Thermal and Piezoelectric Stress in Operating AlGaN/GaN HFET Devices and Effect of the Fe Doping in the GaN Buffer Layer

A. Sarua1*, T. Batten1, H. Ji1, M. J. Uren2, T. Martin2, and M. Kuball1

1H.H. Wills Physics Laboratory, University of Bristol, BS8 1TL, United Kingdom2QinetiQ Ltd., Malvern, Worcestershire, WR14 3PS, United Kingdom *a.sarua@bristol.ac.uk, phone: +44 117 3318110

Keywords: HFET, GaN, reliability, stress, piezoelectric, Fe doping

ABSTRACT  

We investigated the effect of self-heating and applied source-drain voltage (Vds) on the mechanical strain/stress generated in operating AlGaN/GaN HFET devices. Strain/stresses in devices were probed using Raman optical spectroscopy and the data were compared with electrical and thermo-mechanical numerical modeling. The vertical electric field and related piezoelectric stress near the drain-gate region were found to be significantly influenced by applied voltage and doping in the buffer. A higher level of buffer doping increases the piezoelectric stress in the AlGaN/GaN interface, i.e., 2DEG channel region. On the other hand, the determined thermal stress generated by non-uniform self-heating is opposite in sign to the piezoelectric stress and can result in a reduction of the net stress in the operated device.

 

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