Strong interfacial coupling effects of ferroelectric polarization with two-dimensional electron gas in BaTiO₃/MgO/AlGaN/GaN/Si heterostructures

BaTiO₃ (BTO)/MgO/GaN and BTO/MgO/AlGaN/GaN ferroelectric-semiconductor heterostructures with ultrathin MgO buffer layers were constructed by pulsed laser deposition, and an interfacial coupling mechanism between the ferroelectric polarization of BTO and two-dimensional electron gas (2DEG) at the AlGaN/GaN interface was explored for enhancement-mode high electron mobility transistors (HEMTs). The upward ferroelectric self-polarization characteristic of BTO integrated on GaN and AlGaN/GaN was induced by the suspect space-charge region at the BTO/GaN interface, which was directly confirmed by piezoresponse force microscopy. Thus, the 2DEG density at the AlGaN/GaN interface was spontaneously reduced by the ferroelectric field effect of BTO with upward polarization, and the threshold voltage was prominently increased to -0.4 V. More significantly, interfacial coupling correlation between the ferroelectric polarization state and 2DEG was established. Via modulating the ferroelectric polarization state of BTO, continuous regulation of the threshold voltage from -0.4 V to +3.2 V and a large counter-clockwise memory window of 2.2 V were demonstrated. A BTO/MgO/AlGaN/GaN heterostructure could be a promising candidate for GaN-based enhancement-mode HEMTs and non-volatile memory devices.