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Generation and elimination of mobile ions in thermally grown SiO2 on 4H-SiC(0001) were systematically investigated by electrical measurements of MOS capacitors. In contrast to a SiO2/Si system, intrinsic positive mobile ions were found to exist in as-oxidized SiO2/SiC structures, leading to significant instability of SiC-MOS devices. Post-oxidation annealing in Ar ambient mostly eliminates the mobile ions, but they are generated again by subsequent high-temperature hydrogen annealing despite the improved interface quality. The density of the mobile ions was estimated to be several 1012 cm-2. Possible physical origins of the mobile ions are discussed on the basis of the experimental findings. [ABSTRACT FROM AUTHOR]

Germanium oxynitride (GeON) gate dielectrics with surface nitrogen-rich layers were fabricated by plasma nitridation of thermally grown oxides (GeO2) on Ge(100). Insulating features of ultrathin GeO2 layers of around 2-nm-thick were found to improve with plasma treatment, in which leakage current was drastically reduced to over four orders of magnitude. Consequently, Au/GeON/Ge capacitors of an equivalent oxide thickness down to 1.7 nm were achieved while keeping sufficient leakage reduction merit. The minimum interface state density values of GeON/Ge structures as low as 3×1011 cm-2 eV-1 were obtained for both the lower and upper halves of the bandgap without any postnitridation treatments. These results were discussed based on the effects of plasma nitridation on a degraded GeO2 surface for recovering its electrical properties by creating stable nitride layers. [ABSTRACT FROM AUTHOR]

Unusual behavior of bias-temperature instabilities in SiC metal-oxide-semiconductor (MOS) devices is studied. Electrical measurements of SiC-MOS capacitors are used to investigate details of self-generated mobile ions in thermal oxides on 4H-SiC(0001) substrates, such as their polarity, density, distribution, and impact on interface properties. It is found that positive bias-temperature stress (BTS) accumulates self-generated positive mobile ions at the bottom SiO2/SiC interface with an areal density of several 1012 cm-2, and that they induce additional electron trap formation at the interface. Using this knowledge, we demonstrate effective removal of the positive mobile ions with a combination of negative BTS and subsequent etching of the oxide surface. [ABSTRACT FROM AUTHOR]