Analysis Of Irradiation-induced Defects In InP/InGaAs Heterostructure

InP/InGaAs heterojunction bipolar transistors?HBTs?are being widely used in high frequency,radio frequency?RF?and microwave applications.Compared with InP HBTs,InP HBTs integrated with Si-CMOS have better performance and wider applications.However,for space applications,these devices and circuits are inevitably faced with a critical radiation environment,which induces radiation reliability and further limits the development of InP HBT.These device degradations are generally attributed to the defects introduced by irradiation in InP/InGaAs heterojunction.As these defects may create deep level traps in bandgap,and thus affecting device performance.But unfortunately,due to the complexity of the structure of heterojunction in InP/InGaAs HBT,it is difficult to directly characterize the defects in heterojunction.Many works reported have mainly focused on the electrical characteristics changes before and after irradiation,while the quantitative descriptions of the deep level traps after irradiation have not been shown.Furthermore,how these deep level traps respond in device degradation mechanism remain unclear.Therefore,this work aims at the characterization of deep level traps induced by irradiation in InP/InGaAs heterojunction and analyzes their impact on device degradations of InP HBT.Firstly,the quantitative characterizations of deep level trap induced by 3 MeV proton irradiation in InP/InGaAs heterostructure were performed by deep level transient spectroscopy?DLTS?and C-V measurements.Specifically,a simpler InP/InGaAs heterostructure based on the BE junction of InP/InGaAs HBT was designed for DLTS measurements.In the study of proton irradiation,the impact of radiation fluences on deep level traps were studied by varing the fluences from 1×10¹² p/cm² to 5×10¹² p/cm².Results show that an energy level at E_c-0.28 eV has been detected by DLTS in pre-irradiation samples,which may be introduced by process.But new energy levels at E_c-0.36 eV and E_c-0.37 eV have been examined after proton irradiation.Therefore,it is concluded that the energy level is further away from the bottom of the conduction band,and the energy level becomes deeper.At the same time,the interface trap densities were extracted by C-V measurements.It is found that the interface trap densities increasing with irradiation fluences.The SRIM simulation results reveal that traps induced by radiation are likely to be associated with In vacancy.Morever,the impacts of deep level traps on the I-V and C-V characteristics of InP/InGaAs heterojunction were investigated by adding trap models into TCAD.The simulation results are in good agreement with the experimental results.With the increase of energy level and interface trap densities,the reverse leakage current,the recombination current and the junction capacitance increase,while the turn-on voltage decreases.The deep level traps cause a significant increase of the base current of InP/InGaAs HBT and decrease of the current gain?,but the compensation voltage V_offset and knee-point voltage V_knee almost keep unchanged.More specifically,the gain degradation mechanisms caused by the surface trap,the interface trap and the bulk trap were also discussed.It is found that the traps at the base/passivation surface and BE junction are the main causes of degradation of ?.