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Si diffusion into GaN was studied as a function of encapsulant type (SiO 2 or SiN x ) and diffusion temperature. Using a SiO 2 encapsulant, the Si diffusion exhibited an activation energy of 0.57 eV with a prefactor of 2.07 3 10 ÿ4 cm 2 sec ÿ1 in the temperature range 800-1,000°C. An enhancement-mode MgO/GaN-onSi metal-oxide semiconductor field-effect transistor (MOSFET) was fabricated utilizing Si-diffused regions under the source and drain to provide an accumulated channel. The gate leakage through the undoped GaN was low enough for us to achieve good saturation behavior in the drain-current-voltage characteristics. The devices showed improved transconductance and drain current relative to previous devices with Si-implanted source/drain regions.

Structural and morphological properties of GaN buffer layers grown by ammonia molecular beam epitaxy on SiC substrates for AlGaN/GaN high electron mobility transistors Growth of high mobility GaN and AlGaN/GaN high electron mobility transistor structures on 4H-SiC by ammonia molecular-beam epitaxy AlGaN / GaN high electron mobility transistors were grown by molecular beam epitaxy on Si on poly-SiC substrates formed by the Smart Cut™ process. The Smart Cut™ approach is an alternative solution to provide both a high resistivity and an excellent thermal conductivity template needed for power applications. Although the structure has not been optimized, devices with 0.7 m gate length show breakdown voltage of Ͼ250 V, f T of 18 GHz, and f max of 65 GHz.

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Schottky rectifiers fabricated on GaN layers grown on 4 in. diam Si substrates show breakdown voltages ͑V R ͒ of ϳ300 V at room temperature, on-state resistances ͑R ON ͒ of 40 m⍀ cm 2 , and figure-of-merit ͑V B ͒ 2 /R ON of 2.25 MW/cm 2 . The reverse current is thermally activated with activation energies in the range 0.3-0.4 eV and is proportional to contact perimeter at reverse biases up to ϳ100 V. This approach provides a low-cost alternative to GaN rectifiers on sapphire or SiC substrates while still maintaining good breakdown characteristics.