Defects In 4H Research Articles

Midgap Defects in 4H-, 6H- and 3C-SiC Detected by Deep Level Optical Spectroscopy

Midgap Defects in 4H-, 6H- and 3C-SiC Detected by Deep Level Optical Spectroscopy

Micro-Raman Investigation of Growth-Induced Defects in 6H and 4H SiC Crystals Grown by Sublimation Method

Micro-Raman Investigation of Growth-Induced Defects in 6H and 4H SiC Crystals Grown by Sublimation Method

Silicon and carbon vacancies in neutron-irradiated SiC: A high-field electron paramagnetic resonance study

Electron-paramagnetic-resonance (EPR) and electron-spin-echo (ESE) studies have been performed that show that isolated ${V}_{\mathrm{Si}}^{\ensuremath{-}},$ ${V}_{\mathrm{Si}}^{0},$ and ${V}_{C}$ vacancies are the dominant intrinsic paramagnetic defects in SiC treated by room-temperature neutron irradiation with doses up to ${10}^{19}{\mathrm{cm}}^{\ensuremath{-}2}.$ This conclusion is supported by the observation of high concentrations of all these defects in 4H- and 6H-SiC that are almost proportional to the irradiation dose. The 95-GHz EPR spectra at 1.2 K prove that the ground state of ${V}_{\mathrm{Si}}^{0}$ corresponds to $S=1$ and that the zero-field splitting parameter D is positive. A possible energy-level scheme and optical pumping process which induces the spin polarization of the ground triplet state of the ${V}_{\mathrm{Si}}^{0}$ vacancy in SiC is presented. In the EPR spectra of ${V}_{\mathrm{Si}}^{\ensuremath{-}}$ in 4H-SiC an anisotropic splitting of the EPR lines is observed. This splitting is assumed to arise from small differences in the g tensor of the quasicubic (k) and hexagonal (h) sites. Anisotropic EPR spectra with $S=\frac{1}{2}$ that are related to the carbon vacancy have also been observed in the n-irradiated SiC crystals. The hyperfine (hf) interaction with the first shell of Si atoms is almost identical to that observed in electron-irradiated SiC crystals. The observed additional 6.8-G hf splitting with 12 carbon atoms in the second shell is considered as a confirmation for the isolated carbon vacancy model.

Correspondence between Surface Morphological Faults and Crystallographic Defects in 4H–SiC Homoepitaxial Film

Conventional transmission electron microscopy was applied to study the nature of crystallographic defects under some types of surface morphological faults formed on a 4H–SiC film homoepitaxially grown on a (0001) off-cut substrate. “Wavy pit” faults consist of arrays of small surface cavities and half-loops of perfect dislocations expanding towards the direction of their Burgers vector. “Carrot” and “comet” faults are accompanied by stacking faults. The geometry of crystallographic defects under surface faults is closely related to the off-cut direction of the substrate. Formation mechanisms of surface faults are discussed.

Recombination-enhanced defect motion in forward-biased 4H–SiC p-n diodes

The generation and evolution of defects in 4H–SiC p-n junctions due to carrier injection under forward bias have been investigated by synchrotron white beam x-ray topography, electroluminescence imaging, and KOH etching. The defects are Shockley stacking faults with rhombic or triangular shapes bound by partial dislocation loops with dislocation lines along Peierls valleys (〈11-20〉) or along the intersection of the basal plane containing the fault and diode surface. The Burgers vector of all bounding partials was of 1/3〈10-10〉-type. Among six possible types of partial dislocations with these properties, only two were observed in the volume of the epitaxial structure. One was tentatively identified as 30° carbon-core [C(g) 30°] and second as 30° silicon-core [Si(g) 30°] partial dislocation. Only one of them [proposed to be the Si(g) 30° partial] have been observed to move and emit light under forward bias. The other type of bounding dislocation [C(g) 30°] remained stationary during current injection. Low angle grain boundaries have been observed to act as one of a number of possible nucleation sites of stacking faults.

Radiation-Induced Defects in 4H- and 6H-SiC Epilayers Studied by Positron Annihilation and Deep-Level Transient Spectroscopy

Radiation-Induced Defects in 4H- and 6H-SiC Epilayers Studied by Positron Annihilation and Deep-Level Transient Spectroscopy

EPR Study of Single Silicon Vacancy-Related Defects in 4H- and 6H-SiC

EPR Study of Single Silicon Vacancy-Related Defects in 4H- and 6H-SiC

Vacancy-type defects in 6H–SiC caused by N + and Al + high fluence co-implantation

6H–SiC n-type wafers were implanted with Al + and N + ions in two steps: first N + double implantation (65 keV, 5×10 16 cm −2 and 120 keV, 1.3×10 17 cm −2) followed by Al + double implantation (100 keV, 5×10 16 cm −2 and 160 keV, 1.3×10 17 cm −2). The implantation was carried out at a substrate temperature of 800 °C, in order to avoid amorphization. In this way, a buried (SiC) 1− x (AlN) x layer could be created. Variable-energy positron Doppler broadening measurements were performed at room temperature using a magnetic transport beam system in order to characterize the vacancy-type defects created by ion implantation. Depth profiles could be evaluated from the measured Doppler broadening profiles. The defect distribution and the defect size after the complete co-implantation are discussed and the contribution of the different implantation steps to the evolution of this defect structure is shown.

