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The small-signal S parameters of the fabricated double-finger gate AlGaN/GaN high electron mobility transistors (HEMTs) were measured at various direct current quiescent operating points (DCQOPs). Under active bias conditions, small-signal equivalent circuit (SSEC) parameters such as Rs and Rd, and intrinsic parameters were extracted. Utilizing fT and the SSEC parameters, the effective electron velocity ( ν e − e f f ) and intrinsic electron velocity ( ν e − int ) corresponding to each gate bias (VGS) were obtained. Under active bias conditions, the influence mechanism of VGS on ν e − e f f was systematically studied, and an expression was established that correlates ν e − e f f , ν e − int , and bias-dependent parasitic resistances. Through the analysis of the main scattering mechanisms in AlGaN/GaN HEMTs, it has been discovered that the impact of VGS on ν e − e f f should be comprehensively analyzed from the aspects of ν e − int and parasitic resistances. On the one hand, changes in VGS influence the intensity of polar optical phonon (POP) scattering and polarization Coulomb field (PCF) scattering, which lead to changes in ν e − int dependent on VGS. The trend of ν e − int with changes in VGS plays a dominant role in determining the trend of ν e − e f f with changes in VGS. On the other hand, both POP scattering and PCF scattering affect ν e − e f f through their impact on parasitic resistance. Since there is a difference in the additional scattering potential corresponding to the additional polarization charges (APC) between the gate-source/drain regions and the region under the gate, the mutual effects of PCF scattering on the under-gate electron system and the gate-source/drain electron system should be considered when adjusting the PCF scattering intensity through device structure optimization to improve linearity. This study contributes to a new understanding of the electron transport mechanisms in AlGaN/GaN HEMTs and provides a novel theoretical basis for improving device performance. [ABSTRACT FROM AUTHOR]

• A novel method to determine bias-dependent source and drain parasitic series resistances in AlGaN/GaN high electron mobility transistors has been proposed. • The physical mechanism that causes R s and R d to vary with bias voltage is studied. • The bias voltage can affect the magnitude of R s and R d by affecting the optical phonon temperature and the intensity of the inverse piezoelectric effect. The AlGaN/GaN high electron mobility transistors (HEMTs) with T-gate that suitable for high frequency applications were fabricated. A novel method to extract the bias-dependent source and drain parasitic series resistances (R s and R d) of AlGaN/GaN HEMTs is proposed. By analyzing the distributed capacitance and current generator network in the velocity saturated regions of the AlGaN/GaN HEMTs, a new restriction relationship between small-signal equivalent circuit elements is found. The R s and R d can be determined under active bias through wideband S-parameter measurements, which can better reflect the physical mechanism of AlGaN/GaN HEMTs under normal operation. The S-parameters and extrinsic transconductance calculated based the small-signal equivalent circuit element values extracted by the method proposed in this paper are very consistent with the experimental values, which reflects the accuracy of this element extraction method. In this paper, the physical mechanism that causes R s and R d to vary with bias voltage is also studied. This study has a deeper insight into the bias-dependence of R s and R d , which modifies the understanding for physical mechanisms of AlGaN/GaN HEMTs. The research results provide new ideas for establishing small-signal equivalent circuit models containing more physical effects and is of great significance to GaN-based integrated circuit design. [ABSTRACT FROM AUTHOR]

An InAlN/GaN MIS-HEMT with ZrO 2 gate dielectric layer and a Schottky-gate InAlN/GaN HEMT were fabricated. Subsequently, the influence of ZrO 2 gate dielectric layer on polarization Coulomb field (PCF) scattering in InAlN/GaN MIS-HEMT was studied. Compared with InAlN/GaN HEMT, the ZrO 2 gate dielectric layer in InAlN/GaN MIS-HEMT results in fewer additional polarization charge and higher two-dimensional electron gas density at the same gate-source voltage (V GS) conditions. Also, we established that both of these factors weaken PCF scattering intensity. However, the InAlN/GaN MIS-HEMT has a larger gate swing. Therefore, there is a smaller V GS was applied during regular operation of device. When the V GS is small, PCF scattering is the strongest scattering and play non-negligible impact in the size of total electron mobility. This study provides a new theoretical foundation for further enhancing the performance of InAlN/GaN MIS-HEMTs. • The influence of the ZrO 2 gate dielectric layer on PCF scattering in InAlN/GaN MIS-HEMTs was determined. • The ZrO 2 layer leads to fewer Δ ρ G and higher n 2 D E G at the same gate bias conditions, both of these factors weaken PCF scattering intensity. • When the gate bias is small, PCF scattering plays a dominant role in the magnitude of the total electron mobility. • The results of this study have providing a new theoretical basis for further enhancing performance of InAlN/GaN MIS-HEMTs. [ABSTRACT FROM AUTHOR]

• The mechanism of enhanced for PCF scattering in AlN/GaN HFETs has been clarified. • A large number of additional polarization charges (Δ ρ G) are generated under the gate. • Δ ρ G will become saturated with the decrease in gate bias. • The decreases of 2DEG density will enhance the PCF scattering intensity. AlN/GaN heterostructure field-effect transistors (HFETs) was fabricated. Based on the polarization Coulomb field (PCF) scattering theory model, the additional polarization charges and mobility are obtained by iterative calculation method. By analyzing the results, it is found that (i) the electric field strength in the AlN barrier layer is large because it is ultrathin, and the piezoelectric tensor coefficient of AlN material is large; thus, the inverse piezoelectric effect is very strong. A large number of additional polarization charges are generated under the gate, which can generate a strong PCF scattering potential and enhance PCF scattering. What's more, the AlN barrier layer cannot be infinitely strained by the gate bias with the converse piezoelectric effect, and the additional polarization charges will become saturated with the decrease in gate bias. (ii) The AlN barrier layer of AlN/GaN HFETs is ultrathin, the two-dimensional electron gas (2DEG) density under the gate is quickly decreased by the gate bias, and, with the decrease in 2DEG density, PCF scattering is enhanced. [ABSTRACT FROM AUTHOR]