Research On The Electrical Characteristics And Proton Irradiation Effects Of InP/InGaAs HBTs

Comparing with common bipolar transistor,InP/InGaAs HBT has attracted much attention due to its many unique advantages,such as wide bandgap,high saturation electron drift velocity,good conductivity and low noise,so that InP based HBTs can be widely applied in the space-based communication systems such as artificial satellites.Satellites orbiting will subject to a variety of high-energy charged particle radiation,which has a strong impact on these electronic devices,resulting in device failure or abnormality.To assess the device performance in a radiation environment,it is necessary to understand the radiation damage and the mechanism profoundly.Proton is one of the domain particles in space and this dissertation focuses on proton irradiation effect on the InP/InGaAs HBTs.In the dissertation,the irradiation effects on InP/InGaAs PN junction and HBTs are systematically studied experimentally and theoretically.Through the establishment of three-dimensional numerical simulation model,the characteristics of the InP/InGaAs HBTs devices under proton irradiation are simulated.The simulation results provide theoretical guidance to the irradiation experiments.Afterward,the irradiation fluence and energy of the experiment are determined.Based on the analysis of the DC and RF parameters radiation response,the physical mechanisms for the irradiated device degradation are revealed.It is the theoretical foundation for radiation hardening devices.The main studies and contributions are summarized as follows.1.Based on the SRIM simulation,the effects of proton irradiation on InP/InGaAs materials and heterostructures are studied with different fluences at the same energy and different energies at the same fluence in which simulation of different fluences is equivalent to a fluence cumulative process,while the concentration of the vacancy caused by proton irradiation increases with the increase in the incident proton fluence,but the type of vacancy does not change.The damage mechanism of different energies is different and the non-ionizing energy loss(NIEL)theory is used to explain the phenomenon.The NIEL decreases as the proton energy rises,resulting in lowering vacancy density,which well explain that the lower energy protons cause the more serious damage than the higher energy protons.The higher the incident energy,the larger the velocity of the proton.In other words,the smaller the interaction cross-section of the target is,the smaller the damage caused.2.Device model is a bridge connecting circuit design and device technology.An accurate device model can not only characterize the real work of the device,but also to predict the failure in the device under cruel conditions,such as radiation.Through the establishment of three-dimensional numerical simulation model,the characteristics of the InP/InGaAs HBTs devices under proton irradiation are simulated.The simulation results provide theoretical guidance to the irradiation experiments and determine the irradiation fluence and energy in the experiment.Firstly,the numerical simulation models of the InP/InGaAs HBTs device are established,which describe the device speed overshoot and ballistic transport effects correctly.Then the DC and RF characteristics under proton irradiation of different conditions are simulated.The simulation results provide a theoretical support for the irradiation experiments.To simplify the model,only a simple vacancy is put into Sentaurus trap model.3.The effects of proton irradiation on the InP/InGaAs heterostructures and InP/InGaAs HBTs are studied experimentally.The Current-Voltage(?-?)and Capacitance-Voltage(C-V)of the PN heterostructures and the DC and RF characteristics of devices were measured after the proton irradiation with the different energies and fluences.The interface state density of PN junction and the current gain and cutoff frequency degradation of InP/InGaAs HBTs after different proton fluences indicate that the higher-fluence proton causes more severe damage in the condition of same proton energy.However,the lower-energy protons cause much more damage in the condition of same proton fluence.The lower proton energy irradiation induces bigger interface state density and the more severe degradation of the current gain and the cutoff frequency as proton fluence fixed.4.Based on the Sentaurus device simulator and mathematical model,the degradation mechanism of proton radiation effect is discussed in detail.To simplify the simulation,only simple vacancies are put into Sentaurus trapping model.Measured and simulated results match well with each other and the degradation trends of the device parameters are consistent with experimental data.As the fluence of the incident proton increases,the degradation of current gain and cutoff frequency are serious.The degradations induced by 3MeV proton irradiation are much more serious than that of 10MeV.That is to say,more energy is deposited by 3 MeV in the active device region.The collector current changes slightly and the base current increases greatly,therefore leading to current gain dropped down.The increase of base current is caused by the recombination center in the base-emitter space-charge region and at its periphery,while the decrease of cutoff frequency is caused by the increase of the resistance and the capacitance and the decrease of the carrier mobility.In a word,the degradation of the device characteristics is induced by displacement damage after irradiation.