Hole injection and electron overflow improvement in InGaN/GaN light-emitting diodes by a tapered AlGaN electron blocking layer.

A tapered AlGaN electron blocking layer with step-graded aluminum composition is analyzed in nitride-based blue light-emitting diode (LED) numerically and experimentally. The energy band diagrams, electrostatic fields, carrier concentration, electron current density profiles, and hole transmitting probability are investigated. The simulation results demonstrated that such tapered structure can effectively enhance the hole injection efficiency as well as the electron confinement. Consequently, the LED with a tapered EBL grown by metal-organic chemical vapor deposition exhibits reduced efficiency droop behavior of 29% as compared with 44% for original LED, which reflects the improvement in hole injection and electron overflow in our design.

[Influence of K+ and Al3+ on the optical properties of Er3+ doped Sol-gel derived silica glasses].

Al3+ and K+ ions were introduced in Er(3+) -doped silica glass successfully through Sol-gel route. The optical characterizations including absorption spectra, transmission spectra, photofluorescence spectra, up-conversion spectra, Raman spectra and fluorescence decay lifetime were undertaken on the samples. The results show that not only the fluorescence intensity was strenthened by more than 20 and 70 times, but also the lifetime of Er3+ ions in Al(3+) -doped and K+ and Al(3+) -codoped samples was prolonged to 7.1 and 11.2 ms from 4.8 ms, respecticely. And by analysing the results, the authors concluded that the influences of Al3+ and K+ on Er3+ ions are completely different. And the authors found that Er3+ ions in silica glass may have two up-conversion mechanisms: two-phonon absorption and energy-transfer up-conversion using 980 nm excitation.