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Low-energy muon-spin-rotation spectroscopy (LE-$\ensuremath{\mu}\mathrm{SR}$) is employed to study silicon and carbon vacancies in proton-irradiated $4H$-$\mathrm{Si}\mathrm{C}$. We show that the implanted muon is quickly attracted to the negative $\mathrm{Si}$ vacancy (${V}_{\mathrm{Si}}$), where it forms a paramagnetic muonium (${\mathrm{Mu}}^{0}$) state, resulting in a reduction of the diamagnetic fraction. In samples with predominantly $\mathrm{C}$ vacancies (${V}_{\mathrm{C}}$), on the other hand, the formation of ${\mathrm{Mu}}^{0}$ is very short lived and the muon quickly captures a second electron to form a diamagnetic ${\mathrm{Mu}}^{\ensuremath{-}}$ state. The results are corroborated by density-functional calculations, where significant differences in the relaxation mechanism of the nearest-neighbor dangling bonds of the vacancies are discussed. We propose that the LE-$\ensuremath{\mu}\mathrm{SR}$ technique is capable of differentiating between high-spin and negative-$U$ behavior in semiconducting materials. Finally, our findings emphasize the large potential of LE-$\ensuremath{\mu}\mathrm{SR}$ to probe near-surface semiconductor defects, a capability that is crucial for further development of many electronic and quantum technology applications.

We present a detailed first-principles study which explores the configurational space along the relevant reactions and migration paths involving the formation and dissociation of interstitial carbon-oxygen complexes, ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2\mathrm{i}}$, in silicon. The formation/dissociation mechanisms of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2\mathrm{i}}$ are found as occurring via capture/emission of mobile ${\mathrm{C}}_{\mathrm{i}}$ impurities by/from O complexes anchored to the lattice. The lowest activation energies for dissociation of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2\mathrm{i}}$ into smaller moieties are 2.3 and 3.1 eV, respectively. The first is compatible with the observed annealing temperature of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$, which occurs at around $400{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, and below the threshold for ${\mathrm{O}}_{\mathrm{i}}$ diffusion. The latter exceeds significantly the measured activation energy for the annealing of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2\mathrm{i}}\phantom{\rule{4pt}{0ex}}({E}_{a}=2.55$ eV). We propose that instead of dissociation, the actual annealing mechanism involves the capture of interstitial oxygen by ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2\mathrm{i}}$, thus being governed by the migration barrier of ${\mathrm{O}}_{\mathrm{i}}\phantom{\rule{4pt}{0ex}}({E}_{m}=2.53$ eV). The study is also accompanied by measurements of hole capture cross sections and capture barriers of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2\mathrm{i}}$. In combination with previously reported data, we find thermodynamic donor transitions which are directly comparable to the first-principles results. The two levels exhibit close features, conforming to a model where the electronic character of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2\mathrm{i}}$ can be described by that of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ perturbed by a nearby O atom.

The diffusion of the carbon vacancy (VC) in n-type 4H-SiC has been studied using Deep Level Transient Spectroscopy (DLTS). Samples grown along two different crystallographic planes, (0001) or c-cut and (11-20) or a-cut, have been utilized. The samples were implanted with 4.0 MeV C ions to generate VC’s and subsequently annealed at temperatures between 200 and 1500 °C. Following each annealing stage, concentration versus depth profiles of the VCwere obtained. The VCis essentially immobile in both the c-cut and a-cut samples up to at least 1200 °C. The 1400 °C annealing stage, however, resulted in considerable migration, predominantly along the a-direction. Using half the difference in the Full Width at Half Maximum (FWHM) of the initial and diffused concentration profiles as a measure of the diffusion length, we deduced the diffusivity of the VCat 1400 °C to be approximately (3.8±1.1)×10-14cm2/s along the c-axis and (4.1±1.2)×10-13cm2/s along the a-axis, indicating a substantial anisotropy for the VCdiffusion in 4H-SiC.

This study resumes the status of our knowledge about the formation of extended and intrinsic defects in ion implanted 4H-SiC homo-epitaxial wafers during a high temperature post-implantation annealing in presence of homogeneous heating of the ion implanted wafer. A particular attention is given to the implanted dopant concentrations of interest for the fabrication of 4H-SiC electronic devices. The issue to preserve a high electrical activation and at the same time to avoid the formation of defects and/or to reduce those that have been formed is discussed. The case of the Al+ ion implanted 4H-SiC is used as example and original results are presented.

A vertical 4H-SiC p-i-n diode with 2×1020cm-3 Al+ implanted emitter and 1950°C/5min post implantation annealing has been characterized by deep level transient spectroscopy (DLTS). Majority (electron) and minority (hole) carrier traps have been found. Electron traps with a homogeneous depth profile, are positioned at 0.16, 0.67 and 1.5 eV below the minimum edge of the conduction band, and have 3×10-15, 1.7×1014, and 1.8×10-14 cm2 capture cross section, respectively. A hole trap decreasing in intensity with decreasing pulse voltage occurs at 0.35 eV above the maximum edge of the valence band with 1×1013 cm2 apparent capture cross section. The highest density is observed for the refractory 0.67 eV electron trap that is due to the double negative acceptor states of the carbon vacancy.

