Blue/pink/purple electroluminescence from metal–oxide–semiconductor devices fabricated by spin-coating of [tantalum:(gadolinium/praseodymium)] and (praseodymium:cerium) organic compounds on silicon

Abstract

Blue/pink/purple electroluminescence (EL) from metal–oxide–semiconductor (MOS) devices with an indium tin oxide (ITO)/[Gd/(Ta + Gd/Pr)/(Pr + Ce)–Si–O] insulator layer/n+-Si substrate surface is reported. The insulator layers were fabricated from organic liquid sources of Gd or (Ta + Gd/Pr)/(Pr + Ce) mixtures, which were spin-coated on the n+-Si substrate and annealed at 950 °C for 30 min in air. The EL emission could be observed by the naked eye in the dark in the Fowler–Nordheim (FN) tunnel current regions. Peak wavelengths in the measured EL spectra were independent of the positive current. The EL intensity ratio of ultraviolet (UV) to the visible range varied with the composition ratio of the (Ta + Gd) liquids, and an optimum Ta to Gd ratio existed for the strongest blue emission, which could be attributed to the Ta-related oxide/silicate. The pink EL of the device fabricated with the ( ) mixture ratio can be explained by EL emission peaks related to the Pr3+ ions. The purple EL observed from the ( ) device corresponds to the strong and broad emission profile near the 357 nm peak, which cannot be assigned to Ce3+ ions. The results suggest that the EL can be attributed to the double-layer oxides with different compositions in the MOS devices. The upper layer consists of various Ta-, Gd-, Pr-, and Ce-related oxides and their silicates, while the lower SiO x -rich layer contributes to the FN current due to the high electric field, and thus the various EL colors.

Electroluminescence color tuning between green and red from metal–oxide–semiconductor devices fabricated by spin-coating of rare-earth (terbium + europium) organic compounds on silicon

“…The EL spectrum data obtained were corrected with the total wavelength response curve of the system as in our previous work. 34) , respectively. The addition of Ba liquid to Tb liquid increased V R by about 6 V, as observed in our previous study.…”

“…The EL spectrum with wavelengths ranging from 290 to 1000 nm can be detected simultaneously with a resolution of 1.2 nm=pixel as in the setup previously reported. 33,34) The exposure time of the CCD camera for EL spectrum measurements was varied from 0.2 to 10 s depending on the measured I G . The EL spectrum data obtained were corrected with the total wavelength response curve of the system as in our previous work.…”

“…I G steeply increasing with V R was similar to that in the case of EL MOS devices fabricated by heavy Si implantation into SiO 2 12,13,16,36) and by spin-coating organic compound liquids on Si substrates. [31][32][33][34] Figure 2(b) shows the Fowler-Nordheim (FN) plots [i.e., log(I=V 2 ) vs 1=V plots] for the #0…”

“…Finally, we observed a purple EL from a (Pr + Ce) oxide film among the combinations of (Pr + γ) examined, where γ indicates a rare earth, Ca, or Ba. 34) In this study, we demonstrate a simple method of EL color tuning from yellowish green to yellow, and eventually to reddish orange in MOS devices with [(Tb + Ba) + Eu] organic compounds spin-coated on silicon at various concentration ratios of Tb to Eu. The device structure is indium-tin oxide (ITO)=[(Ta + Ba) + Eu]-Si-O insulator layer=n + -Si substrate, similar to that in previous studies.…”

“…The device structure is indium-tin oxide (ITO)=[(Ta + Ba) + Eu]-Si-O insulator layer=n + -Si substrate, similar to that in previous studies. [31][32][33][34] Current versus voltage (I G -V G ) characteristics, EL colors, and EL spectra are presented. The surface insulator layers are analyzed by cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, and X-ray photoelectron spectroscopy (XPS).…”