UC San Diego

This dissertation investigates charge carriers in nanoscale devices through theoretical and numerical means. First we study indirect excitons in coupled quantum wells (CQW), which exhibit evidence of a quantum mechanical state of matter. We examine whether these excitons form bound state biexcitons in CQW. It is proven that stable biexcitons exist only when the distance between electron and hole layers is smaller than a certain critical threshold. Numerical results for the biexciton binding energies are obtained using the stochastic variational method and compared with the analytical asymptotics. The threshold interlayer separation and its uncertainty are estimated. Furthermore, models are proposed to explain recent exciton experiments involving electrostatic traps. These models prove qualitatively correct and allow for estimation of the diffusion coefficient and interaction strength in CQW systems. In addition, we study organic field-effect transistors (FETs). Recent infrared imaging studies of the charge density profile in poly(3- hexylthiophene) (P3HT) FETs show evidence of a density- dependent mobility. A model is presented that concludes the mobility of P3HT has a power-law density dependence, which is consistent with the activated transport in disorder-induced tails of the density of states.