Ivan V. Ilyin

Identification of the deep level defects in AlN single crystals by electron paramagnetic resonance

Electron paramagnetic resonance (EPR) at 9.4 and 35 GHz were studied on two types of AlN single crystals, grown by a sublimation sandwich method. These investigations revealed the presence of transition metals impurities in the first sample: Fe2+ (S=2) and some paramagnetic centers with S=3/2, we suggest Cr3+ or Ni3+ as the possible candidates. The EPR spectra of Fe2+ were observed up to the room temperature. After sample illumination at 5 K with light (wavelength shorter 700 nm) strong EPR signal with a g factor of shallow donors (SDs) and slightly anisotropic linewidth appears. This light-induced EPR signal, once excited at low temperature, still persists after switching off the light and is about constant up to 30 K then it drops quickly. SDs show a negative correlation energy U and oxygen in the N position (ON) is the most probable model. EPR spectra of deep-donor center which was assumed to be the nitrogen vacancy VN have been observed in the second sample. The x-ray irradiation leads to considerable...

Peculiarities of neutron-transmutation phosphorous doping of Si30 enriched SiC crystals: Electron paramagnetic resonance study

We have obtained a high concentration of P donor dopants in 6H‐SiC enriched with Si30 and irradiated with thermal neutrons. It was established that annealing at a relatively low temperature of 1300°C, i.e., 500–600°C lower than that used for annealing SiC with the natural isotope composition after neutron-transmutation doping, gives rise to an electron paramagnetic resonance (EPR) signal corresponding to three different shallow P (sP) donors with large hyperfine interactions. The correlated changes of these sP centers in all the annealing experiments and the similarities to the spectra of shallow N donors demonstrate that these sites have shallow donor levels and a similar electronic structure and that they belong to different lattice sites: two quasicubic and hexagonal. The phosphorus at these three sites is suggested to occupy the C position. Simultaneously the low-temperature EPR signal from another set of P-related donor centers having a small, strongly anisotropic hyperfine interaction is observed. I...

EPR diagnostics of laser materials based on ZnSe crystals doped with transition elements

The electron paramagnetic resonance (EPR) spectra observed in laser materials based on zinc selenide (ZnSe) crystals doped with transition elements have been analyzed and identified. It has been shown that, in addition to working impurities (Cr2+, Co2+, or Fe2+), the diffusion layer exhibits EPR spectra of accompanying impurities due to the diffusion of transition elements (chromium, cobalt, or iron) used in the preparation of active materials for quantum electronics (lasers, switches) operating in the mid-infrared range. EPR diagnostics of these impurities can be used in the development of appropriate regimes for minimizing concentrations of accompanying impurities that adversely affect the performance characteristics of laser materials. It has been found that, during the diffusion of transition metals, ions of the accompanying impurity Mn2+, which is characterized by extremely informative EPR spectra, are embedded in the crystal lattice. It has been proposed to use these ions as ideal markers to control, on the electronic level, the crystal structure of the active diffusion layer.

Identification of nitrogen vacancies in an AlN single crystal: EPR and thermoluminescence investigations

The electronic structure of nitrogen vacancies in specially undoped aluminum nitride single crystals has been determined and the depth of the donor level of these vacancies in the band gap has been found to be ∼75 meV by combined electron paramagnetic resonance and thermoluminescence investigations.

Erbium in silicon carbide crystals: EPR and high-temperature luminescence

Erbium ions have been incorporated for the first time in bulk 6H-SiC crystals during growth, and they were unambiguously identified from the 167Er EPR hyperfine structure. High-temperature luminescence of erbium ions at a wavelength of 1.54 µm has been detected. The observed luminescence exhibits an increase in intensity with increasing temperature. The observation of Er luminescence in 6H-SiC offers a promising potential for development of semiconductor light-emitting devices at a wavelength within the fiber-optics transparency window.

