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We present a new method to fabricate N-face GaN/AlGaN high electron mobility transistors (HEMTs). These devices are extremely promising for ultrahigh frequency applications where low contact resistances and excellent carrier confinement are needed. In this letter, the N-face of a Ga-face AlGaN/GaN epilayer grown on Si (111) is exposed by removing the Si substrate. To provide mechanical support, prior to the substrate removal, the Ga-face of the wafer is bonded to a Si (100) carrier wafer. The resultant N-face GaN/AlGaN heterostructures exhibited record transport properties (mue = 1670 cm2/Vmiddots, ns = 1.6 times 1013/ cm2, and Rsh = 240 Omega/sq). These excellent transport properties rendered N-face HEMTs with 30% higher maximum drain current than Ga-face HEMTs and good RF characteristics (fT = 10.7 GHz middotmum and fmax = 21.5 GHzmiddotmum), comparable to state-of-the-art Ga-face devices.
Date of Publication: Feb. 2009