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| Abstract: | The dielectric properties of vacuum-deposited europium oxide films have been investigated in the frequency range from 1 kHz to 1 MHz at various temperatures (300-543 K). The dielectric constant is found to depend on film thickness and it attains a constant value beyond 1000 Å. Films deposited at higher substrate temperatures (above 423 K) exhibit improved dielectric properties owing to the recovery of stoichiometry. The frequency variation of the loss factor exhibits a minimum which increases with rise in temperature. The breakdown field strength (about 106V cm-1) is found to be thickness dependent and it varies in accordance with the Forlani-Minnaja relation. The films exhibit ohmic conduction with an activation energy of 0.86 eV at low electric fields but at higher fields the conductivity becomes space charge limited. X-ray studies show that the films are amorphous in nature. The a.c. conductivity is proportional to ω at low frequency, whereas a square law dependence is observed at higher frequencies. The optical constants n, α and k and optical band gap are calculated from the UV-visible-near-IR spectra. |
| URI: | http://dyuthi.cusat.ac.in/purl/2652 |
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| Dyuthi-T0334.pdf | (403.4Kb) |
| Abstract: | The dielectric properties of electron beam evaporated Sm2O3 films have been investigated in the frequency range from 1 kHz to 1 MHz at various temperatures (300 K-453 K). The dielectric constant is found to depend on film thickness and it attains a constant value beyond 1000 A. The present electron beam evaporated Sm2O3 films have a high dielectric constant of 43. The frequency dependence of and tan teeta at various temperatures is also studied. |
| URI: | http://dyuthi.cusat.ac.in/purl/2467 |
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| Dyuthi-P0297.pdf | (244.2Kb) |
| Abstract: | AC thin film electroluminescent devices of MIS and MISIM have been fabricated with a novel dielectric layer of Eu2O3 as an insulator. The threshold voltage for light emission is found to depend strongly on the frequency of excitation source in these devices. These devices are fabricated with an active layer of ZnS:Mn and a novel dielectric layer of Eu2O3 as an insulator. The observed frequency dependence of brightness-voltage characteristics has been explained on the basis of the loss characteristic of the insulator layer. Changes in the threshold voltage and brightness with variation in emitting or insulating film thickness have been investigated in metal-insulator-semiconductor (MIS) structures. It has been found that the decrease in brightness occurring with decreasing ZnS layer thickness can be compensated by an increase in brightness obtained by reducing the insulator thickness. The optimal condition for low threshold voltage and higher stability has been shown to occur when the active layer to insulator thickness ratio lies between one and two. |
| URI: | http://dyuthi.cusat.ac.in/purl/2429 |
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| Dyuthi-P0289.pdf | (390.8Kb) |
| Abstract: | The method of preparation of ZnS phosphors doped with praseodymium and copper is given. The electroluminescence (EL) spectrum of ZnS:Pr,Cl has two broad bands at 470 and 570 nm. ZnS:Cu,Pr,Cl gives white emission with spectral peaks at 470, 520, 570 and 640 nm. The EL spectra of both types of phosphor exhibit a conspicuous colour shift as the frequency of the excitation voltage is varied. Detailed investigations show that the relative intensities of spectral peaks are strongly dependent on the frequency of the excitation voltage. The colour shift is explained on the basis of the Schon-Klasens model. |
| URI: | http://dyuthi.cusat.ac.in/purl/2428 |
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| Dyuthi-P0288.pdf | (472.0Kb) |
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