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The effects of interface oxidation on the transport behavior of the 2-D electron gas (2DEG) in AlGaN/GaN heterostructures by plasma-enhanced-atomic-layer-deposited AlN (PEALD-AlN) passivation were investigated using temperature-dependent Hall-effect and X-ray photoelectron spectroscopy (XPS) characterizations. AlGaN/GaN heterostructure with a 4-nm-thick PEALD-AlN passivation exhibits good 2DEG transport behavior and stability at moderately high temperature (e.g., 275 °C). However, serious oxidation of the AlN/GaN (cap layer) interface occurs as the sample is heated up to 400 °C in low-pressure atmosphere, as verified by an increased Ga-O bond in Ga 3d core-level spectra. The oxidation leads to a significant reduction of 2.47 × 1012 cm-2 in the 2DEG density in the channel. A modified AlN passivation structure with Al2O3/AlN (10/4 nm) stack is shown to be able to effectively suppress the oxidation of the AlN/GaN interface, demonstrating an enhanced 2DEG density and high-temperature stability even when the sample is heated up to 500 °C. Based on XPS and 2DEG recovery experiments, it is suggested that acceptor-like deep levels have been generated in the near-surface region of AlGaN/GaN heterostructure because of the oxidation, and trapping of these deep levels results in significant depletion of the 2DEG in the channel. The effects of PEALD-AlN passivation on the strain in the AlGaN barrier of AlGaN/GaN heterostructures are also evaluated with high-resolution X-ray diffraction technique. [ABSTRACT FROM AUTHOR]

Effective interface engineering techniques in III-nitride heterojunction power devices, aiming at yielding high VTH stability in insulated-gate devices and suppressed current collapse in high-voltage switching operation, are of critical significance to enhance device performance and reliability. In this work, we present an interface enhancement technology featuring in situ low-damage NH3/Ar/N2 pre-gate plasma treatment prior to the ALD-Al2O3 deposition for high-performance III-nitride MIS-HEMTs. It is manifest that this technology can effectively remove the native oxide while forming a monocrystal-like nitridation interfacial-layer (NIL) on the III-nitride surface. The Al2O3(NIL)/GaN/AlGaN/GaN MIS-heterostructures with high-quality interface exhibit well-behaved electrical characteristics, including a small subthreshold swing of ∼64 mV/dec, a small hysteresis of ∼0.09 V, tiny f/T dispersions in the C- V characteristics, and low interface trap density of ∼1 × 1012-6 × 1012 cm−2eV−1. Cross-sectional TEM micrograph of the Al2O3/III-nitride gate stack with a monocrystal-like nitridation interfacial-layer (NIL). [ABSTRACT FROM AUTHOR]