Based On Gan Hemt Heterojunction Devices Gold Half Contact New Structure Of The Research

GaN HEMTs is an excellent candidate for RF and microwave application,power electronics and other important area,which is due to its wide gap,high breakdown voltage,high operating temperature,high power density,high2DEG density in channel.In this paper,we focus on the the processing and characterization of gate Schottky contact and source(drain) ohmic contact of HEMTs.First,based on the conventional Ti/Al/Ni/Au ohmic contact,we used the multi-layer structure Ti/Al/Ti/Al/Ti/Al/Ti/Al/Ni/Au found that the Ti/Al ratio is the key factor of ohmic contact resistance and surface morphology:the Al content contribute to the reaction of Ti and AlGaN reducing the contact resistance;Al content too much will lead to the increase of the Al-Au/Al-Ni alloy,exacerbated the generation of surface bulge.For this reason we proposed a new variable Ti/Al ratio multi-layer ohmic contact structure. Experiments show the minimum resistance0.018Ω.mm obtained,the ohmic contact edge is smooth and no cracks due to the less surface bulge after annealing.By means of TEM/EDX analysis, we demonstrated that the new structure can conducive to the reaction in the semiconductor, improve the surface morphology simultaneously. In the processing of the ohmic contact,we resolve the problem of temperature distribution on sample and controlling the thickness of multi-layer ultra-thin metal in evaporation.Finally,bace on the conventional Schottky contact.we found thermal oxide treatment can enhance HEMTs performance,then presented a new type of Schottky gate technology.By changing the thermal oxidation process parameters systematically studied the oxidation temperature on the saturation drain current, breakdown voltage, gate leakage current and other device characteristic.The analysis shows that the thermal oxide treatment can passivate the surface state in the barrier layer. Experimental results show that the samples in the450℃oxygen for20minutes,the reverse gate leakage current reduced by two orders of magnitude,15%increasing in transconductance,and three times higher breakdown voltage as compared to the conventional Schottky HEMTs.