Dynamics of electron-trapping materials for use in optoelectronic neurocomputing

An analytical model governing the dynamics of the trapped-electron density in electron-trapping materials (ETM’s) under simultaneous blue and near-IR illuminations is developed and studied in detail. Experimental results confirming the theoretical findings based on the model are presented, including a new method for experimentally determining a parameter of ETM’s, β, which describes the rate of decay of electron-trap density under constant IR illumination and which is obtained by measurement of the phase shift of the ETM response to IR illumination containing a sinusoidally modulated temporal component. Issues concerning the use of ETM’s as the synaptic connection weights in an optoelectronic neurocomputer are discussed; in particular, we propose a novel scheme for stabilizing the stored weight information in ETM’s during readout and learning; this scheme is based on the dynamic equilibrium of the trapped-electron density established by simultaneous blue and uniform IR illuminations. It is shown that ETM’s are ideally suited for realizing dense, modifiable synapses that have the wide dynamic range needed in implementing large-scale programmable optoelectronic neural networks of pulsed neurons.