Theoretical And Experimental Study On High Power GaN Based RF Optically Controlled Devices

The optoelectronic switching device is a kind of optoelectronic device based on the photoconductivity effect of semiconductor materials.A large number of photogenerated carriers are generated under high bias voltage through a certain energy laser irradiation,resulting in a rapid increase in electrical conductivity.After the laser is removed,the device can quickly recover to the high resistance state before,and realize the rapid opening and shutting down of the device.High power source devices made of optically-controlled semiconductor switching pulse generator with nanosecond or picosecond laser play an important role in the fields of intercommunication,satellite system,antenna and radar system,etc.At present,the common research in China is the use of silicon carbide substrate made of light-controlled devices,its power up to megawatt level while its response speed is nanosecond level.However,based on the current military direction and production and life of people's increasingly high performance requirements,silicon carbide devices are increasingly unable to meet.Because of this,as the third generation of gallium nitride semiconductor materials in the hot material,its forbidden band width,electronic saturated quick speed and high breakdown voltage,and become the next make attention focus in the optical devices,gallium nitride materials is considered application direction of light control device,it could theoretically obtain greater than silicon carbide device power and the response speed of the second order of magnitude,and up to the working frequency of GHz.Therefore,this paper carried out the theoretical analysis of GaN optical control device,and finally tested the performance of the device,and proved the feasibility of this direction.This article firstly introduces the basic principle of gallium nitride light-operated switch and insulation properties of gallium nitride material,and through the analysis of iron compensation in gallium nitride materials and the functional mechanism of photoelectric response characteristics,in order to make up for proper introduction of lattice defects in gan growth and unintended doped decided to compensate,and mixed with iron including gallium nitride iron is the deep acceptor level and major unintentional dopant oxygen is shallow level benefactor.Finally,the high resistance value in the dark state and the small resistance in the on state can be obtained.By Silvaco(TCAD)semiconductor simulation software based on drift-diffusion theory has carried on the finite element simulation analysis,completed the gallium nitride electric iron compensation device model,chose to include carrier mobility model,complex model,trap model,impact ionization model suitable physical models,such as managed to simulate the gallium nitride optical device,and analyzes the trap concentration,voltage,laser wavelength and optical device power density and electrode structure effects on optical device output response.Eventually found the response speed of the concentration of iron trap device play a crucial role,in order to ensure the photoconductive switch conduction ability,need to reduce the iron trap concentration to reduce conduction resistance,at the same time in order to carrier life faster response speed,need to appropriately increase the iron trap concentration,finally found that when the impurity concentration of iron doping concentration is greater than the unintentional 1-2 orders of magnitude,the formation of iron trap center can capture most of the shallow level impurity formation of the free carrier.When doping concentration is 1×10¹⁸ cm^-3 when dark resistivity of 8×10⁹?·cm.When the concentration of the iron trap is 1×10¹⁸ cm^-3 and the optical pulse is excited by 50 ps,the rise time of the electrical signal waveform is 25.94 ps and the fall time is 46.45 ps,which achieves an excellent response speed.At the same time,the power can reach 1.54×10⁷ W when the bias voltage of1×10⁴ V is applied,theoretically meeting the demand of high power.At the same time,the output response characteristics of iron-compensated gallium nitride device and vanadium-compensated silicon carbide device were compared under 50 ps laser multiple pulses.It is found that the response speed of gallium nitride device is better than that of silicon carbide,and the difference of the turn-off time between the two devices is more than 100 ps.Finally,the response characteristics of gallium nitride optical control device under multiple pulses are analyzed,and it is found that the performance of guide and break through under multiple pulses of 50 ps laser is better.When we want to continue to improve the working frequency,that is,shorten the optical pulse width again,we find that the device can not respond to the optical signal in time,and it will not be able to turn off.At present,the operating frequency of the device obtained by simulation is 5.1 GHz.After the simulation of the work done,the actual preparation of the gallium nitride iron compensation optical devices,using 10 mm×5 mm×0.4 mm size iron doped self supporting gallium nitride single crystal as the base,including compensation of iron concentration is 5×10¹⁸ cm^-3,the dark resistance rate is greater than 1×10⁹?·cm.And through the photoconductive testing platform for ultrashort optical pulse trigger signal response of the device under test,the final will be the results of simulation and experiment preparation,comparing the test results of samples found in the output response gallium nitride electric device performance is better than silicon carbide electric device,the device of gallium nitride composite broadening of 20-30 ps,and silicon carbide composite broadening of the device is 121.24 ps,of gallium nitride device of electric signal waveform optical pulse waveform following features than silicon carbide device,the former compound rate of 300%faster than the latter,the frequency of 2.25 GHz,It is higher than the 1.5 GHz level of silicon carbide photocontrolled devices.In order to further improve the working frequency of gallium nitride optical-controlled devices,it can be considered to increase the concentration of iron trap appropriately,or change the electrode to a grid electrode to increase the utilization of laser energy,or change the process from growing gallium nitride on silicon substrate to growing gallium nitride single crystal on sapphire substrate,so as to further reduce the dislocation density.The experimental data of gallium nitride light-controlled device to a certain extent verified the correctness of the simulation theory analysis,and also proved that as a new generation of light-controlled device material gallium nitride will play an important role in high power and high frequency.