The authors have demonstrated an effective method to obtain high light output power of GaN-based light-emitting diodes (LEDs) by simultaneous enhancement of internal quantum efficiency and light extraction efficiency. Micropit InGaN∕GaN LEDs were fabricated on hexagonal-shaped GaN template through wet-etched substrate patterning. The result indicated that under optimized growth condition of high temperature GaN template, micropits could be formed and distributed in an aligned manner by growing on wet-etch patterned sapphire substrate. The LED structures showed superior optical output power, which directly resulted from not only effective elimination of threading dislocation of the epitaxial layers but also significant increase in light extraction efficiency via the inclined facets of aligned micropits.

The effects of growth parameters on growth behavior of Pendeo‐epitaxial GaN layers in 〈1$ \bar 1 $00〉 patterned GaN seed stripes on sapphire were systematically investigated to improve the structural properties of the overgrown layers. It was found that the ratio of lateral to vertical growth rate (γ) is strongly affected by changes in growth temperature, reactor pressure, and V/III ratio, which have an effect on the distribution of crystallographic tilt among the wing regions. Also, the crystallographic anisotropy, which was determined from the results of (0002) X‐ray diffraction rocking curves taken perpendicular and parallel to the seed stripe direction, can be improved with relatively high V/III ratio.

External quantum efficiency of GaN light emitting diode (LED) with SiO 2 -coated grating patterned substrate and/or surface-textured structure were calculated theoretically. Our results show that the enhancement of the reflectance coefficient was obtained by a factor of about 30% in LED chip with SiO 2 -coated grating patterned substrate, compared to conventional LED chip. The grating parameters such as height and width should be optimized above h=w/4. Moreover, by employing surface-textured structure, the loss factor at top surface of LED was reduced dramatically by decreasing of total internal reflectance at GaNepoxy interface as the incident angle is higher than the critical angle. Therefore, external quantum efficiency can reach up to about 60% if internal quantum efficiency corresponds to about 90% because of reducing the total loss parameter at top and bottom surface of LED.

Hillocks formed on pendeo-epitaxial GaN (PE-GaN) films grown by metalorganic chemical vapor deposition were observed by scanning electron microscopy, atomic force microscopy and high-resolution transmission electron microscopy. In order to suppress hillock formation on PE-GaN films, a two-step growth technique was employed. In the first-step growth, whose growth temperature and V/III ratio were relatively low, it was necessary to suppress hillock formation on the surface, and reduce the crystallographic tilt in the wing regions of PE-GaN films. In the second-step growth, whose growth temperature and V/III ratio were relatively high, complete coalescence without tilt in the wing regions was achieved by a high lateral growth rate.

GaN/AlxGa1–xN distributed Bragg reflectors (DBRs) for the near‐ultraviolet region have been grown on sapphire substrates by metal‐organic chemical vapor deposition. In order to suppress the generation of cracks and V‐shaped defects on the surface of the DBRs, AlGaN/AlN superlattices and step‐graded multiple AlGaN layers were inserted prior to or during the growth of the DBRs. By optimizing those layers, the reflectivity of a 40‐pair GaN/Al0.35Ga0.65N DBR was increased up to 96% without any cracks and V‐shaped defects. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)