Ballistic aggregation on two-dimensional arrays of seeds with oblique incident flux: Growth model for amorphous Si on Si

Amorphous silicon (Si) structures on two-dimensional arrays of seeds on a Si substrate were experimentally prepared at near room temperature using a physical vapor deposition system with an 85 degrees oblique incident flux. In the stationary deposition case where the substrate is fixed at a position, the Si on the seeds form a ballistic inclined fanlike structure with an initial cone shape and the fan size R grows with time in a power law form t(p), where p similar to 1. We show that with a swing rotation where the substrate is rotated back-and-forth azimuthally, the fan size grows slower (p < 1) relative to that of the stationary deposition case and then saturates at a size depending on the swing angle. We proposed a modified ballistic deposition model considering the ballistic sticking, shadowing, surface diffusion, and substrate rotation in a three-dimensional Monte Carlo simulator. The evolution of the fanlike structures at different deposition times was simulated for both stationary deposition and swing rotation. The growth of the fan size R with time t in simulations was quantitatively analyzed and the exponents p similar to 1.0 and p similar to 0.46 were extracted for the stationary deposition and the swing rotation, respectively. For stationary deposition, the exponent 1 does not change significantly with the strength of surface diffusion. However, the fan-out angle decreases with the increased strength of surface diffusion. For swing rotation, the reduced exponent 0.46 at the initial stages of growth is primarily due to the self-shadowing of the fan itself under rotation. At the later stages of growth, the saturation of the fan size produces uniform rods and is due to the global shadowing from the adjacent fan structures. The morphology and the exponent obtained from our simulations are consistent with our experimental observations.