Over the last 25 years, radiowave detection of neutrino-generated signals, using cold polar ice as the neutrino target, has emerged as perhaps the most promising technique for detection of extragalactic ultra-high energy neutrinos (corresponding to neutrino energies in excess of 0.01 Joules, or 1017 electron volts). During the summer of 2021 and in tandem with the initial deployment of the Radio Neutrino Observatory in Greenland (RNO-G), we conducted radioglaciological measurements at Summit Station, Greenland to refine our understanding of the ice target. We report the result of one such measurement, the radio-frequency electric field attenuation length $L_\alpha$. We find an approximately linear dependence of $L_\alpha$ on frequency with the best fit of the average field attenuation for the upper 1500 m of ice: $\langle L_\alpha \rangle = ( ( 1154 \pm 121) - ( 0.81 \pm 0.14) \, ( \nu /{\rm MHz}) ) \,{\rm m}$ for frequencies ν ∈ [145 − 350] MHz.

A study of temperature dependent Hall effect (TDH), electron paramagnetic resonance (EPR), photoluminescence (PL) and secondary ion mass spectrometry (SIMS) measurements has been made on high purity semi-insulating (HPSI) 4H-SiC crystals grown by the physical vapor transport technique. Thermal activation energies from TDH varied from a low of 0.55 eV to a high of 1.5 eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Carrier concentration measurements indicated the deep levels had to be present in concentrations in the low 1015 cm-3 range. Several defects were detected by EPR including the carbon vacancy and the carbon-silicon divacancy. PL measurements in the near IR showed the presence of the UD-1, UD-2 and UD-3 emission lines that have been found in HPSI material. No correlation between the relative intensities of the PL lines and the TDH activation energies was seen. SIMS measurements on nitrogen, boron and other common impurities indicate nitrogen and boron concentrations higher than those of individual deep levels as determined by TDH or of intrinsic defects as determined by EPR such as the carbon vacancy or the divacancy. It is determined that several different defects with concentrations greater than or equal to 1x1015 cm-3 are required to compensate the residual nitrogen and boron.

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

Optically-detected electron-nuclear double resonance (ODENDOR) studies at 24 GHz on high-resistivity GaN films grown on Al2O3 have been combined with x-ray diffraction measurements to obtain information on the location of the residual shallow donors. Strong ODENDOR assigned to 69,71Ga lattice nuclei was detected on the g=1.951 effective-mass donor resonance found on the 2.2 eV emission bands. The x-ray studies reveal that the layers are under biaxial compression with high values of strain (∼ 2–3 × 10−3). The quadrupole splittings for 69Ga are smaller than those reported for strain-free samples by 15–25 %. The dominant sources of the local electric field gradient (EFG) responsible for the splittings are attributed to the wurtzite crystal structure and the strain fields that arise from the lattice constant mismatch and the difference in thermal expansion coefficients. An EFG/strain relationship of 3 × 1022 Vm−2 per unit strain at the 69,71Ga nuclei is deduced. The ODENDOR can be described with asymmetry parameter η=0. This provides evidence that the donors are in the crystallites rather than near grain boundaries.

We have made an attempt to obtain electronic and atomic structure information on the residual defects that exist in high-resitivity GaN epitaxial layers from optically-detected magnetic resonance (ODMR) experiments performed on the broad 3.0 and 2.2 eV photoluminescence (PL) bands observed from these films. The first observation of magnetic resonance on this 3.0 eV band reveals two ODMR signals. The first resonance is sharp (FWHM ∼ 3.5 mT) with g ∼ 1.950 and is assigned to effective-mass (EM) donors based on previous studies. The second feature is much broader (FWHM ∼18 mT) with a donor-like g-value of ∼ 1.977. This new resonance may be associated with partially EM-like donor states located ∼ 54 - 57 meV below the conduction band edge proposed recently to be involved in this 3.0 eV PL band.

