Influence of polarization Coulomb field scattering on the electrical properties of normally-off recessed gate AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistor with ALD-Al2O3 gate dielectric stack

Abstract

In this study, normally-off recessed gate AlGaN/GaN MIS-HEMT with ALD-Al2O3 gate dielectric stack was fabricated. The influence of polarization Coulomb field (PCF) scattering on electrical properties of normally-off recessed gate AlGaN/GaN MIS-HEMTs with ALD-Al2O3 gate dielectric stack was studied. Based on the measured I-V data, the electrical parameters such as additional polarization charge (ΔρG), electron mobility (μ), gate-source (G-S) parasitic resistance (RS) and gate-drain (G-D) parasitic resistance (RD) were obtained by iterative calculation method. Through systematic analyzed of these results, it was found that the positive G-S voltage (VGS) induces tensile strain in the ultra-thin AlGaN barrier layer, which was AlGaN remaining after etching and existsed between the gate dielectric and the GaN channel, resulting in positive ΔρG under the gate. With the increase of VGS, the inverse piezoelectric effect in the ultra-thin AlGaN layer increases and the amount of ΔρG increases. At the same time, the positive VGS induces two-dimensional electron gas (2DEG) underneath the gate, which is also positively correlated with the VGS. Compared withΔρG, the 2DEG density (n2DEG) has a greater effect on the PCF scattering strength. We also found that the influence of PCF scattering on RS and RD is different, which is related to the difference between G-S distance and G-D distance. This study provides a new theoretical basis for normally-off recessed gate AlGaN/GaN MIS-HEMTs to improving μ and reducing parasitic resistance.