| 1. |
- Hallin, Christer, et al.
(författare)
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Improved Ni ohmic contact on n-type 4H-SiC
- 1997
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 26:3, s. 119-122
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the structural, chemical and electronic properties of Al/Ni/ Al-layers evaporated on 4H silicon carbide and then annealed at 1000°C for 5 min. The structure was investigated before and after annealing by transmission electron spectroscopy from cross-sectional specimens. With x-ray photoelectron spectroscopy, both element distribution and bonding energies were followed during sputtering through the alloyed metal-semiconductor contact. Voids are found in both annealed Ni/4H-SiC and Al/Ni/Al/4H-SiC contact layers, though closer to the metal-semiconductor interface in the former case. The first aluminum-layer is believed to prevent voids to be formed at the interface and also to reduce the oxide on the semiconductor surface. The contact was found to be ohmic with a specific contact resistance ρc - 1.8 × 10−5 Ωcm2 which is more than three times lower ρc than for the ordinary Ni/4H-SiC contact prepared in the same way.
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| 2. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Characterization of ohmic and Schottky contacts on SiC
- 1999
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 343-344, s. 637-641
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Tidskriftsartikel (refereegranskat)abstract
- The interface chemistry of nickel and tungsten based contacts on SiC has been investigated by XPS on as-deposited samples and after contact formation. After annealing at 950 °C for 10 min, Ni/SiC and Ni/Si/SiC ohmic contacts are formed due to the chemical reactions, as a result of which Ni2Si appears. However, Ni/Si (instead of pure Ni) deposition on SiC leads to modification of the diffusion processes and formation of a contact layer free of carbon. After annealing at 1200 °C for 4 min, the WN (W)/SiC systems are characterized by strong interface reactions resulting in W5Si3 and W2C formation in the contact layer. The 800 °C annealed WN/SiC contact is characterized by a chemically inert interface, and is found to be of a Schottky type.
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| 3. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Interface chemistry of a Ti/ Au/ Pt/ Ti/ SiC structure
- 1997
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 121/122, s. 208-212
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) is used to investigate the chemical reactions and diffusion processes at Ti/Au/Pt/Ti/SiC interfaces for as deposited and annealed at 575°C for 10 min structures. The distribution of the elements and the change in their chemical state has been studied. The XP spectra indicate titanium carbide and platinum silicides formation at the SiC interface, which is preceded by the dissociation of SiC due to the reactivity of Ti at 575°C. TiC represents a barrier to the further diffusion of Ti to the SiC bulk and the Ti layer makes the diffusion of Pt into SiC difficult. The element distribution of the annealed structure demonstrates that Pt has diffused through almost the whole gold layer to the surface, an alloy of the two metals being formed.
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| 4. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Interface chemistry of WN/4H-SiC structures
- 1999
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 151:3-4, s. 225-232
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Tidskriftsartikel (refereegranskat)abstract
- The interface chemistry of WN/4H–SiC structures has been studied by means of X-ray photoelectron spectroscopy (XPS). XPS investigations have been performed on as deposited, 800°C and 1200°C annealed (4 min) samples. The as deposited and 800°C annealed samples are characterized by chemically inert interfaces. Complete nitrogen out-diffusion from the WN layer, significant carbon diffusion into the contact layer, tungsten carbide and tungsten silicide formation occur during the 1200°C annealing process. The 800°C annealed WN/4H–SiC contacts are found to be of a Schottky type with a barrier height of 0.91 eV. The Schottky barrier height and the ideality factor show no significant changes during 100 h storage at 500°C under nitrogen and during operation at increasing temperature up to 350°C in air.
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| 5. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Microhardness of 6H-SiC epitaxial layers grown by sublimation
- 1999
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Ingår i: Crystal research and technology (1981). - 0232-1300 .- 1521-4079. ; 34:8, s. 943-947
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Tidskriftsartikel (refereegranskat)abstract
- Knoop microhardness of 6H-SiC layers grown by sublimation epitaxy was investigated. The microhardness-load curves for all of the samples were measured and then used to extract the load-independent microhardness values. The relationships of these values to the growth time and growth rate were studied. The microhardness-depth profiles indicated that the layer/substrate interface region had a microhardness value that differed significantly from that of both the epi-layer and the substrate.
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| 6. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Structural properties of 6H-SiC epilayers grown by two different techniques
- 1997
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Ingår i: Materials Science and Engineering B. - 0921-5107. ; 46:1-3, s. 345-348
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we investigated the structural properties of 6H-SiC homoepitaxial layers utilizing microhardness and X-ray characterization techniques. The growth was performed by chemical vapour deposition (CVD) and liquid phase epitaxy (LPE) under various growth conditions. The depth Knoop hardness profiles represent decreasing curves due to the indentation size effect. With load increasing the curves saturate reaching microhardness values comparable with the known Vickers ones. At about 0.4 μm beneath the layer surfaces the curves show small plateaus which may be attributed to structural inhomogeneity. This is suggested by X-ray diffraction spectra taken from the same samples, which contain additional peaks besides the typical ones for 6H-SiC.
