Semiconductor nanostructures have unique optical and electronic properties that have inspired research into their technological applications and basic science. This thesis presents approaches to the fabrication and characterization of optoelectronic devices incorporating individual semiconductor nanostructures.

Nanowires of the II-VI semiconductors CdSe and CdS were synthesized using nanoparticle-catalysed solution-liquid-solid growth. Single-component nanowires and heterostructure nanowires with axial compositional modulation were generated using this method. Individual nanowires and nanocrystals were then incorporated into devices with a three-terminal field-effect transistor geometry.

An experimental platform was developed which allows for simultaneous electrical characterization of devices and measurement of their optical properties. This setup enables the measurement of spatially and spectrally resolved electroluminescence (EL) and photoluminescence (PL) from individual nanostructures and nanostructure devices. It also allows the measurement of photon coincidence histograms for emitted light and the acquisition of photocurrent images via laser scanning microscopy.

Electroluminescence was observed from individual CdSe nanocrystals contacted by gold electrodes. Concomitant transport measurements at low temperature showed clear evidence of Coulomb blockade at low bias voltage, with light only emitted from devices exhibiting asymmetric tunnel couplings between the nanocrystal and electrodes. Combined analyses of the data indicate that the resistances of the tunnel barriers are bias voltage dependent and that light emission results from the inelastic scattering of tunneling electrons.

Three-terminal devices incorporating individual CdSe nanoNvires exhibited EL localized near the positively-biased electrode. Characterization of these devices by scanning photocurrent microscopy (SPCM) and Kelvin probe microscopy (KPM) indicates that while there are n-type Schottky barriers at the metal-semiconductor interface at low bias, the potential profile of the device at high bias cannot be described using an ideal back-to-back Schottky diode model. Instead, accumulation of charge carriers gives rise to an abrupt potential drop near the positively-biased electrode where EL is observed. This large potential drop leads to impact ionization, producing electronhole pairs that recombine to emit light.

Preliminary work on CdS/CdSe bilayer nanowires contacted individually by the conducting polymer poly(3-hexylthiophene) (P3HT) indicates that this hybrid structure may provide a route to light emission with a narrow spectral distribution by inducing band-edge recombination of carriers. Because of widespread interest in the photovoltaic properties of nanocrystal/P3HT devices, initial photocurrent measurements on the nanowire/P3HT interface are also being explored. These measurements may provide a means to study charge separation efficiencies, which are difficult to determine in ensemble devices.