| 1. |
- Edwards, NV, et al.
(författare)
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Real-time assessment of overlayer removal on 4H-SiC surfaces : Techniques and relevance to contact formation
- 2000
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 338-3, s. 1033-1036
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Tidskriftsartikel (refereegranskat)abstract
- We applied real-time spectroscopic ellipsometric (SE) measurements to assess the removal of overlayer material from 4H-SiC Si- and C-face surfaces in order to investigate the final step of an otherwise standard RCA cleaning regimen commonly used to prepare SiC surfaces for contact formation. The selected treatments (buffered hydrofluoric acid (HF), concentrated HF, dilute HF and 5% HF in Methanol) removed 4 to 40 Angstrom of effective SiO2 overlayer thickness from these surfaces. We also found that the concentrated HF treatment yielded the best surface, i.e. the most abrupt bulk-to-ambient transition region.
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| 2. |
- Edwards, NV, et al.
(författare)
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Real-time assessment of selected surface preparation regimens for 4H-SiC surfaces using spectroscopic ellipsometry
- 2000
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Ingår i: Surface Science. - : Elsevier. - 0039-6028 .- 1879-2758. ; 464:1, s. L703-L707
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Tidskriftsartikel (refereegranskat)abstract
- Spectroscopic ellipsometry (SE) was used to assess the removal of overlayer material from 4H-SiC (0001) and (0001) [Si- and C-face] surfaces in real time and, in particular, the critical final step of an otherwise standard RCA cleaning regimen commonly used to prepare SiC surfaces for contact formation. The treatments selected [buffered hydrofluoric acid (HF), concentrated HF, and dilute HF] removed 4-40 Angstrom of effective SiO2 overlayer thickness from these surfaces. The concentrated HF treatment yielded the best surface, i.e. that with the most abrupt transition region between bulk and surface and with the most oxide material removed. A fourth treatment regimen (sequential application of methanol, water, and 5% HF in methanol) was also developed for comparison with the full RCA clean. (C) 2000 Elsevier Science B.V. All rights reserved.
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| 3. |
- Kassamakova, L, et al.
(författare)
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Al/Si ohmic contacts to p-type 4H-SiC for power devices
- 2000
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 338-3, s. 1009-1012
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Tidskriftsartikel (refereegranskat)abstract
- The formation of Al/Si/p-4H SiC ohmic contacts at temperatures as low as 750 degreesC is reported in this paper. The dependence of electrical properties and contact morphology have been investigated as a function of the annealing regime in the interval 600-700 degreesC. The lowest contact resistivity of 3.8x10(-5) Omega .cm(2) was obtained at 700 degreesC annealing, however the most reproducible results were in the low 10(-4) Omega .cm(2) range. It has been established that the predominate current transport mechanism in the Al/Si/SiC contacts is thermionic-field emission. Atomic force microscopy showed that the addition of Si to the contact layer improves its morphology, and the pitting of annealed Al is not observed. The contacts developed are stable during ageing at 500 degreesC and at operating temperatures up to 450 degreesC. After the contacts testing with current density of 10(3) A/cm(2) at temperatures up to 450 degreesC, their contact resistivity decreases slightly.
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| 4. |
- McCaffrey, JP, et al.
(författare)
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Determination of the size, shape, and composition of indium-flushed self-assembled quantum dots by transmission electron microscopy
- 2000
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Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 88:5, s. 2272-2277
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Tidskriftsartikel (refereegranskat)abstract
- Single and multiple layers of self-assembled InAs quantum dots (QDs) produced by the indium-flush technique have been studied by transmission electron microscopy (TEM) in an effort to develop techniques to reproducibly grow QDs of uniform size and shape. To monitor the changes in QD dimensions, plan-view samples of capped single layers were studied as well as cross-sectional samples of QDs in multiple layers and stacks. The changes in the observed round- and square-shaped QD images under various plan-view TEM imaging conditions, as well as the contrast reversal in the center of QD images viewed in cross-section are modeled using the many-beam Bloch-wave approach, including strain. The sizes and shapes of the QDs are determined through the interpretation of the observed (primarily strain) contrast in plan-view and the observed (primarily atomic number) contrast in cross-sectional TEM. (C) 2000 American Institute of Physics. [S0021-8979(00)03217-5].
