IMPROVEMENT OF MICROSTRUCTURE OF AMORPHOUS SILICON-GERMANIUM ALLOYS BY HYDROGEN DILUTION

The microstructures of two sets of hydrogenated amorphous silicon-germ anium (a-Si1-xGex:H) alloys prepared by the plasma-enhanced, chemical- vapor-deposition technique with and without hydrogen dilution of the s ource gases (silane and germane) have been analyzed by small-angle x-r ay scattering (SAXS), infrared vibrational spectroscopy, and flotation density measurements. Optoelectronic properties of codeposited films have also been characterized. Hydrogen dilution suppresses dihydride/p olyhydride formation, reduces bonded H content, and reduces the SAXS-d etected microstructure for x>0. Studies of anisotropy in the SAXS inte nsity indicate an increased amount of oriented microstructure as Ge is added, consistent with a trend toward columnarlike growth in both und iluted and hydrogen-diluted films, but the diluted films have a signif icantly reduced degree of such oriented microstructure. The improvemen t in the microstructure of a-Si1-xGex:H films by H-2 dilution correlat es with concomitant improvement of optoelectronic properties. The modi fication of microstructure due to H-2 dilution of the source gases is discussed in terms of growth mechanisms of alloy films. (C) 1995 Ameri can Institute of Physics.