In this article, we report on the effective transconductance ( g _m ) and gain linearity improvement of submicrometer gate AlN-barrier-based transistors using GaN/InGaN coupling-channel structures. The fabricated AlN/GaN/InGaN coupling-channel high electron mobility transistor (CC-HEMT) showed flat g _m profile, greatly reduced g _m derivatives, and constant dynamic source resistance compared with an AlN/GaN HEMT using the same fabrication process. The highest extrinsic current gain cutoff frequency ( f _T ) of 55 GHz and the maximum oscillation frequency ( f _max ) of 80 GHz were obtained for 0.15- μm gate-length transistors, both of which remain constant values across wide input voltage ( V _GS ) of 4 V. Moreover, a significant theoretical OIP3 value boost by 7.1 dB has been observed using the CC-HEMT as compared to the AlN/GaN HEMT. The superior linearity performance of the CC-HEMT can be attributed to the strong channel-to-channel coupling effect. The drain bias-dependence of g _m , f _T , and f _max versus V _GS profiles illustrate that the linearity characteristics of the CC-HEMT greatly improve with an increase in V _DS . These results demonstrate the AlN/GaN/InGaN material system as a viable platform for high frequency requiring high-linearity applications.

This work reports recent progress in the sub-6 GHz power performance of GaN-based HEMTs grown on high resistivity silicon substrates with passivation implanted termination (PIT) process. Thanks to the mitigated electric field crowding at the gate edge and the suppressed negative fixed charge-induced carrier depletion, the fabricated HEMTs demonstrate a low leakage current, a high ON/OFF current ratio of 10 ⁸ , and improved breakdown voltage associated with a current collapse at 40 V drain quiescent condition of as low as 5.6%. S-band continuous-wave large signal measurements yield a high power-added efficiency (PAE) of 69%, a drain efficiency (DE) of 72%, and an output power density ( ${P}_{\text{out}}$ ) of 7.2 W/mm at ${V}_{\text{DS}}=30$ V. Moreover, the transistor delivers a maximum ${P}_{\text{out}}$ up to 10.2 W/mm with a peak PAE of 63.8% at ${V}_{\text{DS}}=40$ V. The PAE and ${P}_{\text{out}}$ as a function of drain bias indicate that the transistors remain constant high PAE and linearly increased ${P}_{\text{out}}$ over a wide range of drain voltage variation. These excellent results have demonstrated the PIT process could be an attractive technique to facilitate the application of high-performance and cost-competitive GaN-on-Si HEMTs for 5G wireless base stations.

In this letter, the AlGaN/GaN/graded-AlGaN:Si-doped/ GaN double channel (GDC-SI) high electronic mobility transistors (HEMTs) with high saturation current density and linearity have been reported for low voltage applications. Compared with the standard AlGaN/GaN/AlGaN/GaN double channel GaN (SDC) HEMTs, the GDC-SI HEMTs exhibited the higher saturation current, the broader and flatter transconductance profile, the lower transconductance ( g _m ) derivatives, and lower on-resistance ( R _on ). Due to the Si-doped graded bottom barrier present in GDC-SI HEMTs, the profile of current gain cutoff frequency ( f _T ) and the maximum oscillation frequency ( f _max ) were flatter with the bias voltage increased. The output power density of 0.75 W/mm and power added efficiency (PAE) of 58% were achieved for GDC-SI HEMTs, at the drain voltage of 7 V and the test frequency of 3.6GHz. The output third-order intercept point (OIP3) of 39.3 dBm and saturation current density of 1909 mA/mm are achieved, which are the state-of-the-art saturation current and OIP3 in the double-channel GaN HEMTs.

In this letter, we apply an oxidation technique for p-GaN to a normally-off p-GaN/AlGaN/GaN HEMT to improve the threshold voltage and gate reliability. Oxygen-plasma and low-temperature Oxygen post-annealing treatment (OPAT) of p-GaN before the deposition of gate metal has introduced a 5 nm oxidation interlayer, resulting in a significant improvement in gate breakdown voltage, from 10.4 V to 20.6 V. Thanks to this interlayer, the threshold voltage of p-GaN gate HEMTs is increased from 1.9 V to 4.6 V, while an almost same on-state resistance and a higher drain breakdown voltage are obtained. Time-dependent gate breakdown measurement shows OPAT-HEMTs have a maximum on-state gate drive voltage of 9.2 V for a 10-year lifetime with a 63 % gate failure rate. In addition, a more stable threshold voltage under gate stress indicates the promising application of this technology in GaN power devices.

In this article, the superior power performance of a double-channel high-electron-mobility transistor (HEMT) operating at a high drain voltage of sub-6 GHz was demonstrated using a heterostructure of Al $_{\text{0}.\text{3}}$ Ga $_{\text{0}.\text{7}}$ N/GaN/Al $_{\textit{x}}$ Ga $_{\text{1}-\textit{x}}$ N/GaN, $\textit{x}$ ranging from 0.3 to 0, top-down double channel with graded barrier HEMT (DCGB-HEMT). In comparison to single channel HEMT (SC-HEMT), DCGB-HEMT exhibits superior direct current (dc) characteristics, including a wider gate voltage swing, a higher saturation current (up to 1307.80 mA/mm), and a higher OFF-state breakdown voltage (up to 165 V). Through TCAD simulation, the breakdown voltage was increased because the graded barrier reduces the peak value of the electric field at the gate’s edge on the drain side. Compared to SC-HEMT, DCGB-HEMT’s current collapse (CC) decreased from 23.35% to 9.82%. Electrons from the upper channel are more effectively prevented from being captured by acceptors in a buffer induced by Fe-doping by a thicker 3-D electron gas (3DEG) forming between the bottom channel and graded bottom barrier, prevailing over a thinner 2-D electron gas (2DEG). DCGB-HEMT’s maximum power-added efficiency (PAE) increased from 56% to 70.4%. DCGB-HEMTs exhibit superior PAE due to their improved gate control, lower leakage, and improved CC at high drain voltage.

A high-linearity and high-gain AlGaN/GaN HEMTs with a 100-nm gate were demonstrated. The device employs transitional recessed gate (TRG) along the gate width for millimeter wave power application. The gradually changing gate recess depth was created using transitional dosed photoetching. Accurate etching ensured that the FET-elements have a continued V _ts offset in the local equivalent threshold voltage (V _th ) in different areas. The device exhibits a high I _d,max of 1.12 A/mm and a high peak extrinsic gm of 374 mS/mm with an improved gate swing > 2.6 V, much higher than that of Fin-HEMT. Excellent RF performance was shown, including f _T /f _max = 61.8/148.8 GHz, G _as /G _linear = 9.98/ 12dB at 30 GHz. To the best of our knowledge, this is the best associated gain and linearity performance reported to date for AlGaN/GaN HEMTs. This letter has great potential for high gain and linearity millimeter wave power applications, which are needed for future communication systems.