ATOMIC-SCALE STRUCTURE AND ELECTRONIC-PROPERTIES OF GAN GAAS SUPERLATTICES/

We have investigated the atomic-scale structure and electronic propert ies of GaN/GaAs superlattices produced by nitridation of a molecular b eam epitaxially grown GaAs surface. Using cross-sectional scanning tun neling microscopy (STM) and spectroscopy, we show that the nitrided la yers are laterally inhomogeneous, consisting of groups of atomic-scale defects and larger clusters. Analysis of x-ray diffraction data in te rms of fractional area of clusters (determined by STM), reveals a clus ter lattice constant similar to bulk GaN. In addition, tunneling spect roscopy on the defects indicates a conduction band state associated wi th an acceptor level of N-As in GaAs. Therefore, we identify the clust ers and defects as nearly pure GaN and N-As, respectively. Together, t he results reveal phase segregation in these arsenide/nitride structur es, in agreement with the large miscibility gap predicted for GaAsN. ( C) 1996 American Institute of Physics.