Investigations On The Electrical Properties Of 4H-SiC Power MOSFET Under Mechanical Strains

4H-SiC metal-oxide-semiconductor field-effect transistors（MOSFETs）are becoming promising candidates in power electronics applications,owing to the high switching capability and low energy loss.The low channel mobility limits the performance of 4H-SiC power MOSFETs due to the high density of the Si O₂/4H-SiC interface states.Most of the existing reports focused on the process optimizations to enhance the channel mobility by decreasing the interface state density.On the other hand,the band structure modulation induced by the strain can also improve carrier mobility,known as strain technology.The strain technology has been widely used in the SiCMOS and Si power devices for the performance boost.The mechanical strains affect the 4H-SiC quite differently because it is a hexagonal crystal,according to theoretical studies.Thus,it is essential to comprehensively investigate the electrical properties of the 4H-SiC power MOSFETs under both biaxial and uniaxial mechanical strains.Firstly,we obtain the influence of mechanical strain on 4H SiC energy band structure through the first principle from which we extract the energy band structure and effective mass of electrons of4H-SiC under strain.Then,the influence of strain on the distribution of electrons between different conduction valleys in the inversion layer has been calculated by self-consistently solving the Schrodinger Poisson equation.In the following,we reveal the influence of various forms of mechanical strain on the effective mass of electrons in the inversion layer.The results show that biaxial strain has little effect on the inversion layer’s electron effective mass and uniaxial strain will effectively modulate the electron effective mass of the inversion layer.Secondly,the effects of six forms of mechanical strain（biaxial,parallel and perpendicular uniaxial tensile and compressive strains）on the electrical characteristics of 4H SiC Power MOSFET are investigated thoroughly.The results show that when the gate voltage is 4V,the current capacity of the device can be increased by about 10%under both 300MPa parallel,perpendicular and biaxial compressive strains.However,with the increase of gate voltage,the effect of strain on the current capability of the device decreases sharply.At the same time,mechanical strain will change the threshold of the device.Under the same gate driving voltage,biaxial strain has nearly no effect on the output current of the device while uniaxial compressive strain can be used to increase the output current while uniaxial tensile strain decreases the output current.Finally,the change in the average effective mass of carriers in different channel directions in the（0001）SiC MOSFET inversion layer under strain conditions is predicted by using theoretical calculations.Our calculation results show that when the channel direction and the strain direction are both reasonable,uniaxial tensile strain or uniaxial compressive strain can improve the electron mobility of the inversion layer.The general guidance for the application of strain technology in 4H-SiC power MOSFET is brought up.