Polarization effects in ferroelectric gate AlGaN/GaN High Electron Mobility Transistors

The impact of polarization effects induced by a ferroelectric layer on the on-state performance of ferroelectric gate AlGaN/GaN HEMTs has been studied by using experiments and extensive TCAD simulations. Stress-free and high quality crystalline (111) lead-zirconate-titanate ($\mathrm{P}\mathrm{b}(\mathrm{Z}\mathrm{r}_{x}\mathrm{T}\mathrm{i}_{1-x})\mathrm{O}_{3}$ or PZT) films on top of GaN have been successfully obtained by adopting a single magnesium-oxide (MgO) monolayer as a buffer layer. By adjusting the zirconium composition (x) of PZT, solely the spontaneous polarization in PZT is varied. In addition a onedimensional electrostatic model has been derived showing the impact of the polarization in the ferroelectric gate on the 2DEG sheet density and threshold voltage ($V_{\mathrm{T}\mathrm{H}}$), which is in good agreement with TCAD simulations. The experimental data show for $x=0.20$ a minimum on-resistance $(R_{\mathrm{O}\mathrm{N}})$ of $\sim 9.7\mathrm{k}\Omega$ and for $x=0.52$ a minimal $V_{\mathrm{T}\mathrm{H}}$ of -3.3V. The results are important for providing a guide line to optimize ferroelectric gate AlGaN/GaN HEMTs.