We report on SiO 2 / AlGaN / GaN metal-oxide-semiconductor heterostructure field-effect transistors ͑MOSHFETs͒, which exhibit a 6.7 W / mm power density at 7 GHz. Unpassivated and SiO 2-passivated heterostructure field-effect transistors ͑HFETs͒ were also investigated for comparison. Deposited 12 nm thick SiO 2 yielded an increase of the sheet carrier density from 7.6ϫ 10 12 to 9.2ϫ 10 12 cm −2 and a subsequent increase of the static drain saturation current from 0.75 to 1.09 A / mm. The small-signal rf characterization of the MOSHFETs showed an extrinsic current gain cutoff frequency f T of 24 GHz and a maximum frequency of oscillation f max of 40 GHz. The output power of 6.7 W / mm of the MOSHFETs measured at 7 GHz is about two times larger than that of HFETs. The results obtained demonstrate the suitability of GaN-based MOSHFETs for high-power electronics.

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We present the epitaxial growth of Ge and Ge 0.94 Sn 0.06 layers with 1.4% and 0.4% tensile strain, respectively, by reduced pressure chemical vapor deposition on relaxed GeSn buffers and the formation of high-k/metal gate stacks thereon. Annealing experiments reveal that process temperatures are limited to 350 °C to avoid Sn diffusion. Particular emphasis is placed on the electrical characterization of various high-k dielectrics, as 5 nm Al 2 O 3 , 5 nm HfO 2 , or 1 nmAl 2 O 3 /4 nm HfO 2 , on strained Ge and strained Ge 0.94 Sn 0.06 . Experimental capacitance− voltage characteristics are presented and the effect of the small bandgap, like strong response of minority carriers at applied field, are discussed via simulations.

AlGaN/GaN HEMTs on silicon substrates have been fabricated and their static and small-signal RF characteristics investigated. The AlGaN/GaN material structures were grown on (111) p-Si by LP-MOVPE. Devices exhibit a saturation current of 0.91 A/mm, a good pinchoff and a peak extrinsic transconductance of 122 mS/mm. A unity current gain frequency of 12.5 GHz and max =0.83wereobtained.Thehighestsaturationcurrentreported so far, static output characteristics of up to 20 V and breakdown voltage at pinchoff higher than 40 V demonstrate that the devices are capable of handling 16 W/mm static heat dissipation.

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