| In recent years,with the development of social economy,semiconductor devices have played an important role in various industrial applications.However,traditional Si-based devices have gradually been unable to meet many application needs due to their performance limitations.More and more research is focused on developing new semiconductor materials to further improve device performance.As a novel semiconductor material,Ga N has become one of research hotspots due to its superior material properties such as high breakdown field strength,high electron mobility and high operating temperature.Ga N material and devices have been included into many major strategic R&D plans in some countries,and their market share has also been growing at a high rate with bright future prospects..Compared with lateral power devices,vertical power devices could achieve higher breakdown voltage?BV?,higher current density,improved heat dissipation without increasing chip size.As a result,vertical power devices are being extensively studied.The p-i-n power diode plays an important role in many fields including rectification,power supply and transient voltage suppression circuit,etc.Among them,high avalanche capability of the diode plays an important role in protecting the circuit against issues such as transient surges and other safety problems.The focus of this work is to design and study Ga N-based p-i-n power diodes with high performance and avalanche characteristics.First,we successfully designed and prepared Ga N-based p-i-n vertical power diodes with avalanche characteristics.However,the device still suffers from problems such as relatively low breakdown voltage and serious device degradation due to field crowding effect.Next,a Ga N-based p-i-n power diode with an inclined mesa termination structure was designed and fabricated.Experiments show that the new mesa termination structure significantly improves the performance of the device.In addition,this thesis also conducts a preliminary comparative analysis on the effects of two commonly used passivation layers,Si O2 and Si Nx,on the electrical performance of the device.The main research work of this thesis is summarized as follows:1.A Ga N-based p-i-n power diode with avalanche capability has been designed,fabricated and tested successfully.The breakdown voltage of the device derived from I-V measurement is?355V,the on-resistance is 2.848 m?·cm2,and the turn-on voltage is 3.4V.We characterized the avalanche characteristics of the device in a UIS circuit.It is found that the device could withstand more than100,000 times of avalanche breakdown events at low avalanche energy.With the increase of avalanche energy,the number of avalanche breakdowns that the device can withstand significantly decreases,and the device shows obvious degradation.We have studied the degradation mechanism of avalanche process systematically,including electroluminescence test analysis,Silvaco TCAD simulation analysis,pulse I-V test and scanning electron microscopy analysis.It is found that the degradation of the device is due to permanent thermal damage caused by non-uniform field strength distribution within the device during the avalanche process.2.Based on the degradation mechanism study of the Ga N-based p-i-n power diode with vertical mesa structure,we designed and fabricated a novel Ga N vertical power diode with an inclined mesa termination structure,and have compared their performance.It is found that the breakdown voltage of the new device is increased from 355V to 480V,and there is no obvious degradation after repeated I-V tests.The on-resistance is 1.0m?·cm2.Compared with the localized hot carrier light emission pattern of the vertical mesa device,the inclined mesa device shows uniform light emission across the device mesa.In addition,the avalanche breakdown voltage obtained in UIS test is up to 714V and the maximum breakdown current is up to 5.68A.Moreover,the device exhibits multiple-self-quenching phenomenon at high avalanche energies.Finally,it is concluded that the inclined mesa termination structure can well alleviate electric field accumulation effect around mesa edge of the device,thereby improves device performance.3.The effects of Si O2 and Si Nx passivation layer on avalanche performance of Ga N p-i-n power diodes with an inclined mesa termination were preliminarily compared and studied.Based on I-V characteristics,the breakdown voltage of the Si O2-passivation diode is found?480V,which is considerably higher than that of the Si Nx-passivated device??352V?.The hot carrier luminescence measurement of avalanche process indicates that the Si O2-passivated diode shows more uniform light emission across device mesa than that of the Si Nx-passivated diode.The poor performance of the Si Nx-passivated diode is attributed to the fixed positive charges existing within the Si Nx passivation film.These fixed positive charges cause enhanced electrical field crowding effect around device edge and then degrade the device avalanche capability. |
PDF Full Text Request