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| 2. |
- Beshkova, Milena, et al.
(författare)
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Low-pressure sublimation epitaxy of AlN films - growth and characterization
- 2004
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Ingår i: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 76, s. 143-146
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial layers of aluminum nitride have been grown at temperatures 1900-2400degreesC on 10 x 10 mm(2) 4H-SiC substrate via sublimation recondensation in an RF heated graphite furnace. The source material was polycrystalline sintered AlN. A maximum growth rate of about 100 mum/h was achieved at 2400degreesC and seed to source distance of 1 mm. The surface morphology reflects the hexagonal symmetry of the seed suggesting an epitaxial growth. This was confirmed by X-ray diffraction (XRD). The spectra showed very strong and well-defined (0002) reflection position at around 36.04degrees in symmetric Theta-2Thetascans for all samples. Micro-Raman spectroscopy reveals that the films have a wurtzite structure. It is evidenced by the appearance of the A(1) (TO) (at 601 cm(-1)) and E-2((2)) (at 651 cm(-1)) lines in the spectra. Secondary-ion mass spectroscopy (SIMS) results showed a low concentration of carbon incorporation in the AlN films. A correlation between the growth conditions and properties of the AlN layers was established.
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| 3. |
- Beshkova, Milena, et al.
(författare)
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Properties of AlN layers grown by sublimation epitaxy
- 2003
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Ingår i: Materials Science Forum, Vols. 433-436. ; , s. 995-998
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Konferensbidrag (refereegranskat)abstract
- Epitaxial layers of aluminum nitride (AlN)less than or equal to 80 mum thick have been grown at the temperatures 1900 and 2100 degreesC on 10x10mm(2) 4H-SiC substrates via sublimation recondensation in a RF heated graphite furnace. The source material was polyerystalline sintered AlN. A maximum growth rate of 80 mum/h was achieved at 2100degreesC and seed to source separation of I mm. The surface morphology reflects the hexagonal symmetry of the seed that suggesting an epitaxial growth. All crystals show strong and well defined single crystalline XRD patterns. Only the (002) reflection positioned at around 36.04 was observed in symmetric Theta-2Theta scan. The rocking curves FWHM (full width half maximum) and peak positions arc reported.
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| 4. |
- Beshkova, Milena, et al.
(författare)
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Sublimation epitaxy of AIN layers on 4H-SiC depending on the type of crucible
- 2003
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Ingår i: Journal of materials science. Materials in electronics. - 0957-4522 .- 1573-482X. ; 14:10-12, s. 767-768
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial layers of aluminum nitride less than or equal to335 mum thick have been grown attemperatures of 1900 and 2100degreesC on 10 x 10 mm(2) (0001)-oriented alpha(4H) silicon carbide (SiC), with growth times of 1 and 4h, via sublimation-recondensation in a RF-heated graphite furnace. The source material was polycrystalline AIN. The sublimation process was performed in three types of graphite (C) crucible: C-1, C-2 with inner diameters of 35 and 51 mm, respectively, and C-3 with the same inner diameter as C-1, but coated with a layer of TaC. The surface morphology reflects the hexagonal symmetry of the substrate, suggesting an epitaxial growth for samples grown in C-1 and C-3 crucibles for all growth conditions. The same symmetry is observed for AIN layers grown in the C-2 crucible, but only at 2100degreesC. X-ray diffraction analyses confirm the epitaxial growth of AIN samples with the expected hexagonal symmetry. A high-resolution X-ray diffractometer was used to assess the quality of the single crystals. A full width at half maximum of 242 arcsec was achieved for an AIN layer grown in the crucible coated with TaC. (C) 2003 Kluwer Academic Publishers.
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| 5. |
- Ciechonski, Rafal, et al.
(författare)
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Effect of boron on the resistivity of compensated 4H-SiC
- 2003
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Ingår i: Journal of electronic materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 32:5, s. 452-457
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Tidskriftsartikel (refereegranskat)abstract
- High-resistivity 4H-SiC samples grown by sublimation with a high growth rate are studied. The measurements show resistivity values up to a high of 104 Ωcm. The secondary ion mass spectroscopy (SIMS) results revealed a presence of only common trace impurities such as nitrogen, aluminum, and boron. To understand the compensation mechanism in these samples, capacitance deep-level transient spectroscopy (DLTS) on the p-type epilayers has been performed. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donorlike level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.
