3.8 W/mm RF Power Density for ALD Al2O3-Based Two-Dimensional Hole Gas Diamond MOSFET Operating at Saturation Velocity

This letter reports the small-signal and large-signal performances at high drain voltage (V
_DS
) ranging up to 60 V for a 0.5 μm gate length two-dimensional hole gas diamond metal-oxide-semiconductor field-effect transistor with a 100-nm-thick atomic-layer-deposited Al
₂
O
₃
film on a IIa-type polycrystalline diamond substrate with (110) preferential surfaces. This diamond FET demonstrated a cutoff frequency (f
_T
) of 31 GHz, indicating that its carrier velocity was reaching 1.0 × 10
⁷
cm/s for the first time in diamond. In addition, a f
_T
of 24 GHz was obtained at V
_DS
= -60 V, thus giving a f
_T
× V
_DS
product of 1.44 THz·V. This diamond FET is promising for use as a high-frequency transistor under high voltage conditions. Under application of a high voltage, a maximum output power density of 3.8 W/mm (the highest in diamond) with an associated gain and power added efficiency were 11.6 dB and 23.1% was obtained when biased at V
_DS
= -50 V using a load-pull system at 1 GHz.