EFFECTIVE INTERFACES AND URBACH SLOPES OF A-SIH A-SINXH MULTILAYERS/

Optical and structural measurements are presented for glow discharge m ultilayer structures of hydrogenated amorphous silicon (a-Si:H) and hy drogenated amorphous silicon nitride (a-SiN(x):H). Two sets of samples are presented. For set A, the barrier thickness as well as the number of double layers are kept constant whereas. for set B, samples have b oth constant composition and total thickness. Small-angle X-ray reflec tivity measurements (reflectometry) are analyzed using a theoretical m odel based on the transfer matrix method. This analysis yields an effe ctive width between 1.5 and 2.0 nm for the interfaces. The increase of the Urbach slope parameter with decreasing well layer thickness is me asured by photothermal deflection spectroscopy and by Fourier transfor m photoacoustic spectroscopy. This dependence is analyzed by taking in to account the effective interface thickness and it is studied by usin g the optical absorption model of Abe and Toyozawa (J. Phys. Soc. Jpn. 50, 2185 (1981)). Both sets of samples show the same behavior. which leads to the conclusion that the Urbach slope increase is due to inter face effects.