Self-catalyzed metal organic chemical vapor deposition growth of vertical ß-Ga2O3 nanowire arrays.

Self-catalyzed metal organic chemical vapor deposition (MOCVD) growth of Ga2O3 nanowires on GaN layers prepared on a sapphire substrate has been studied. Nanowire orientations are found to be growth temperature dominated. The vertical yields over total (VOT) curve shows a maximum peak beyond 70% around 480 °C, based on scanning electron microscope observations. X-ray diffraction patterns revealed a primary ß-(-201) normal orientation of as grown nanowires all over the studied temperature interval. Further transmission electron microscopy characterization had confirmed ß-(-201) normal axial orientation of these vertical nanowires, which have well crystallinity. The ß-(010)//GaN(110) in-plane epitaxial relationship is consistent with reported Ga2O3 film/nanowire growth. Nanowires crystallized in ß-[001] axial orientation were considered to be the inclined ones. Based on contrast experiments, the temperature dominated growth behavior is considered a thermodynamic process. The two observed crystalline orientation might have distinguishable but similar system energy, which results in coexistence of multi orientation nanowires over a large temperature span and an optimum temperature window for vertical ß-(-201) normal orientation. The presented optimized ß-Ga2O3 nanowire arrays with highest VOT close to 90% should effectively promote development of reliable high performance devices based on Ga2O3 nanowires.

[GaN-based white-light-emitting diodes with low color temperature and high color rendering index].

The luminescence properties of high color rendering white LED depending on the proportions of mixed phosphor powders were investigated by adopting green and red phosphors stimulated by a 440 nm InGaN/GaN based blue LED. The results show that when the proportion of A/B type silica gels and green/red phosphor powders is 0.5 : 0.5 : 0.2 : 0.03, two luminance bands are stimulated and their wavelength peaks are 535 and 643 nm, respectively. The minimum color temperature can reach 3 251 K, while the color rendering is as high as 88. 8. Compared with the traditional white LED fabricated by yellow YAG-phosphors-coated high efficiency 460 nm blue LED, the color temperature is lower and the color rendering index can be increased by almost 26%.