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Enriched Zn82Se is a very promising material for the detection of the neutrionoless double beta decay. The 82Se isotope acts as the source of the decay, and ZnSe detects the scintillation and bolometric events. Due to the high cost in the preparation of the Zn82Se material, the optimization of its properties, especially those related to the scintillation process, is mandatory. It is well known that excellent scintillation efficiency in ZnSe is obtained when the material presents close donor–acceptor pairs, as, for example, the A-centers. In this work, neutron irradiation was used to study formation of point defects in enriched and non-enriched ZnSe samples. Applying instrumental neutron activation analysis (INAA) and inductively coupled plasma mass spectroscopy, the enrichment of Zn82Se samples was determined to ∼95%, in addition, trace impurities such as Cu, I, and Na were quantified by INAA at the μg/g level. Based on electron paramagnetic resonance (EPR) and photo-EPR measurements, we show that irradiation with fast neutrons induced point defects such as the isolated zinc vacancy (VZn) and a new low-symmetric donor center called NC1, which we tentatively assign to Zn di-interstitials. Low-temperature photoluminescence measurements of the neutron-irradiated Zn82Se revealed three broad PL bands centered in the visible spectral range. Based on the INAA analysis shown in this work, we attribute the previously unidentified 540 nm PL band in the Zn82Se sample to recombination between shallow donors and deep copper acceptors. The formation of point defects by neutron irradiation and their stability are discussed. [ABSTRACT FROM AUTHOR]

MoS2 monolayers, a two-dimensional (2D) direct semiconductor material with an energy gap of 1.9 eV, offer many opportunities to be explored in different electronic devices. Defects often play dominant roles in the electronic and optical properties of semiconductor devices. However, little experimental information about intrinsic and extrinsic defects or impurities is available for this 2D system, and even for macroscopic 3D samples for which MoS2 shows an indirect bandgap of 1.3 eV. In this work, we evaluate the nature of impurities with unpaired spins using electron paramagnetic resonance (EPR) in different geological macroscopic samples. Regarding the fact that monolayers are mostly obtained from natural crystals, we expect that the majority of impurities found in macroscopic samples are also randomly present in MoS2 monolayers. By EPR at low temperatures, rhenium donors and sulfur vacancy acceptors are identified as the main impurities in bulk MoS2 with a corresponding donor concentration of about 108-12 defects/cm² for MoS2 monolayer. Electrical transport experiments as a function of temperature are in good agreement with the EPR results, revealing a shallow donor state with an ionization energy of 89 meV and a concentration of 7×1015cm-3, which we attribute to rhenium, as well as a second deeper donor state with ionization energy of 241 meV with high concentration of 2×1019cm-3 and net acceptor concentration of 5×1018cm-3 related to sulfur vacancies. [ABSTRACT FROM AUTHOR]

Point defects in wide-bandgap semiconductors, such as hexagonal boron nitride (h-BN), have driven enormous amounts of research due to their interesting optical properties such as quantum emission at room temperature. Defect engineering by particle irradiation is a very interesting strategy for producing quantum emitters in a controlled way. The identification of most point defects is done by electron paramagnetic resonance and related advanced techniques. Following our recent works, we present new data about point defects produced by neutron irradiation at room temperature and investigate their thermal stability in crystalline, flake and ultrafine h-BN powder. Our experimental data indicate the formation of the nitrogen antisite defect next to a nitrogen vacancy in its neutral charge state, (NBVN)0, with spin S= 1/2 in all types of h-BN showing strong axial hyperfine interaction (A|| ≈ 95 MHz and A⊥ ≈ 5 MHz). It is thermally stable up to ~600 şC, which is similar to the disappearance of the negative charged boron vacancy,. In addition, after neutron irradiation of h-BN powder samples, a spin S= 1/2 point defect is observed presenting an axial superhyperfine interaction with two equivalent nitrogen nuclei (14N, I = 1, 99.68%), which we tentatively assign to the CNVB defect. It is thermally stable up to ~850 şC. Another, yet-unidentified S = 1/2 center acts as a charge compensating defect at specific annealing temperatures. Our experimental results are compared and discussed with theoretical models available in the literature. [ABSTRACT FROM AUTHOR]

Hexagonal molybdenite (MoS2) is one of the most promising two-dimensional (2D) semiconductors, known with n-type and p-type conduction, with possible applications in electronic, opto-electronic, and spintronic devices. In this work, highly pure geological samples of 2H-MoS2 were investigated by temperature-dependent electron paramagnetic resonance (EPR) and Hall effect measurements. The low-temperature (<55 K) EPR spectra were consistently explained as holes (S = 1/2) trapped on shallow As acceptors on sulfur sites leading to a four-line hyperfine-split spectrum (75As: I = 3/2, 100%) in axial symmetry and with a concentration of 5(1) ppm (∼2 × 1017 cm−3). Electrical measurements indicate p-type conduction with a free carrier concentration of about 5 × 1017 cm−3 at room temperature and an ionization energy of 52 meV associated with the shallow As acceptors, which is consistent with the ionization energy determined from the hydrogenic model of shallow acceptors in 2H-MoS2. These values are in strong contrast to the unrealistic value of 0.7 meV reported in the literature obtained from the analysis of temperature-dependent EPR measurements. Possible explanations are related to temperature-dependent spin-lattice relaxation effects, affecting strongly EPR line intensities and making impossible their use in obtaining the ionization energy. [ABSTRACT FROM AUTHOR]