Delay-time analysis in radio-frequency β -Ga2O3 field effect transistors

β-Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) with gate lengths (Lg) of 50–1000 nm were fabricated, employing a thin channel layer formed by a shallow Si-ion implantation doping to maintain a high aspect ratio between an Lg and a gate-to-channel distance. The MOSFETs with Lg = 200 nm had a maximum drain current density of about 250 mA/mm and a peak extrinsic transconductance of 17 mS/mm. The short-channel effect was well suppressed for the devices with Lg ≥200 nm, leading to excellent RF device characteristics represented by a record maximum oscillation frequency of 27 GHz at Lg = 200 nm. From simple delay-time analysis on the MOSFETs, the effective electron velocity passing through a region under the gate was estimated to be about 2 × 106 cm/s. Moreover, it was analyzed that the parasitic channel charging delay occupied a substantial proportion of the total delay due to a large sheet resistance of the Ga2O3 channel and thus limited their high-frequency device performance. These results suggest that both suppressing the short channel effect with a reduction in Lg to the sub-0.1-μm range and minimizing the access resistance are important to further improve RF device characteristics of Ga2O3 MOSFETs.