| The research and application of gallium nitride(GaN)material is the frontier and hotspot of semiconductor research at present.The third generation of wide band gap semiconductor material GaN has outstanding advantages such as high electron drift velocity,strong critical breakdown field,high thermal conductivity,small dielectric constant and good chemical stability.It meets the working requirements of high voltage,high power,high frequency,high temperature,high linearity and high efficiency semiconductor devices and has broad application prospects and research value in the preparation and development of optoelectronic devices and light emitting devices.The important parameters of carrier transport characteristics in semiconductors are the key parameters for controlling the quality,performance and reliability of microelectronic devices.Therefore,studying the transport properties of carriers in gallium nitride material and the physical scattering mechanisms of analytical material are of great significance for improving gallium nitride semiconductor devices.In this paper,the multi-particle Monte Carlo simulation of the transport properties of photo-gener ated carriers in gallium nitride high-voltage photoconductive materials at 300K temperature is used.The calculation assume that the ionization impurity concentratiol of the material is 1×1016cm-3,the wavelength of the Gaussian light pulse is 532nm and the corresponding photon energy is 2.33eV,which satisfies the basic condition of two-photon absorption.The band structure adopt a three-energy valley model including the main valley ?1 and two satellite valleys(?2?L-M),and considers six scattering mechanisms that play an important role in semiconductor transport characteristics:ionized impurities scattering,acoustic wave piezoelectric scattering and acoustic waveform potential scattering by elastic scattering treated;polar optical wave scattering,optical waveform potential scattering and valley scattering by inelastic scattering treated.Through the selection of physical models and parameters related to band structures and scattering mechanisms,selection of appropriate electric field adjustment time step,initial distribution of photo-generated carriers,free flight and scattering processing and charge distribution and electric field calculation investigated the transport properties of photo-generated carriers in gallium nitride high voltage photoconductive materials.Through the study of the average drift velocity-time relationship of photo-generated carriers in gallium nitride high voltage photoconductive material under different applied electric fields found that the drift velocity of photo-generated carriers exhibit overshoot when the applied electric field is 200kV/cm and the peak velocity reaches 4.8×107cm/s.When the applied electric field is 300kV/cm,the drift velocity of photo-generated carriers is very obvious overshoot phenomenon,the peak speed can reach 7.4×107cm/s.The larger the applied electric field,the faster the drift speed of the photo-generated carriers increases and the final steady state drift speed also increases.Under the different applied electric fields,the steady-state drift velocity of photo-generated carriers in gallium nitride is much smaller than the transient drift velocity,indicating that the transport properties of materials are mainly affected by transient transport.Through the study of the occupation rate and average energy of photo-generated carriers in each valley of gallium nitride high voltage photoconductive materials found that most photo-generated carriers transition to the first satellite valley T2 when the applied electric field is 300kV/cm.And the applied electric field increases to 500kV/cm,most of the photo-generated carriers transition to the higher second satellite valley L-M.The photo-generated carriers gain sufficient energy under the applied electric field to cause a negative differential mobility effect from the main valley transition to the satellite valley.In addition,the greater effective mass of the satellite valley and the non-parabolic nature of the energy band will also have a corresponding impact on the negative differential mobility. |
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