Millimeter-Wave Donor–Acceptor-Doped DpHEMT

In this article, we present GaAs millimeter-wave pseudomorphic high-electron-mobility transistor (pHEMT) using sophisticated AlGaAs-InGaAs-GaAs heterostructure with an In
_0.22
Ga
_0.78
As quantum well located inside an external quantum well formed by space charge regions in AlGaAs layers. In a heterostructure with this design, high mobility [5800 cm
²
/(V · s)] and high density (4.7 × 10
¹²
cm
^-2
) of two-dimensional electron gas at 300 K were obtained. The localization of hot electrons in an external quantum well leads to an increase in their drift velocity and to enhance the dc and RF performances of the device. A field-effect transistor based on such a heterostructure with a T-gate of 0.14 μm in length shows a specific current density of about 0.7 A/mm, transconductance of about 250 mS/mm, gate-drain breakdown voltage in the range 23-31 V, which corresponds to more than 2 W/mm specific output RF power according to a simple estimate. The transistor demonstrates impressive RF characteristics, the maximum stable gain (MSG) of more than 15 dB at 40 GHz and more than 10 dB at 67 GHz, f
_t
= 45 GHz and f
_max
= 250 GHz. The MSG at 40 GHz increases with increasing distance between the gates in the drain and is almost constant in the range 25-55 GHz.