| 1. |
- Booker, Ian Don, et al.
(författare)
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Carrier lifetime in p- and n-type 4H-SiC
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Temperature-dependent time-resolved photoluminescence measurements made in the temperature range from 77 K to 1000 K on free-standing as grown n-type 4H-SiC and p-type 4H-SiC epilayers, which are either as-grown or annealed at 1000 °C, 1400 °C or 1700 °C, are analyzed. The development of the instantaneous carrier lifetime over temperature, calculated from the decay curves of all n- and p-type samples, is found to be identical in the entire temperature range. With increasing annealing temperature only the magnitude of the lifetime in p-type 4H-SiC decreases while the trend remains identical to that in the as-grown n-type sample. Annealing thus only increases the density of the main recombination center which appears to control lifetime in as-grown n- and p-type material. The results implies that the lifetime in all samples may be governed by the same intrinsic defect, which we suggest to be Z1/2.
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| 2. |
- Booker, Ian Don, et al.
(författare)
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Donor and double donor transitions of the carbon vacancy related EH6/7 deep level in 4H-SiC
- 2016
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 119:23
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Tidskriftsartikel (refereegranskat)abstract
- Using medium- and high-resolution multi-spectra fitting of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), optical O-DLTS and optical-electrical (OE)-MCTS measurements, we show that the EH6∕7 deep level in 4H-SiC is composed of two strongly overlapping, two electron emission processes with thermal activation energies of 1.49 eV and 1.58 eV for EH6 and 1.48 eV and 1.66 eV for EH7. The electron emission peaks of EH7 completely overlap while the emission peaks of EH6 occur offset at slightly different temperatures in the spectra. OE-MCTS measurements of the hole capture cross section σp 0(T) in p-type samples reveal a trap-Auger process, whereby hole capture into the defect occupied by two electrons leads to a recombination event and the ejection of the second electron into the conduction band. Values of the hole and electron capture cross sections σn(T) and σp(T) differ strongly due to the donor like nature of the deep levels and while all σn(T) have a negative temperature dependence, the σp(T) appear to be temperature independent. Average values at the DLTS measurement temperature (∼600 K) are σn 2+(T) ≈ 1 × 10−14 cm2, σn +(T) ≈ 1 × 10−14 cm2, and σp 0(T) ≈ 9 × 10−18 cm2 for EH6 and σn 2+(T) ≈ 2 × 10−14 cm2, σn +(T) ≈ 2 × 10−14 cm2, σp 0(T) ≈ 1 × 10−20 cm2 for EH7. Since EH7 has already been identified as a donor transition of the carbon vacancy, we propose that the EH6∕7 center in total represents the overlapping first and second donor transitions of the carbon vacancy defects on both inequivalent lattice sites.
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| 3. |
- Ivanov, Ivan Gueorguiev, et al.
(författare)
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High-Resolution Raman and Luminescence Spectroscopy of Isotope-Pure (SiC)-Si-28-C-12, Natural and C-13 - Enriched 4H-SIC
- 2014
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Ingår i: Silicon Carbide and Related Materials 2013, PTS 1 AND 2. - : Trans Tech Publications Inc.. ; , s. 471-474
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Konferensbidrag (refereegranskat)abstract
- The optical properties of isotope-pure (SiC)-Si-28-C-12, natural SiC and enriched with C-13 isotope samples of the 4H polytype are studied by means of Raman and photoluminescence spectroscopies. The phonon energies of the Raman active phonons at the Gamma point and the phonons at the M point of the Brillouin zone are experimentally determined. The excitonic bandgaps of the samples are accurately derived using tunable laser excitation and the phonon energies obtained from the photoluminescence spectra. Qualitative comparison with previously reported results on isotope-controlled Si is presented.
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| 4. |
- Lundqvist, Björn, et al.
(författare)
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Thermal conductivity of isotopically enriched silicon carbide
- 2013
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Ingår i: THERMINIC 2013 - 19th International Workshop on Thermal Investigations of ICs and Systems, Proceedings. - : IEEE. ; , s. 58-61, s. 58-61
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Konferensbidrag (refereegranskat)abstract
- Since the semiconductor silicon carbide presents attractive opportunities for the fabrication of novel electronic devices, there is significant interest in improving its material quality. Shrinking component sizes and high demands for efficiency and reliability make the capability to release excess heat an important factor for further development. Experience from Si and Diamond tells us that isotopic enrichment is a possible way to increase the thermal conductivity. We have produced samples of 4H-SiC that contain 28Si and 12C to a purity of 99.5%. The thermal conductivity in the c-direction of these samples has been measured by a transient thermoreflectance method. An improvement due to enrichment of at least 18% was found. The result is valid for a temperature of 45K above room temperature. A preliminary study of the temperature dependence of the thermal conductivity demonstrates a strong temperature dependence in agreement with earlier reports for 4H. © 2013 IEEE.
