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(a) Schematic of a GaN MOS-HEMT encapsulated by a high-stress DLC liner stressor. Cross-sectional TEM images of the TaN/HfAlO gate stack on AlGaN/GaN (box labeled A) and the 40 nm DLC on AlGaN/GaN (box labeled B) are shown in (b). Elemental profile of C, Al, and Ga in the DLC/AlGaN/GaN stack in region B is obtained using secondary ion mass spectrometry. The region in which the C concentration is high is the DLC layer.
(a) Simulated lateral stress (in units of GPa) contributed by a 40 nm DLC with an intrinsic stress of 6 GPa in an AlGaN/GaN MOS-HEMT with of 400 nm. The stress contours are labeled. The contour interval is 200 MPa. Stress simulation was done using SENTAURUS software (Ref. 24). (b) Stress along horizontal lines at the depth of 2 nm below AlGaN/GaN interface (, denoted by dark gray symbols) and 5 nm below AlGaN/GaN interface (, denoted by light gray symbols) below the AlGaN/GaN interface. A peak compressive stress of −1.2 GPa is observed in under the gate near the S/D edges. The tensile stress contributed by the DLC liner in the region between the gate and S/D contacts and at the AlGaN/GaN interface is .
(a) and characteristics of AlGaN/GaN MOS-HEMTs with DLC (black symbols) and without DLC liner (white symbols), measured at (circles) and (squares). Gate length is 400 nm. From the fabricated devices, sheet resistance of and specific contact resistivity of were obtained. Gate leakage is around and for device without and with DLC . (b) characteristics of the same pair of devices in (a), where is varied in steps of 2 V from −2 to 4 V. 22% enhancement of saturation current is observed for the device with DLC over the control device at of 6 V and of 12 V.
(a) The peak transconductance of AlGaN/GaN MOS-HEMTs with DLC liner shows enhancement over the control devices (without DLC) at . The enhancement is larger than for . (b) Cumulative distribution of source and drain series resistance for devices with DLC (black) and without DLC (white). ranges from 300 to 1000 nm. The DLC liner contributed to a 14% lower median . The inset illustrates the extraction of .
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