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We investigated the atomic structures of the interface states (gap states) at the SiO2/4H-SiC(0001) interface using hard x-ray photoelectron spectroscopy (HAXPES), operando hard x-ray photoelectron spectroscopy, extended x-ray absorption fine structure, and first principles molecular dynamics (FPMD) calculations. For the interface states, two types were observed: continuous interface states in the whole gap and interface states with discrete energy levels near the conduction band minimum (CBM). From HAXPES, we found that carbon clusters and carbon vacancies were formed at the SiO2/4H-SiC(0001) interface. FPMD calculations on the SiO2/4H-SiC(0001) interface showed that the interface states in the whole gap were attributed to the various atomic geometries of the CßSi3 species and the carbon clusters with various sizes and surrounding atoms. For the interface states with a discrete energy level near the CBM, we could not find their atomic structure using our current calculations. We calculated the carbon vacancies prepared on the side of an SiC substrate at the SiO2/4H-SiC(0001) interface, indicating the formation of a discrete energy level in the midgap. It is likely that carbon vacancies formed at the step of the interface may modulate the midgap energy level to energy below the CBM. Therefore, we propose that the interface states with discrete energy levels near the CBM could be attributed to the carbon vacancies formed on the steps at the SiO2/4H-SiC(0001) interface. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy measurements were used to obtain the energy distribution of interface states at ultrathin oxide/Si(100) interfaces under biases between the metal overlayer and the Si substrate of the metal-oxide-semiconductor (MOS) devices. The MOS devices were fabricated using phosphorus-doped n-type Si(100) wafers which were cleaned using the RCA method, cut into 1 X 1 cm sq pieces and etched in 5 vol % hydrofluoric acid. Results indicate that cyanide treatment increased the electrical characteristics of the MOS tunneling diodes.

Pure germanium nitride (Ge3N4) thin films were successfully formed on n-type Ge (111) substrate using an atmospheric-pressure (AP) nitrogen plasma. Their film structures and electrical properties were then examined in detail. Synchrotron radiation photoelectron spectroscopy clearly revealed that the Ge3N4 thin films formed by AP plasma had superior oxidative resistance compared to those made using conventional plasma techniques. Films fabricated at 500 °C showed only minor post-oxidation, even after exposure to air, which is a potentially very useful feature for passivation layers at high-permittivity (high-k) dielectric film-Ge interfaces. The films also showed excellent electrical properties. Capacitance-voltage measurements revealed no hysteresis or kinks, indicating that the trap-state density was low at the Ge3N4-Ge interface. The leakage current density is also lower than in films fabricated using other plasma systems. Direct-tunneling current simulations revealed that the effective tunneling mass increased due to the formation of high-quality Ge3N4 thin films, resulting in superior leakage current. These results suggest that our nitridation technique would show major benefits in Ge field-effect transistors. [ABSTRACT FROM AUTHOR]

The surface and bulk electronic structures of In0.7Ga0.3N epilayers are investigated by angle-resolved hard X-ray photoelectron spectroscopy (HX-PES) combined with soft X-PES. The unintentionally and Mg-doped In0.7Ga0.3N (u-In0.7Ga0.3N and In0.7Ga0.3N:Mg, respectively) epilayers are grown by radio-frequency plasma-assisted molecular beam epitaxy. Here three samples with different Mg concentrations ([Mg] = 0, 7 × 1019, and 4 × 1020 cm−3) are chosen for comparison. It is found that a large downward energy band bending exists in all samples due to the formation of a surface electron accumulation (SEA) layer. For u-In0.7Ga0.3N epilayer, band bending as large as 0.8 ± 0.05 eV occurs from bulk to surface. Judged from the valence band spectral edge and numerical analysis of energy band with a surface quantum well, the valence band maximum (VBM) with respect to Fermi energy (EF) level in the bulk is determined to be 1.22 ± 0.05 eV. In contrast, for In0.7Ga0.3N:Mg epilayers, the band bending increases and the VBM only in the bulk tends to shift toward the EF level owing to the Mg acceptor doping. Hence, the energy band is considered to exhibit a downward bending structure due to the coexistence of the n+ SEA layer and Mg-doped p layer formed in the bulk. When [Mg] changes from 7 × 1019 to 4 × 1020 cm−3, the peak split occurs in HX-PES spectra under the bulk sensitive condition. This result indicates that the energy band forms an anomalous downward bending structure with a singular point due to the generation of a thin depleted region at the n+p interface. For In0.7Ga0.3N:Mg epilayers, the VBM in the bulk is assumed to be slightly lower than EF level within 0.1 eV. [ABSTRACT FROM AUTHOR]