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The characteristics of a resistive-switching RAM (ReRAM) device are investigated using a HfO2 thin film. HfO2 is prepared using the solution-coating method. In the HfO2-precursor solution, hafnium isopropoxide is used as a solute and ethylene glycol monomethyl ether as a solvent. Additionally, diethanolamine (DEA) is used as a chemical modifier. The solution is prepared by adjusting the solvent to achieve concentrations of 0.1 mol l−1, 0.5 mol l−1, and 0.5 mol l−1 + DEA (4 eq). After applying the solution on Pt, the films are obtained by spin coating and sintering. The HfO2-ReRAM is fabricated using Al as the top electrode, and bipolar properties are obtained for all three concentrations. A fabricated HfO2-ReRAM device with an average thickness of approximately 28 nm exhibits a ON/OFF current ratio of 104. In the high-resistance state, conduction is mainly due to the Pool–Frenkel conduction and Schottky emission, whereas in the low-resistance state, conduction is mainly ohmic.

Mg codoping into Eu-doped GaN (GaN:Eu) changed the dominant optical site and increased the photoluminescence (PL) intensity at room temperature (RT). From the ratio of PL integrated intensity at 25 K to that at 300 K, PL efficiency of the GaN:Eu,Mg layer was evaluated to be as high as 77%. On the basis of this experiment, GaN:Eu-based LEDs grown by NH3 MBE were fabricated. Clear rectification characteristics with a turn-on voltage of 3.2 V were observed and a pure red emission was observed by the naked eye at RT. For the electroluminescence (EL) spectra, two predominant peaks of higher-efficiency optical sites A and C were selectively enhanced and the EL intensity was improved. This result suggests that GaN:Eu was very effective for realizing red-light-emitting devices using the nitride semiconductor.