Electron Transport in Silicon Nanocrystal Devices: From Memory Applications to Silicon Photonics.

摘要

The push to integrate the realms of microelectronics and photonics on the silicon platform is currently lacking an efficient, electrically pumped silicon light source. One promising material system for photonics on the silicon platform is erbium-doped silicon nanoclusters (Er:Si-nc), which uses silicon nanoclusters to sensitize erbium ions in a SiO2 matrix. This medium can be pumped electrically, and this thesis focuses primarily on the electrical properties of Er:Si-nc films and their possible development as a silicon light source in the erbium emission band around 1.5 micrometers. Silicon nanocrystals can also be used as the floating gate in a flash memory device, and work is also presented examining charge transport in novel systems for flash memory applications.;To explore silicon nanocrystals as a potential replacement for metallic floating gates in flash memory, the charging dynamics in silicon nanocrystal films are first studied using UHV-AFM. This approach uses a non-contact AFM tip to locally charge a layer of nanocrystals. Subsequent imaging allows the injected charge to be observed in real time as it moves through the layer. Simulation of this interaction allows the quantication of the charge in the layer, where we find that each nanocrystal is only singly charged after injection, while holes are retained in the film for hours.;Work towards developing a dielectric stack with a voltage-tunable barrier is presented, with applications for flash memory and hyperspectral imaging. For hyperspectral imaging applications, film stacks containing various dielectrics are studied using I-V, TEM, and internal photoemission, with barrier tunability demonstrated in the Sc2O3/SiO2 system.;To study Er:Si-nc as a potential lasing medium for silicon photonics, a theoretical approach is presented where Er:Si-nc is the gain medium in a silicon slot waveguide. By accounting for the local density of optical states effect on the emitters, and carrier absorption due to electrical pumping, it is shown that a pulsed excitation method is needed to achieve gain in this system. A gain of up to 2 db/cm is predicted for an electrically pumped gain medium 50 nm thick. To test these predictions Er:Si-nc LEDs were fabricated and studied. Reactive oxygen sputtering is found to produce more robust films, and the electrical excitation cross section found is two orders of magnitude larger than the optical cross section. The fabricated devices exhibited low lifetimes and low current densities which prevent observation of gain, and the modeling is used to predict how the films must be improved to achieve gain and lasing in this system.