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| 6. |
- Gogova, Daniela, et al.
(författare)
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Investigation of the structure of tungsten oxide films obtained by chemical vapor deposition
- 2000
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Ingår i: European Physical Journal. - 1286-0042 .- 1286-0050. ; 11:3, s. 167-174
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Tidskriftsartikel (refereegranskat)abstract
- Thin amorphous and polycrystalline tungsten oxide films have been prepared by Chemical Vapor Deposition (CVD) from metallorganic precursor - tungsten hexacarbonyl - at atmospheric pressure. The dependence of the composition and the structure of tungsten oxide films on the technological conditions has been investigated by XPS, XRD, DTA-TGA and Raman spectroscopy. As a result it has been established that: at high values of the flow-rates of the reaction gases amorphous films of very low density have been obtained, in the XPS spectra of the understoichiometric WO3-y (0 < y < 0.3) films besides W6+, also W5+ and W4+ states have been observed. First to observe in the Raman spectra of amorphous CVD-WO3 films is the band at similar to 950 cm(-1), characteristic for terminal W6+=O bonds in result of the presence of structural water. The existence of structural water in the amorphous material has been established by thermal analyze, also.
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| 7. |
- Jacobson, H., et al.
(författare)
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Structural impact of LPE buffer layer on sublimation grown 4H-SiC epilayers
- 2003
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 256:3-4, s. 276-282
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work was to study the effect of a liquid phase epitaxy buffer layer on the development of defects in sublimation grown epitaxial layers of 4H-SiC. The results were analyzed with the aid of optical microscope, scanning electron microscope, high-resolution X-ray diffraction and synchrotron white beam X-ray topography. A pronounced effect of the liquid phase epitaxy buffer layer on formation of dislocations and micropipes is observed in the sublimation epitaxy layers. It has been shown that during sublimation growth of epilayer with a thin liquid phase epitaxy buffer layer (0.1µm) defects may undergo transformation and stacking faults can be formed. Sublimation grown epilayers grown on a thick liquid phase epitaxy buffer layer (1µm) also showed a symmetrical distribution of misfit dislocations along the <112¯0> and [11¯00] directions. © 2003 Elsevier B.V. All rights reserved.
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| 8. |
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| 9. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Behavior of background impurities in thick 4H-SiC epitaxial layers
- 2001
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Ingår i: Appl. Surf. Sci., Vol. 184. ; , s. 242-246
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Konferensbidrag (refereegranskat)abstract
- Behavior of background impurities in 4H-SiC layers is studied in terms of several growth process parameters. The layers were produced by sublimation epitaxy in Ta and Hf, as well as in graphite growth cell environment. Cathodoluminescence imaging and spectroscopy of cleaved samples demonstrate the impurity - thickness uniformity along thick (40-260 µm) layers. The effect of the Ta and Hf environment on the levels of residual impurities is considered through calculations of cohesive energies of Ta-X and Hf-X diatomic molecules and comparing them with those obtained for N-, Al- and B-containing vapor molecules. © 2001 Elsevier Science B.V. All rights reserved.
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| 10. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Cathodoluminescence identification of donor-acceptor related emissions in as-grown 4H-SiC layers
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:5, s. 2890-2895
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Tidskriftsartikel (refereegranskat)abstract
- A comparative analysis of cathodoluminescence spectra in 4H-SiC layers with different N, Al, and B content is reported. The layers were produced by sublimation epitaxy and residual impurity concentrations were determined by secondary ion mass spectrometry. Epilayers doped with B in a wide concentration range, 5x10(15)-3x10(18) cm(-3), were achieved. Evidence of N, Al, and B related emissions by cathodoluminescence experiments is presented. Differences in the luminescence emitted by the layers are established that are attributed to different B content and impurity cooperation. The characteristics of broad green emission, originating from B-related centers, at 4.6 K, 300 K, as well as in high temperature annealed layers are discussed. The experimental results suggest that boron is involved in more than one deep acceptor center.
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