We report electrically-detected magnetic resonance (EDMR) and electroluminescence-detected magnetic resonance (ELDMR) results on InGaN/AJGaN single-quantum-well light emitting diodes. The dominant feature detected by either technique is a broad resonance (ΔB ≈ 13 mT) at g ≈ 2.01 which is enhanced by high current stressing. Our ELDMR measurements show that, depending on bias, this defect is predominately associated with either an increase or a decrease in electroluminescence at resonance while our EDMR measurements show that this resonance is associated with an increase in current at resonance before stressing and a decrease after stressing. We suggest that this is associated with a nonradiative recombination path, in parallel with the radiative recombination path and with recombination in the depletion region of a contact. A second resonance, more prominent before stressing, with g ≈ 1.99 and ΔB ∽ 7 mT is very similar to the deep donor trap, previously observed in double heterostructure diodes and is associated with a decrease in both the current and electroluminescence at resonance.

A review of MeV-ion beam induced crystallization (IBIEC) and interfacial amorphization (IBIIA) in III-V compounds (GaAs, InAs, GaP, InP) is given. The kinetics of IBIEC and IBIIA is studied as a function of the temperature, the density of the displacements v, and the ion dose rate j. Reversal temperatures TR for IBIEC ↔ IBIIA transitions are determined for the different materials showing characteristic dependences on v and j. The IBIEC rate is shown to be controlled by point defect diffusion towards the a/c-interface and additionally modified by the interface structure. The suppression of microtwin and stacking fault formation during IBIEC is explained by the fact that the ion beam modifies the orientation dependence of the crystallization kinetics avoiding the disintegration and (111)-faceting of the (100)-interface. For all the compound materials investigated the IBIEC process is stopped above critical temperatures and doses. The capture of diffasing defects by crystallites growing in the amorphous layers is considered to be responsible for the stopping of the IBIEC interface. Ways are demonstrated to avoid stopping, to achieve complete epitaxial regrowth also of thick layers, and to minimize the generation of stable damage in the crystallized layers. The limited temperature ranges for undisturbed IBIEC and IBIIA in III/V-compounds are explained by low nucleation barriers and high growth rates both of crystallites and of amorphous zones.

For the first time, ion beam induced epitaxial crystallization (IBIEC) has been found in SiC. The effect of 300 keV Si+ irradiation through an amorphous surface layer in single crystalline 6H-SiC at 477±5°C has been investigated by RBS/C and XTEM. A shrinkage of the amorphous layer was found after ion irradiation at this temperature which is caused by both an ion dose independent thermal regrowth of about 20 nm and an additional ion beam induced epitaxial crystallization with a rate of about 1.5 nm/ 1016 cm-2.

For the first time, ion beam induced epitaxial crystallization (IBIEC) hasbeen found in SiC. The effect of 300 keV Si+ irradiation throughan amorphous surface layer in single crystalline 6H-SiC at 477+5°C has beeninvestigated by RBS/C and XTEM. A shrinkage of the amorphous layer was foundafter ion irradiation at this temperature which is caused by both an iondose independent thermal regrowth of about 20 nm and an additional ion beaminduced epitaxial crystallization with a rate of about 1.5 nm/ 1016 cm−2.

Si1−xGex/Si heterostructures with varying layer-thicknesses have been characterized using photoluminescence and magnetic resonance detected on photoluminescence. Three of the four samples studied exhibit sharp photoluminescence bands at different energies. For a 120 Å Si/40 Å Si1−xGex heterostructure, magnetic resonance of an electron in the Si and of a hole in the Sil. xGex layers were observed. These results indicate cross-interface, or Type II, excitonic recombination. Further, anisotropie magnetic resonance spectra indicate the presence of dangling-bonds defects in the heterostructures.

Optical and magnetic properties of donors in high AlAs-fraction AlxGa1−x As have been determined using optically-detected magnetic resonance. Many samples exhibit a sharp resonance at g = 1.95 detected on midgap luminescence. One high-quality sample exhibits an exhange-broadened line which reveals a distribution in donor-acceptor pair separations on moderately deep emission. A second high-quality sample exhibits the donor ODMR on donor-to-shallow- acceptor photoluminescence.