Heteroepitaxy of Hf_0.5Zr_0.5O₂ ferroelectric gate layer on AlGaN/GaN towards normally-off HEMTs

Ferroelectric gate High Electron Mobility Transistors (HEMTs) stands out as a promising route for normally-off HEMTs. HEMTs based on perovskite ferroelectrics, however, suffer from low threshold voltage, electrical instability, and CMOS process incompatibility. In this work, fluorite Hf_0.5Zr_0.5O₂ (HZO) was designed to serve as ferroelectric gate layer for normally-off HEMTs, and HZO/MgO/AlGaN/GaN/Si ferroelectric-semiconductor heterostructure was constructed by pulsed laser deposition. The epitaxial relationship was revealed to be [112¯](1 1 1) HZO//[112¯](1 1 1) MgO//[101¯0](0002) GaN, and corresponding domain matching mechanism was determined as 6a_MgO=5a_HZO. Strong coupling effect between ferroelectric polarization of HZO and two-dimensional electron gas (2DEG) at AlGaN/GaN interface was confirmed by continuous modulation of threshold voltage from −3.8 V to +3.2 V through regulating polarization state of 15 nm HZO. Moreover, relatively weak depolarization effect of HZO on AlGaN/GaN was observed, which was crucial for device electrical stability. In addition, ultrahigh threshold voltage of +5.5 V was detected in designed heterostructure with 50 nm HZO. Our work demonstrates that epitaxial HZO ferroelectric gate layer on AlGaN/GaN possesses high threshold voltage, good device electrical stability and great semiconductor process compatibility, emerging as great potential for developing and miniaturizing high-performance normally-off HEMTs.