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• 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]

Identically-sized AlGaN/GaN HFETs were fabricated on three AlGaN/GaN heterostructure with differing AlGaN barrier layer thicknesses of 15.5 nm, 19.3 nm and 24.7 nm. Based on polarization Coulomb field (PCF) scattering theory, additional polarization charges and electron mobility under the gate were calculated, and the relationship between AlGaN barrier layer thickness and P C F scattering in AlGaN/GaN H F E T s was determined. For the AlGaN/GaN H F E T s with a thicker AlGaN barrier layer, when the same gate bias was applied to the gate, the inverse piezoelectric effect (IPE) of the barrier layer was weaker, resulting in fewer additional polarization charges. The AlGaN/GaN H F E T s with a thicker AlGaN barrier layer also possessed a higher 2DEG sheet charge density, diminishing the P C F scattering intensity. It can be concluded that increasing the AlGaN barrier layer thickness reduces the IPE and raises the 2DEG sheet charge density, both of which decreases the PCF scattering intensity. The results of this study have guiding value toward the optimization of AlGaN/GaN HFETs materials and structures. • The relationship between AlGaN barrier layer thickness and polarization Coulomb field (PCF) scattering was determined. • Both of the reduce of additional polarization charges and the increase of the 2DEG density will weaken the PCF scattering. • PCF scattering intensity can be diminished by increasing the AlGaN barrier layer thickness. • The results of this study have guiding value toward the optimization of AlGaN/GaN HFETs materials and structures. [ABSTRACT FROM AUTHOR]

The AlGaN/GaN heterostructure field-effect transistors (HFETs) with the same size were fabricated on two AlGaN/GaN heterojunction materials with different Al composition. Based on the polarization Coulomb field (PCF) scattering theory model, the additional polarization charges and electron mobility are calculated. By analyzing the results, it is found that the increase of the Al composition in barrier layer will result in the increase of the additional polarization charges and the channel 2DEG density. Although HFETs with a higher Al composition in barrier layer have higher additional polarization charges, because of the higher density of 2DEG, the additional polarization charge has a weaker scattering effect on 2DEG, and the intensity of the PCF scattering is weaker. The contribution of additional polarization charges and 2DEG density to PCF scattering is opposite. The intensity of PCF scattering increases or decreases with the increase of Al composition, depending on which influence of the additional polarization charges and the 2DEG density is dominant.. • The influence mechanism of Al composition in AlGaN barrier layer on PCF scattering in AlGaN/GaN HFET has been clarified. • The increase of Al composition will result in the increase of the additional polarization charges and the 2DEG density. • The contribution of the additional polarization charges and 2DEG density to PCF scattering is opposite. • The PCF scattering increases or decreases with the increase of Al composition, depending on which above factors is dominant. [ABSTRACT FROM AUTHOR]

In this work, two AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with different ratios of gate length (L G) to gate-drain distance (L GD) were used to compare the effects of ratio of L G to L GD on the source access resistance (R GS) at 300 K , 350 K , and 400 K. The results showed that the ratio of L G to L GD had a significant effect on R GS at the above-mentioned each temperature, which can be attributed to the polarization Coulomb field (PCF) scattering. In addition, the effects of the ratio of L G to L GD on R GS in the two AlGaN/AlN/GaN HFETs prepared in this work were different at different temperatures. This indicated that elevated-temperature performance of AlGaN/AlN/GaN HFETs can be improved by optimizing the ratio of L G to L GD based on PCF scattering. [Display omitted] • The effects of the ratio of L G to L GD on R GS in AlGaN/AlN/GaN HFETs are investigated at different temperatures. • It is found that the ratio of L G to L GD has a significant effect on R GS at each testing temperature. • PCF scattering is responsible for the effects of the ratio of L G to L GD on R GS. • R GS can be modulated by optimizing the ratio of L G to L GD based on PCF scattering. [ABSTRACT FROM AUTHOR]