Growth and Characterization of GaN As(P) for High Efficiency Solar Cells: Final Subcontract Report, 29 July 1999--28 September 2003

This report describes the characterization of GaAs1-xNx and GaP1-xNx alloys using scanning tunneling microscopy (STM) and ballistic electron emission microscopy (BEEM). One objective was to understand the origins of the giant bandgap bowing of these compound semiconductor alloys as a function of nitrogen concentration. The STM and BEEM have been used to characterize GaNxAs1-x and GaNxP1-x as afunction of composition. The reduction in bandgap has been measured. Detailed studies of the band structure as a function of N composition has led to a basic understanding of the materials system. The major results of this work include: (i) determination of relative contributions of the G- and L-like bands of GaNxAs1-x to the BEEM spectra; (ii) determination of the composition dependence of theAu/ G- and L-like bands of GaNxAs1-x Schottky barrier height; (iii) development of a model to describe the BEEM results at nonepitaxial metal/semiconductor interfaces; and (iv) ballistic electron emission spectroscopy studies of of GaNxP1-x samples that demonstrated possible splitting in the degeneracy of the X valley due to the nitrogen. The data were qualitatively described by the recentperturbed host states model of Kent and Zunger.