Heteroepitaxial Growth Mode Transitions in the Presence of a Schwoebel Barrier at an Island Edge
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Heteroepitaxial Growth Mode Transitions in the Presence of a Schwoebel Barrier at an Island Edge Vladimir I. Trofimov, Vladimir G. Mokerov Institute of Radioengineering & Electronics of RAS, Dept. of micro- and nanoelectronics 11 Mokhovaya str. 101999 Moscow Russia, [email protected] ABSTRACT A recently developed model for homoepitaxial growth on a singular surface in the presence of a Schwoebel barrier at an island edge is extended to the case of heteroepitaxy (without lattice mismatch) by introducing different adatom mobilities in the first layer (heterodiffusion) and in all the next ones (self-diffusion).The model consists of an infinite set of rate equations for adatom and 2D island areal densities and coverage in successive layers. Growth behaviour depending on the model parameters is studied with emphasis on the transient growth regimes: layer-by-layer (LL) to a smooth multilayer (SML) and SML to a rough 3D growth. It is shown that a slower heterodiffusion relative to the self-diffusion leads to a smoother initial growth and thus retards the LL 60/JURZWKWUDQVLWLRQZKHUHDVDIDVWHUKHWHURGLIIXVLRQOHDGVWRDURXJKHULQLWLDOJURZWKDQG assists that transition and especially SML 'JURZWKWUDQVLWLRQ at a higher Schwoebel barrier. It is found also that in a smooth growth regime nucleation kinetics eventually acquires a universal scaling form and the corresponding exponents are determined. INTRODUCTION An interest in a long-standing problem of molecular-beam epitaxial (MBE) growth has been greatly renewed in the last few years due to constantly widening its applications in modern materials science. In particular, many papers have focused on the effects of the Schwoebel stepedge barrier to interlayer diffusion which can dramatically affect MBE growth on both vicinal and singular surfaces (e.g., [1-6]). Recently, we have developed a simple kinetic model for homoepitaxial growth on a singular surface [7], based on the combination of a rate equation approach and a feeding zone [8] that allows to account for the diffusion-mediated interaction between neighbouring growing layers in the presence of the Schwoebel barrier. With this model it has clearly been demonstrated how with increasing repulsive Schwoebel barrier height homoepitaxial growth mode crosses over from atomically smooth layer-by-layer (LL) growth with oscillating surface roughness to a smooth multilayer (SML) growth with a time-stable roughness and finally to a rough 3D growth, and corresponding “phase diagram” of the growth mode in parametric space has been constructed (Figure 1). Here we extend the model to the case of heteroepitaxy (without lattice mismatch) by introducing different adatom surface mobilities in the first layer (heterodiffusion) and in all the next layers (self-diffusion) and study MBE growth behaviour depending on the model parameters with emphasis on the transient growth regimes. We show that the difference between homo- and heteroepitaxy is dramatically dependent on the ratio between hetero- and self-diffusion coefficients: a slo
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