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| 5. |
- Robbie, K, et al.
(författare)
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Study of contact formation by high temperature deposition of Ni on SiC
- 2000
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 338-3, s. 981-984
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Tidskriftsartikel (refereegranskat)abstract
- We report the observation, by scanning tunneling microscopy (STM), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and atomic force microscopy (AFM), of island formation on SIC during high temperature deposition and annealing of thin Ni films. Ni films with a nominal thickness of 2.5 monolayers were sputter deposited onto H-2-etched single crystal 6H-SiC (0001) substrates heated to 600 degreesC in an ultrahigh vacuum STM system. After the substrates were annealed to 800-1000 degreesC, island formation was observed by STM. The islands were 0.1-0.5 mum in diameter, similar to 30 nm high, and separated by similar to2 mum from each other, with an exceptionally flat top with a peculiar 'stitched' surface structure. A second type of island, similar to1.5 mum in diameter, similar to 10 nm high, and separated by similar to 10 mum from each other, was observed by ex situ AFM and SEM. Microspot AES showed that the first islands are composed of Ni and C, while the second islands are composed of Ni, C, and Si. AES lineshape studies showed that the carbon in both types of islands is graphitically bound as opposed to the carbon in the substrate which is carbidically bound. From comparisons to literature, we believe that the first islands are a new type of graphite intercalation compound. An indexing of Ni on the top graphite sheets is presented for each anneal temperature.
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| 6. |
- Virojanadara, Chariya, et al.
(författare)
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Schottky barrier height studies of Au/4H-SiC(0001) using photoemission and synchrotron radiation
- 2002
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 31:12, s. 1353-1356
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Tidskriftsartikel (refereegranskat)abstract
- The Schottky barrier height (SBH) of Au on 4H-SiC(0001) has been studied using photoemission and synchrotron radiation. The Au was deposited in-situ on clean and well-ordered root3 X roots R30degrees reconstructed SiC surfaces prepared by in situ heating at similar to950degreesC. The SBH was determined from the shift observed in the Si 2p core level, in addition to the initial band bending determined for the clean surface. The results were compared with values obtained by electrical, capacitance-voltage (C-V), and current-voltage (I-V) characterization methods. A favorable comparison between the three independent, SBH determination methods was found.
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| 7. |
- Wahab, Qamar Ul, et al.
(författare)
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Designing, physical simulation and fabrication of high-voltage (3.85 kV) 4H-SiC Schottky rectifiers processed on hot-wall and chimney CVD films
- 2000
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Ingår i: Materials Science Forum, Vols. 338-342. ; , s. 1171-1174
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Konferensbidrag (refereegranskat)abstract
- Physical simulation, fabrication and characterization of high-voltage Ni/4H-SiC Schottky rectifiers are studied. We demonstrate a blocking voltage of 3.85 kV by utilizing a 43 mum thick low doped 4H-SiC epilayer in vertical hot-wall Chimney CVD reactor. A high breakdown voltage of 3.56 kV was achieved on a layer grown by conventional hot-wall CVD reactor. The reverse leakage current on CVD sample was as low as 5 x 10(-6) A cm(-2) at 3.5 kV just before the breakdown.
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| 8. |
- Wahab, Qamar Ul, et al.
(författare)
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Improvements in the electrical performance of high voltage 4H-SiC Schottky diodes by hydrogen annealing
- 2001
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Ingår i: Materials Science Forum, Vols. 353-356. ; , s. 691-694
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Konferensbidrag (refereegranskat)abstract
- A significant improvement in all the important parameters of the diodes were observed by annealing in H-2 at 300 degreesC. The forward current increased from 55 mA to 100 mA at a bias voltage of 2.5 V. The reverse leakage current measured at -500 V was reduced from 3.5 x 10(-9) to 4.8 x 10(-10) Amps for a 0.5 mm diameter diode. The average value of the barrier height increased by at least 0.2 eV, measured by Capacitance-Voltage and Current-Voltage technique indicating the increase of both static and effective barrier heights. The average value of ideality factor also improved and a best value of 1.06 was obtained for the hot-wall CVD grown samples after Hz annealing. Hydrogen atoms may passivate the dangling bends at the metal-semiconductor interface and thus by saturating the dangling bonds reduce the interface state density.
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