n型GaN过渡族难熔金属欧姆电极对比

Comparative study of n-GaN transition group refractory metal Ohmic electrode

研究了过渡族难熔金属Hf体系Hf/Al电极在不同退火条件下与In型GaN的欧姆接触特性,并与Ti基Ti/Al电极进行了对比.采用圆点型传输线模型测量了Hf/Al和Ti/Al电极的比接触电阻率.结果表明,同等退火条件下的Hf/Al电极,相比于传统Ti/Al电极,展现出了更加优越的欧姆接触性能.在N2氛围中低温650℃条件下退火60 s的Hf/Al电极得到了最低的比接触电阻率为4.28×10^-5Ω·cm^2.本文还利用深度剖析的俄歇电子能谱仪对电极的结构特性进行了分析,经历退火的Hf/Al电极样品中金属与金属,金属与GaN之间发生了相互扩散.对Hf/Al,Ti/Al电极表面进行了扫描电子显微镜表征,两种电极均表现出颗粒状的粗糙表面.

Ohmic contact is directly related to the performance of GaN device and is one of the important factors affecting device performance.In recent years,many research groups have studied the electrode materials and annealing conditions of n-type GaN Ohmic contacts.In this paper,the ohmic contact properties and structural characteristics of the Hf/Al electrode of a transition group metal refractory metal Hf system under different annealing conditions are studied,and compared with those of the Ti-based ohmic contact Ti/Al electrode.The specific contact resistivity of each electrode is measured by a dot-type transmission line model,and the structural characteristics of the electrode are analyzed by using an Auger electron spectrometer which can be analyzed in depth.The results show that the Hf/Al electrode under the same annealing condition exhibits superior ohmic contact performance compared with the conventional Ti/Al electrode.At the same time,the lowest specific contact resistivity of the Hf/Al electrode annealed in an N2 atmosphere at a low temperature of 650 ℃ for 60 s is 4.28×10^-5 Ω·cm^2.The in-depth analysis of Auger electron spectrum shows that the Hf/Al electrode has a solid phase reaction with the n-type GaN material.In addition,the cross section of each electrode is observed by auger electron spectroscopy.In the Hf/Al electrode sample,the metal-semiconductor interface does not show voids after annealing.This situation occurs at the sample interface where the Ti/Al electrode is annealed at 650 ℃ for 60 s in N2 atmosphere and annealed at 850 ℃ for 30 s in N2 atmosphere.This is one of the reasons why the Hf/Al electrode sample has a lower specific contact resistivity.At the same time,the surface of Hf/Al electrode and Ti/Al electrode annealed at 850 ℃ are characterized by using scanning electron microscope.It is found that the surfaces of both electrodes subject to high temperature annealing show a similar granular rough surface,and this rough surface has a certain influence on the electrical properties of the GaN device.The rough surface formed by the electrode under such high temperature annealing conditions is an urgent problem to be solved in the future research.In summary,the study in this paper indicates the use of Hf/Al to form an ohmic contact with n-type GaN under a low temperature annealing condition.