Overbias and Quantum Tunneling in Light-Emitting Memristors

A nanoscale dielectric gap clamped between two metal electrodes may undergo a large resistance change from insulating to highly conducting upon applying an electrical stress. This sudden resistive switching is largely exploited in memristors for emulating synapses in neuromorphic neural networks. Here, we show that volatile resistive switching can be accompanied by a release of electromagnetic radiation spanning the visible spectral region. Of note, we find that the spectrum is characterized by photon energies exceeding the maximum kinetic energy of electrons provided by the switching voltage. This so-called overbias emission can be described self-consistently by a thermal radiation model featuring an out-of-equilibrium electron distribution generated in the device with an effective temperature exceeding 2000 K. The emitted spectrum is understood in terms of hot electrons radiatively decaying to resonant optical modes occurring in a nanoscale SiO2 matrix located between two Ag electrodes. We further show that the same device can sustain different emission mechanisms depending on the nature, the intricacy and historicity of its memristive gap. Specifically, when operated in a nonvolatile state, we identify inelastic electron tunneling as an additional process providing photon emission from the device. The correlation between resistive switching and the onset of light emission in atomic scale photonic memristor brings alternative venues to generate light on chip and their exploitation in optical interconnects. Photons emitted during memristive switching can also be monitored to follow the neural activation pathways in memristor-based networks.