Simulation of polarization pinning effect in PZT/AlGaN/GaN metal-ferroelectric-semiconductor heterostructure

The influence of ferroelectric polarization on the electrical properties of PZT/AlGaN/GaN metal-ferroelectric-semiconductor (MFS) structure is investigated by capacitance-voltage (C-V) measurements. A distinct unsymmetrical shift of the C-V profile is observed that when swept positively, the C-V curve shifts to the right with increasing the negative starting voltage, while hardly move with different starting positive voltage when swept in the opposite direction. To understand this, a pinning effect model is developed and incorporated into self-consistent calculation, with taking history-dependent electric field effect into account. Owing to the strong polarization of underlying AlGaN layer, the switchable polarization of ferroelectric is initially pinned at -1.55 μC/cm² and does not change after positive bias operation. When increasing the negative sweeping voltage, the partially switched ferroelectric dipoles are increased, which results in the right-shift of the C-V curves, in agreement with the experiment.