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Carlsson, Patrick; Son, N. T.; Gali, Ádám; Isoya, Junichi; Morishita, Norio; Ohshima, Takeshi; Magnusson, Björn; Janzén, Erik

doi:10.1103/physrevb.82.235203

Cited by 14 publications

(9 citation statements)

References 31 publications

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“…The EPR spectrum of the SI1 (10 18 cm −2 ) sample in dark displays clear contributions from the positively-charged carbon vacancy V C + , the EI-4 centre, 34 and another unidentified spin-one defect, as indicated in Fig. 4(c).…”

Section: Epr Resultsmentioning

confidence: 92%

Excitation properties of the divacancy in 4H -SiC

et al. 2018

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We investigate the quenching of the photoluminescence (PL) from the divacancy defect in 4H-SiC consisting of a nearest-neighbour silicon and carbon vacancies. The quenching occurs only when the PL is excited below certain photon energies (thresholds), which differ for the four different inequivalent divacancy configurations in 4H-SiC. Accurate theoretical ab initio calculation for the charge-transfer levels of the divacancy show very good agreement between the position of the (0/−) level with respect to the conduction band for each divacancy configurations and the corresponding experimentally observed threshold, allowing us to associate the PL decay with conversion of the divacancy from neutral to negative charge state due to capture of electrons photoionized from other defects (traps) by the excitation. Electron paramagnetic resonance measurements are conducted in dark and under excitation similar to that used in the PL experiments and shed light on the possible origin of traps in the different samples. A simple model built on this concept agrees well with the experimentallyobserved decay curves.

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Section: Epr Resultsmentioning

confidence: 92%

Excitation properties of the divacancy in 4H -SiC

et al. 2018

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“…The majority of prior computational work on defects in 4H-SiC has concentrated on ground state properties. In particular, the calculation of hyperfine tensors enables comparison between computational and electron paramagnetic resonance results facilitating experimental assignment [17][18][19][30][31][32][33][34]. Defect formation energies as a function of the Fermi level have been computed [20,30,[34][35][36][37][38] to determine charge state stabilities and transition levels.…”

Section: Introductionmentioning

confidence: 99%

“…In particular, the calculation of hyperfine tensors enables comparison between computational and electron paramagnetic resonance results facilitating experimental assignment [17][18][19][30][31][32][33][34]. Defect formation energies as a function of the Fermi level have been computed [20,30,[34][35][36][37][38] to determine charge state stabilities and transition levels. Evaluation of excited states for defects in 4H-SiC have been focused on first excited states and corresponding ZPLs, which have been calculated for the NV center [12,20,39,40] and for the neutral divacancy defect using constrained DFT [12,39,41].…”

Section: Introductionmentioning

confidence: 99%

Charge state switching of the divacancy defect in 4H -SiC

et al. 2018

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Optical charge state switching was previously observed in photoluminescence experiments for the divacancy defect in 4H-SiC. The participating dark charge state could not be identified with certainty. We use constrained DFT to investigate the mechanism of charge state conversion from the bright neutral charge state of the divacancy defect to the positive and negative charge states including corresponding recovery of the neutral charge state. While we can confirm that the positive charge state is dark, we do not find evidence that the negative charge state is dark.We compute similar absorption energies required for conversion of the neutral defect to both charge states. However, the formation of the positive charge state requires a series of excitations involving a 2-photon excitation, while the creation of the negative charge state is achieved through a single 2-photon process. Calculated absorption energies for the recovery of the neutral defect from the positive charge state fit the experimental value better than from the negative charge state. Defect formation energies as a function of the Fermi energy show a very small Fermi energy range in which the negative charge state is most stable, while the positive charge state exhibits a wide stability range. Overall, our computational results give more support to the identification of the dark charge state as the positive over the negative charge state in the mechanism of optical charge state switching.

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“…The allowed transition between two levels has to follow the selection rules in which ΔM S =±1 and ΔM I =0. The forbidden transitions with ΔM I =±1 might become partly allowed in some particular cases [94,95]. For a spin center which has S=1/2 and a hyperfine interaction with an impurity having a nuclear spin I=1/2 and 100% natural abundance, the energy level will split into four levels under an external magnetic field B.…”

Section: Hyperfine Interactionmentioning

confidence: 99%

Electron Paramagnetic Resonance Studies of Point Defects in AlGaN and SiC

Trinh¹

2015

Linköping Studies in Science and Technology. Dissertations

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Point defects in semiconductor materials are known to have important influence on the performance of electronic devices. For defect control, knowledge on the model of defects and their properties is required. Information on defects, such as the symmetry and the localization of spins, is essential for identification of defects and understanding their electronic structure. Such information can be obtained from Electron Paramagnetic Resonance (EPR). In many cases, the energy levels of defects can be determined from photoexcitation EPR (photo-EPR) or temperature dependence of the EPR signal. The thesis contains six papers, focusing on the identification and electronic structure investigation of defects and impurities in Al x Ga 1-x N (x~0.7-1) and silicon carbide (SiC) using EPR in combination with other electrical characterizations and density functional theory calculations.The two first papers concern EPR studies of silicon (Si) in AlGaN alloys. Due to its direct and wide band gap which can be tailored from 3.4 eV for GaN to 6.2 eV for AlN, high-Al-content wurtzite Al x Ga 1-x N (x≥0.7) has been considered as a promising material for fabrication of compact, highefficiency and non-toxic deep ultraviolet light-emitting diodes (LEDs) and laser diodes (LDs) for replacing low-efficiency and toxic mercury lamps in water/air purification and sterilization. Si is commonly used for n-type doping in AlGaN and AlN, but the conductivity of Si-doped Al x Ga 1-x N was often reported to drop abruptly at high Al content (x>0.7) and the reason was often speculated to be due to either carrier compensation by other deep levels or Si itself when it transforms from a shallow donor to a DX (or negative-U) center which acts as an acceptor. In paper 1, we showed that Si already forms a stable DX center in Al x Ga 1-x N with x ~0.77. However, with the Fermi level locating only ~3 meV below the neutral charge state, E d , Si still behaves as a shallow donor. Negligible carrier compensation by oxygen (O) in Al 0.77 Ga 0.23 N:Si layers was observed, suggesting that at such Al content, O does not seem to hinder the n-type doping in the material. In paper 2, we found the coexistence of two Si DX centers, the stable DX1 and the metastable DX2, in Al x Ga 1-x N for x≥0.84. For the stable DX1 center, abrupt deepening of the energy level of the negative charge state DX -, E DX , which determines the ionization energy E a of the Si donor, with increasing of the Al content for x≥0.83 was observed. The dependence of E a on the Al content in Al x Ga 1-x N:Si layers (0.79≤x≤1) was determined. The results explain the drastic decrease of the conductivity as often reported for Al x Ga 1-x N:Si in previous transport studies. For the metastable DX2 center, we found that the E DX level remains close to E d for x=0.84÷1.SiC is a wide band-gap semiconductor having high-thermal conductivity, high breakdown field, and large saturated electron drift velocity which are iv essential properties for high-voltage and high-power devices. In paper 3, the identif...

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EPR andab initiocalculation study on the EI4 center in4H- and6H-SiC

Cited by 14 publications

References 31 publications

Excitation properties of the divacancy in 4H -SiC

Excitation properties of the divacancy in 4H -SiC

Charge state switching of the divacancy defect in 4H -SiC

Electron Paramagnetic Resonance Studies of Point Defects in AlGaN and SiC

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