Emission bands of nitrogen-implantation induced luminescent centers in ZnO crystals: experiment and theory

High quality ZnO crystals with the sharp band-edge excitonic emission and very weak green emission were implanted by nitrogen ions. An additional red emission band was observed in the as-implanted ZnO crystal and investigated as a function of temperature. By employing the underdamped multimode Brownian oscillator model for the general electron-phonon coupling system, both the original green and nitrogen-implantation induced red emission bands were theoretically reproduced at different temperatures. Excellent agreement between the theory and the experiment enables us determine the energetic positions of the pure electronic levels associated with the green and red emission bands, respectively. The determined energy level of the red emission band is in good agreement with the data obtained from the deep-level transient spectroscopy measurements. © 2012 American Institute of Physics.published_or_final_versio

On the Definition of Averagely Trapped Surfaces

Previously suggested definitions of averagely trapped surfaces are not well-defined properties of 2-surfaces, and can include surfaces in flat space-time. A natural definition of averagely trapped surfaces is that the product of the null expansions be positive on average. A surface is averagely trapped in the latter sense if and only if its area $A$ and Hawking mass $M$ satisfy the isoperimetric inequality $16\pi M^2 > A$, with similar inequalities existing for other definitions of quasi-local energy.Comment: 4 page

Deep-level defects in n-type 6H silicon carbide induced by He implantation

Defects in He-implanted n -type 6H-SiC samples have been studied with deep-level transient spectroscopy. A deep-level defect was identified by an intensity with a logarithmical dependence on the filling pulse width, which is characteristic of dislocation defects. Combined with information extracted from positron-annihilation spectroscopic measurements, this defect was associated with the defect vacancy bound to a dislocation. Defect levels at 0.380.44 eV (E1 E2), 0.50, 0.53, and 0.640.75 eV (Z1 Z2) were also induced by He implantation. Annealing studies on these samples were also performed and the results were compared with those obtained from e- -irradiated (0.3 and 1.7 MeV) and neutron-irradiated n -type 6H-SiC samples. The E1 E2 and the Z1 Z2 signals found in the He-implanted sample are more thermally stable than those found in the electron-irradiated or the neutron-irradiated samples. © 2005 American Institute of Physics.published_or_final_versio

Gallium implantation induced deep levels in n-type 6H-SIC

Two Ga-acceptor levels, located at EV+0.31eV and EV+0.37eV, respectively, have been observed in the gallium implantation manufactured p+n diodes using deep level transient spectroscopy. The behavior of the implanted gallium is very similar to that of implanted aluminum, except that the positions of the introduced levels are different. This result strongly supports the recent model, which was used to explain the discrepant results between boron and aluminum implantation induced deep levels. Besides the two acceptor levels, a thermally stable electron trap is also observed and has been tentatively attributed to a Ga-related complex. © 1999 American Institute of Physics.published_or_final_versio

Aluminum-implantation-induced deep levels in n-type 6H–SiC

Deep-level defect centers on the n-side of p+n junction diodes formed by low and elevated temperature aluminum-ion implantation into n-type 6H–SiC have been studied using deep-level transient spectroscopy. Two shallow Al-acceptor levels have been observed in the n region just beyond the implantation depth through their minority-carrier emission signatures. The dominant level is situated at 0.26 eV above the valence band and is accompanied by a shallower level of small intensity. Comparison with photoluminescence results suggests the dominant level (labeled Ak) and the shallower level (labeled Ah), are associated with the cubic and hexagonal lattice sites, respectively. Unlike previously reported results, which show many different implantation-induced donors within the implantation region, only one deep donor level at EC – 0.44 eV is found to occur in the postimplantation region, indicating that the various crystal damage sites occur with different spatial distributions. ©1998 American Institute of Physics.published_or_final_versio

Nature of red luminescence band in research-grade ZnO single crystals: A “self-activated” configurational transition

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Anomalous behaviors of E1 E2 deep level defects in 6H silicon carbide

Deep level defects E1 E2 were observed in He-implanted, 0.3 and 1.7 MeV electron-irradiated n -type 6H-SiC. Similar to others' results, the behaviors of E1 and E2 (like the peak intensity ratio, the annealing behaviors or the introduction rates) often varied from sample to sample. This anomalous result is not expected of E1 E2 being usually considered arising from the same defect located at the cubic and hexagonal sites respectively. The present study shows that this anomaly is due to another DLTS peak overlapping with the E1 E2. The activation energy and the capture cross section of this defect are EC -0.31 eV and σ∼8× 10-14 cm2, respectively. © 2005 American Institute of Physics.published_or_final_versio

Deep level defects E1/E2 in n-type 6H silicon carbide induced by electron radiation and He-implantation

6H-SiC samples subjected to He-implantation and e--irradiation (Ee=0.2MeV-1.7MeV) were investigated by deep level transient spectroscopy (DLTS). E1/E2 were identified in the He-implanted and the e--irradiated samples with Ee≥0. 3MeV. Considering the minimum e- energy required to displace the atoms in the lattice, the E1/E2 creation was related to the C-atom displacement. Similar to previous reports, the peak intensity and the capture cross sections of E1/E2 anomalously varies from samples to samples. It was shown that these anomalies were due to the presence of a DLTS peak overlapping with the E1/E2 signals. © 2005 American Institute of Physics.published_or_final_versio

Deep level transient spectroscopic study of oxygen implanted melt grown ZnO single crystal

Deep level traps in melt grown ZnO single crystal created by oxygen implantation and subsequent annealing in air were studied by deep level transient spectroscopy measurement between 80 and 300 K. The E C-0.29 eV trap (E3) was the dominant peak in the as-grown sample and no new defects were created in the as-O-implanted sample. The single peak feature of the deep level transient spectroscopy (DLTS) spectra did not change with the annealing temperature up to 750 °C, but the activation energy decreased to 0.22 eV. This was explained in terms of a thermally induced defect having a peak close to but inseparable from the original 0.29 eV peak. A systematic study on a wide range of the rate window for the DLTS measurement successfully separated the Arrhenius plot data originated from different traps. It was inferred that the E3 concentration in the samples did not change after the O-implantation. The traps at E C-0.11, E C-0.16 and E C-0.58 eV were created after annealing. The E C-0.16 eV trap was assigned to an intrinsic defect. No DLTS signal was found after the sample was annealed to 1200 °C. © 2011 IOP Publishing Ltd.postprin