Simulation of Radiation Effects in AlGaN/GaN HEMTs

Abstract

AlGaN/GaN high electron mobility transistors (HEMTs) are desirable for space applications because of their relative radiation hardness. Predictive modeling of these devices is therefore desired; however, physics-based models accounting for radiation-induced degradation are incomplete. In this work, we show that a partially ionized impurity scattering mobility model can explain the observed reduction in mobility. Electrostatic changes can be explained by confinement of negative charge near the 2DEG in the GaN buffer layer. Simulation results from FLOODS (a TCAD simulator) demonstrate that partial ionization of donor traps is responsible for this phenomenon. Compensation of the acceptor traps by the ionized donors in the GaN confine the acceptor traps (negative space charge) to a thin layer near the AlGan/GaN interface. The simulation results show that near equal concentrations of acceptor traps and donor traps of 1 × 10 17 cm −3 can account for the performance degradation of HEMTs given 5 MeV proton radiation at a fluence of 2 × 10 14 cm −2 . Our results imply that device performance can be accurately simulated by simultaneously accounting for mobility and electrostatic degradation in TCAD solvers using the presented approach. Over the last ten years, there has been a significant amount of research evaluating the effects of radiation on the performance of GaNbased high electron mobility transistors (HEMTs). In general, protonbased radiation damage to AlGaN/GaN HEMTs results in mobility degradation and an increase in the threshold voltage, both of which lead to reductions in peak transconductance and drain current. 1-17The change in mobility has the potential to be greater in magnitude than changes observed in the other parameters. For example Lu et al. measured 40% reduction in mobility and only a 0.1V shift (3% change) in threshold voltage and 13% reduction in drain saturation current for a specific case of proton radiation.14 Additionally, Gaudreau measured a decrease in carrier concentration by a factor of two and a decrease in mobility by a factor of a thousand in response to proton radiation. 1More insight is needed with respect to how radiation defects affect both electron mobility and device electrostatics. Confirmed physics-based models will allow prediction of device performance that depends on the coupled interplay of both parameters.Changes in device performance are primarily attributed to charged point defects, including vacancies and interstitials created by the radiation damage.18 While both donor-and acceptor-like traps are expected to be created during irradiation, it has been shown that a majority of acceptor-like traps are necessary to explain the positive shifts in threshold voltage. [6][7][8]19 Coulombic interaction with charged, radiationinduced defect states has been suggested as the physical reason for mobility reduction. 3,5,6,20 However preliminary calculations show that the concentration of ionized traps responsible for mobility reduction is incompatible with the reduced change in thresh...

Deep traps in GaN-based structures as affecting the performance of GaN devices

“…Thus, modeling of proton damage in AlGaN/GaN HEMTs based on assuming the introduction of deep traps contributing to partial 2DEG depletion and to 2DEG electrons scattering was successful in predicting the devices performance with radiation (see Ref. [338]). These studies are very important, particularly for understanding the nature of current collapse in various AlGaN/GaN HEMTs structures and more research is definitely necessary on that front.…”

CHARACTERISTICS OF 1.6 MeV PROTON-IRRADIATED GaN-BASED SENSORS

“…Detection of both the electrical and optical signals also may be applicable for characterization of HEMTs [27]- [29].…”

Total Dose Radiation Damage: A Simulation Framework

“…Data from [32], [33], [41], [46]. Figure reprinted from [48]. defect states has been suggested as the physical reason for mobility reduction [29], [31], [32], [46].…”

“…This phenomenon results in a small effect on the threshold voltage. In this example, the trap energy levels were fixed and the concentration was varied [48]. Only when the concentrations were roughly equal did we get the small shift in threshold that was measured.…”

“…When either dominated, the shift became large. We also investigated trap levels to get an overall understanding of the interplay of concentration, trap level and compensation on the response of the device [48].…”