Synthesis and characterization of III-V semiconductor nanocrystals

In the size regime where the diameter of a semiconductor particle is smaller than the bulk exciton diameter for the respective material, the cluster exhibits quantum confinement effects where many of its properties are determined by the size of the particle. Properties that are affected are wide ranging, from optical properties such as the energy of absorption or emission to structural properties including changes in melting point or solid-solid phase transition pressures.; Traditionally, the development of such nanocrystal systems has concentrated on II-VI semiconductors, particularly CdSe and CdS, as the ability to synthesize high quality nanocrystals of these materials has become highly developed. The more technologically relevant III-V semiconductors have proven to be more difficult to prepare as nanocrystals due to the nature of their chemistry and this thesis deals with the development and characterization of several III-V semiconductor nanocrystal systems, particularly InP, InAs, and GaAs.; The InP and InAs nanocrystals are synthesized using the solution phase reaction of InCl{dollar}sb3{dollar} and E(Si(CH{dollar}sb3)sb3)sb3{dollar} (E = P, As) in trioctylphosphine oxide (TOPO) or trioctylphosphine (TOP). The nanocrystals can be isolated in sizes ranging from 20 to 70 A in diameter and consist of crystalline cores with the same structure as the corresponding bulk material and surfaces which are terminated by coordinating molecules. The nanocrystals are soluble in a variety of organic solvents. Structurally, the nanocrystals have been studied using powder XRD, TEM, and XPS. The optical properties have been examined using absorption and emission spectroscopy as well as transient holeburning experiments. The nanocrystals exhibit quantum confinement effects as evidenced by size dependent shifts in both absorption and emission well to the blue of the bulk band gap of the material.; The development of GaAs nanocrystals has been limited by an inability to produce discrete, soluble particles as the growing domains agglomerate; however, the size of the crystalline domain can be controlled. Solid-state MAS NMR and powder XRD measurements have been carried out to gain a better understanding of the morphology of these samples and there is evidence that the nanocrystalline material consists of fused particle-like material.