ORDERING EFFECTS IN RAMAN-SPECTRA OF COHERENTLY STRAINED GAAS1-XNX

Raman spectra of coherently strained layers of GaAs1-xNx grown on (001 ) GaAs with x=0-0.05 by metalorganic molecular-beam epitaxy are report ed. The optical phonons of the GaAs and GaN types, as well as disorder -activated acoustical phonons, are observed. A strongly confined GaAs optical mode at similar to 255 cm(-1), indicating the ordering of As a nd N atoms, is also detected. The GaAs- and GaN-type optical phonons e xhibit strong diagonal components, forbidden for the zinc-blende struc ture. A bond polarizability analysis of the Raman selection rules show s that these components are activated by the trigonal distortion of th e alloy lattice. The trigonal distortion arises from the formation of ordered {111}-(GaN)(m)(GaAs)(n) clusters with n=m=1. [S0163-1829(97)03 947-7].