Optical Communication using Nanowires and Molecular Memory Systems

Sammanfattning: Neuromorphic computational networks, inspired by biological neural networks, provide a possible way of lowering computational energy cost, while at the same time allowing for much more sophisticated devices capable of real-time inferences and learning. Since simulating artificial neural networks on conventional computers is particularly inefficient, the development of neuromorphic devices is strongly motivated as the reliance on AI-models increases. A neuromorphic device inspired by the insect brain and capable of navigation, has previously been proposed, where optically communicating semiconductor nanowires form the basis of the network, and a state-of-the-art molecular dye exhibiting reversible bleaching provides the synaptic weights. This Thesis explores integral sub-components of that device, contributing concrete results towards its realization. The molecular dye is combined with a nanowire array solar cell device in order to fashion a high-sensitivity nanoscale device with integrated memory functionality. Compared to purely electronic "memory-resistors", this approach features a greater potential for multiplexing due to the wavelength sensitivity of different molecular dye species. The effects of dye concentration, deposition method, film thickness and annealing on the molecular photophysics are explored, identifying starting points for a design optimization process. A high degree of repeatability of the memory functionality is shown, even at prolonged high-intensity illumination. Additionally, opto-electronic single nanowire ciruits, where the open-circuit voltage generated by the illumination of a p-i-n InP nanowire gates an InAs nanowire, are characterized in high-precision Optical Beam Induced Current experiments. Depending on the orientation of the InP nanowire, increase or decrease of the InAs conductance is achieved, suggesting that the circuits could be implemented as excitatory and inhibitory nodes in a nanowire-based neural network. Finally, the optical emission of single InP nanowire devices, previously shown to be able to communicate with each other, is experimentally confirmed and studied.