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| 5. |
- Nemati, Nasrin, 1988, et al.
(författare)
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Experimental Investigation of the Effect of Random Packings on Heat Transfer and Particle Segregation in Packed-Fluidized Bed
- 2021
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 60:28, s. 10365-10375
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Tidskriftsartikel (refereegranskat)abstract
- The heat transfer coefficient, pressure drop, and vertical segregation in a bubbling fluidized bed reactor containing random packings were investigated. The bed material was silica sand in the size range of 90−400 μm. Experiments were done for bed temperatures ranging from 400 to 900 °C and superficial gas velocities up to 0.411 m/s. Five different types of packings were evaluated: (i) RMSR (25 mm stainless steel thread saddle ring), (ii) Hiflow (25 mm stainless steel pall ring), (iii) RR6 (6 mm ceramic Raschig ring), (iv) RR10 (10 mm ceramic Raschig ring), and (v) ASB (12.7 mm aluminum silicate balls). The RMSR packing showed an increase in the heat transfer coefficient (up to 1243 W/m2 K), as compared to bubbling beds with no packings (up to 1124 W/m2 K). Also, beds with RMSR and Hiflow packings had a lower pressure drop and vertical segregation compared to low void factor packings such as RR6, RR10, and ASB.
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| 6. |
- Nguyen, Son Tien, et al.
(författare)
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Energy levels and charge state control of the carbon antisite-vacancy defect in 4H-SiC
- 2019
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 114:21
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Tidskriftsartikel (refereegranskat)abstract
- The carbon antisite-vacancy pair (CSiVC) in silicon carbide (SiC) has recently emerged as a promising defect for applications in quantum communication. In the positive charge state, CSiVC+ can be engineered to produce ultrabright single photon sources in the red spectral region, while in the neutral charge state, it has been predicted to emit light at telecom wavelengths and to have spin properties suitable for a quantum bit. In this electron paramagnetic resonance study using ultrapure compensated isotope-enriched 4H-(SiC)-Si-28, we determine the (+|0) level of CSiVC and show that the positive and neutral charge states of the defect can be optically controlled.
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| 7. |
- Nguyen, Son Tien, et al.
(författare)
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Ligand hyperfine interactions at silicon vacancies in 4H-SiC
- 2019
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Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 31:19
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Tidskriftsartikel (refereegranskat)abstract
- The negative silicon vacancy (V-Si(-)) in SiC has recently emerged as a promising defect for quantum communication and room-temperature quantum sensing. However, its electronic structure is still not well characterized. While the isolated Si vacancy is expected to give rise to only two paramagnetic centers corresponding to two inequivalent lattice sites in 4H-SiC, there have been five electron paramagnetic resonance (EPR) centers assigned to V-Si(-) in the past: the so-called isolated no-zero-field splitting (ZFS) V-Si(-) center and another four axial configurations with small ZFS: T-V1a, T-V2a, T-V1b, and T-V2b. Due to overlapping with Si-29 hyperfine (hf) structures in EPR spectra of natural 4H-SiC, hf parameters of T-V1a have not been determined. Using isotopically enriched 4H-(SiC)-Si-28, we overcome the problems of signal overlapping and observe hf parameters of nearest C neighbors for all three components of the S = 3/2 T-V1a and T-V2a centers. The obtained EPR data support the conclusion that only T-V1a and T-V2a are related to V-Si(-) and the two configurations of the so-called isolated no-ZFS V-Si(-) center, V-Si(-) (I) and V-Si(-) (II), are actually the central lines corresponding to the transition I-1/2 amp;lt;-amp;gt; I + 1/2 of the T-V2a and T-V1a centers, respectively.
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| 8. |
- Niethammer, Matthias, et al.
