A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al 2 O 3 gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge. These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001).

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In this paper, we demonstrate the critical design considerations for GaN-based microwave power varactors for the purpose of achieving high breakdown voltage, high Q-factor and high linearity. The extraction of these parameters from a real GaN-based power varactor diode is also presented. High values of these parameters are obtained, which is critical for the applications in the wireless base-station communications.

Enhanced hot camer degradation with stress V, in the valence-band tunneling regime is observed. This degradation is attributed to channel hole creation by valence-band electron tunneling. The created holes provide for Auger recombination with electrons in the channel and thus increase hot electron energy. The valence-band tunneling enhanced hot carrier degradation becomes more serious as gate oxide thickness is reduced. In ultra-thin gate oxide nMOSFETs, our result shows that the valence-band tunneling enhanced degradation, as opposed to max. Ib stress induced degradation, exhibits positive dependence on substrate bias. This phenomenon may cause a severe reliability issue in positively biased substrate or floating substrate devices.