GaN Super Heterojunction Field Effect Transistor

ganfetex16.in : GaN Super Heterojunction Field Effect Transistor

Requires: Blaze
Minimum Versions: Atlas 5.28.1.R

Field plate (FP) technologies are generally used in order to manage surface electric field distribution of GaN HEMTs. Recently, GaN Super Heterojunction Field Effect Transistors (Super HFETs) based on the polarization junction (PJ) concept have been demonstrated [1, 2]. This concept is based on the compensation of positive and negative polarization charges at heterointerfaces such as AlGaN/GaN to achieve similar effect to RESURF or Super Junction (SJ) in silicon devices. In this example, we will demonstrate device simulation of GaN Super HFETs in comparison with the experimental data based on [1, 2].

The Super HFET structure consists of an undoped double-hetero GaN/AlGaN/GaN structure with a p-GaN cap layer. The feature of the Super HFET structure is the presence of the 2-D hole gas (2DHG) induced by negative polarization charge at the upper GaN/AlGaN heterointerface as well as the 2-D electron gas (2DEG) at the lower AlGaN/GaN heterointerface. The computation of 2DEG and 2DHG due to polarization effect was performed automatically during the simulation with our built-in model and can be seen in tonyplot.

Performance of GaN device and convergence can be significantly influenced by the presence of defects. We introduced bulk and interface traps in the simulation. Threshold voltage and substrate leakage current are controlled by a concentration of acceptor and donor traps in the GaN buffer layer, respectively. Moreover, we put the interface traps to represent Fermi level pinning at the bottom of the GaN buffer. This assumption is properly valid because an actual GaN epitaxial layer has quite many defects around the interface with the substrate. It should be noticed that even with traps and a floating undoped-GaN buffer region convergence is very ggod.

The simulation results of the Id-Vg and Id-Vd characteristics can be seen in tonyplot. Very good agreement between simulations and experiments were obtained.

Breakdown characteristics and impact ionization rate distribution is also shown in tonyplot and were simulated by using slow transient simulation. An increase of the gate current (including the base current) is observed near breakdown and the value is of the same order as the drain current. In addition, it should be noticed that impact ionization occurs near the drain-side edge of p-GaN region. These results indicate that breakdown voltage is dominated by the hole current into the base electrode through the p-GaN layer.

To load and run this example, select the Load button in DeckBuild > Examples. This will copy the input file and any support files to your current working directory. Select the Run button in DeckBuild to execute the example.

References:

[1]. A. Nakajima, Y. Sumida, M. H. Dhyani, H. Kawai, and E. M. S. Narayanan, "GaN-based super heterojunction field effect transistors using the polarization junction concept " EEE Electron Device Lett., vol. 32, no. 4, p.p. 542-544, Apr. 2011.

[2]. A. Nakajima, Y. Sumida, M. H. Dhyani, H. Kawai, and E. M. S. Narayanan, "High density 2-D hole gas induced by negative polarization at GaN/AlGaN heterointerface " Appl. Phys. Express, vol. 3, no. 12, p. 121004, Dec. 2010.