In this work InAlN/GaN high electron mobility transistors (HEMTs) with 40-200 nm rectangular gates and 300-700 nm source-to-drain distances were fabricated on Si substrates. The device with 40 nm gate and 300 nm source-to-drain distance exhibited a high drain current of 2.66 A/mm, a transconductance (gm) of 438 mS/mm and a high current gain cut-off frequency (fT) of 250 GHz. To the best of our knowledge, this is the highest fT value reported so far for GaN based transistors on Si. An effective electron velocity of 1.1 × 107 cm/s was extracted which is comparable to those reported for InAlN/GaN HEMTs on SiC. These excellent results indicate that GaN HEMTs on Si have a great potential for low-cost emerging mm-Wave applications.

Electro-optic modulators (EOMs) are pivotal in bridging electrical and optical domains, essential for diverse applications including optical communication, microwave signal processing, sensing, and quantum technologies. However, achieving the trifecta of high-density integration, cost-effectiveness, and superior performance remains challenging within established integrated photonics platforms. Enter thin-film lithium niobate (LN), a recent standout with its inherent electro-optic (EO) efficiency, proven industrial performance, durability, and rapid fabrication advancements. This platform inherits material advantages from traditional bulk LN devices while offering a reduced footprint, wider bandwidths, and lower power requirements. Despite its recent introduction, commercial thin-film LN wafers already rival or surpass established alternatives like silicon and indium phosphide, benefitting from decades of research. In this review, we delve into the foundational principles and technical innovations driving state-of-the-art LN modulator demonstrations, exploring various methodologies, their strengths, and challenges. Furthermore, we outline pathways for further enhancing LN modulators and anticipate exciting prospects for larger-scale LN EO circuits beyond singular components. By elucidating the current landscape and future directions, we highlight the transformative potential of thin-film LN technology in advancing electro-optic modulation and integrated photonics.

In this letter, we demonstrated an AlN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) on a Si substrate with in-situ SiN as gate dielectric with excellent mm-wave performance at low supply voltages. Benefited from the thin in-situ SiN, a low ohmic contact resistance ${R} _{C}$ of $0.2 \sf {\Omega } \cdot \text {mm}$ was obtained. The device with a T-shape gate featuring 80 nm gate foot length ( ${L} _{G}$ ) and 620 nm total gate metal thickness shows a maximum drain current ( ${I} _{D}$ ) of 1.95 A/mm, a peak transconductance ( ${g} _{\text {mmax}}$ ) of 500 mS/mm, and a cut-off frequency/a maximum oscillation frequency ( ${f} _{T}/{f} _{\text {max}}$ ) of 165/255 GHz. To the best of our knowledge, the ${f} _{T}$ and ${f} _{\text {max}}$ are the highest among the reported AlN/GaN transistors on Si substrates. 28 GHz load-pull measurements at low drain voltages of 3.5/5/6 V show maximum output power densities ( ${P} _{\text {out},\text {max}}$ ) of 0.36/0.73/1.04 W/mm and peak power-added efficiencies (PAE) of 40%/42%/43%, respectively. These excellent results show that AlN/GaN HEMTs on Si have a great potential for power amplifiers (PAs) in mobile mm-wave front-end applications.

In this letter, we report an InAlN/GaN high electron mobility transistor (HEMT) with a planar nanostrip channel design to improve its transconductance g _m and cutoff frequency f _T linearity. The planar nanostrips were formed by partial arsenic ion implantation isolation in the channel under the gate. Devices with a gate length (L _g ) of 80 nm and a source-to-drain distance (L _sd ) of 1 μm were fabricated. A conventional device and a device with a fin-like nanowire channel were also fabricated together for comparison. It was observed that the nanostrip and nanowire channel structures can both suppress the access resistance increase at the high output current level, and thereby improve the device's g _m and f _T linearity. Compared to the one using etching to form a fin-like nanostrip channel, the GaN HEMT with a planar nanostrip channel has demonstrated reduced parasitic capacitance and improved RF performance.

In this work, a 100 nm-gate Al ₂ O ₃ /InAlN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) with a planar nanostrip-channel was fabricated on a Si substrate and its DC, small-signal RF and two-tone intermodulation characteristics were measured. The use of a planar nanostrip-channel and MIS structure allows these devices to have close to 10 dB better intermodulation distortion than traditional InAlN/GaN high electron mobility transistors. In addition, the GaN planar nanostrip-channel MISHEMT shows five orders of magnitude lower gate current I _g , 30% higher current drivability and much improved g _m and f _T gate voltage swing than a planar nanostrip-channel GaN HEMT with a Schottky gate. This allows the planar nanostrip-channel GaN MISHEMT to be able to operate at higher input gate voltage (more than V _g = +4 V) and achieve higher output current with better linearity performance.

InAlN/GaN metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) with a 120 nm T-gate and gate recess on a silicon substrate were fabricated. A thin 1.5 nm HfO $_{2}$ was prepared by plasma-enhanced atomic layer (PEALD) deposition as the gate dielectric. The high electron mobility transistors (HEMTs) exhibited a maximum drain current ( I $_{\text{dmax}}$ ) of 1.5 A/mm, a peak transconductance ( g $_{\text{mmax}}$ ) of 495 mS/mm, a cut-off frequency ( f $_{\text{T}}$ ) of 95 GHz, and a maximum oscillation frequency ( f $_{\text{max}}$ ) of 115 GHz. The fabricated MISHEMTs exhibited a minimum noise figure (NF $_{\text{min}}$ ) of 1.3 dB with an associated gain ( G $_{\text{a}}$ ) of 7.7 dB at 30 GHz, and NF $_{\text{min}}$ of 1.7 dB and G $_{\text{a}}$ of 6 dB at 40 GHz. These excellent results show the great potential of the InAlN/GaN-on-Si HEMTs in the application of millimeter wave (mm-Wave) low noise amplifiers (LNAs).