The Simulation Of InAs/AlSb HEMT At Cryogenic Temperature

As the represent of Sb-based compound semiconductor devices, InAs/AlSb HEMTs is characterized by the high electron mobility,high peak velocity, as well as by the very high conduction band discontinuity in the In As/AlSb quantum well. This, combined with the narrow gap of the InAs channel,makes the InAs/AlSb HEMT a great potential device for high speed and low dissipation applications,which trigger a research upsurge of international science workers,and it is expected to become the future mainstream research direction of HEMT device.In recent years, a large number of reports have appeared about the material, the devices’ performance and the circuits application.However,due to our under development on InAs/AlSb HEMTs, the device now is still on fabrication in China, leading that the investigation of the device characteristics can be only by simulation. Therefore,this thesis can fill the blank in research on simulation of the InAs/AlSb HEMT and have a great significance on basic study of the device.In this thesis, the main work is the cryogenic simulation of the InAs/AlSb HEMT. First, the simulation structure as the upper AlSb barrier with Te modulation doped to obtain a compromise between the electron mobility(17300 cm2/V·s)and 2DEG concentration(2.5×1012cm-2)at room temperature has been determined.Second, the performance of electron mobility and concentration under cryogenic temperature has been studied by the Hall experiment under cryogenic temperature(77K~300K).Compared with at 300 K, the mobility increases significantly by two and a half times to 45000 cm2/V·s at 77 K.Meanwhile, the concentration of the 2DEG decreases slightly,from 2×1012cm-2 at 300 K to 1.7×1012cm-2 at 77 K. The results present the influence of temperature on various scattering mechanisms for electron movement, such as ionized impurity scattering, lattice vibration scattering and interface roughness scattering by theoretical formula.It is concluded that lattice vibration scattering reduces as temperature decreasing,wheras the other scattering mechanisms do not change with temperature, and in different temperature range, the main scattering mechanism is not the same one. At ultra low temperature, the electron mobility is mainly determined by the ionized impurity scattering and interface roughness scattering mechanism. At a certain temperature,which is determined by the doping impurity concentration, space width, interface roughness parameters of AlSb/InAs quantum wells, the acoustic phonon scattering comprising of the deformation potential acoustic and piezoelectric acoustic scattering becomes into the main restriction for the electron mobity. At higher temperature, the polar optical phonon scattering mainly restricts the mobility. The 2DEG is formed by the ionized impurity of the wide gap AlSb, moving into the InAs channel, which decreases as the ionization reduces due to the decrease of temperature. Third, the simulation in this thesis adopts ISE TCAD software, utilizing the Hydrodynamic model, high filed saturation mobility model and SRH recombination model, the parameters of the mobility model are modified to approach the realisitic data by the experiment results of the Hall experiment. Finally, different temperature nodes(the lowest temperature is down to 100 K to ensure convergence)are setting to simulate the electrical characteristics of the device at different temperature. Compared with the normal temperature result, the conclusions are obtained as following: 1) the mobility increases as the temperature decreasing, which lead to the the saturation drain current at 100 K increasing to two times larger than the current at 300 K, and the source drain resistance decreasing. 2) the phonon scattering suppression and the lower transit time at low temperature leads to an increasing transconductance gm. 3) the threshold voltage VT increases due to the decrease of electron concentration at low temperature. 4)the gate leakage current Ig decreases by the reason that the schottky reverseing saturation current and the impact ionization holes current decrease at cryogenic temperature. 5)the intrinsic frequency fT and the maximum oscillation frequency fmax increases by the cause that the transconductance increases, and the source drain resistance, the gate source capacitance and the source drain capacitance decrease.