講演情報
[15p-W8E_101-13]第一原理計算によるGaN–SiO2界面のホールトラップ研究
〇趙 元晟1,2,3、白石 賢二1,4、押山 淳1,4 (1.名大IMASS、2.(株)QUEMIX、3.東大院理物理、4.東北大CIES)
キーワード：
半導体、MOS、ホールトラップ
GaN-based metal–oxide semiconductor field-effect transistors (MOSFETs) are promising for future power devices. However, the emergence of hole traps at the interface between GaN and gate oxides such as SiO2 is one of the greatest obstacles to high-performance GaN MOSFETs. During the fabrication of GaN/SiO2 MOS structure, a GaOx layer with 1~2 nm thickness is commonly believed to spontaneously form at the interface. In this work, we have successfully forged realistic GaN/GaOx/SiO2 models for both c and m interfacial planes without any dangling bonds by melt-quench molecular dynamics simulations with machine-learned interatomic potential. The structures are then carefully optimized and investigated using density functional theory (DFT) with accurate HSE exchange-correlation functional. It is revealed that although dangling bonds are absent, when one electron is removed from the system, the hole can still be trapped at three types of positions: (1) 2 or 3-coordinated O atoms in GaOx layer, (2) O atoms in Si–O–Ga structure, and (3) N atoms exactly at the interface. In all cases, upon hole trapping, the bond length at the center O/N atom increases significantly, raising electrostatic potential and causing an unoccupied electronic state to be raised to the GaN band gap. The thermodynamic transition level ε(+/0) for all the traps are found to be generally located at 0~1 eV above GaN valence band maximum. These results show that the hole traps at the interface are likely to be intrinsic to the GaOx interfacial layer and might not be easily eliminated. We also discuss the possible mechanism of hole trap suppression by heavy Mg doping as found experimentally.