Step bunching during Si(001) homoepitaxy caused by the surface diffusion anisotropy

TL;DR

This study reveals that surface diffusion anisotropy causes step bunching during Si(001) homoepitaxy, with experimental and simulation evidence showing the instability's dependence on temperature and diffusion properties.

Contribution

The paper identifies diffusion anisotropy as a key factor in step bunching, providing experimental and simulation evidence for a new instability mechanism in Si(001) growth.

Findings

Step bunching occurs under step-flow growth conditions.

The instability vanishes at low and high temperatures.

Diffusion anisotropy alone can cause step bunching without step edge barriers.

Abstract

Scanning tunneling microscopy experiments show that the unstable growth morphology observed during molecular beam homoepitaxy on slightly vicinal Si(001) surfaces consists of straight step bunches. The instability occurs under step- flow growth conditions and vanishes both during low-temperature island growth and at high temperatures. An instability with the same characteristics is observed in a 2D Kinetic Monte Carlo model of growth with incorporated Si(001)- like diffusion anisotropy. This provides strong evidence that the diffusion anisotropy destabilizes growth on Si(001) and similar surfaces towards step bunching. This new instability mechanism is operational without any additional step edge barriers.