Analysis of germanium epiready wafers for III-V heteroepitaxy

Abstract

Frequently,whengrowing III–V semiconductors on germanium substrates, unexpected differences between nominally identical substrates are encountered. Using atomic force microscopy (AFM), we have analysed a set of germanium substrates sharing the same specifications.The substrates come from the same vendor but different results come about in terms of the morphology of the epilayers produced by the same epitaxial routine(i.e. substrateW1 produce depilayers with good morphology while substrate WX produce depilayers with defects). The morphological analysis has been carried out on(a)epiready substrates; (b)samples after a high-temperature bake at 700 1C; and(c)on the samples after a hydride (PH3) annealingat640 1C. In the two first stages all substrates(both W1 and WX) show the same good morphology with RMS roughness below A˚ in all cases. It is in the third stage(annealinginPH3) that the morphology degrades and the differences between the samples become apparent. After phosphine exposureat640 1C, the RMS roughness of both substrates approximately doubles, and their surface appears as full of peaks and valleys on the nanometer scale. Despite the general appearance of the samples being similar, a careful analysis of their surface reveals that the substrates that produce bad morphologies(WX) show higher peaks, and some of their roughness parameters, namely, surface kurtosis and the surface skewness, are considerably degraded.