Scaling Between Channel Mobility and Interface State Density in SiC MOSFETs (original) (raw)
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Systematic Analysis of the High- and Low-Field Channel Mobility in Lateral 4H-SiC MOSFETs
Materials Science Forum, 2014
In this work, we investigate the impact of Al-implantation into n-MOSFET channel regions together with its p-doping concentration upon the mobility limiting scattering mechanisms in the channel. For this purpose, a study of the interface trap density, interface trapped charge density, field-effect mobility, and Hall mobility is carried out for normally-off n-MOSFETs with different doping profiles and concentrations in the channel region. The trend of the field-effect and the Hall mobility as well as the differences thereof will be discussed. Based on the determined mobilities in the range from 11.9 cm2/Vs to 92.4 cm2/Vs, it will be shown that for p-doping concentrations above 5·1016 cm-3 Coulomb scattering is the dominant scattering mechanism for both, low- and high-field mobility. In contrast, for p-doping concentrations below 5·1016, cm-3 further scattering mechanisms will be considered that may account for the observed mobility trend at high electric fields.
Interface state density and channel mobility for 4H-SiC MOSFETs with nitrogen passivation
Applied Surface Science, 2001
Interface state density and channel mobility have been characterized for 4H-SiC MOSFETs fabricated with dry thermal oxides and subsequently passivated with nitric oxide. The interface trap density at 0.1 eV below the conduction band edge decreases from approximately 8 Â 10 12 to 1 Â 10 12 eV À1 cm À2 following anneals in nitric oxide (NO) at 1175 8C for 2 h. The room temperature field effect channel mobility increases by an order of magnitude to approximately 35 cm 2 /V s following the passivation anneal. The field effect channel mobility of passivated MOSFETs shows almost no change with increasing temperature, while the mobility for unpassivated devices increases with increasing temperature and is thermally activated ($T 1.9 ) due to decreased Coulomb scattering by electrons trapped at the acceptor-like interface states near the conduction band. Over the temperature range 300-473 K, threshold voltage changes of about À0.8 and À3.7 V, respectively, are observed for devices processed with and without NO passivation. #
Microelectronic Engineering, 2006
Besides its favorable physical properties, high performant MOSFETs (metal-oxide-semiconductor field-effect transistors) fabrication in silicon carbide (SiC) remains an open issue due to their low channel mobility values. The effect of charge trapping and the scattering at interface states have been invoked as the main reasons for mobility reduction in SiC thermal oxidized MOS gated devices. In this paper, we propose a compact electron mobility model based on the well-established Lombardi mobility model to reproduce the mobility degradation commonly observed in these SiC devices. Using 2D electrical simulations along with the proposed model and taking into account interface traps Coulomb scattering, the experimental field-effect mobility of 4H-SiC MOSFET devices has been fitted with a good agreement. .es (A. Pérez-Tomás). www.elsevier.com/locate/mee Microelectronic Engineering 83 (2006) 440-445
IEEE Electron Device Letters, 2000
In the family of wide band gap materials (silicon carbide, the group III nitrides and diamond), SiC is the only semiconductor that has a native oxide, and metal-oxide-semiconductor field effect transistors (MOSFETs) have been fabricated using both 4H-and 6H-SiC. The 4H polytype has higher bulk carrier mobility [1], and is hence the polytype of choice for power MOSFET fabrication. However, reported channel mobilities for 4H n-channel, inversion mode devices are substantially lower than for 6H-MOSFETs. For power device applications, the advantage provided by 4H-SiC of lower epilayer resistance for a given operating voltage is compromised by the low channel mobility. Schorner, et al. [2] attribute the poorer performance of 4H devices to a large, broad interface state density located at approximately 2.9eV above the valence band edge in both polytypes. More of these states lie in the band gap for 4H-SiC (Egap ~ 3.3eV) compared to 6H-SiC (Egap ~ 3eV) where they act to reduce channel mobility through field termination, carrier trapping and Coulomb scattering. Afanasev, et al. proposed that interface states in SiC/SiO2 structures result from carbon clusters at the interface and defects in a nearinterface sub-oxide that is produced when the oxidation process is terminated. The large interface trap density near the conduction band edge proposed by Schorner, et al. has been observed experimentally for both n-SiC and p-SiC . Li, et al. [7] originally reported improvements in the electrical performance of dry oxides on 6H-SiC annealed in nitric oxide (NO). We have grown oxides on 4H-SiC using standard thermal techniques [8] and conducted post oxidation anneals in . We find that the interface state density near the conduction band edge in n-4H-SiC can be reduced to levels comparable to the interface state density near the conduction band edge in 6H-SiC. Furthermore, the effective channel mobility for inversionmode 4H-SiC MOSFETs improves significantly following high temperature anneals in nitric oxide.
