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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]

• 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]

In this study, a split-gate AlGaN/GaN heterostructure field-effect transistor with an auxiliary gate was fabricated. Through experiment and analysis, it was discovered that by applying a constant potential (usually 0 V or negative potential) to the auxiliary gate, a negative bias can be formed between the auxiliary gate and the channel. This consumes the two-dimensional electron gas in the channel, leading to significant improvements in the saturation characteristics of split-gate devices. By applying different potentials to the main gate and the auxiliary gate, a variety of device working modes can be obtained, and the threshold voltage can be altered across a large range. These advantages make split-gate devices with auxiliary gates more suitable for increasingly complex integrated circuit applications. [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]

This paper demonstrates the improvement of device linearity in AlGaN/GaN heterostructure field effect transistors (HFETs) using polarization Coulomb field (PCF) scattering and investigates the relationship between device linearity and PCF scattering under 10 and 20 V drain bias. The mobility of the gate-to-source region in AlGaN/GaN HFETs is calculated using the Monte Carlo method. We find that PCF scattering decreases with an increase in gate bias (from −3 to −0.5 V) under high field conditions, leading to lower gate-to-source resistance. Under 20 V drain bias, linearity is worse than under 10 V drain bias. The transconductance drop is significant in AlGaN/GaN HFETs, which damages linearity. By adopting an appropriate drain bias, PCF scattering can alleviate transconductance drop and improve the linearity of AlGaN/GaN HFETs. [ABSTRACT FROM AUTHOR]

E-mode P-GaN/AlGaN/GaN heterostructure field-effect transistors (HFETs) of various sizes were fabricated, and their parasitic source resistance (RS) was measured. The measurement results showed that RS varied greatly with changing gate bias, and the degree of RS change also differed with the gate bias of different-sized device samples. Through theoretical analysis, it is found that polarization Coulomb field (PCF) scattering caused by the device process and gate bias can affect electron mobility ( μ GS ) in the gate-source region, which causes the variations in μ GS for different-sized devices and same-sized devices under different gate biases. When μ GS changes with the device size and gate bias, the RS will change accordingly. Our study is the first to discover the gate bias dependency of RS for E-mode P-GaN/AlGaN/GaN HFETs due to PCF scattering, which provides a new idea for further in-depth studies on the RS of E-mode P-GaN/AlGaN/GaN HFETs and device performance optimization. [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]

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]

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]