Reliability Study Of GaN HEMTs In External Static Electric Field

The theoretical method GaN is a typical representative of the third generation semiconductor materials.With the commercial promotion of 5G,GaN based RF devices have entered a golden era of development and are widely used in the aerospace field.However,the development of GaN based high electron mobility transistors(GaN HEMTs)in the aerospace field cannot be separated from the reliability research in the space electric field or lightning.Therefore,studying the reliability of GaN HEMTs devices in space electrostatic fields is of great significance for promoting their production applications and career development in the aerospace field.When encountering space electrostatic fields or lightning,power electronic devices used in the aerospace field are basically in two states:no electrical bias state and with electrical bias state.The state of no electrical bias refers to the GaN HEMTs device having a drain source bias and a gate source bias of 0 bias.The GaN HEMTs device has no channel current,and the state of electrical bias indicates that the GaN HEMTs device has a drain source bias voltage.The gate source bias voltage can be 0 bias or other bias voltage,and the GaN HEMTs device has channel current.Polarization Coulomb Field scattering(PCF scattering)has an important impact on the performance of GaN HEMTs devices.In this paper,combined with the scattering theory of polarization Coulomb field,through the PCF scattering of GaN HEMTs devices AlGaN barrier layer caused by uneven strain distribution under the external electrostatic field,the impact of external electrostatic field on the electrical performance of GaN HEMTs devices is studied and analyzed.The specific research content is as follows:1)The Effect of External Electrostatic Field on the Strain Difference of Barrier Layer in AlGaN/GaN HEMTs Devices.Combining the scattering theory of polarized Coulomb field,using the inverse piezoelectric effect and the calculation formula of additional polarized charge density,the AlGaN/GaN HEMTs device under the action of an external electrostatic field can be quantitatively calculated.The additional polarized charge density corresponding to the strain difference between the AlGaN barrier layer under the gate and the AlGaN barrier layer of the gate source and the gate drain,the greater the strain difference,the higher the corresponding additional polarized charge density,The carrier mobility of polarized Coulomb field scattering can be calculated from the additional polarized charge density,and the influence of the external electrostatic field on the channel current of AlGaN/GaN HEMTs devices can be analyzed.It can be concluded that the strength of the external electrostatic field is closely related to the strain difference of the AlGaN barrier layer of the AlGaN/GaN HEMTs device corresponding to the additional polarization charge density.Just based on the correlation between the external electrostatic field and the strain difference of the AlGaN/GaN HEMTs device barrier layer,we can quantitatively study and analyze the impact of the external electrostatic field on the electrical characteristics of the AlGaN/GaN HEMTs device.2)The Effect of External Electrostatic Field on the Electrical Characteristics of AlGaN/GaN HEMTs Devices without Electrical Bias.The AlGaN/GaN HEMTs devices used in this section include two types of devices:gate length 4 um,gate width 104 um,gate source spacing 5 um,and gate drain spacing 30 um and 5 um,respectively.The electrostatic field intensity when an external electrostatic field is applied for 100s:-10 kV/cm,-5 kV/cm,5 kV/cm,10 kV/cm,20 kV/cm.The electrostatic field intensity at 10000s of external electrostatic field:-10 kV/cm,10 kV/cm.According to the electrical performance test results and the polarized Coulomb field scattering theory,the additional polarized charge density corresponding to the barrier layer strain difference of AlGaN/GaN HEMTs devices is calculated,and the carrier mobility of polarized Coulomb field scattering can be calculated from the additional polarized charge density.It is concluded that the applied positive electrostatic field makes the strain difference between the AlGaN barrier layer,the gate source and the gate drain AlGaN barrier layer under the gate of the non electrically biased AlGaN/GaN HEMTs device decrease,the additional polarization charge density under the gate decreases,the PCF scattering weakens,and the electron mobility under the gate increases,leading to the increase of the source leakage current.However,with the increase of the intensity of the positive electrostatic field,time,and the gate drain spacing of the device,the part of the increase of the source leakage current of the AlGaN/GaN HEMTs device gradually disappears;The applied negative electrostatic field increases the strain difference between the AlGaN barrier layer under the device gate and the gate source and the gate drain AlGaN barrier layer,increases the additional polarization charge density under the gate,enhances the PCF scattering,and decreases the electron mobility under the gate,resulting in a decrease in the source leakage current.With the increase of the negative electrostatic field strength,time,and the device gate drain spacing,the source leakage current of the AlGaN/GaN HEMTs device decreases more significantly.However,when the external static electric field intensity reaches 20 kV/cm or the external static electric field reaches-10kV/cm,10kV/cm for a time of 10000 seconds and is left standing for 24 hours,the absolute magnitude of the gate leakage current of the device will increase from 10-9A to 10-4A,resulting in more defects in the barrier layer below the gate and degradation of the device’s electrical characteristics.3)The Effect of External Electrostatic Field on the Electrical Characteristics of Electrically Biased AlGaN/GaN HEMTs Devices.The AlGaN/GaN HEMTs devices used in this experiment and the applied electrostatic field conditions are the same as when there is no electrical bias state.While applying the applied electrostatic field,an electrical bias of VDS=20V and VGS=0V is applied to the device with a gate drain spacing of 30 um;In order to ensure that the transverse electric field intensity(source drain channel direction)of different size device channels is consistent,an electrical bias of VDs=8V and VGs=0V is applied to the device with a gate drain spacing of 5 um.Based on the electrical performance test results and the polarization Coulomb field scattering theory,the strain difference of the device barrier layer under the above experimental conditions is calculated quantitatively,which corresponds to the additional polarization charge density and the electron mobility below the gate.Using the crosslight simulation software to compare the electric field strength in the vertical channel direction of the barrier layer under the gate of the electrically biased and non-electrically biased devices,it is concluded that the addition of a positive electrostatic field of 10kV/cm will make the capacitance value of the barrier layer under the gate of the electrically biased device become negative in the cut-off region and increase in the saturation region,indicating that it produces a defect trap,which traps electrons,resulting in a decrease in the source leakage current and an increase in the gate leakage current.And with the increase of the applied electrostatic field time or the increase of gate leakage distance,the degradation of the electrical characteristics of the device is more obvious.it is concluded that the external positive and negative electrostatic fields will increase the strain difference between the AlGaN barrier layer under the gate,the gate source and the gate drain AlGaN barrier layer,increase the additional polarization charge density below the gate,enhance the PCF scattering,and reduce the electron mobility below the gate,It leads to the decrease of source leakage current,and with the increase of the intensity of positive and negative electrostatic field,time and gate drain spacing,the additional polarization charge density under the gate of AlGaN/GaN HEMTs device increases,the PCF scattering increases,and the source leakage current decreases and increases;The capacitance voltage characteristic curve corresponding to the increase in gate leakage current of the device indicates that a large number of defects are generated in the barrier layer below the gate.Compared to the non electrically biased state,the applied electrostatic field of-10kV/cm and 10kV/cm was applied for a period of 10000 seconds before being left standing for 24 hours,which increased the absolute magnitude of gate leakage current in the electrically biased state device from 10-9A to 10-3A.At the same time,the gate lost its ability to regulate the channel current,and the electrical characteristics of the device deteriorated more severely.