Growth-induced interface roughness of GaAs/AlAs-layers studied by X-ray scattering under grazing angles

Linear theory of unstable growth on rough surfaces

“…In a recent paper 6 Gyure, Zinck, Ratsch and Vvedensky (GZRV) presented experimental and numerical results for the early time development of unstable homoepitaxy from a rough substrate, which show a more complex scenario: It was observed that the competition between smoothening of the initial roughness and the instability associated with the incipient mound structure can lead to a minimum in the total surface width. A similar effect was predicted previously in the context of noise-induced roughening 7 , and related experimental observations have been reported both for thin metal films 8 and semiconductor multilayers 9 . Qualitatively, the minimum originates from the wavelength dependence of smoothing and (de-terministic or stochastic) roughening rates: If the roughness spectrum of the substrate has sufficient weight at short wavelengths, which are efficiently smoothened by capillarity effects 10 , then the decrease of the substrate contribution to the surface width can temporarily dominate the long wavelength roughening induced by growth.…”

“…To relate the behavior of W (t) to microscopic parameters we need to express the coefficients α and κ of (2) in terms of the two length scales governing unstable homoepitaxy 3,5 : The typical terrace size 13 l D and the Ehrlich-Schwoebel-length 12 l ES = a (D/D ′ − 1) = a (e ∆E/kBT − 1) (9) defined in terms of the in-layer lattice spacing a , the in-layer (interlayer) surface diffusion constant D (D ′ ) and the step edge barrier ∆E. Comparison of the two length scales allows to distinguish conditions of strong (l ES ≫ l D ) and weak (l ES ≪ l D ) step edge barriers; in the first case α ≈ F l 2 D , in the second α ≈ F l D l ES .…”

Nonmonotonic roughness evolution in unstable growth

“…Under suitable conditions this leads to the somewhat counterintuitive possibility of a minimum of the total surface roughness at a nonzero film thickness. This phenomenon has been observed in several growth experiments [7][8][9], and a theoretical description has been worked out on the level of linear continuum theories of kinetic roughening [10] and unstable growth [11].…”

Microstructural Study of a Passivation Layer on GaAs: An Application of X-Ray Reflectivity Under Grazing Angles Using a Synchrotron Source

“…Of course, no interface is perfectly smooth, and as Klemradt et al showed in their analysis of the roughness of interfaces in a GaAs heterostructure, 16 there are no abrupt interfaces, even for highly perfect, epitaxial layers. The roughness they found was of the order of a couple of atomic layers.…”

“…(1) in Ref. 16], by taking into account that the index of refraction, n, is less than one. This gives rise to a total reflection regime up to a critical angle, α c , above which the X-ray beam penetrates the film, or films, in the case of a multilayer sample.…”