Model of GaN crystal. Two types of large circles correspond to Ga atoms at two terrace types, differing by step atomic structure leading, ultimately, to different step kinetics. From the bottom to the top, the terrace heights increase by one atomic Ga–N layer at each step. Positions of N atoms are marked by dots.
Potential felt by a particle close to the two step types. Steps go up from right to left side. Ga adatom that is attached at the step, jumping from upper terrace has to overcome Schwoebel barrier. Steps differ by Ga bonding energy, that determines the adatom probability of the detachment from the step.
Stationary pattern of double terrace structure of different width, having straight steps. The initial all terraces width was 20 lattice constants. Simulation was carried out for system of the size of lattice constants, for , , , and . Steps are perpendicular to , i.e., parallel to direction.
Step pattern evolution of the steps, initially oriented perpendicularly to and , for the following evolution times: 0, , and MC steps, is presented from the top to the bottom. Step anisotropy is given by . , , and for the system of size lattice constants, eight shaped terraces were prepared. For comparison, initial step shape is drawn in thin black line.
Step pattern evolution for systems having anisotropic (—left) and isotropic steps (—right). Initially steps were bend 19° to the crystallographic directions. Consecutive evolution plots are presented from top to bottom for the number of MC steps, changing from 0 to , and finally to . The system size was lattice constants, with 12 initially shaped terraces. The other parameters are: , , .
Phase diagram of the surface step patterns, obtained from Eqs. (12) and (13), plotted in vs coordinates. The shaded regions correspond to the relative width of terraces , given by the solution of Eq. (12). For other regions, one of the terraces disappears.
Evolution of the steps, presented for low Schwoebel barrier, at the left, and for high, , at the right hand side. Steps initially were oriented as in Fig. 5, with the initial terrace width equal to 20 lattice constants. The other parameters of the systems were: , . The number of MC steps changes from top down, from 0 to , and finally to .
Domains for large particle flux, . Upper row shows system with for steps perpendicular to direction at right hand side and with steps perpendicular to direction at left hand side. Bottom row shows isotropic system, i.e., for at right hand side and anisotropic system after longer evolution. Three first cases present the surface after steps and the last one after steps. In these simulations and (no Schwoebel barrier).
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