ATOMIC CONFIGURATIONS OF ER CENTERS IN GAAS-ER,O AND ALGAAS-ER,O STUDIED BY SITE-SELECTIVE LUMINESCENCE SPECTROSCOPY

Er-doped GaAs codoped with oxygen was studied by site-selective measur ements of photoluminescence spectra and photoluminescence-excitation s pectra directly exciting the 4f-shell electrons of one kind of Er cent er at a time. Within one sample, more than 10 kinds of distinctly diff erent Er centers, showing different Er-related spectra, were observed, although its host-excited photoluminescence spectrum is dominated by the luminescence from one kind of Er center. The atomic configuration of that center has been identified as an Er atom located at the Ga sub lattice with two adjacent oxygen atoms (Er-2O center). Seven kinds of Er centers in GaAs:Er, O and two kinds of Er centers in AlGaAs:Er, O w ere studied in detail. The numbers of lines and the magnitudes of ener gy separations among the lines in each spectrum indicate that the Er a toms of all nine kinds of centers are coupled with oxygen atoms and ha ve noncubic symmetry. The nine Er centers were grouped into several cl asses according to similarities in their spectra which should reflect symmetries of the Er centers. The atomic configurations of two classes of Er centers are discussed in detail. The Er centers of both classes have a nearest-neighbor site atomic configuration similar to that of the Er-2O center with a symmetry close to rhombic C-2 upsilon, but Er centers in the two classes have different types of deviation from C-2 upsilon due to the difference in the second-nearest-neighbor atomic co nfigurations of the Er Atoms. We also discuss a large difference in th e efficiency of the Er-related luminescence under host photoexcitation caused by the difference in the second-nearest-neighbor atomic config urations. (C) 1997 American Institute of Physics.