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We have demonstrated wide-range modulation of Schottky barrier height (SBH) of NiGe∕Ge(100) interfaces by using a valence mending adsorbate, sulfur, segregation during Ni germanidation. Implanted sulfur atoms, segregated during Ni germanidation, are expected to act as dangling bond terminator at the NiGe∕Ge interface. The experimental results show that the strong Fermi level pinning feature of NiGe∕Ge interfaces was alleviated, and SBH of NiGe∕n-Ge(100) gradually decreased from 0.61to0.15eV with an increase in the implanted sulfur dose. This method opens a way to realize Ge channel complementary metal-oxide-semiconductor field-effect transistors with metal source/drain.

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We fabricated non-recessed-gate enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs) with a gate length L g of 120 nm. As gate metals, Ni/Pt/Au and Mo/Pt/Au were used. The Ni/Pt/Au-gate HEMTs with rapid thermal annealing (RTA) at 500°C were normally-off at a gate-source voltage V gs of 0 V, indicating E-mode operation. Moreover, the Mo/Pt/Au-gate HEMTs also showed E-mode device operation without RTA. The fabricated E-mode HEMTs with both gate metals showed high RF performance. We obtained a cutoff frequency f T of more than 50 GHz and a maximum oscillation frequency f max of approximately 100 GHz.

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We fabricated sub-50-nm-gate i-AlGaN/GaN high electron mobility transistors (HEMTs) on sapphire and measured their DC and RF characteristics at room temperature. The fabricated HEMTs exhibited true device operation and good pinch-off characteristics down to a gate length L g of 25 nm. For the HEMTs with a source-drain spacing L sd of 2 µm, we obtained the L g dependence of the cutoff frequency f T under a drain-source voltage V ds of 3 V. The peak f T was measured to be 102 GHz at L g = 35 nm. At L g = 25 nm, f T started to decrease due to the short-channel effect. The highest f T of 110 GHz was obtained by reducing L sd from 2 to 1.5 µm and by increasing V ds from 3 to 4 V. . However, obtaining the electron peak velocity requires a much higher electric field for GaN (~140 kV/cm) than for In 0.53 Ga 0.47 As (~4 kV/cm). Reducing gate length L g is a straightforward method of obtaining a very high electric field, similar to applying a high voltage. For AlGaN/GaN HEMTs, the shortest reported L g is 50 nm [3]. We previously developed a fabrication technique for sub-50-nm-gate HEMTs for the InAlAs/InGaAs material system using electron beam (EB) lithography [4].In the present work, we used this technique to fabricate sub-50-nm-gate i-AlGaN/GaN HEMTs on sapphire and successfully tested true device operation.