| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
H2, Direct Correlation between Access Region Trap Generation and Field-Induced Degradation in AlGaN/GaN High Electron Mobility Transistors |
| Author(s) |
Anup Sasikumar, Aaron Arehart, Stephen Kaun, Man Hoi Wong, James S. Speck, Umesh K. Mishra, Steven A. Ringel |
| On-Site Speaker (Planned) |
Anup Sasikumar |
| Abstract Scope |
Deep levels are prominent and mostly undesirable in wide band-gap devices, especially AlGaN/GaN high electron mobility transistors (HEMTs). These levels are considered responsible for RF-to-DC dispersion, knee-walkout, and threshold voltage <i>V</i><sub>T</sub> shifts among other reliability issues in HEMTs<sup>1</sup>. In order to address such reliability issues, it becomes imperative to understand these levels and the role they play in HEMT degradation. Here we perform constant drain current-based deep level optical and (thermal) transient spectroscopy<sup>2</sup> (C<i>I</i><sub>D</sub>-DLOS/DLTS) on AlGaN/GaN HEMTs before and after electrical DC stressing to investigate the impact of stress and its correlation to defects within the material structure.
The HEMTs in this study are 30 nm Al<sub>0.3</sub>Ga<sub>0.7</sub>N/800 nm GaN structures grown on 4H-SiC using plasma assisted molecular beam epitaxy (PAMBE). The access regions were passivated with 180 nm of SiN<i>x</i> using plasma enhanced chemical vapor deposition. A typical device had a <i>V</i><sub>T</sub>=-4.5 V and a maximum drain current of 1.1 A/mm at <i>V</i><sub>GS</sub>=0 V. These HEMTs were subjected to semi-on DC stressing for 13 hours with <i>V</i><sub>GS</sub>=-2.25 V, <i>V</i><sub>DS</sub>=17.5 V, and <i>I</i><sub>DS</sub> ~0.45 A/mm and compared to unstressed devices with nearly identical electrical behavior. Constant current-based drain-access sensitive ‘drain-lag’ measurements reveal a dominant exponentially decaying transient with time-constant <i>τ</i>~30 ms. This transient has been observed previously<sup>3,4</sup> and attributed to a <i>E</i><sub>C</sub>-0.57 eV electron trap physically located in the HEMT access region. These previous studies<sup>3,4</sup> were performed on AlGaN/GaN HEMTs from three different sources grown by metalorganic chemical vapor deposition (MOCVD). In this work, on PAMBE HEMTs, the signature <i>E</i><sub>C</sub>-0.57 eV drain-lag signal increased by ~2x post-DC stressing similar to the Arehart <i>et al.</i><sup>3</sup> report on MOCVD HEMTs post-RF stressing. Drain access sensitive C<i>I</i><sub>D</sub>-DLOS measurements revealed even deeper levels at <i>E</i><sub>C</sub>-1.3 eV and <i>E</i><sub>C</sub>-3.8 eV matching previous results for AlGaN<sup>5</sup> with total trap concentrations <i>n</i><sub>T</sub>~9×10<sup>12</sup> cm<sup>-2</sup> that remained unaffected by DC-stressing. Room temperature 500 ns pulsed <i>I</i>-<i>V</i> show a knee-walkout in the DC stressed sample with negligible <i>V</i><sub>T</sub> shift. The knee-walkout in the pulsed <i>I</i>-<i>V</i> observed in the stressed sample suggests an increase in drain access resistance. The negligible change in deep trap concentrations extracted from C<i>I</i><sub>D</sub>-DLOS values suggests that observed knee-walkout in the pulsed <i>I</i>-<i>V</i> measurements was mostly due to the <i>E</i><sub>C</sub>-0.57 eV electron trap thereby directly correlating it with HEMT degradation. We are presently performing under-gate sensitive C<i>I</i><sub>D</sub>-DLTS/DLOS to probe deep traps in the gated region and better understand the negligible <i>V</i><sub>T</sub>-shift post DC-stressing. |
| Proceedings Inclusion? |
Undecided |