氮化物HFET器件二维输运瓶颈与极化工程

Gallium nitride, as one of the most attractive material of the third generation wide bandgap semiconductor, exhibit great potential for high-power microwave applications and have been extensively developed during the last decades. More recently, with rapid improvement of long-term reliability, the application process of GaN power devices and MMIC is speeding up, which plays a more and more imporpant role in improving the performance and functionality of national defence and economy. Although the extraordinary performance of GaN HFETs over those on traditional compound semiconductor,the physics behind the transport mechanism in the low dimensional III-nitrides heterostructure devices is still not completely understood. The advantage of the superior properties of GaN, such as high electron saturation velocity and high breakdown voltage, have not been fully exploited. Further effort are being done on the investigation of the function of polarization effect, which is unique property of III-nitrides, in the two-dimensional carrier transport of heterostructure. Deep comprehension on the relationship between the material properties and the transport mechanism in low-dimentional heterostructure turns out to be crucial for the development of next generation GaN devices and integrated circuits. This project aims at understanding the physics behind the electrical characteristics in low-dimentional III-nitrides heterosturcture. The two-dimensional carrier transport properties would be extensivly investigated with different quantum well structure, subband distribution and the electron state under different operation. The saturation mechanism of the electron velocity in low-dimensional heterostructure, which is distinctly different to that in the bulk material, would be disclosed. Based on the polarization and two-dimensional energy band engineering, optimum GaN-based heterostructure with improved electron saturation velocity will be designed, by which a GaN HFET device with ft≥200GHz is being developed. This work would be of great importance for expansion of III-nitride applications and provide a strong physical foundation for the development of new generaton high frequency device and circuits technology.

作为第三代宽禁带半导体材料的代表，GaN在微波大功率应用领域发挥着独特优势并取得长足的发展。特别在近几年随着可靠性技术的突破，GaN功率器件实用化进程不断加快，对国民经济发展和国防能力能升的促进作用正日益显现。尽管如此，GaN体材料高电子饱和漂移速度和高击穿电压的优势尚未完全开发，其特有的极化效应以及体材料低维化引起的诸多深层次物理问题仍有待解决，深刻认识GaN基低维异质结构材料与器件特性之间的内在关系成为突破下一代GaN电子器件技术的瓶颈。本项目通过深入开展GaN基异质结构器件微观输运特性与材料极化、量子阱结构、子带分布、电子状态的关系研究，揭示二维载流子饱和漂移速度限制机理，并基于极化工程和二维能带裁剪设计，建立GaN高电子漂移速度异质结构材料和器件设计方法，实现ft≥200GHz的GaN HFET 器件，为完善氮化物半导体材料应用体系、发展新一代高频电子器件和电路奠定物理基础。

毫米波/亚毫米波器件是雷达、成像、精确制导及高速数据通讯系统的核心元器件，也是国际固态微波功率器件领域的技术制高点。作为第三代半导体微波功率器件，GaN HEMT具有输出功率密度大、工作电压高、耐高温、抗辐照等优点，成为新一代固态微波功率器件的主导型器件，特别在毫米波及以上频段，与GaAs、InP基器件相比，GaN HEMT器件的优势更加明显。进一步提高器件频率和功率，不仅需要材料外延、器件工艺等技术水平的提升，更需要对GaN材料特性和器件载流子强场输运、射频跨导崩塌等一系列物理问题有深刻的认识，通过理论创新充分挖掘GaN材料高频、大功率的本征潜力。.本项目重点研究了极化掺杂的GaN HEMT器件中二维电子气浓度、迁移率、饱和漂移速度及二维电子状态与异质结构能带和器件性能之间的关系，揭示了高频GaN HEMT器件中载流子微观输运机理，提出了新的局域电子气模型，从新的角度阐明了GaN高频器件射频跨导崩塌现象，发现了超薄势垒超高频器件不能输出有效功率的本质原因；揭示限制电子饱和漂移速度的物理机制，设计出具有低热声子效应的双沟道异质结构；突破了GaN高频器件结构设计和纳米栅工艺等关键技术，分别研制出截止频率ft达300GHz以及最高振荡频率fmax超过400GHz的高频器件。.本项目研究该成果对深入III族氮化物低维物理研究、揭示纳米栅长高频器件高场微观输运机理，发展新一代GaN高频电子器件具有重要的科学意义和实际价值。所建立的高频器件结构设计方法可从基础材料层面提高GaN HEMT器件在高频下功率输出能力，在以雷达为代表的信息化装备中具有广阔的应用前景。