NANOMETER-SCALE STUDIES OF NITRIDE ARSENIDE HETEROSTRUCTURES PRODUCEDBY NITROGEN PLASMA EXPOSURE OF GAAS/

We have investigated the nanometer-scale structure and electronic prop erties of nitride/arsenide superlattices produced by nitridation of a molecular beam epitaxially grown GaAs surface. Using cross-sectional s canning tunneling microscopy and spectroscopy, we find that the nitrid ed layers are not continuous films, but consist of groups of atomic-sc ale defects and larger clusters. We identify the defects and clusters as N-As and GaN with dilute As concentration, respectively. Thus, the nitrided regions consist of alloys from both sides of the miscibility gap predicted for the GaAsN system. In addition, spectroscopy on the c lusters reveals an upward shift of the band edges and band gap narrowi ng, with significant change in the conduction band structure. We estim ate the contribution of strain to band gap narrowing in terms of an el asticity calculation for a coherently strained spherical GaN cluster e mbedded in GaAs.