Investigation Of Low Resistance Ohmic Contact Based On AlGaN/GaN Heterojunction

With the improvement of the level of science and technology,the communication industry has developed rapidly.The relationship between semiconductor technology and wireless communication,radar communication,aerospace and space communication is becoming more and more closely.At present,the first,second generation of semiconductor materials can not meet the demand of higher frequency and higher power electronic devices.The third generation semiconductor materials based on GaN have superior performance under the condition of high frequency and high power,witch obvious advantages in terms of microwave power devices.GaN is a new high-gap compound semiconductor material,which has the characteristics such as wide band gap,high breakdown voltage,high saturated electron speed and high thermal conductivity.The AlGaN/GaN heterostructure can produce 2DEG(Two Dimensional Electron Gas)with high electron concentration.AlGaN/GaN HEMT(High Electron Mobility Transistor)has obvious advantages in the fields of high frequency,high power,high efficiency and low noise.It can meet the increasing power and linearity requirements of the power amplifier,which is according with the development trend of the miniaturization and high reliability of the communication system.In this paper,we have studied the low resistance ohmic contact of AlGaN/GaN heterojunction.The main results are as follows:1.The Ohmic contact optimization by thermal annealing doping.The feasibility of doping to semiconductor by thermal annealing process was verified by experiments.And the annealing process parameters suitable for the doping of AlGaN barrier layers by Si and Ge semiconductors were determined.Then,several samples were doped with different doping schemes.The device was made and the ohmic contact characteristics of the device are tested and analy zed.The contact resistance and surface morphology of AlGaN/GaN HEMT doped by Ge semiconductor are obviously improved.2.The Ohmic contact optimization by etching region of source and drain.The source and drain region on the AlGaN barrier layer of the sample was etched by different etching time.By testing the etching depth of the test piece and the size of the ohmic contact of the sample,it is concluded that etching the thickness of AlGaN barrier layer can reduce the ohmic contact resistance of the device although the 2DEG is damaged.If the etching depth is too deep,the2DEG of the AlGaN/GaN heterojunction will be seriously damaged,which results greatly degradation of ohmic contact performance.3.The integration of two ohmic contact optimization schemes.We intergrated two ideas of ohmic contact optimization,and desinged the appropriate ohmic contact production plan.A high quality ohmic contact device with low contact resistance and good surface morphology is obtained,which contact resistance is reduced by 54%.Then the electrical characteristics of devices are characterized and analyzed.The electrical characteristics of AlGaN/GaN HEMT are analyzed,and the ability of the devices to be applied in high frequency and high power is evaluated comprehensively.In this thesis,ohmic contact is optimized through the above research,which lays the foundation for the development of microwave and millimeter wave devices.