Single crystalline bulk and epitaxially grown gallium oxide (β–Ga2O3) was irradiated by 0.6 and 1.9 MeV protons to doses ranging from 5 × 109 to 6 × 1014 cm−2 in order to study the impact on charge carrier concentration and electrically active defects. Samples irradiated to doses at or above 2 × 1013 cm−2 showed a complete removal of free charge carriers in their as-irradiated state, whereas little or no influence was observed below doses of 6 × 1012 cm−2. From measurements at elevated temperatures, a thermally activated recovery process is seen for the charge carriers, where the activation energy for recovery follow a second-order kinetics with an activation energy of ∼1.2 eV. Combining the experimental results with hybrid functional calculations, we propose that the charge carrier removal can be explained by Fermi-level pinning far from the conduction band minimum (CBM) due to gallium interstitials (Gai), vacancies (VGa), and antisites (GaO), while migration and subsequent passivation of VGa via hydrogen-derived or VO defects may be responsible for the recovery. Following the recovery, deep level transient spectroscopy (DLTS) reveals generation of two deep levels, with energy positions around 0.75 and 1.4 eV below the CBM. Of these two levels, the latter is observed to disappear after the initial DLTS measurements, while the concentration of the former increases. We discuss candidate possibilities and suggest that the origins of these levels are more likely due to a defect complex than an isolated point defect.
Using a combination of deep level transient spectroscopy, secondary ion mass spectrometry, proton irradiation, and hybrid functional calculations, we identify two similar deep levels that are associated with Fe impurities and intrinsic defects in bulk crystals and molecular beam epitaxy and hydride vapor phase epitaxi-grown epilayers of β-Ga2O3. First, our results indicate that FeGa, and not an intrinsic defect, acts as the deep acceptor responsible for the often dominating E2 level at ∼0.78 eV below the conduction band minimum. Second, by provoking additional intrinsic defect generation via proton irradiation, we identified the emergence of a new level, labeled as E2*, having the ionization energy very close to that of E2, but exhibiting an order of magnitude larger capture cross section. Importantly, the properties of E2* are found to be consistent with its intrinsic origin. As such, contradictory opinions of a long standing literature debate on either extrinsic or intrinsic origin of the deep acceptor in question converge accounting for possible contributions from E2 and E2* in different experimental conditions.
Abstract. We propose the use of eye-movements as a biometric. A case study investigating potentials of eye-movement data for biometric purposes was conducted. Twelve participants' eye-movements were measured during still and moving objects viewing. The measured data includes pupil sizes and their dynamics, gaze velocities and distances of infrared reflections of the eyes. For still object viewing of 1 second duration, identification rate of 60 % can be obtained by using dynamics of pupil diameters. We suggest an integration of the eyemovement-based identification into general video-based biometric systems.
Particle irradiation is known to give rise to several majority carrier traps in the band gap of n-type 4H-SiC, in the 0.4-1.6 eV energy range below the conduction band edge (E C ). Among these traps, the EH1 (E C -0.4 eV) and the EH3 (E C -0.7 eV) are the least thermally stable ones and not much is known on their microscopic origin. In order to understand the nature of EH1 and EH3, their annealing kinetics was studied by means of deep level transient spectroscopy and the results were interpreted by invoking the diffusion-limited theory. It is found that EH1 and EH3 are two different charge states of the same defect, labeled EH-center, that anneals out with an activation energy of ∼1.1 eV and whose nature is related to a carbon interstitial. Our study shows that the EH-center is not the same as the S-center defect which was reported by previous studies found in the literature.
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