Study On The Influence Of Uniaxial Stress In Different Directions On The Performance Of AlGaN/GaN HEMT Devices

Al GaN/GaN High Electron Mobility Transistor(HEMT)has high carrier concentration and high mobility,and shows excellent performance in the fields of high frequency and high power.On the one hand,HEMT devices may be affected by external stresses during actual use,affecting their characteristics.It is very important to study the mechanism of the effect of stress on the HEMT device.On the other hand,related literature shows that the density of the energy band and the two-dimensional electron gas will change with the polarization charge of the piezoelectric effect.The HEMT device can be used as a pressure sensor,so it is very important to expand and deepen the application of HEMT devices.In this paper,the effect of uniaxial plane stress in different directions on the performance of Al GaN/GaN HEMT devices is mainly studied.First,the residual stress of the sample without stress is evaluated.Then,the four-point bending device was used to apply a stress from 0 ° to 90 ° relative to the channel direction.The experimental results of the uniaxial stress in different directions on the output characteristics and C–V characteristics of the sample were compared.The characteristics and pulse I–V characteristics were measured,the trap state inside the sample was studied,and the effect of uniaxial stress in different directions on the trap state of the sample was studied in depth.The details are as follows:(1)The change of the output characteristics of the sample when the direction of the strain changes from 0 ° to 90 ° relative to the channel direction is measured.The output current decreases with increasing tensile strain,because the drain current decreases with increasing tensile strain.(2)The measurement results of the C–V curve show that for the same strain level,the density of the two-dimensional electron gas(2DEG)decreases monotonously to different degrees according to the strain direction.Transforming strains in different directions into equivalent strains parallel to the channel direction shows that the theoretical calculation change of 2DEG density is consistent with the experimental measurement results.(3)Calculated the corresponding electron mobility,which shows a downward trend under tensile strain.Under uniaxial strain,the change of effective mass in different directions is different,and the strain effect on the effective mass of electrons in GaN may also depend on the direction of strain.In addition,under tensile strain,the conduction band of GaN slopes upward,which causes the 2DEG density to decrease,and the 2DEG moves toward the interface of the Al GaN/GaN heterojunction.The scattering effect can be enhanced,such as interface roughness scattering,which results in a decrease in the average free time of electrons and thus a decrease in electron mobility.(4)In addition,using the transient current method,it can be determined that due to the effect of tensile strain,the detrapping time constant increases,which is attributed to the trap level moving away from the conduction band.