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 IG under EL emission corresponded to the Fowler–Nordheim (FN) tunnel current. The EL intensity increased proportionally to IG to the n-th power, where n was about 1.2, and the EL spectra were independent of IG. 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 4F9/2–6HJ/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+DyOx+(Gd + Dy)–Si–O]/[Gd2O3+La2O3/CaO/BaO+(Gd + La/Ca/Ba)–Si–O] silicate, while the underlayer was composed of SiOx-rich oxide with various rare earth and alkaline earth oxides.