Both contact resistivity of Au—Ti—Pd—n-Si ohmic contact and mechanism of current flow are studied in the 100—360 K temperature range. A method is proposed for reduction of error in determination of contact resistivity based on analysis of statistical dependences of the measured contact resistivity values (which are in the range of (0.9—2)•10–5 Ω•cm2). On the basis of the contact resistivity temperature dependence, it is found for an ohmic contact with barrier height of 0.22 eV that the field mechanism of current flow is predominant in the 100—200 K temperature range, while thermal-field emission with activation energy of 0.08 eV is predominant in the 200—360 K temperature range.
High-resistance cadmium telluride single crystals are promising material for production of ionizing radiation detectors. To increase crystal resistance, they are doped with chlorine. The detector quality depends on uniformity of chlorine impurity distribution over crystal. It is known that low-dose microwave irradiation can homogenize impurity distribution in a specimen. In the present work, we made an attempt to improve the detector material quality by using such post-technological treatment, as well as to study state variation for impurity-defect complexes. To this end, the effect of microwave irradiation on transformation of impurity-defect complexes in CdTe:Cl single crystals was investigated using low-temperature photoluminescence. It is shown that activation of ClTe donor centers by microwave irradiation for 10 s and presence of VCd acceptor centers in the specimens under investigation effectively facilitate formation of (VNd–ClTe) defect centers at which excitons are bound. Detailed investigations of the band form for donor-acceptor pairs (DAPs) in CdTe:Cl single crystals made it possible to determine the Huang—Rhys factor (that characterizes electron-phonon interaction in CdTe:Cl DAPs) as a function of microwave treatment duration. It is shown for single crystals with NCl = 5·1017 cm–3 and 5·1019 cm–3 that the Huang—Rhys factor grows with microwave irradiation dose. This is related to both homogenization of donor and acceptor centers distribution and increase of donor—acceptor spacing. It is shown that microwave irradiation of CdTe:Cl single crystals results in concentration reduction for separate cadmium vacancies VCd because of formation of (VNd—ClTe) defect centers at which excitons are bound.
Шинкаренко В.В. Етно-художня культура як складова професійної компетентності майбутнього вчителя.У статті шляхом зіставлення, порівняння, узагальнення наукової інформації обґрунтовано слушність організації навчального процесу на основі народних традицій. Розкрито засоби й методи народного виховання, запропоновано рекомендації з практичного використання отриманих результатів задля ефективного формування компетентності майбутнього вчителя.
The emission uniformity of LED chips in the entire range of brightness and colors is the problem in LED displays manufacture process. It was approved that at lowering brightness gradations appearing the radiation nonuniformity between LED chips, and the higher disorders will be seen on the lesser emission levels. The RGB LED chips, observed by us, were based on AlGaInP (red), In0.3Ga0.7N/GaN (green), and In0.2Ga0.8N/GaN (blue) and had nominal working current 20 mA. Analysis of the current-voltage characteristics and capacitance-voltage characteristics showed the presence of inhomogeneous semiconductor junctions and ohmic contacts in blue LEDs structures that are the source of possible irregularities in the final emission of LED displays. The variation of voltages (at current 10 mA) was 2.81—2.98 V for blue structures, and 1.9—2.0 V for red ones. Some of the blue structures had additional parasite current-flow mechanism at low current. Rise time and fall time of electroluminescence pulse of blue structures were measured. The shortest LED pulse time in LED displays is limited by duration of 6—8 ns. The quality of LED displays may be improved by implementing the preliminary control of LED chips in a narrower range of voltage variation at operating currents, or more narrow interval of I—V variation. This additional LEDs sorting will of course reduce the percentage of the total amount of light-emitting diodes, but may improve the image (video, photo) quality at translations by using a lower brightness gradations.
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