, a broad emission together with multiple sharp ones were observed after furnace annealing at 750 degr ees C which were ascribed to emissions of excitons bound to nitrogen-n itrogen (N-N) pairs.