Determination of interface roughness and its correlation in amorphous-silicon/ amorphous-germanium multilayers

Abstract

The importance of surfaces and interfaces of materials is increasing in many technological areas. In the microelectronic industry, for example, the J current trend is toward even faster and smaller electronic devices. Devices such » as metal-oxide semiconductor field effect transistors (MOSFET) function by manipulating the density of electrons trapped in a potential well at the oxide-semiconductor interface. The insulator-semiconductor interface will play an increasingly important role in the performance of this and similar devices. A clear understanding of the role played by the interface and how the interface morphology may affect the device performance is necessary. The possibility of constructing multilayered structures, which increase the interface to volume ratio, has opened a number of possibilities in the study of interface morphology and its relation with growth. In this work I study surface and interface roughness in hydrogenated amorphous-silicon/ amorphous-germanium multilayers by means of x-ray scattering techniques. Specular and diffuse x-ray scattering measurements were performed in order to study how roughness propagates from interface to interface during growth, as well as to examine the lateral length scale of the roughness, which is related to the surface diffusion process. Interface roughness was found to increase sub-linearly with distance of the interface from the substrate. The root mean square roughness near the substrate was found to be about 0.3 nm whereas at the surface the best fit was found for 18 nm of rms roughness. It was found that interface roughness was highly correlated from layer to layer and a correlation length of 30 nm was obtained. The fact that roughness is correlated from interface to interface on a scale given by the correlation length suggests that lateral diffusion during growth was of order, of or below, 30 nm.