Angle-Resolved Photoelectron Spectroscopy Studies of Initial Stage of Thermal Oxidation on 4H-SiC (0001) on-Axis and 4° Off-Axis Substrates

t is a key for improving the performance of SiC MOSFET to clarify SiO2/SiC interface structure formed by thermal oxidation. We have investigated the initial stage of thermal oxidation on 4H-SiC (0001) on-axis and 4° off-axis substrates using angle-resolved photoelectron spectroscopy. The changes of the Si 2p3/2 and C 1s photoelectron spectra show that the off-axis has an influence on the chemical bonding state of SiO2/SiC. On the other hand, there isn't difference in the oxidation rate between on-axis 4H-SiC(0001) and 4° off-axis 4H-SiC(0001).

Source:IOPscience

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Effect of carbon in Si oxide interlayers of the Al2O3/4H-SiC structure on interfacial reaction by oxygen radical treatment

The interface state density of Al2O3/4H-SiC can be decreased by oxygen radical treatment at room temperature, so we have systematically investigated the mechanism of the interfacial reaction at Al2O3/4H-SiC during oxygen radical treatment. In this study we focus on the characteristics of the Si oxide interlayer, namely whether carbon atoms are included in the film or not, because the interfacial reactions induced by oxygen radical treatment for Al2O3/4H-SiC and Al2O3/Si are different. It is revealed that decarbonization of the SiC x O y layer occurs when the SiC x O y surface is directly exposed to oxygen radicals. Then, the difference in the interfacial reaction caused by oxygen radical treatment between Al2O3/4H-SiC and Al2O3/Si is investigated by intentionally forming SiC x O y and SiO2 interlayers at the Al2O3/4H-SiC interface. Finally, the possible reaction mechanism is discussed on the basis of experimental results. All the results are qualitatively (but clearly) understood by considering that decarbonization of SiC x O y occurs as the starting point.

Source:IOPscience

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Mechanism of phosphorus passivation of near-interface oxide traps in 4H–SiC MOS devices investigated by CCDLTS and DFT calculation

Interfacial charge trapping in 4H–SiC MOS capacitors with P doped SiO2 or phospho-silicate glass (PSG) as a gate dielectric has been investigated with temperature dependent capacitance–voltage measurements and constant capacitance deep level transient spectroscopy (CCDLTS) measurements. The measurements indicate that P doping in the dielectric results in significant reduction of near-interface electron traps that have energy levels within 0.5 eV of the 4H–SiC conduction band edge. Extracted trap densities confirm that the phosphorus induced near-interface trap reduction is significantly more effective than interfacial nitridation, which is typically used for 4H–SiC MOSFET processing. The CCDLTS measurements reveal that the two broad near-interface trap peaks, named 'O1' and 'O2', with activation energies around 0.15 eV and 0.4 eV below the 4H–SiC conduction band that are typically observed in thermal oxides on 4H–SiC, are also present in PSG devices. Previous atomic scale ab initio calculations suggested these O1 and O2 traps to be carbon dimers substituted for oxygen dimers (CO=CO) and interstitial Si (Sii) in SiO2, respectively. Theoretical considerations in this work suggest that the presence of P in the near-interfacial region reduces the stability of the CO=CO defects and reduces the density of Sii defects through the network restructuring. Qualitative comparison of results in this work and reported work suggest that the O1 and O2 traps in SiO2/4H–SiC MOS system negatively impact channel mobility in 4H–SiC MOSFETs.

Source:IOPscience

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Fermi-level pinning at metal/4H-SiC contact induced by SiC x O y interlayer

We investigated the impact of defects formed at the SiO2/4H-SiC interface on the Schottky barrier height of metal/4H-SiC(0001) contacts. We found that an ultra-thin SiC x O y layer remains on the 4H-SiC surface after SiO2 sputtering at various powers and its removal by diluted hydro fluoride solution. Ni, Mo, or Al was deposited on 4H-SiC surface without and with a residual SiC x O y layer. It was found that metal/4H-SiC contacts without a residual SiC x O y layer exhibit ideal Schottky property, while Fermi-level pinning (FLP) is caused for metal/4H-SiC contacts with a residual SiC x Oy layer, and the degree of FLP increases increasing sputtering power of SiO2. The pinning position was estimated to be ~0.8 eV below the conduction band minimum of 4H-SiC, which does not correspond to the charge neutrality level of 4H-SiC. Finally, we proposed a physical model where a SiC x O y interlayer causes FLP, and the model was experimentally verified by intentionally forming a SiC x O y interlayer.

Source:IOPscience

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Magnetism in transition metal (Fe, Ni) co-doped 4H-SiC: a first-principles study

The electronic structure and magnetic properties of (Fe, Ni) co-doped 4H-SiC-based dilute magnetic semiconductors were investigated by first-principles calculations. The (Fe, Ni) co-doped 4H-SiC exist spin-polarization due to the introduction of dopant atoms, resulting in splitting. The co-doped system is more prone to a ferromagnetic state, and the magnetization energy is larger than some known room temperature diluted magnetic semiconductors, indicating that the room temperature ferromagnetism (FM) is higher. The results show that the (Fe, Ni) co-doped 4H-SiC system is ferromagnetic at room temperature with E FM −398.8 meV. The (Fe, Ni) co-doped 4H-SiC system exhibits strong magnetic properties due to strong coupling between Fe and Ni, resulting in strong spin polarization of nearby C atoms. We also studied the effect of silicon vacancies in the (Fe, Ni) co-doped 4H-SiC system. The results show that all the configurations are FM, and the FM is significantly reduced compared with the system without silicon vacancies. These results have potential applications in electronic or spintronic devices.

Source:IOPscience

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