| 1. |
- Ayedh, H. M., et al.
(author)
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Controlling the carbon vacancy concentration in 4H-SiC subjected to high temperature treatment
- 2016
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In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015. - : Trans Tech Publications. - 9783035710427 ; , s. 414-417
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Conference paper (peer-reviewed)abstract
- The carbon vacancy (VC) is the major charge carrier lifetime limiting-defect in 4H-SiC epitaxial layers and it is readily formed during elevated heat treatments. Here we describe two ways for controlling the VC concentration in 4H-SiC epi-layer using different annealing procedures. One set of samples was subjected to high temperature processing at 1950 °C for 3 min, but then different cooling rates were applied. A significant reduction of the VC concentration was demonstrated by the slow cooling rate. In addition, elimination of the VC’s was also established by annealing a sample, containing high VC concentration, at 1500 °C for a sufficiently long time. Both procedures clearly demonstrate the need for maintaining thermodynamic equilibrium during cooling.
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| 2. |
- Ayedh, H. M., et al.
(author)
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Formation and annihilation of carbon vacancies in 4H-SiC
- 2016
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In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015. - : Trans Tech Publications. - 9783035710427 ; , s. 331-336
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Conference paper (peer-reviewed)abstract
- The carbon vacancy (VC) is a major point defect in high-purity 4H-SiC epitaxial layers limiting the minority charge carrier lifetime. In layers grown by chemical vapor deposition techniques, the VC concentration is typically in the range of 1012 cm-3 and after device processing at temperatures approaching 2000 °C, it can be enhanced by several orders of magnitude. In the present contribution, we show that the cooling rate after high-temperature processing has a profound influence on the resulting VC concentration where a slow rate promotes elimination of VC. Further, isochronal annealing of as-grown and as-oxidized epi-layers protected by a carbon-cap was undertaken between 800 °C and 1600 °C. The results reveal that thermodynamic equilibrium of VC is established rather rapidly at moderate temperatures, reaching a VC concentration of only a few times 1011 cm-3 after 40 min at 1500 °C. Hence, the concept of eliminating VC’s by annealing at moderate temperatures under C-rich equilibrium conditions shows great promise and enables reannealing of high-temperature processed wafers, in contrast to the procedures commonly used today to eliminate VC. In-diffusion of carbon interstitials and out-diffusion of VC’s are discussed as the kinetics processes establishing the thermodynamic equilibrium.
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| 3. |
- Elahipanah, Hossein, et al.
(author)
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Modification of etched junction termination extension for the high voltage 4H-SiC power devices
- 2016
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In: Silicon Carbide and Related Materials. - : Trans Tech Publications. - 9783035710427 ; , s. 978-981
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Conference paper (peer-reviewed)abstract
- High voltage 4H-SiC bipolar junction transistors (BJTs) with modified etched junction termination extension (JTE) were fabricated and optimized in terms of the length (LJTE) and remaining dose (DJTE) of JTEs. It is found that for a given total termination length (Σ LJTEi), a decremental JTE length from the innermost edge to the outermost mesa edge of the device will result in better modification of the electric field. A breakdown voltage (BV) of 4.95 kV is measured for the modified device which shows ~20% improvement of the termination efficiency for no extra cost or extra process step. Equal-size BJTs by interdigitated-emitter with different number of fingers and cell pitches were fabricated. The maximum current gain of 40 is achieved for a single finger device with the emitter width of 40 μm at IC = 0.25 A (JC = 310 A/cm2) which corresponds to RON = 33 mΩ.cm2. It is presented that the current gain decreases by having more fingers while the maximum current gain is achieved at higher current density.
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| 4. |
- Kostov, Konstantin Stoychev, et al.
(author)
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Impact of package parasitics on switching performance
- 2016
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In: Materials Science Forum. - : Trans Tech Publications Ltd. - 9783035710427 ; , s. 1057-1060
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Conference paper (peer-reviewed)abstract
- The package parasitics are a serious obstacle to the high-speed switching, which is necessary in order to reduce the switching power losses or reduce the size of power converters. In order to design new packages suitable for Silicon Carbide (SiC) power transistors, it is necessary to extract the parasitics of different packages and be able to predict the switching performance of the power devices placed in these packages. This paper presents two ways of simulating the switching performance in a half-bridge power module with SiC MOSFETs. The results show that the parasitic inductances in the power module slow down the switching, lead to poor current sharing, and together with the parasitic capacitances lead to oscillations. These negative effects can cause failures, increased losses, and electromagnetic compatibility issues.
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| 5. |
- Kuroki, S. I., et al.
(author)
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Characterization of 4H-SiC nMOSFETs in harsh environments, high-temperature and high gamma-ray radiation
- 2016
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In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015. - : Trans Tech Publications Ltd. - 9783035710427 ; , s. 864-867
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Conference paper (peer-reviewed)abstract
- Characteristics of 4H-SiC nMOSFETs with arsenic-doped S/D and NbNi silicide contacts in harsh environments of high-temperature up to 450°C, and high gamma-ray radiation up to over 100 Mrad, were investigated. At high temperature, field effect mobility increased as proportional to T3/2, and threshold voltage was shifted with temperature coefficients of -4.3 mV/K and -2.6 mV/K for oxide thicknesses of 10 nm and 20 nm, respectively. After Co60 gamma-ray exposure of 113 Mrad, the field effect mobility was varied within 8% for oxide thickness of 10 nm, however for 20 nm oxide thickness, this variation was 26%. The threshold voltage shifts were within 6%.
