基于极化调控技术的氮化镓增强型HEMT器件

Normally-off GaN-based HEMTs have many advantages over the traditional normally-on devices, including low unnecessary power assumption, circuit design simplicity, high system stability, and operation safety. In this project, LiNbO3 ferroelectric gate is designed to deplete 2DEG and achieve normally-off device operation, according to the theory of polarization engineering. Compared with the techniques available for normally-off devices, polarization engineering is superior due to the damage-free 2DEG transport property and compatible process with insulated-gate devices. The ferroelectric gate dielectric is prepared using transfer method, which can realize very thin high-quality films because of the reduced lattice mismatch and thermal diffusion compared with the direct deposition methods. Interfacial layer is designed to improve the interface quality between ferroelectric film and nitride layers, and recess etching to enhance the polarization engineering. In addition, the modeling of polarization engineering for ferroelectric gate heterostructures and HEMTs will be carried out in this project, to help the design and fabrication of polarization-control devices. The study in this project is of great importance for GaN-based power switches, in terms of both theory and application.

GaN基增强型HEMT器件与耗尽型器件相比，可以降低关态功耗和电路设计复杂度，提高系统稳定性和安全性。本课题拟基于极化调控原理，采用一维铁电体LiNbO3铁电调控层实现对沟道2DEG的耗尽和增强型器件应用。与现有增强型器件相比，该极化调控技术可以保证异质结2DEG的完整性，避免沟道输运特性损伤，并且可以采用绝缘栅器件兼容工艺完成器件制作。采用转移技术制备铁电调控层，与直接生长方法相比，可以避免界面晶格失配和热扩散的影响，实现较薄的高质量铁电薄膜制备。采用界面缓冲层技术改善铁电调控层与氮化物材料之间的界面质量，并在栅下区域适度刻蚀凹槽，提高铁电调控层的极化调控效果。本课题在实现高质量铁电薄膜制备和增强型器件的同时，拟建立铁电介质栅异质结构和增强型器件的极化调控模型，为极化调控器件的设计和研制提供理论依据。本课题对于推动GaN功率开关器件的发展具有重要的理论意义和应用价值。

异质结材料强的极化效应使得GaN基HEMT通常为耗尽型器件，在电路应用中不仅会引起额外的关态功耗和电路设计复杂度，还会影响系统稳定性和安全性。本项目旨在通过氮化镓HEMT器件的极化调控理论和铁电介质栅器件结构与关键工艺研究，解决氮化镓增强型HEMT器件难以实现的问题。围绕项目研究目标，按计划开展了氮化镓器件界面缺陷理论及改善技术、氮化镓器件上高质量铁电薄膜制备工艺、氮化镓增强型HEMT器件设计与制作、铁电介质栅氮化镓器件的极化调控规律与机制等方面的研究。取得的重要结果与数据包括：1）以铁电介质栅氮化镓HEMT器件的界面可靠性需求为牵引目标，进一步完善了氮化镓功率器件界面缺陷理论及界面调控方法体系；2）以凹槽铁电介质栅氮化镓HEMT器件设计及界面可靠性需求为牵引，开发了氮化镓增强型MOSFET器件界面修复工艺；3）引入界面缓冲层技术，通过直接生长技术和转移方法在氮化镓HEMT器件上分别制备了厚度为30nm和20nm的高质量铁电薄膜；4）基于两种铁电薄膜制备技术分别研制了铁电介质栅氮化镓增强型HEMT器件，器件表现出优良的沟道输运特性和开关态性能，器件整体性能达到国际先进水平开；5）基于研制的铁电介质栅氮化镓增强型HEMT器件，深入开展了器件极化调控机理和阈值电压调控模型研究，形成系统性的氮化镓器件极化调控理论报告成果。本项目基于极化调控理论和铁电介质栅器件结构，对异质结沟道载流子实现了无损调控，解决了预期研究的相关关键科学与技术问题，为极化调控器件的设计和研制提供了理论依据。本项目对于推动GaN功率开关器件的发展具有重要的理论意义和应用价值。