Ti/4H-SiC Schottky diode breakdown voltage with different thickness of 4H-SiC epitaxial layer

Breakdown voltage for Ti/4H-SiC type Schottky diode with six guard rings have been calculated theoretically and by mean of numerical simulations. It is shown that the breakdown voltage can be increase at the minimum on 100 V in case when thickness of the n-type 4H-SiC epitaxial layer increase from 18 up to 22 μm. It is established that the breakdown voltage value for Ti/4H-SiC type Schottky diode with guard rings calculated by mean simulation in ATLAS program and theoretically have good approximation. Thus, above approach gives the possibility for projection of diode structure with different 4H-SiC epitaxial layer thickness with higher breakdown voltage value.

Source:IOPscience

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Ultra high voltage MOS controlled 4H-SiC power switching devices

Ultra high voltage (UHV, >15 kV) 4H-silicon carbide (SiC) power devices have the potential to significantly improve the system performance, reliability, and cost of energy conversion systems by providing reduced part count, simplified circuit topology, and reduced switching losses. In this paper, we compare the two MOS based UHV 4H-SiC power switching devices; 15 kV 4H-SiC MOSFETs and 15 kV 4H-SiC n-IGBTs. The 15 kV 4H-SiC MOSFET shows a specific on-resistance of 204 mΩ cm2 at 25 °C, which increased to 570 mΩ cm2 at 150 °C. The 15 kV 4H-SiC MOSFET provides low, temperature-independent, switching losses which makes the device more attractive for applications that require higher switching frequencies. The 15 kV 4H-SiC n-IGBT shows a significantly lower forward voltage drop (VF), along with reasonable switching performance, which make it a very attractive device for high voltage applications with lower switching frequency requirements. An electrothermal analysis showed that the 15 kV 4H-SiC n-IGBT outperforms the 15 kV 4H-SiC MOSFET for applications with switching frequencies of less than 5 kHz. It was also shown that the use of a carrier storage layer (CSL) can significantly improve the conduction performance of the 15 kV 4H-SiC n-IGBTs.

Source:IOPscience

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Impact of crystal faces of 4H-SiC in SiO2/4H-SiC structures on interface trap densities and mobilities

The impact of crystal faces of 4H-SiC in SiO2/4H-SiC structures on interface trap densities and mobilities were examined by a method that utilizes Hall effect measurements and split capacitance–voltage measurements to clarify the mechanism of high field-effect mobilities in SiO2/4H-SiC and . The characterization results show that high field-effect mobilities in nitrided SiO2/4H-SiC  and  are caused by both lower interface trap densities near the conduction band edge and higher Hall mobilities compared to those in nitrided SiO2/4H-SiC (0001) and .

Source:IOPscience

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Chloride-based fast homoepitaxial growth of 4H-SiC films in a vertical hot-wall CVD*

Chloride-based fast homoepitaxial growth of 4H-SiC epilayers was performed on 4° off-axis 4H-SiC substrates in a home-made vertical hot-wall chemical vapor deposition (CVD) system using H2−SiH4−C2H4−HCl. The effect of the SiH4/H2 ratio and reactor pressure on the growth rate of 4H-SiC epilayers has been studied successively. The growth rate increase in proportion to the SiH4/H2ratio and the influence mechanism of chlorine has been investigated. With the reactor pressure increasing from 40 to 100 Torr, the growth rate increased to 52 μm/hand then decreased to 47 μm/h, which is due to the joint effect of H2 and HCl etching as well as the formation of Si clusters at higher reactor pressure. The surface root mean square (RMS) roughness keeps around 1 nm with the growth rate increasing to 49 μm/h. The scanning electron microscope (SEM), Raman spectroscopy and X-ray diffraction (XRD) demonstrate that 96.7 μm thick 4H-SiC layers of good uniformity in thickness and doping with high crystal quality can be achieved. These results prove that chloride-based fast epitaxy is an advanced growth technique for 4H-SiC homoepitaxy.

Source:IOPscience

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Investigation of spatial charge distribution and electrical dipole in atomic layer deposited Al2O3 on 4H-SiC

Charge distribution and electrical dipole in an Al2O3/4H-SiC structure are investigated by capacitance–voltage measurement and x-ray photoelectron spectroscopy (XPS). The charge densities in Al2O3 and at the Al2O3/4H-SiC interface are negligible and  −6.89  ×  1011 cm−2, respectively. Thus the small charge amount indicates the suitability of Al2O3 as a gate dielectric. The dipole at the Al2O3/4H-SiC interface is  −0.3 to  −0.91 V. The XPS manifests electron transfer from Al2O3 to 4H-SiC. The dipole formation is explained by a gap state model and the higher charge neutrality level of Al2O3 than the Fermi level of 4H-SiC, which confirms the feasibility of the gap state model on investigating band lineup at heterojunctions. The electrical dipole at the Al2O3/4H-SiC interface is critical for threshold voltage tuning. These results are helpful in engineering the SiC based gate stacks.

Source:IOPscience

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