Simulation Research On Breakdown Characteristics Of Vertical Diamond Avalanche Diode

The diamond material has a theoretical breakdown field strength of 10MV/cm,excellent carrier mobility（electron 4500 cm²/Vs,hole 3800 cm²/Vs）,saturation drift velocity（electron 1.5×10⁷cm/s,hole 1.1×10⁷cm/s）,and small dielectric constant（5.45）,highest thermal conductivity in nature（2200W/m-K）.Therefore,diamond materials have broad application prospects in the fields of high frequency,high temperature and high pressure.Pulse power technology is widely used,and pulse switch is the key technology.Conventional switching devices,such as silicon and gallium arsenide,have low voltage tolerance,slow rise and limited power flow,which limits the development of pulse power technology.The diamond based avalanche diode has the advantages of high voltage,fast time response and excellent heat dissipation,and is suitable for pulse power switch applications.However,it is difficult for diamond N type doping to realize the PN junction or PIN structure of conventional silicon based avalanche diode because of the difficulty of diamond based avalanche diode.Based on the above background,a new type of metal-p doped-metal（M-P-M）vertical diamond avalanche diode structure is proposed in this paper,the electrical characteristics of avalanches are studied by using the simulation software of Silvaco-ATLAS device.The detailed research work is as follows.1、The static characteristics of vertical structure diamond avalanche diode are analyzed and discussed.In this paper,the simulated diamond avalanche diode is vertical structure,the lower cathode is lightly doped p layer,the barrier height is set at 1.5 e V,and the lower anode is heavily doped p layer.SRH model,parallel electric field dependent model,concentration dependent model and collision ionization model are used in the simulation.The impact ionization model uses Watanabe,Kamakura and Hiraiwa models respectively.The M-P-M vertical diamond avalanche diode structure has avalanche breakdown under the three impact ionization models,the collision ionization of Kamakura et al and Hiraiwa et al takes place in the whole P^-region,while the model collision ionization proposed by Watanabe et al only takes place in the nearly half P^-region below the cathode.The avalanche breakdown voltage increases slowly with the increase of diamond avalanche diode temperature from300K to 600K with a gradient of 50K.2、The structure of the device is optimized according to the characteristics of avalanche breakdown voltage.The length of the P^-region of the Avalanche diode increases to 4μm,6μm,8μm and 10μm,and the avalanche breakdown voltage increases gradually.The avalanche breakdown voltage increases obviously when the P^-region length changes from4μm to 8μm,in the range from 8μm to 10μm,the increase of avalanche breakdown voltage decreases,and the doping concentrations in the P^-region are 1×10¹⁵cm^-3、5×10¹⁵cm^-3、2×10¹⁶cm^-3、5×10¹⁶cm^-3 and 1×10¹⁷cm^-3,respectively,the avalanche breakdown voltage decreases obviously when the doping concentration changes from 1×10¹⁷cm^-3 to 2×10¹⁶cm^-3,but the doping concentration in the P^-region is 1×10¹⁵cm^-3 and 5×10¹⁵cm^-3,the increasing range of avalanche breakdown voltage of diode devices is obviously reduced.3、Based on the M-P-M vertical diamond avalanche diode structure designed in this paper,the delayed breakdown characteristics are investigated.The rise time of the output voltage is 0.26 ns,which is 48%higher than that of the input voltage.In the delayed breakdown process of diode devices,the resistance change inside the device can be divided into two parts,one is the sharp reduction of resistance in the avalanche breakdown process,the other is that the internal resistance of the device remains unchanged after avalanche breakdown.4、The delayed breakdown characteristics of M-P-M vertical diamond avalanche diode structure are optimized according to the thickness and doping concentration of the P^-region and the load resistance.The P^-layer thickness changes to 4μm,5μm and 6μm,and the output voltage amplitude decreases,but the rise time of output voltage decreases.When the doping concentration of P^-layer is changed,it is 2×10¹⁵cm^-3、7×10¹⁵cm^-3、3×10¹⁶cm^-3、5×10¹⁶cm^-3 and 7×10¹⁶cm^-3,,respectively,but when the doping concentration is 2×10¹⁵cm^-3 and 7×10¹⁵cm^-3,the rise time of the output voltage is almost the same.In the range of load resistance R from 10Ωto 350Ω,the output voltage amplitude decreases gradually,and the rise time of diode output voltage has a minimum value in this range.