Japanese Journal of Applied Physics, 2019
Low interface state density (D it) and high field-effect mobility (μ μ fe) at SiO 2 /4H-SiC (03̅ 38̅) Metal-oxide-semiconductor (MOS) interfaces are known. In order to understand the behavior and the scattering mechanisms induced electrons in more detail, we fabricated the Hall-bar lateral MOSFETs on the 4H-SiC (03̅ 38̅) substrate with various channel doping concentrations and evaluated the trapped electron densities and the Hall mobilities by split capacitance-voltage and Hall-effect measurements. Our results demonstrated that more than 80% of the induced electrons at the SiO 2 /4H-SiC MOS (03̅ 38̅) interfaces contribute to the current conduction as the free electrons. The majority of the electron traps seemed to be located mainly at the edge of the conduction band because the trapped electron density increased around the threshold voltage and was saturated in the high gate voltage region.
Advanced processing for mobility improvement in 4H-SiC MOSFETs: A review
Materials Science in Semiconductor Processing, 2018
This paper reviews advanced gate dielectric processes for SiC MOSFETs. The poor quality of the SiO 2 /SiC interface severely limits the value of the channel field-effect mobility, especially in 4H-SiC MOSFETs. Several strategies have been addressed to overcome this issue. Nitridation methods are effective in increasing the channel mobility and have been adopted by manufacturers for the first generations of commercial power devices. Gate oxide doping techniques have also been successfully implemented to further increase the channel mobility, although device stability is compromised. The use of high-k dielectrics is also analyzed, together with the impact of different crystal orientations on the channel mobility. Finally, the performance of SiC MOSFETs in harsh environments is also reviewed with special emphasis on high temperature operation.
Journal of Electronic Materials, 2005
High field-dependent electron transport characteristics in 4H-SiC were measured successfully using a nanosecond-pulsed technique. It should be noted that the velocity-field characteristics of SiC are different from GaAs in that SiC does not have velocity overshooting behavior. Without the overshooting behavior, the current density of SiC metal-semiconductor field-effect transistors (MESFETs) is restricted fundamentally by the low drift velocity in the low-field, parasitic regions. These parasitic regions not only limit the current density but also are responsible for a significant shift of the threshold voltage.
Using a First Principles Coulomb Scattering Mobility Model for 4H-SiC MOSFET Device Simulation
Materials Science Forum, 2006
A physics based device simulator for detailed numerical analysis of 4H-SiC MOSFETs with an advanced mobility model that accounts for the effects of bulk and surface phonons, surface roughness and Coulomb scattering by occupied interface traps and fixed oxide charges, has been developed. A first principles quasi-2D Coulomb scattering mobility model specifically for SiC MOSFETs has been formulated. Using this, we have been able to extract the interface trap density of states profile for 4H-SiC MOSFETs and have shown that at room temperature, Coulomb scattering controls the total mobility close to the interface. High temperature, low field simulations and experiments show that the current increases with increase in temperature. The effect of Coulomb scattering decreases with increase in temperature causing an increase in the total mobility near the interface at low gate voltages.