Insights into the off-state breakdown mechanisms in power GaN HEMTs

N Zagni,F.M Puglisi,P Pavan,A Chini,G Verzellesi

doi:10.1016/j.microrel.2019.06.066

N Zagni, F.M Puglisi + Show 3 more

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https://doi.org/10.1016/j.microrel.2019.06.066

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Abstract

We analyze the off-state, three-terminal, lateral breakdown in AlGaN/GaN HEMTs for power switching applications by comparing two-dimensional numerical device simulations with experimental data from device structures with different gate-to-drain spacing and with either undoped or Carbon-doped GaN buffer layer. Our simulations reproduce the different breakdown-voltage dependence on the gate-drain-spacing exhibited by the two types of device and attribute the breakdown to: i) a combination of gate electron injection and source-drain punch-through in the undoped HEMTs; and ii) avalanche generation triggered by gate electron injection in the C-doped HEMTs.

Highlights

In AlGaN/GaN HEMTs for power switching applications, the three-terminal off-state breakdown voltage (VBR) is typically extended up to the vertical breakdown limit by compensating the unintentional conductivity in the buffer through Carbon (C) doping and by increasing the lateral gate-to-drain spacing (LGD) [1]
Simulation results for the C-doped devices were not compared with experiments for LGD > 6 μm because measurements were limited to VDS = 1000 V [1], and no breakdown occurred in this range for the longer devices
We have analysed the off-state, three-terminal, lateral breakdown of AlGaN/GaN HEMTs for power switching applications, by comparing twodimensional numerical device simulations with experimental data from device structures with different LGD and with either undoped or Carbondoped GaN buffer layers

Summary

Introduction

In AlGaN/GaN HEMTs for power switching applications, the three-terminal off-state breakdown voltage (VBR) is typically extended up to the vertical breakdown limit by compensating the unintentional conductivity in the buffer through Carbon (C) doping and by increasing the lateral gate-to-drain spacing (LGD) [1]. VBR is typically found to scale about linearly with LGD with a VBR/ LGD slope that is smaller than the critical field for avalanche (ECRIT = 3.9 MV/cm [2]) This is often considered to be an indication that avalanche generation should be ruled out as the VBR limiting phenomenon. To assuming a quite idealized, constant electric-field distribution throughout the access region between gate and drain The latter is on the contrary two-dimensional and, above all, characterized by intense accumulation spots at the drain-end of the gate, under the field-plate end (if present), and at the drain contact border. It is critically impacted by the intrinsic or doping-related traps in the buffer. Numerical device simulations are probably the only means by which the role possibly played by avalanche generation in the off-state breakdown can be clarified

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