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| 7. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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XPS characterization of tungsten based contact layers on 4H-SiC
- 1999
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 337:1-2, s. 180-183
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Tidskriftsartikel (refereegranskat)abstract
- Annealed W (WN)/4H–SiC interfaces have been compared on the basis of X-ray photoelectron spectroscopy (XPS) studies. The 1200°C annealed W (WN)/4H–SiC structures are characterized by intense interface reactions leading to tungsten carbide and tungsten silicide formation in the contact layers. The 800°C annealed WN/4H–SiC structure exhibits a chemically inert interface, and the 800°C annealed WN/4H–SiC contact is found to be of a Schottky type with a barrier height of 0.94 eV and an ideality coefficient of 1.09.
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| 8. |
- Kassamakova, L, et al.
(författare)
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Study of the electrical, thermal and chemical properties of Pd ohmic contacts to p-type 4H-SiC : dependence on annealing conditions
- 1999
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Ingår i: Materials Science and Engineering: B. - 0921-5107 .- 1873-4944. ; 61-62, s. 291-295
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Tidskriftsartikel (refereegranskat)abstract
- The electrical and chemical properties of Pd ohmic contacts to p-type 4H-SiC, together with their thermal stability, have been studied in the annealing temperature range 600–700°C. The ohmic behaviour of as-deposited and annealed contacts has been checked from I–V characteristics and the contact resistivity has been determined by the linear TLM method in order to determine the electrical properties and the thermal stability. An ohmic behaviour was established after annealing at 600°C, while the lowest contact resistivity 5.5×10−5 Ω.cm2 was obtained at 700°C. The contact structure, before and after annealing, was investigated using X-ray photoelectron spectroscopy depth analysis. As-deposited Pd films form an abrupt and chemically inert Pd/SiC interface. Annealing causes the formation of palladium silicide. After formation at 600°C the contact structure consists of unreacted Pd and Pd3Si. During annealing at 700°C, Pd and SiC react completely and a mixture of Pd3Si, Pd2Si and C in a graphite state is found in the contact layer. The examination of the thermal stability shows that after a 100 h heating at 500°C, only the contacts annealed at 700°C did not suffer from a change in resistivity. This can be explained by a more complete reaction between the Pd contact layer and the SiC substrate at this higher annealing temperature.
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| 9. |
- Kassamakova, L., et al.
(författare)
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Thermostable Ti/Au/Pt/Ti Schottky contacts on n-type 4H-SiC
- 1998
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 13:9, s. 1025-1030
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Tidskriftsartikel (refereegranskat)abstract
- The electrical properties and interface chemistry of Ti/Au/Pt/Ti Schottky contacts to n-type 4H-SiC have been investigated with respect to their utilization for MESFETs operated at high temperatures. The electrical properties of these contacts were studied at room temperature as well as during thermal treatment. The barrier height determined from I-V characteristics was calculated to be 1.17 eV with an ideality factor of 1.09. These parameters were examined by ageing and temperature dependence tests as criteria for the thermal stability and reliability of the contacts. The barrier height and ideality factor did not change after prolonged heating at a constant temperature of and operating temperatures up to , which confirmed the contact stability. Diodes used in the measurements showed a low leakage current at 100 V reverse voltage and room temperature ( A) as well as at ( A) and breakdown voltage above 400 V. The chemical interface properties were studied by x-ray photoelectron spectroscopy for as-deposited, annealed and heated contacts. Annealing at for 10 min led to formation of TiC and in a restricted region close to the SiC interface. The data revealed a chemically stable Ti/SiC interface after annealing, which is of importance for stable rectifying characteristics during long-term operation.
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| 10. |
- Marinova, Ts., et al.
(författare)
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Nickel based ohmic contacts on SiC
- 1997
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Ingår i: Materials Science and Engineering B. - 0921-5107. ; 46:1-3, s. 223-226
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Tidskriftsartikel (refereegranskat)abstract
- We have compared the chemical and structural properties of Ni/SiC and Ni2Si/SiC interfaces. In the case of Ni/SiC, the contact formation is initiated by the dissociation of SiC, due to the strong reactivity of nickel at 950 °C. Ni2Si is formed and carbon accumulates, both at the interface and throughout the metal layer. At the interface, many Kirkendall voids are observed by TEM. Despite this poor interface morphology, low contact resistances have been measured. But the presence of carbon in the contact layer and at the interface is a potential source of contact degradation at high temperature. In the case of Ni/Si multilayers evaporated on SiC instead of pure Ni, the contact formation is preceded by Ni and Si mutual diffusion in the deposited layer yielding Ni2Si. Therefore, a smaller amount of carbon is released from SiC. Low carbon segregation, abrupt interface and low contact resistance characterize this contact. The thermal stability of Ni2Si contacts is illustrated with ageing experiments carried out at 500 °C.
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