Metastable defects in 6H–SiC: experiments and modeling

Using various junction space-charge techniques, annealing, and simulation, a metastable defect in 6H SiC have been characterized. We suggest a configuration coordinate diagram with three configurations, where two of them can only exist when the defect is occupied by one or more electrons. The thermal ionization energies for the different configurations were measured and the thermal barriers for two of the transitions have been determined. It is also shown that the transformation process is governed by electron capturing to the defect.

Characterization of SiC Implanted with B or Al Using Thermal Admittance Spectroscopy

AbstractWe have measured the thermal activation energies of electrically active defects in 4H- and 6H-SiC implanted with either Al or B ions, using Thermal Admittance Spectroscopy. The net acceptor concentrations were monitored using room temperature low frequency Capacitance-Voltage measurements. The substrates were n/n+ epilayers. The implantations plus annealing produced p-type layers that were acceptable for characterization. The specimens were annealed in Ar at 1600 ° C, after which Ni Schottky diodes were fabricated on the specimens. Annealing times were 5, 15, 30, and 60 min. In some of the specimens, a shallow level was found that did not correspond to known levels. As the annealing progressed, energy shifts were noted for some of the detected levels. In some specimens, the implanted p-type impurity and the n-type residual dopants in the substrate were simultaneously detected. Measurements of electrically active ptype species were compared to “control” specimens implanted with Ar. From this comparison, we conclude that at least one shallow donor level is introduced into the bandgap by the implantation process, and is not annealed out. The defects associated with the implantation may affect actual device performance of diodes by destabilizing the lattice occupation of the implanted dopant atoms (energy shift with annealing), and act as lifetime killers.

Negatively charged vacancy defects in 6H–SiC after low-energy proton implantation and annealing

We have used pulsed-slow-positron-beam-based positron lifetime spectroscopy to investigate the nature of acceptors and charge states of vacancy-type defects in low-energy proton-implanted 6H–SiC(H). We can infer from the temperature dependence of the lifetime spectra that neutral and negatively charged vacancy clusters exist in the track region. Depending on annealing, they give rise to positron lifetimes of 257±2, 281±4 and 345±2 ps, respectively. The 281 ps cluster has likely an ionization level near the middle of the band gap. By comparison with theory, the 257 and 280 ps are identified as (V C–V Si) 2 and (V C–V Si) 3 clusters, respectively. In addition, other acceptors of ionic type act as strong trapping centers at low temperature ( T<150 K). Neutral monovacancy-like complexes are also detected with a lifetime of 160±2 after 900°C annealing.

DLTS study of defects in 6H- and 4H-SiC created by proton irradiation

Experiments on proton irradiation with energy of 150 KeV, 8 MeV and 1 GeV were made. Capacitance–voltage characteristics measured at 650 K showed that 8 MeV and 1 GeV proton irradiation of 6H-SiC leads to an increase of uncompensated donor concentration. However, donor concentration in 6H-SiC remains unaffected after 150 keV proton irradiation. Deep centers were investigated by deep levels transient spectroscopy (DLTS). Results of C–V measurements are interpreted using DLTS data. The results obtained show the possibility of uzing proton irradiation for producing local high-resistance regions in SiC devices not intended for high-temperature applications.

Luminescence characterization of titanium related defects in 6H–SiC

Photoluminescence (PL), thermally stimulated luminescence (TSL) and their photo-excitation spectra in hexagonal type SiC were studied between the temperatures of 5 and 300 K. Titanium related TSL glow peak is observed close to 140 K in compensated crystals 6H–SiC with corresponding thermal ionisation energy of a trap close to 170 meV. The spectral distribution of TSL has a maximum at 1.8 eV in 6H–SiC and 2.43 eV in 4H–SiC. A specific structure in the photo-excitation spectrum of PL close to the exciton gap E gx=3.023 eV is revealed, exclusively in 6H–SiC material. This indicates an essential role of excitons in the resonance energy transfer to the Ti-related centers in silicon carbide. The results are discussed in a model of isoelectronic centers composed of either individual Ti atoms or Ti–N pair representing a complex of the electronic trap and recombination center.

Nitrogen passivation by implantation-induced point defects in 4H–SiC epitaxial layers

Ion implantation causes damage to the crystal lattice resulting in the loss of free charge carriers. In this study, low dose implantations using different ions and implantation doses are made to resolve the initial carrier loss in nitrogen-doped epitaxial layers. A strong dependence of compensation on nitrogen concentration is seen, showing that nitrogen is passivated by implantation-induced point defects. An activation energy of 3.2 eV for the dissociation of the passivated nitrogen center is obtained.

