Formation of InAs quantum dots on GaAs(100) by chemical beam epitaxy

The formation of quantum dots is very important for optoelectronic applications as well as for nanometer-scale science [1]. For this reason, various formation methods have been investigated. The most favored process involves the etching of quantum wells by nanolithography [2–4]. This process, however, suffers from some drawbacks, such as the limited resolution of lithography and the defects created by etching. It has been shown that the growth of a highly lattice-mismatched semiconductor layer on a substrate can lead to the spontaneous formation of semiconductor clusters with sizes in the quantum range. A promising method for clean and defect-free formation of dot structures directly on epilayer surface is the Stranski-Krastanow (S-K) growth method. This growth mode begins with an initial two-dimensional (2D) layer deposition on the substrate. After a critical layer deposition thickness is achieved, the surface transformation into three-dimensional (3D) highly strained dots occurs coherently on the heterostructure interface. The advantages of this dot fabrication technique are that nanolithography and etching or implantation-induced process are not necessary. InAs which has a 7% lattice mismatch with GaAs is known to grow on GaAs initially as a strained 2D layer, and then as gradually relaxed 3D dots [5]. Such growth has been observed in InAs/GaAs [5–9] and InGaAs/GaAs systems [10,11] formed by metalorganic chemical vapor deposition (MOCVD) or by molecular beam epitaxy (MBE). In this study, we have further investigated the growth mechanism and structural defects in the self-organized InAs dots grown by chemical beam epitaxy (CBE) on a GaAs(100) substrate tilted by 2◦ toward (110). We found that there were no misfit dislocations in the InAs islands at 1 monolayer (ML). These InAs islands formed at a 1-ML coverage can be utilized as quantum dots.