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| 6. |
- Linnarsson, Margareta K., et al.
(author)
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Alkali metal re-distribution after oxidation of 4H-SiC
- 2016
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In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015. - : Trans Tech Publications Ltd. - 9783035710427 ; , s. 677-680
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Conference paper (peer-reviewed)abstract
- Relocation of alkali metals sodium, potassium and cesium during oxidation of 4H-SiC has been studied by secondary ion mass spectrometry. The alkali metal source has been introduced by ion implantation before oxidation into n- and p-type 4H-SiC samples. Dry oxidation of SiC has been performed at 1150 ºC during 4, 8 and 16 h. In the formed oxide, the main part of the alkali metals diffuses out via the SiO2 surface. Close to the moving SiO2/SiC interface, a minor amount of alkali metals is retained. In the SiC material, the main amount of implanted alkali atoms is not redistributed during the oxidation, although a minor amount diffuses deeper into the samples. For ptype 4H-SiC, the diffusion deeper into the samples of the studied alkali metals decreases as the mass increases, Na+<K+<Cs+, but the sodium mobility is substantial already at 1150 °C.
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| 7. |
- Nagatsuma, H., et al.
(author)
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4H-SiC nMOSFETs with As-Doped S/D and NbNi silicide ohmic contacts
- 2016
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In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015. - : Trans Tech Publications Ltd. - 9783035710427 ; , s. 573-576
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Conference paper (peer-reviewed)abstract
- 4H-SiC nMOSFETs with As-doped S/D and NbNi silicide ohmic contacts were demonstrated for radiation-hard CMOS electronics. The threshold voltage Vth was designed to be 3.0 V by TCAD simulation, and was 3.6 – 3.8 V at the fabricated devices. On / off ratio was approximately 105.
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| 8. |
- Salemi, Arash, et al.
(author)
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Geometrical effect dependency on the on-state characteristics in 5.6 kV 4H-SiC BJTs
- 2016
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In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015. - : Trans Tech Publications Ltd. - 9783035710427 ; , s. 958-961
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Conference paper (peer-reviewed)abstract
- The influence of varying the emitter-base geometry, i.e., the emitter width (WE), emitter contact-emitter edge distance (Wn), and base contact-emitter edge (Wp) on the on-state characteristics in 5.6 kV implantation free 4H-SiC BJTs is investigated. The BJTs present a clear emitter size effect pointing out that surface recombination has a significant influence on current gain (β). The results show that the influence of varying Wp on the β is higher than Wn. A distance of 3 μm between emitter contact and base contact to the emitter edge (Wn = Wp = 3 μm) is the optimized value to have a BJT with a high β, and low on-resistance (RON) at a given WE.
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| 9. |
- Sun, Jianwu, et al.
(author)
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Solar driven energy conversion applications based on 3C-SiC
- 2016
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In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015. - : Trans Tech Publications Ltd. - 9783035710427 ; , s. 1028-1031
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Conference paper (peer-reviewed)abstract
- There is a strong and growing worldwide research on exploring renewable energy resources. Solar energy is the most abundant, inexhaustible and clean energy source, but there are profound material challenges to capture, convert and store solar energy. In this work, we explore 3C-SiC as an attractive material towards solar-driven energy conversion applications: (i) Boron doped 3C-SiC as candidate for an intermediate band photovoltaic material, and (ii) 3C-SiC as a photoelectrode for solar-driven water splitting. Absorption spectrum of boron doped 3C-SiC shows a deep energy level at ~0.7 eV above the valence band edge. This indicates that boron doped 3C-SiC may be a good candidate as an intermediate band photovoltaic material, and that bulk like 3C-SiC can have sufficient quality to be a promising electrode for photoelectrochemical water splitting.
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| 10. |
- Suvanam, Sethu Saveda, et al.
(author)
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Interface analysis of p-type 4H-SiC/Al2O3 using synchrotron-based XPS
- 2016
-
In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015. - : Trans Tech Publications Ltd. - 9783035710427 ; , s. 693-696
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Conference paper (peer-reviewed)abstract
- In this paper, the interface between Al2O3 and p-type 4H-SiC is evaluated using x-ray photoelectron spectroscopy (XPS) measurements. These studies are made on dielectricsemiconductor test structures with Al2O3 as dielectric with different pre- and post-deposition treatments. XPS measurements on the as-deposited samples with two different pre-surface cleaning methods have shown no formation of a SiO2 interlayer. However, after the post deposition rapid thermal annealing (RTA) at 1100 °C in N2O for 60 s, a SiO2 interlayer is formed. The surface band bending was determined from Si 2p core level peak shifts measured using XPS. These results suggest that Al2O3 deposited on the p-type 4H-SiC have a net positive oxide charge which is complementary to that of Al2O3 on n-type 4H-SiC. From these shifts it was found that the asdeposited RCA cleaned sample had an oxide charge of 5.6×1013 cm-2, as compared to standard cleaned samples, having 4.6×1013 cm-2. A further reduction in oxide charge was observed after annealing at 1100 °C in N2O, down to a value of 4×1013 cm-2.
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