Heteroepitaxy of Hf0.5Zr0.5O2 ferroelectric gate layer on AlGaN/GaN towards normally-off HEMTs

Fluorite Hf 0.5 Zr 0.5 O 2 ferroelectric film is integrated with AlGaN/GaN sucessfully and the HEMT device performance goes beyond those compsed of pervokite ferroelectric layer. • Ferroelectric gate High Electron Mobility Transistors (HEMTs) stands out as a promising route for normally-off HEMTs. In last decade, the ferroelectric doped-HfO 2 , which shows ferroelectricity at nanoscale and has great advantages of Silicon compatibility , simplicity of chemistry , and low toxicity , has sparked great interest. In this work, Hf 0.5 Zr 0.5 O 2 (HZO) has been successfully adopted as ferroelectric gate layer to integrate with AlGaN/GaN heterostructure with epitaxial relationship clearly revealed. Moreover, the threshold voltage can be effectively modulated by the ferroelectric polarization of HZO, demonstrating that HZO thin film could serve as prominent gate layer to develop high-performance and miniaturized ferroelectric-gated 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 0.5 Zr 0.5 O 2 (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 [11 2 ¯ ](111) HZO // [11 2 ¯ ](111) MgO // [10 1 ¯ 0](0002) GaN, and corresponding domain matching mechanism was determined as 6 a MgO = 5 a 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 15nm 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.