Nitrogen deactivation by implantation-induced defects in 4H–SiC epitaxial layers

Ion implantation causes free charge carrier reduction due to damage in the crystalline structure. Here, nitrogen-doped 4H silicon carbide (n type) epitaxial layers have been investigated using low ion doses in order to resolve the initial stage of the charge carrier reduction. It was found that the reduction of free carriers per ion-induced vacancy increases with increasing nitrogen content. Nitrogen is suggested to be deactivated through reaction with migrating point defects, and silicon vacancies or alternatively interstitials are proposed as the most likely candidates.

EPR Study of Proton Implantation Induced Intrinsic Defects in 6H- and 4H-SiC

EPR Study of Proton Implantation Induced Intrinsic Defects in 6H- and 4H-SiC

Intrinsic Defects in Silicon Carbide Polytypes

Electron paramagnetic resonance (EPR) has been used for investigation of intrinsic defects in 4H and 6H SiC. At W-band frequency (similar to 95 GHz), the detailed structures of most of the EPR spectra in 4H and 6H SiC irradiated with electrons have been observed. We report our observation of two new EPR spectra, labelled EI1 ' and EI3 ', which are other configurations of the vacancy-related EI1 and EI3 centers. The transformation from the EI1 and EI3 centers to the EI1 ' and EI3 ' configurations, respectively, can be realised by annealing. Two new EPR spectra, labelled EI5 and EI6, with trigonal symmetry and spin S=1/2 were observed in irradiated p-type material. The EI5 and EI6 centers can be identified as the C vacancy and Si antisite in the positive-charge state.

Doping of n-type 6H–SiC and 4H–SiC with defects created with a proton beam

Deep centers in n-type 4H–SiC and 6H–SiC irradiated with 8 MeV protons have been investigated by capacitance spectroscopy and electron paramagnetic resonance (EPR). Samples were fabricated by sublimation epitaxy or commercially produced by CREE Inc. Research Triangle Park, NC. It is showed that irradiation of wide-band gap semiconductors may lead to an increase in the concentration of uncompensated donors in an n-type material. The spectrum of deep centers in both SiC polytypes is independent of the technology of material growth or type of charged particles. However, the parameters and behavior of the radiation defects in 6H– and 4H–SiC are different. A conclusion about the possible nature of the irradiation induced centers is made on the basis of annealing behavior and EPR data. The obtained results show that proton irradiation can be used in SiC device fabrication technology for producing local high-resistance regions in the semiconductor.

Carbon-vacancy related defects in 4H- and 6H-SiC

Electron paramagnetic resonance (EPR) was used to study intrinsic defects in 4H- and 6H-SiC irradiated with 2.5 MeV electrons with doses ranging from 1×10 17 to 2×10 18 cm −2. In p-type 4H- and 6H-SiC, the dominant EPR signal, labeled EI1, associates with a defect centre having a low symmetry and an effective electron spin S=1/2. For both polytypes, its g-tensor was determined as g z=2.0015, g x=1.9962 and g y=2.0019, where g z and g x lie in the (11 2 0) plane and the z-axis makes an angle ∼41 degrees with the c-axis. Hyperfine interaction with a 29Si atom located at two equivalent sites in the nearest neighbour shell was detected, confirming that the defect resides at the carbon site. In heavily irradiated 4H- and 6H-SiC, a new EPR spectrum having an electron spin S=1, labeled EI3, was observed. In both polytypes, the EI3 centre has a low symmetry, an isotropic g-value of 2.0063 and a fine structure parameter | D|∼5.5×10 −2 cm −1. The observed hyperfine interaction with four 29Si atoms in the nearest neighbour shell confirms the involvement of the carbon vacancy in the defect. The defect is suggested to be a complex centre involving a carbon vacancy.

A complex defect related to the carbon vacancy in 4H and 6H SiC

Electron paramagnetic resonance (EPR) was used to study defects in 4H and 6H SiC irradiated with 2.5 MeV electrons at room temperature. When the dose of irradiation reaches ∼ 5 × 1017 electrons/cm2, an EPR spectrum appears. In both 4H and 6H SiC, the defect associated with this spectrum has C1h symmetry with an effective electron spin S = 1 and an isotropic g-value of 2.0063 ± 0.0002. The crystal-field parameter was determined as D = 1.65 and D = 1.67 GHz for 4H and 6H SiC, respectively. The principal crystal-field axis lies in the (112̄0) plane and makes an angle of ∼ 46° with the c-axis for both polytypes. A clear hyperfine structure from 29Si due to the interaction with four nearest silicon neighbours was observed, confirming that the defect is related to the carbon vacancy. The similarity in all respects including the annealing behaviour of the spectrum in both polytypes suggests that it belongs to the same defect. Based on the formation and its electronic structure, the defect is suggested to be a complex with one of the components being the carbon vacancy.