Electrical determination of current injection and internal quantum efficiencies in AlGaN-based deep-ultraviolet light-emitting diodes.

We propose a method to determine the current injection efficiency (CIE) and internal quantum efficiency (IQE) of light-emitting diodes (LEDs) during current injection. The method is based on fourth-order polynomial fitting of a modified rate equation to electroluminescence data. Our method can extract the CIE at low injection current densities, unlike conventional methods that generally assume the CIE to be unity. We apply the method to AlGaN-based deep-ultraviolet LEDs. Results show that the CIE was only approximately 51% at low injection current densities and was almost independent of injection current density up to 100 A/cm2. The peak IQE was 77%.

Entrainment in a chemical oscillator chain with a pacemaker.

Entrainment by a pacemaker was investigated experimentally and numerically in a chain of chemical oscillators using coupled discrete Belousov-Zhabotinsky reaction oscillators. The spontaneous frequency of each oscillator depended on the concentration of catalyst ions. The coupling strengths among the nearest neighbor oscillators were controlled by changing the spacing distance (d) between beads. When the coupling strength was sufficiently strong, the pacemaker entrained other oscillators in the chain. Subsequently, the trigger waves propagating from a pacemaker were observed. The range of trigger wave propagation area, i.e., the number of entrained oscillators, depended on d. Numerical simulation for the system described the experimental results well. Furthermore, photic noise maximized the strength of entrainment at an optimal noise intensity.