High mobility electrons in selectively doped GaAs/n-AlGaAs heterostructures grown by MBE and their application to high-speed devices

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Quasi-two-dimensional electron gas accumulating at the heterojunction interface in selectively doped GaAs/n-Al x Ga 1- x As ( x ≈ 0.3) grown by MBE was found to show extremely high mobilities of 8030 cm 2/V ·s at 300 K, 117,000 cm 2/V ·s at 77 K, and 244,000 cm 2/V ·s at 5 K. The mobility attained at 5 K is higher than any reported so far for MBE-grown semiconductor materials. Enhancement-mode high electron mobility transistors (E-HEMTs) have been fabricated from the heterostructures. An E-HEMT with a large gate ( L G = 350 μm) showed a field effect mobility as high as 59,000 cm 2/V ·s at 77 K. Furthermore, an E-HEMT with a small gate ( L G = 2 μm) exhibited transconductance as high as 193 mS/mm at room temperature and 409 mS/mm at 77 K; the latter is, to our knowledge, the highest transconductance ever reported for field effect transistors.