Search

• 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]

• 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]

• 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]