Photoluminescence in Mn-implanted GaAs—An explanation on the ∼1.40-eV emission

The emission properties of Mn-implanted layers in GaAs are investigated with respect to changes in excitation intensity, temperature, substrate, and encapsulation. The substrates used were n-type conducting and Cr-doped semi-insulating crystals. The depth-dependent measurements of the Mn emission show an increase of the diffusion coefficient with dose for Si3N4 encapsulated samples, whereas a suppression of Mn diffusion is observed for SiO2 encapsulated samples. A large energy shift from ∼1.36 to 1.41 eV is observed for Mn emission at 4.2 °K at various excitation intensities. The energy shift increases with the concentration of compensating donors in the n-type substrate material. The excitation-dependent emissions are due to the donor-acceptor pair type transitions in the normal and the random-impurity-potential-disturbed energy states of the bands. Another emission becomes dominant at T≳∼30 °K following the quenching of the donor-acceptor pair type transitions with an increase of the temperature. An activation energy 95±15 meV is obtained from the temperature quenching of the emission intensity and the energy shift is observed to follow the band-gap variation. The possible radiative mechanisms are discussed.