The current work is devoted to studying the evolution of deep level defects in the lower half of the 4H-SiC bandgap after high temperature processing and ion implantation. Two as-grown and pre-oxidized 4H-SiC sets of samples have been thermally treated at temperatures up to 1950 °C for 10 min duration using RF inductive heating. Another set of as grown samples was implanted by 4.2 MeV Si ions at room temperature (RT) with different doses (1-4×108 cm-2). The so-called “D-center” at EV+0.6 eV dominates and forms after the elevated heat treatments, while it shows no change after the ion implantations (EV denotes the valence band edge). In contrast, the concentration of the so-called HK4 level at EV+1.44 eV increases with the implantation dose, whereas it anneals out after heat treatment at ≥ 1700 °C.

We address the key factors limiting charge carrier lifetime in 4H-SiC epilayers by demonstrating a viable method for eliminating carbon vacancy (VC) related Z1/2 lifetime killer sites and by introducing a novel approach in depth-resolved characterization of the carrier lifetimes across the epitaxial layer, which allows monitoring the efficacy of the proposed defect reduction scheme also exposing surface and interface recombination effects. We show that a moderate-temperature annealing conducted at 1500 °C for 6 hours under C-rich thermodynamic equilibrium conditions in effect eliminates carbon vacancies in epilayers to the levels below the detection limit (1011 cm-3) of DLTS measurements. The efficient reduction of VC-related Z1/2 sites upon thermal treatment is further proven by a significant increase of the minority carrier lifetime from 0.3µs to 1 µs, the upper limit apparently set by epilayer thickness dependent lifetime. Equally important is the extensive range of defect elimination as evidenced by consistently enhanced lifetime throughout entire 40 μm-thick epilayer, thus suggesting immediate practical implication as a lifetime control method suitable for variable thickness 4H-SiC epilayers.

The carbon vacancy (VC) is the major charge carrier lifetime limiting-defect in 4H-SiC epitaxial layers and it is readily formed during elevated heat treatments. Here we describe two ways for controlling the VC concentration in 4H-SiC epi-layer using different annealing procedures. One set of samples was subjected to high temperature processing at 1950 °C for 3 min, but then different cooling rates were applied. A significant reduction of the VC concentration was demonstrated by the slow cooling rate. In addition, elimination of the VC’s was also established by annealing a sample, containing high VC concentration, at 1500 °C for a sufficiently long time. Both procedures clearly demonstrate the need for maintaining thermodynamic equilibrium during cooling.

In this contribution, we report on the electrical characterization of point defects in 4H-SiC p+in diodes. Ten electrically active levels have been detected in the base region of the devices, by employing Deep Level Transient Spectroscopy (DLTS) and Minority Carrier Transient Spectroscopy (MCTS). Of these ten levels, six are majority carrier traps, in the 0.1-1.7 eV energy range below the conduction band edge, and four were minority carrier traps located in the 0.13-0.4 eV energy range above the valence band edge. We found that, during DLTS measurements, both majority and minority carrier traps can be detected and we explain this by considering the behavior of the quasi-Fermi levels. At last, we studied the impact of proton irradiation on the minority charge carrier lifetime.

The carbon vacancy (VC) is a major point defect in high-purity 4H-SiC epitaxial layers limiting the minority charge carrier lifetime. In layers grown by chemical vapor deposition techniques, the VC concentration is typically in the range of 1012 cm-3 and after device processing at temperatures approaching 2000 °C, it can be enhanced by several orders of magnitude. In the present contribution, we show that the cooling rate after high-temperature processing has a profound influence on the resulting VC concentration where a slow rate promotes elimination of VC. Further, isochronal annealing of as-grown and as-oxidized epi-layers protected by a carbon-cap was undertaken between 800 °C and 1600 °C. The results reveal that thermodynamic equilibrium of VC is established rather rapidly at moderate temperatures, reaching a VC concentration of only a few times 1011 cm-3 after 40 min at 1500 °C. Hence, the concept of eliminating VC’s by annealing at moderate temperatures under C-rich equilibrium conditions shows great promise and enables re-annealing of high-temperature processed wafers, in contrast to the procedures commonly used today to eliminate VC. In-diffusion of carbon interstitials and out-diffusion of VC’s are discussed as the kinetics processes establishing the thermodynamic equilibrium

Reliable single-photon emission is crucial for realizing efficient spin-photon entanglement and scalable quantum information systems. The silicon vacancy (VSi) in 4H-SiC is a promising single-photon emitter exhibiting millisecond spin coherence times, but suffers from low photon counts, and only one charge state retains the desired spin and optical properties. Here, we demonstrate that emission from VSi defect ensembles can be enhanced by an order of magnitude via fabrication of Schottky barrier diodes, and sequentially modulated by almost 50% via application of external bias. Furthermore, we identify charge state transitions of VSi by correlating optical and electrical measurements, and realize selective population of the bright state. Finally, we reveal a pronounced Stark shift of 55 GHz for the V1′ emission line state of VSi at larger electric fields, providing a means to modify the single-photon emission. The approach presented herein paves the way towards obtaining complete control of, and drastically enhanced emission from, VSi defect ensembles in 4H-SiC highly suitable for quantum applications., npj Quantum Information, 5 (1), ISSN:2056-6387

