Papers by Keyword: MOS Interface

Abstract: We performed electron-spin-resonance (ESR) and electrically-detected-magnetic-resonance (EDMR) spectroscopy on 4H-SiC(1120)/SiO₂ interface defects to study differences between polar-face and non-polar-face 4H-SiC MOS interfaces. We found that in the non-polar-face MOS system, interface defects prefer to form spin-less states of doubly-occupied states and/or empty states, probably due to charge transfer between Si and C atoms at the interfaces.

Abstract: In this paper, the effect of different post oxide deposition nitridation processes in NO on n-channel lateral MOSFETs fabricated on implanted 4H-SiC were investigated. In particular, the electrical behavior of the MOSFETs was deeply investigated not only in terms of SiO₂/SiC interface state density and field effect mobility, but also considering the threshold voltage stability effect. The aim of this work was to explore to which extent post oxide deposition annealing in NO is beneficial for the MOS interface behavior and when their detrimental effects start to become predominant on the device performances. Here, the separation of the trapping states at the interface – either close to the conduction and valence band edges – and the near interface oxide traps are reported for the different duration of the post oxide deposition annealing. In fact, cyclic gate bias stress was employed in order to analyze the behavior of the trapping states and to correlate them with the variation of the benefits in terms of the channel mobility (that saturates at about 80 cm²V^-1s^-1), and on the threshold voltage instability effect. In particular, prolonged PDAs may induce an increase of the amount of trapping states close to the valence band edge and inside the insulator of about 20% and 50 %, respectively.

Abstract: We investigated the effects of γ-ray irradiation to single photon sources (SPSs) embedded in 4H-SiC metal-oxide-semiconductors field-effect transistors (MOSFETs). After the γ-ray irradiation, the number of SPSs was temporarily increased. However, the ratio of unstable SPSs was increased with increasing the radiation dose, and such unstable ones gradually disappeared. Finally, the density of the SPSs nearly recovered that before the irradiation. We discuss a possible explanation on these phenomena in terms of interactions between mobile hydrogen atoms and interface defects.

Abstract: The reaction-limiting process for the oxidation of SiC(0001) was investigated by density functional theory calculation. I found that the oxygen molecule insertion to the interfacial SiC bonds is the limiting process and the barrier is 3.21 eV. It is also found that the CO detachment is not limiting process because the barrier becomes small when the interfacial C atom is surrounded by three O atoms.

Abstract: We investigated single photon sources (SPSs) in 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) by means of confocal microscope techniques. We found SPSs only in 4H-SiC/SiO₂ interface regions of wet-oxide C-face MOSFETs. The other regions of MOSFETs such as source, drain and well did not exhibit SPSs. The luminescent intensity of the SPSs at room temperature was at least twice larger than that of the most famous SPSs, the nitrogen-vacancy center, in diamond. We examined four types of C-face and Si-face 4H-SiC MOSFETs with different oxidation processes, and found that the formation of the SPSs strongly depended on the preparation of SiC/SiO₂ interfaces.

Abstract: We demonstrate our new local deep level spectroscopy system improved for more accurate analysis of trap states at SiO₂/4H-SiC interfaces. Full waveforms of the local capacitance transient with the amplitude of attofarads and the time scale of microseconds were obtained and quantitatively analyzed. The local energy distribution of interface state density in the energy range of E_C − E_it = 0.31–0.38 eV was obtained. Two-dimensional mapping of the interface states showed inhomogeneous contrasts with the lateral spatial scale of several hundreds of nanometers, suggesting that the physical origin of the trap states at SiO₂/SiC interfaces is likely to be microscopically clustered.

Abstract: High channel mobility 4H-SiC MOSFETs have been demonstrated by phosphorus and arsenic implantation prior to thermal oxidation in N₂O. The maximum field-effect mobility of 81 and 114 cm²/Vs were achieved, respectively. The MOSFET fabrication was done on lightly aluminium doped p-type epitaxial layers and on heavily aluminium implanted p-well.

Abstract: The electrical characteristics of the SiC metal-oxide-semiconductor field effect transistor (MOSFET) have been limited by large amount of states at the SiO₂/SiC interface. In this study, the accuracy of the energy level of the interface states extracted by hypothetical high frequency extreme, which is conventionally used, is experimentally examined. Conductance measurements at low temperature between 65 K and 100 K reveal that the extracted energy distribution of the interface states at nitrided SiO₂/SiC interface close to the conduction band edge depends on the measurement temperature. It is demonstrated that conductance method at 65K enables us more accurate evaluation of the interface states at the SiO₂/SiC interface and found that the interface states density (D_it) of nitride SiO₂/SiC interface is over 10¹³ cm^-2eV^-1 at energy level of 0.1 eV below the conduction band edge.

Abstract: Electrical properties of the gate oxides thermally grown in N₂O on n-type and p-type 4H-SiC have been compared using conventional MOS structure and inversion-channel MOS structure, respectively. Sufficient difference in the electrical properties of the gate oxides grown on n-type and p-type 4H-SiC was revealed. We conclude that the gate oxide process optimisation using inversion-channel MOS devices is superior as compared to the conventional MOS structure.

Abstract: The effect of the alternative nitridation process of the 4H-SiC/SiO₂ interface by introduction of a thin silicon nitride layer on the electrical properties of the gate oxide has been investigated. C-V and G-V measurements on inversion-channel MOS devices revealed similar results to the conventional N₂O oxidation. Higher field-effect mobility values are achieved due to lower interface roughness of the alternative nitridation process. However, insignificant degradation of the reliability was observed.