Ultraviolet and white electroluminescence from metal–oxide–semiconductor devices fabricated by spin-coating of gadolinium organic compounds on silicon

Abstract

Ultraviolet (UV) and white electroluminescence (EL) from metal–oxide–semiconductor (MOS) devices with indium–tin oxide (ITO)/[(Gd/(Gd + Dy/La/Ca/Ba)–Si–O] insulator layers/n+-Si substrate are reported. The insulator layers were fabricated from mixtures of organic liquid sources of (Gd) or [Gd+(Dy/La/Ca/Ba)], which were spin-coated on the n+-Si substrate and annealed at 950 °C for 30 min in air. The current I G under EL emission corresponded to the Fowler–Nordheim (FN) tunnel current. The EL intensity increased proportionally to I G to the n-th power, where n was about 1.2, and the EL spectra were independent of I G. The MOS device with the [(Gd + Dy)–Si–O] layer had the weakest EL in the UV range among the measured devices, while it had the strongest EL in the visible wavelength range. The UV and visible range EL originated from the intrashell transitions of 6P7/2–8S7/2 in Gd3+ and 4F9/2–6H J /2 (J = 9, 11, 13, and 15) in Dy3+, respectively. The devices with [(Gd/(Gd + La/Ca/Ba)–Si–O] layers emitted strong UV EL, which originated from the intrashell transitions of 6P7/2–8S7/2 in Gd3+, and had the moderate intensity of EL in the visible range. The insulator layers of EL devices had a thickness of 25–30 nm and the double layer structure, whose top surface layer contained [Gd2O3+DyO x +(Gd + Dy)–Si–O]/[Gd2O3+La2O3/CaO/BaO+(Gd + La/Ca/Ba)–Si–O] silicate, while the underlayer was composed of SiO x -rich oxide with various rare earth and alkaline earth oxides.

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

“…3 can be attributed to the sharp EL spectral peaks, whereas the many small peaks overlaid on the broad emission profiles enhances the interference patterns, as observed in previous studies. 33,34) Figure 4(b) shows the Eu concentration dependence of the EL peak intensity ratio of 702 nm ( 5 D 0 -7 F 4 transitions of Eu 3+ ) to 549 nm ( 5 D 4 -7 F 5 transitions of Tb 3+ ) at constant +I G values of 100 and 200 µA. The peaks at 549 and 702 nm were used as the metrics of EL emissions originating from Tb 3+ and Eu 3+ in the #2[+Eu1]-#10[+Eu400] devices, respectively, because they have the highest EL intensity without mutual interferences between Tb 3+ and Eu 3+ , as shown in Fig.…”

“…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…”

“…More than ten kinds of rare-earth elements and more than twenty kinds of other elements of metals, semimetals, and semiconductors were examined as α. 33) As a result, a relatively strong bluish white EL was observed from a (Gd + Ta) oxide film, for which the energy transfer from Gd 3+ ions to the blue emission level related to tantalum oxide was suggested. Then, we focused on Ta and fabricated (Ta + β) oxide films, where β indicates a rare earth or [Cs, Ca, Ba, Ti, Zr, V, Sn, or Bi], and observed a pale pink EL from the (Ta + Pr) oxide film.…”

“…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).…”