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The performance of ultra-wide bandgap semiconductors like ${\beta }$ -Ga2O3 is critically dependent on achieving high average electric fields within the active region of the device. In this article, we show that dielectrics like BaTiO3 with extremely high dielectric constant can provide an efficient field management strategy by improving the uniformity of electric field profile within the gate–drain region of lateral field-effect transistors. Using this strategy, we achieved high average breakdown field of 1.5 and 4 MV/cm at gate–drain spacing ( ${L}_{\text {gd}}$ ) of 6 and $0.5~{\mu }\text{m}$ , respectively in ${\beta }$ -Ga2O3, at a high channel sheet charge density of $1.6\,\,{\times }\,\,10^{{13}}$ cm−2. The high channel charge density along with the high breakdown field enabled a record power figure of merit ( ${V}_{\text {br}}^{{2}}/{R}_{\text {ON}}$ ) of 376 MW/cm2 at a gate–drain spacing of ${3}~{\mu }\text{m}$ .

As an ultra-wide bandgap semiconductor, $\beta $ -Ga2O3 has attracted great attention for high-power, high-voltage, and optoelectronic applications. However, until now, high-frequency performance of gallium oxide devices has been limited to relatively low current gain cutoff frequencies below 5 GHz. Here, we show that highly localized delta-doping designs can enable high-sheet-charge density to enable devices with short gate lengths that allow high-frequency operation. Field-effect transistors with a gate length of 120 nm on such delta-doped $\beta $ -Ga2O3 are reported here with extrinsic unity current gain frequency of 27 GHz. The device has a peak drain current of 260 mA/mm, transconductance (gm) of 44 mS/mm, and three-terminal off-state breakdown voltage of 150 V. These results demonstrate that the potential of $\beta $ -Ga2O3 for future RF and millimeter-wave device applications.

We report on the high-field transport characteristics and saturation velocity in a modulation-doped $\beta $ -(AlxGa1–x)2O3/Ga2O3 heterostructure. The formation of a 2-D electron gas (2DEG) in the modulation-doped structure was confirmed from the Hall measurements, and the 2DEG channel mobility increased from 143 cm $^{2}/\text{V}\cdot \text{s}$ at room temperature to 1520 cm $^{2}/\text{V}\cdot \text{s}$ at 50 K. The high electron mobility at 50 K made it feasible to achieve velocity saturation inside the channel. The saturation velocity was estimated based on both pulsed current–voltage measurements and small-signal radio frequency (RF) measurements. The measured velocity–field profile suggested a saturation velocity above $1.1\times 10^{7}$ cm/s at 50 K. The small-signal RF characteristics were measured for the fabricated modulation-doped field-effect transistors with a Pt-based Schottky contact. The current gain cutoff frequency ( $\text{f}_{\text {t}}$ ) and maximum oscillation frequency ( $\text{f}_{\text {max}}$ ) showed significant increases from 4.0/11.8 GHz at room temperature to 17.4/40.8 GHz at 50 K for the device with gate length of $\text{L}_{{\textsf {G}}} = 0.61\,\,\mu \text{m}$ . The analysis of the low temperature $\text{f}_{\text {t}}$ based on device simulations indicated a peak velocity of $1.2\times 10^{7}$ cm/s. The three-terminal off-state breakdown measurement further suggested an average breakdown field of 3.22 MV/cm. The high saturation velocity and high breakdown field in $\beta $ -Ga2O3 make it a promising candidate for high-power and high-frequency device applications.