Macrosteps dynamics and the growth of crystals and epitaxial layers

TL;DR

This paper analyzes the stability of step patterns on vicinal surfaces during crystal growth, revealing mechanisms of macrostep formation and their influence on surface morphology and defect formation.

Contribution

It introduces a new scenario for macrostep creation based on step train dynamics, highlighting the role of step density ratios and kinetics.

Findings

Step coalescence is not indicated by standard surface analysis.

Macrosteps form through step train instability driven by specific kinetic conditions.

Single step motion remains crucial for crystal growth despite macrostep presence.

Abstract

Step pattern stability of the vicinal surfaces during growth was analyzed using various surface kinetic models. It was shown that standard analysis of the vicinal surfaces provides no indication on the possible step coalescence and therefore could not be used to elucidate macrostep creation during growth. A scenario of the instability, leading go macrostep creation was based on the dynamics of the step train. The critical is step motion at the rear of the train which leads to double and multiple step creation. The condition is that the step density ratio in and out of the train lower than 2 prevents double step formation irrespective of the kinetics. For higher step density ratio low density of the step promotes single step stability. Fast step kinetics from lower terrace stabilizes the single steps slow (high barrier) is promoting step coalescence. The incorporation kinetics from upper terrace role is close to neutral. The creation of double step creates slow the step in front to accelerate and catch the previous double step while those behind catch up the double step creating multistep structure. The multistep are not mobile as the alimentation leads to emission of single step which moves forward. The final structure consist of macrosteps and superterraces with the number of single steps moving forward. Thus the single step motion is essential crystal growth mode despite the presence of the macrosteps. The macrostep are prone to creation of the overhangs which results from surface dynamics coupling to impingement from the mother phase. The angular preferential access of the bulk material to the macrostep edge, leads to diffusive instability. Therefore it is expected that harmful influence of the macrosteps by creation of inclusions and dislocation is stronger during growth from the liquid phase.