InAs nanostructures on GaAs
InAs on GaAs provides an opportunity to prepare unique devices due to 1) the narrow bandgap of InAs, 2) different surface Fermi-level location, and 3) lattice mismatch. Historically, while InAs was an attractive material for realizing surface two-dimensional electron gas or optoelectronic devices that works in the infrared, its incorporation into Si or GaAs based structures was found to be a difficult task. However, the situation changed after people realized that the non-planar structures that form upon epitaxial growth by molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD), due to the 7% lattice mismatch, could be used as quantum dots (QDs). This occurs through a process known as Stranski-Krastanov (SK) mode, where the initial InAs layer grown on GaAs(001) is strained, but sustain a planar structure, but convert into three-dimensional (3D) structure when the total deposition exceeds what is called the "critical thickness" (1.7 monolayer in this case). The SK QDs have been extensively studied, and today, lasers, photodetectors/sensors, solar cells, etc., are realized using InAs QDs. Nevertheless, since the SK growth is a self-organizing process, limitation remains in the control of the QD size, morphology, and consequently the optical and electronic properties. Further, we have addressed that for the application of the so-called interband solar cells, disk-like shaped structures, which we call the quantum well islands (QWIs) could be advantageous over QDs. We have been investigating both the control and mechanisms of InAs nanostructure growth on GaAs(001). In the present talk, we would like to provide an overview together with some of our latest results.