Evidence of the Ground Triplet State of Silicon-Carbon Divacancies (P6, P7 Centers) in 6H SiC: An EPR Study

P6 and P7 centers, which are responsible for semi-insulating properties of SiC, were shown to be neutral Si-C divacancies (VSi-VC)o having a triplet ground state. The EPR experiments that were performed at very low temperatures and in complete darkness exclude the possibility of a thermal or optically excited triplet state and, as a result, the existing model of excited triplet state P6 and P7 centers was discarded. The optical alignment process which induces the spin polarization of the ground triplet 3A state of the P6, P7 centers in SiC was interpreted to be caused by strong spin selectivity of the intersystem crossing (ISC) nonradiative transitions from an excited 3E state to a metastable singlet 1A state. The luminescence and optical absorption are caused by transitions between spin sublevels of 3A and 3E states. The analogy in properties of a divacancy in SiC and the N-V defect in diamond allows considering the divacancy in SiC as a potential defect for the single defect spectroscopy.

Peculiarities of Neutron-Transmutation Phosphorous Doping of SiC Enriched with 30Si Isotope: Electron Paramagnetic Resonance Study

High concentration of two types of P donors up to 1017 cm-3 in SiC enriched with 30Si after neutron transmutation doping (NTD) has been achieved. It was established that annealing at sufficiently low temperature of 1300oC, that is 500-600°C lower compared with annealing of NTD SiC with natural isotope composition, gives rise to the EPR signal of shallow P donors, labeled sPc1, sPc2 and sPh. The correlated changes of the EPR spectra of the three sP centres in all the experiments and the qualitative similarities with spectra of shallow N donors prove that these centres have shallow donor levels and a similar electronic structure and belong to different lattice sites. The annealing at 1700°C results in a transformation of one type of P donors (sPc1, sPc2 and sPh) into another type having low temperature EPR spectra labeled dP.

Identification of the Triplet State N-V Defect in Neutron Irradiated Silicon Carbide by Electron Paramagnetic Resonance

Two types of a new triplet centers labeled as N-V have been observed in heavily neutron irradiated (dose of 1021 cm-2) and high-temperature annealed (2000°C) 6H-SiC crystals. The centers have an axial symmetry along c-axis. Anisotropic hyperfine splitting due to the one 14N nucleus has been observed. The EPR spectra of N-V defects in the triplet state in 6H-SiC reveal strong temperature dependence. The parameters of these centers are similar to that for well-known N-V center in diamond. It seems to consist of silicon vacancy and carbon substitutional nitrogen in the adjacent lattice cites oriented along c-axis. Similar to the diamond N-V centers in SiC have been produced by neutron irradiation and high-temperature annealing of the crystals containing nitrogen. For the first shell the structure of the N-V defect in 6H-SiC is practically identical with that in diamond. The charge state of this defect seems to be +1 compare with neutral state for nitrogensilicon vacancy defect in 6H-SiC with S=1/2.

High-Temperature Stable Multi-Defect Clusters in Neutron Irradiated Silicon Carbide: Electron Paramagnetic Resonance Study

The high-temperature stable defect complexes in 6H-SiC crystals created by heavy neutron irradiation and following high-temperature annealing have been discovered by EPR. After annealing at 1500°C at least five new axially symmetric centers with the electron spin S = 1/2 and S = 1 were shown to arise in 6H-SiC crystals. The striking feature of all discovered centers is a strong hyperfine interaction with a great number (up to twelve) of equivalent host Si (C) atoms. Two models, a four-vacancy complex VSi-3VC, and a split-interstitial antisite (C2)Si or a pair of two antisites (C2)Si-SiC are discussed. There is a good probability that some of new centers could be related to the famous D1 and DII centers. After annealing at 2000°C the dc1-dc4 centers disappeared and a new triplet center labeled as N-V in the form of a silicon vacancy and a nitrogen atom in neighboring carbon substitutional position has been observed. The parameters of this center are similar to that for well-known N-V center in diamond.

Deep-Level Defects in AlN Single Crystals: EPR Studies

Electron paramagnetic resonance (EPR) at X-band (9.4 GHz) and Q-band (35 GHz) have been used to study defects in two samples of AlN monocrystals, grown by a sublimation sandwich method. These investigations reveal the presence of Fe2+ impurities in the reddish sample. The spectra of substitutional Fe2+ are highly anisotropic and could be observed even up to the room temperature. After illumination the signals showing the DX behavior were detected in the same sample. We assume these signals to arise due to the presence of the shallow donor center namely the isolated substitutional oxygen ON occupying the nitrogen position. In the second slightly amber-coloured sample EPR measurements before and after X-ray showed the presence of a deep-donor center which was assumed to be nitrogen vacancy VN. Based on thermoluminescence measurements the depth of the level was estimated to 0.45-0.5 eV.