Ni/Au/n-GaN肖特基二极管可导位错的电学模型

可导线性位错被普遍认为是GaN基器件泄漏电流的主要输运通道,但其精细的电学模型目前仍不清楚.鉴于此,本文基于对GaN肖特基二极管的电流输运机制分析提出可导位错的物理模型,重点强调:1)位于位错中心的深能级受主态(主要Ga空位)电离后库仑势较高,理论上对泄漏电流没有贡献; 2)位错周围的高浓度浅能级施主态电离后能形成势垒高度较低的薄表面耗尽层,可引发显著隧穿电流,成为主要漏电通道;3)并非传统N空位,认为O替代N所形成的浅能级施主缺陷应是引发漏电的主要电学态,其热激活能约为47.5 meV.本工作亦有助于理解其他GaN器件的电流输运和电学退化行为.

Physical model of conductive dislocations in GaN Schottky diodes

The excessive leakage current, commonly observed in GaN Schottky barrier diodes (SBDs), severely degrades device electrical performance and long-term reliability. This leakage current relates to the dislocation-related conductive states as observed by microscopy. Up to now, various transport models have been proposed to explain the leakage current, but none of them can clearly describe in physics the electrically active dislocations. One just equivalently regarded the electric defect as a continuum conductive defect state within the forbidden band, without considering the microscopic electrical properties of the dislocations. Here in this work, on the basis of numerical simulation, we propose a phenomenological model for the electrically active dislocations to explain the leakage conduction of the GaN Schottky diodes, which are fabricated on a freestanding bulk substrate n-GaN wafer with a low dislocation density of about 1.3×10⁶ cm^-2. In this model, we emphasize that the acceptor-like traps at the core of dislocations could capture electrons from the nearby donor-like traps, resulting in a high Coulomb potential and a decreasing potential at the donor-like sites. In this case, the core of dislocations would be negatively charged, and not favor the electron transport due to a strong Coulomb scattering effect, while the shallow donor-like traps around them can lead to a significant tunneling leakage component. This model is consistent well with the common observation of the localized currents at the edges of the surface V-defects in GaN. The shallow donor-like defects in GaN induced by the substitution of oxygen for nitrogen (O_N), rather than the nitrogen vacancies, act as the dominant donor impurities responsible for the significant leakage current, which has a density on the order of 10¹⁸ cm^-3 and an activation energy of about 47.5 meV, because 1) it has been demonstrated that during the material growth, oxygen diffusion toward the surface pits of dislocations via nitrogen vacancies could produce an exponentially decayed distribution with a density of at least 10¹⁷ cm^-3, in good agreement with our derivation; 2) by the first principle calculation, the thermal activation energy of the oxygen-related donors is determined to be about 50 meV, which is very close to our derived 47.5 meV. According to this model, we propose that reducing the O_N defect density during device growth is a feasible method to suppress the high leakage current in GaN-based SBDs. In addition, this study can also improve our understanding of the leakage current in other GaN-based devices.