EFFECT OF GA SI INTERDIFFUSION ON OPTICAL AND TRANSPORT-PROPERTIES OFGAN LAYERS GROWN ON SI(111) BY MOLECULAR-BEAM EPITAXY/

Optical and transport properties of wurtzite GaN layers, grown by plas ma-assisted molecular-beam epitaxy on Si(111) substrates, have been in vestigated. An emission at 3.455 eV, analyzed by continuous-wave and t ime-resolved luminescence in undoped and Si-doped GaN layers, is assig ned to excitons bound to Si donors with an optical binding energy of 5 0 meV. A common origin of this peak, for undoped and Si-doped GaN, is backed by secondary-ion-mass spectroscopy that evidences a Si diffusio n from the substrate into the GaN layer for growth temperatures above 660 degrees C. Simultaneously, Ga diffusion into the Si substrate gene rates a highly p-type conductive layer at the GaN/Si interface, leadin g to unreliable Hall data in undoped and lightly doped layers. Positro n annihilation reveals a concomitant vacancy cluster generation at the GaN/Si interface in samples grown above 660 degrees C. No traces of t he ''yellow band'' are detected either in undoped or in Si-doped sampl es. [S0163-1829(98)00827-3].