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In this study, the ungated AlGaN/GaN devices with special mesa structures were designed. The hypothesis of effective width expansion was tested experimentally by using ungated samples with different sizes, and an empirical expression for calculating the conduction channel effective width was given according to the experimental results. Finally, split-gate AlGaN/GaN heterostructure field-effect transistors (HFETs) with different gate lengths were prepared, and the channel electron mobility of split-gate samples was calculated by using the empirical expression and polarization Coulomb field (PCF) scattering theoretical model. The results showed that, for split-gate AlGaN/GaN HFETs, with the increase in the gate length, the total amount of additional polarization charges underneath the gate increases, resulting in the enhancement of the PCF scattering intensity. [ABSTRACT FROM AUTHOR]

• Normally-off recessed gate AlGaN/GaN MIS-HEMTs with ALD-Al 2 O 3 gate dielectric stack was fabricated. • The effect mechanism of PCF scattering on electrical properties of normally-off recessed gate AlGaN/GaN MIS-HEMTs was studied and clarified. • For the region underneath the gate, the increase in V GS resulted in an increase in Δ ρ G and n 2 D E G , moreover, the effect of n 2 D E G for PCF scattering is more significant than Δ ρ G. • For the gate-source region and gate-drain region, the parasitic resistance changes with V GS owing to the effect of PCF scattering, moreover, the effect of PCF scattering on the R S _ C H is stronger than R D _ C H . • This study perfects the carrier transport model of normally-off recessed gate AlGaN/GaN MIS-HEMTs and provides a new theoretical foundation for the device of this type to improving the electron mobility and reducing parasitic resistance. In this study, normally-off recessed gate AlGaN/GaN MIS-HEMT with ALD-Al 2 O 3 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-Al 2 O 3 gate dielectric stack was studied. Based on the measured I-V data, the electrical parameters such as additional polarization charge (Δ ρ G), electron mobility (μ), gate-source (G-S) parasitic resistance (R S) and gate-drain (G-D) parasitic resistance (R D) were obtained by iterative calculation method. Through systematic analyzed of these results, it was found that the positive G-S voltage (V GS) 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 Δ ρ G under the gate. With the increase of V GS , the inverse piezoelectric effect in the ultra-thin AlGaN layer increases and the amount of Δ ρ G increases. At the same time, the positive V GS induces two-dimensional electron gas (2DEG) underneath the gate, which is also positively correlated with the V GS. Compared with Δ ρ G , the 2DEG density (n 2 D E G ) has a greater effect on the PCF scattering strength. We also found that the influence of PCF scattering on R S and R D 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. [ABSTRACT FROM AUTHOR]

In this study, a novel AlGaN/GaN heterostructure field-effect transistor based on open-gate technology was fabricated. Sample transistors of different structures and sizes were constructed. Through measurements, it was found that by changing the width of the opening, the threshold voltage of the device could be easily modulated across a larger range. The open-gate device had two working modes with different transconductance. When the gate-source voltage VGS ≤ − 4.5 V, only the open region was conductive, and a new working mechanism modulated the channel current. Corresponding theoretical analysis and calculations showed that its saturation mechanism was related to a virtual gate formed by electron injection onto the surface. Also, the gate-source voltage modulated the open channel current by changing the channel electron mobility through polarization Coulomb field scattering. When used as class-A voltage amplifiers, open-gate devices can achieve effective voltage amplification with very low power consumption. [ABSTRACT FROM AUTHOR]