  This work reports a nanostructure resonant tunnelling diode-photodetector
(RTD-PD) device and demonstrates its operation as a controllable,
optically-triggered excitable spike generator. The top contact layer of the
device is designed with a nanopillar structure 500 nm in diameter) to restrain
the injection current, yielding therefore lower energy operation for spike
generation. We demonstrate experimentally the deterministic optical triggering
of controllable and repeatable neuron-like spike patterns in the nanostructure
RTD-PDs. Moreover, we show the device's ability to deliver spiking responses
when biased in both regions adjacent to the negative differential conductance
(NDC) region, the so-called 'peak' and 'valley' points of the current-voltage
($I$-$V$) characteristic. This work also demonstrates experimentally key
neuron-like dynamical features in the nanostructure RTD-PD, such as a
well-defined threshold (in input optical intensity) for spike firing, as well
as the presence of spike firing refractory time. The optoelectronic and
chip-scale character of the proposed system together with the deterministic,
repeatable and well controllable nature of the optically-elicited spiking
responses render this nanostructure RTD-PD element as a highly promising
solution for high-speed, energy-efficient optoelectronic artificial spiking
neurons for novel light-enabled neuromorphic computing hardware.
