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.
Group III nitride-based blue-light-emitting diodes having a moth-eye structure at the bottom of the semi-insulating transport 6H-SiC substrate were fabricated. The light extraction efficiency and the corresponding output power were increased 3.8 times compared with those of the LED having the conventional structure. We also study a theoretical simulation using based on the RCWA method with three-dimensional Maxwell's equations. The results of theoretical analysis agree with these findings.
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.
A new candidate for the lattice-matched metallic substrate, i.e. ZrB2, for the growth of group-III nitrides is proposed. A low-temperature-deposited-buffer layer is found to be essential for the growth of GaN on ZrB2. Highly luminescent violet-light-emitting diodes fabricated on ZrB2 perform as well as or even superior to those fabricated on sapphire. ZrB2 is easily etched by the solution of HF and HNO3. Fabrication of a nitride-based flexible display is expected using a thin
free-standing GaN film.