MOVPE self-assembly and physical properties of free-standing III-V nanowires

Quasi 1-dimensional (quasi-1D) semiconductor nano-crystals (so-called nanowires) represent the forefront of today’s solid state physics and technology. These systems, having two of their dimensions comparable to the wavelengths of the electronic or phononic wavefunctions, are expected to show a variety of quantum confinement effects, such as density of state singularities, molecular-like states extending over large distances, high luminescence efficiencies and low lasing threshold: these properties have led to consider quasi-1D nanostructures as the fundamental building blocks for the realization of novel types of photonic and electronic nano-devices. The high surface-to-volume ratio of these nanostructures allows also to exploit the role of surface states (and their ambient-driven changes) in determining the nanostructure carrier transport and optical excitation/recombination properties. Despite the abovementioned attractive physical and technological assets, until very recently, not too many studies were performed on quasi-1D semiconductor systems, whilst twodimensional (2D) structures − quantum wells − have been under study already for more than three decades and quasi zero-dimensional (0D) objects − quantum dots, QDs − have been in the focus of researchers for nearly two decades. The main reason for such discrepancy resides in the difficulty of fabricating these nanostructures. In the recent past, quasi-1D nanostructures of III-V compound semiconductors have been generally grown on three-dimensional patterned (V-grooved) substrates (Kapon, 1994), or on high-index (such as {n11}-oriented) substrate planes (Notzel & Ploog, 2000). In such cases the major nanowire dimension was running in the substrate plane, with the consequence, however, that interactions with the substrate may dominate over 1D effects. These difficulties have lead to consider free-standing quasi-1D nano-crystals having negligible interaction with the substrate. Free-standing nanowires based on III-V compound semiconductors are nowadays in the focus of intense research activities throughout the world; this in reason of the prominent role of these compounds in the optoelectronic arena. Demonstration of resonant tunnelling diodes (Bjork et al. 2002; Wensorra et al., 2005), single electron transistors (Thelander et al., 2003; Thelander et al., 2005), and photodetectors (Pettersson et al., 2006) based on quasi-1D nanostructures of III-V compounds have been reported. Also intense single photon sources have been fabricated by embedding InGaP quantum dots in free-standing GaP nanowires Source: Nanowires, Book edited by: Paola Prete, ISBN 978-953-7619-79-4, pp. 414, March 2010, INTECH, Croatia, downloaded from SCIYO.COM