We investigate the migration mechanism of the carbon vacancy (V-C) in silicon carbide (SiC) using a combination of theoretical and experimental methodologies. The V-C, commonly present even in state-of-the-art epitaxial SiC material, is known to be a carrier lifetime killer and therefore strongly detrimental to device performance. The desire for V-C removal has prompted extensive investigations involving its stability and reactivity. Despite suggestions from theory that V(C )migrates exclusively on the C sublattice via vacancy-atom exchange, experimental support for such a picture is still unavailable. Moreover, the existence of two inequivalent locations for the vacancy in 4H-SiC [hexagonal, V-C(h), and pseudocubic, V-C(k)] and their consequences for V-C migration have not been considered so far. The first part of the paper presents a theoretical study of V(C )migration in 3C- and 4H-SiC. We employ a combination of nudged elastic band (NEB) and dimer methods to identify the migration mechanisms, transition state geometries, and respective energy barriers for V(C )migration. In 3C-SiC, V-C is found to migrate with an activation energy of E-A = 4.0 eV. In 4H-SiC, on the other hand, we anticipate that V-C migration is both anisotropic and basal-plane selective. The consequence of these effects is a slower diffusivity along the axial direction, with a predicted activation energy of E-A = 4.2 eV, and a striking preference for basal migration within the h plane with a barrier of E-A = 3.7 eV, to the detriment of the k-basal plane. Both effects are rationalized in terms of coordination and bond angle changes near the transition state. In the second part, we provide experimental data that corroborates the above theoretical picture. Anisotropic migration of V-C in 4H-SiC is demonstrated by deep level transient spectroscopy (DLTS) depth profiling of the Z(1/2) electron trap in annealed samples that were subject to ion implantation. Activation energies of E-A = (4.4 +/- 0.3) eV and E-A = (3.6 +/- 0.3) eV were found for V-C migration along the c and a directions, respectively, in excellent agreement with the analogous theoretical values. The corresponding prefactors of D-0 = 0.54 cm(2)/s and 0.017 cm(2)/s are in line with a simple jump process, as expected for a primary vacancy point defect. Funding Agencies|Research Council of Norway; University of Oslo through the frontier research project FUNDAMeNT [251131]; University of Oslo through the Norwegian Micro- and Nanofabrication Facility [NorFAB 245963]; Fundacao para a Ciencia e a Tecnologia (FCT) [UID/CTM/50025/2019]; FEDER funds through the COMPETE 2020 Program; NATO SPS programme [985215]; Swedish Energy Agency Energimyndigheten project [43611-1]; Swedish Government Strategic Research Area in Materials Science (AFM)

The carbon vacancy (VC) is a major limiting-defect of minority carrier lifetime in n-type 4H-SiC epitaxial layers and it is readily formed during high temperature processing. In this study, a kinetics model is put forward to address the thermodynamic equilibration of VC, elucidating the possible atomistic mechanisms that control the VC equilibration under C-rich conditions. Frenkel pair generation, injection of carbon interstitials (Ci’s) from the C-rich surface, followed by recombination with VC’s, and diffusion of VC’s towards the surface appear to be the major mechanisms involved. The modelling results show a close agreement with experimental deep-level transient spectroscopy (DLTS) depth profiles of VC after annealing at different temperatures.

The carbon vacancy (V-C) is a prominent defect in as-grown 4H-SiC epitaxial layers for high power bipolar devices. V-C is electrically active with several deep levels in the bandgap, and it is an efficient "killer" of the minority carrier lifetime in n-type layers, limiting device performance. In this study, we provide new insight into the equilibration kinetics of the thermodynamic processes governing the V-C concentration and how these processes can be tailored. A slow cooling rate after heat treatment at similar to 2000 degrees C, typically employed to activate dopants in 4H-SiC, is shown to yield a strong reduction of the V-C concentration relative to that for a fast rate. Further, post-growth heat treatment of epitaxial layers has been conducted over a wide temperature range (800-1600 degrees C) under C-rich surface conditions. It is found that the thermodynamic equilibration of V-C at 1500 degrees C requires a duration less than 1 h resulting in a V-C concentration of only similar to 10(11) cm(-3), which is, indeed, beneficial for high voltage devices. In order to elucidate the physical processes controlling the equilibration of V-C, a defect kinetics model is put forward. The model assumes Frenkel pair generation, injection of carbon interstitials (C-i's) from the C-rich surface (followed by recombination with V-C's), and diffusion of V-C's towards the surface as the major processes during the equilibration, and it exhibits good quantitative agreement with experiment. Published by AIP Publishing.