Short-Range Lateral Ordering of GeSi Quantum Dots Due to Elastic Interactions

Abstract

GeSi alloy film growth on Si (001) represents perhaps the most intensively studied of all heteroepitaxial materials systems. This is truly a model system for exploring fundamental scientific issues, offering complete chemical miscibility of the constituents, relatively low volatility, a simple diamond cubic lattice, a range of lattice misfit up to 4% for pure Ge on Si, and a nearly linear dependence of lattice parameter on alloy composition [1]. Furthermore, the atomic structure and the nature of surface diffusion processes on the Si (001) surface have been extensively characterized. Finally, the obvious importance of Si to microelectronics, and the rapidly increasing technological importance of Ge and GeSi, lends additional motivation to studies of this material system.

In this chapter we will examine ordering processes occurring during molecular beam epitaxial growth (MBE) of dilute GexSi_1−x alloys, x = 0.2 − 0.3, on Si (001). We will distinguish between the formation of long-range order within dense quantum dot (QD) arrays, which we will refer to as extended order, and local ordering processes that can produce symmetric quantum dot molecules (QDMs). These strain-induced mechanisms take place under different deposition conditions; ideal QD arrays form “near-to-equilibrium”, whereas QDMs form under “kinetically limited” conditions. Operational definitions of these terms shall be provided later.