In attempt to prepare a high performance AlxGa1-xN based UV-B LED, a computer simulation has been performed on
a typical UV-LED structure to find out the effect of threading dislocations on non-radiative recombination process. UVB
LED structures were formed on using GaN and AlN based layers for comparison. Cracks were generated in the device
structure formed on GaN underlayer. No cracks were observed on the device structure formed on AlN under layer.
Much better structure was formed when the base AlN was grown by high temperature MOVPE.
Light extraction efficiency of nitride-based blue-light-emitting diodes on SiC substrate is theoretically investigated using
rigorously coupled wave analysis method. Rigidly periodic moth eye structure is found to show superior light extraction
efficiency compared with conventional rectangular parallelepiped or pseudo-moth eye structures. High-throughput
technology by laser interference lithography for the fabrication of rigidly periodic moth eye structure is established using
a 244 nm laser as the light source.
We have fabricated UV-emitters such as UV-light emitting diode (UV-LED) and UV-laser diode (UV-LD) on sapphire substrates. The combination of low-temperature-deposited AlN interlayer and lateral seeding epitaxy (Hetero-ELO) yielded crack-free and low-dislocation-density AlGaN. The light output power of GaN/AlGaN multi-quantum wells active layer based UV-LED monotonically decreased with the increase of threading dislocations. Moreover, we have demonstrated a UV-LD grown on this low-dislocation-density AlGaN. The lasing wavelength under pulsed current injection at room temperature was 350.9 nm. We also present violet and UV-LEDs grown on ZrB2 substrate. The violet LED exhibits excellent linearity of L-I characteristic and sharp single spectrum, and vertical conduction through nitride and ZrB2 interface has been confirmed in the UV-LED. We also present the growth of AlN single crystals by sublimation method.