| Spacecraft are exposed to a complex radiation environment in outer space.The electronic device failure due to radiation particles becomes an important factor limiting the time of normal operation for spacecraft.With the development of semiconductor technology,GaN-based semiconductor devices have been considered by researchers.The excellent electrical properties(high frequency,high power density and high switching speed,etc.)and radiation resistance of GaN-based devices are well suited for use in space communication system and power supply system of spacecraft.In this paper,the proton irradiation effect on the switching characteristics(subthreshold swing and transconductance)of AlGaN/GaN HEMT(high electron mobility transistor)is investigated from both material and device levels using a combination of experiments and simulations.The main results of this study are as following:(1)Preparation for AlGaN/GaN HEMT proton irradiation experiments.The advantages and disadvantages of different substrate materials and growth techniques for heterostructure material are compared.And a suitable substrate material(Si)and growth technique(Metal-Organic Chemical Vapor Deposition,MOCVD)are selected to prepare the heterostructure materials and devices for irradiation experiments.The radiation environment in outer space is analyzed.The main source of radiation(proton)is chosen as the particle for the irradiation experiments,and the overall experimental outline is developed.(2)The AlGaN/GaN heterostructure materials were exposed to protons with different energies and characterized before and after irradiation using Hall measurements.Both the electron density and mobility in the heterostructure material have a decrease after irradiation and the extent of variation increases with proton energy decreasing.The degradation is attributed to the proton induced vacancy defects inside the materials.Combined with SRIM simulation for further analysis of material degradation,the results show that protons induce multiple defects,with the dominant defect being the Gavacancies.As the proton energy increases,the number of vacancies at the AlGaN/GaN interface gradually decreases.And the main distribution of displacement damage is gradually moving away from the AlGaN/GaN interface.This is the main reason for the degradation of materials decreases with proton energy increasing.(3)The proton irradiation influence on the subthreshold swing and transconductance of AlGaN/GaN HEMTs is studied in terms of device size.The AlGaN/GaN HEMTs with different gate-drain distances were prepared and exposed to 0.4 Me V protons.And there are differences in variation of subthreshold swing and maximum transconductance between devices with different gate-drain distances.For the devices with larger gate-drain distance,the subthreshold swing has no change obviously and maximum transconductance gets increased after irradiation.The subthreshold swing and maximum transconductance of devices with smaller gate-drain distance both decreased obviously.Extraction of the transport characteristics reveals that these phenomena are due to proton induced change in polarization scattering effect,which is closely related to device size.(4)The proton irradiation influence on the subthreshold swing and transconductance of AlGaN/GaN HEMTs is studied in terms of proton energy.The devices with two different gate-drain distances,which have obvious changes in transport characteristics after 0.4 Me V proton irradiation,were prepared and exposed to 0.6 Me V and 1 Me V protons.It is found that the differences in subthreshold swing and transconductance between the device with different sizes at low proton energies still exist.And the differences gradually disappear with proton energy increasing.By extracting the transport characteristics and combining them with SRIM simulations,it is concluded that as the proton energy increases,the effect of vacancy defects on the carriers in the channel is gradually weakened,and the magnitude of the weakening or enhancement of the polarization scattering effect is gradually reduced.Finally,according to the results of the study,the corresponding irradiation reinforcement is proposed. |