(författare)
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Vector Magnetometry Using Silicon Vacancies in 4H-SiC Under Ambient Conditions
- 2016
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Ingår i: PHYSICAL REVIEW APPLIED. - : AMER PHYSICAL SOC. - 2331-7019. ; 6:3
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Tidskriftsartikel (refereegranskat)abstract
- Point defects in solids promise precise measurements of various quantities. Especially magnetic field sensing using the spin of point defects has been of great interest recently. When optical readout of spin states is used, point defects achieve optical magnetic imaging with high spatial resolution at ambient conditions. Here, we demonstrate that genuine optical vector magnetometry can be realized using the silicon vacancy in SiC, which has an uncommon S = 3/2 spin. To this end, we develop and experimentally test sensing protocols based on a reference field approach combined with multifrequency spin excitation. Our work suggests that the silicon vacancy in an industry-friendly platform, SiC, has the potential for various magnetometry applications under ambient conditions.
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| 9. |
- Stenberg, Pontus, et al.
(författare)
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Defects in silicon carbide grown by fluorinated chemical vapor deposition chemistry
- 2018
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Ingår i: Physica. B, Condensed matter. - : ELSEVIER SCIENCE BV. - 0921-4526 .- 1873-2135. ; 535, s. 44-49
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Tidskriftsartikel (refereegranskat)abstract
- Point defects in n- and p-type 4H-SiC grown by fluorinated chemical vapor deposition (CVD) have been characterized optically by photoluminescence (PL) and electrically by deep-level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS). The results are considered in comparison with defects observed in non-fluorinated CVD growth (e.g., using SiH4 instead of SiF4 as silicon precursor), in order to investigate whether specific fluorine-related defects form during the fluorinated CVD growth, which might prohibit the use of fluorinated chemistry for device-manufacturing purposes. Several new peaks identifying new defects appear in the PL of fluorinated-grown samples, which are not commonly observed neither in other halogenated chemistries, nor in the standard CVD chemistry using silane (SiH4). However, further investigation is needed in order to determine their origin and whether they are related to incorporation of F in the SiC lattice, or not. The electric characterization does not find any new electrically-active defects that can be related to F incorporation. Thus, we find no point defects prohibiting the use of fluorinated chemistry for device-making purposes.
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| 10. |
- Stenberg, Pontus
(författare)
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Fluorinated SiC CVD
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For the emerging semiconductor material silicon carbide (SiC) used in high power devices, chemical vapor deposition (CVD) is the most prominent method to create the electrically active SiC epitaxial layers in the device. The process of growing such epitaxial layers is to use a hydrocarbon and silane diluted in hydrogen flow through a hot chamber where chemical reactions take place in such manner that Si and C finally deposit on the surface creating epitaxial SiC. The addition of chlorine (Cl) to the process has been thoroughly investigated due to its ability to reduce homogeneous nucleation in the gas phase attributed to the stronger Si-Cl bond compared to the Si-Si bond. In this thesis the fluorinated chemistry has been investigated, since the Si-F bond is even stronger than the Si-Cl bond and the fluorinated chemistry for SiC CVD has remained poorly understood.Using SiF4 as Si precursor in growth experiments combined with thermal equilibrium calculations of gas phase composition and quantum chemical computations of the surface chemistry first the silicon chemistry in the CVD process has been probed. It is shown that while growth rates on the order of 35 µm/h can be achieved with a fluorinated chemistry, the deposition chemistry is very sensitive to the mass flows of the precursors and not as robust as the chlorinated CVD chemistry which routinely yields 100 µm/h over wide conditions. By using the position for the onset of epitaxial growth along the gas flow direction as a new measurable, together with modeling, it is conclude that SiF is the main Si growth species with SiHF as a minor Si species contributing to growth.The carbon chemistry in a fluorinated SiC CVD process has been probed by a similar approach. Here it is found that the slow kinetics of the SiF4 molecule needs to be matched by a carbon precursor with comparable slow kinetics. It is shown that methane is a suitable carbon precursor in combination with SiF4.Before a fluorinated CVD chemistry can be adopted in device processing, the effect of fluorine on the dopant incorporation must be understood since dopant incorporation is of paramount importance in semiconductor manufacturing. Dopant incorporation studies for n-type doping with N using N2 and p-type doping with Al using TMAl in fluorinated CVD of homoepitaxial SiC are presented. It is found to be possible to control the doping in SiC epitaxial layers when using a fluorinated CVD chemistry for both n- and p-type material using the C/Si ratio as in standard SiC CVD. However, large area doping uniformity seems to be a challenge for a fluorinated CVD chemistry, most likely due to the very strong Si-F and Al-F bonds. It is found that no additional optically or electrically active defects are created due to the use of fluorine in the CVD process.Finally, the fluorinated chemistry is compared to the chlorinated and brominated chemistries for SiC CVD and an overall model for halogen addition to SiC CVD is presented.
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