Building a depletion-region width modulation model and realizing memory characteristics in PN heterostructure devices

Memristive systems have potential applications in nonvolatile memories and even unexplored functionalities in electronics. However, progress has been delayed by difficulties in the controllability of memory behaviors and the dependence on material conductivity. Considering this, a new depletion-region width modulation model is proposed to realize and explain memory characteristics. The coexistence of memristive and memcapacitive behaviors is demonstrated in p-CuAlO₂/n-ZnO, p⁺-Si/n-ZnO and p-NiO/n-ZnO heterostructure devices. A high external electric field induces the migration of oxygen ions and electrons/holes between the p-type and n-type semiconductor layers. It can regulate the oxygen vacancy concentration of the n-type side and cation vacancy concentration of the p-type side, changing the depletion-region width and modulating device conductivity and capacitance. Several essential synaptic functions were accurately imitated, including spike-timing-dependent plasticity (STDP) and "learning-experience" behaviors. This work provides new opportunities in fabricating a memristor and memcapacitor based on a PN heterostructure for synaptic simulation.