Study On Structure And Technology Of GaN Based Terahertz Gunn Diode

Terahertz?THZ?is located between the microwave and the far-infrared.The electromagnetic waves on both sides of the terahertz wave have been developed and applied earlier.The terahertz technology has developed rapidly in recent years and has been highly valued by international powers.As one of the terahertz solid state source devices,the Gunn Diode has high operating frequency,high reliability,low noise,wide frequency band,long working life and is expected to be high.The Gunn diodes working with traditional semiconductor materials can achieve limited operating frequency,low output power and conversion efficiency,and the unique advantages of the wide bandgap semiconductor material GaN have been proved to significantly improve the performance of Gunn diodes.However,there is still no report about the realization of the GaN-based terahertz source Gunn diode process.How to promote the rapid formation of GaN-based Gunn diode dipole domains to increase the operating frequency and improve the conversion efficiency has been a hot topic.In this paper,three kinds of device structures are designed and simulated separately to improve the output frequency and conversion efficiency of the device.For the first time,the fabrication of GaN-based terahertz source Gunn diodes was attempted,and two device structures in the design were prepared.The specific research content is as follows:According to the working mechanism of Gunn diodes,the design standard parameters of Gunn diodes for GaN materials are given.Based on the above parameters,a GaN Gunn diode with a Notch structure is designed for the problem of the long dead zone length and low output frequency present in Gunn diodes.The design parameters are given and the feasibility of the design is proved theoretically.According to the design structure,electrical simulation verification was performed.The electric field distribution diagram,electron concentration distribution diagram,DC characteristic diagram,oscillation waveform and spectrum analysis diagram were obtained.The oscillation frequency was 212.5 GHz,the conversion efficiency was 4.8%,and the DC power consumption was 2323.8 mW.For the problem that the operating frequency of the above devices is not high enough and the DC power consumption is large,a Gunn diode with an AlGaN emitter layer is designed,that is,an AlGaN emitter layer is added between the cathode ohmic contact layer and the transit layer.The design parameters are given and verified by simulation.We find that the output oscillation is stable when the applied voltage is 43V.The operating frequency is350GHz,the conversion efficiency is 6%,and the DC power consumption is 1709.68mW.The comparison found that the design can improve the frequency of about 140GHz,increase the conversion efficiency by 1.2%,and reduce the DC power consumption by600mW,which proves that our design is effective.As a terahertz radiation source,conversion efficiency is a very important measure.In order to increase the conversion efficiency of the device,we inserted AlGaN/GaN between the cathode ohmic contact and the transit layer.The simulation results show that the device output frequency is 187.71GHz,the conversion efficiency is 6.4%,and the power consumption is 1983mW.The comparison shows that the conversion efficiency has indeed been improved,but the operating frequency has decreased.Therefore,it is concluded that for the design of terahertz source devices,the three indexes of operating frequency,conversion efficiency,and output power need to be comprehensively considered,and a single index cannot be pursued blindly.Based on the above research conclusions,considering that the difficulty of the third device manufacturing process and the performance of the device have yet to be further improved,we only prepared the first two device structures above.Including the growth of the epitaxial layer material,the design of the Pad test structure and the preparation of the device.The GaN Notch layer Gunn diode anode ohmic contact specific contact resistivity is 3.03×10^-6?.cm²,and the cathode ohmic contact specific contact resistivity is 6.9×10^-6?.cm².The ohmic contact specific contact resistivity of the AlGaN Notch layer Gunn diode are1.081×10^-4?.cm² and 7.05×10^-5?.cm².There is no negative resistance characteristic by the DC test.The main reason for the analysis is that the designed Pad test structure has a small gap,insufficient metal thickness in the process.A solution was given to the above problems and a test pattern was redesigned to prepare the device.