The design and the preparation of GaN-based high-voltage DC light emitting diode are realized. It is found that the device, whose chip structure is truncated pyramid using the epitaxial wafer whose subsrate is a patterned sapphire substrate, has a higher luminous efficiency than other chip structures. The luminous efficiency increases up to 116.06 lm/W when the device is packaged into white LED at a color temperature of 4500 K which is driven by 20 mA, and the corresponding voltage is 50 V. The I-V curve shows that the threshold voltage is 36 V, corresponding to a drive current of 1.5 mA. The optical power increases approximately linearly with the increase of driving current when the driving current increases from 15 mA to 50 mA, and the luminous efficiency in this range decreases more slowly with the increase of driving current, indicating that the GaN-based high-voltage DC LED is favourably driven by large current density, and severe efficiency droop will not appear as the drive current density increases, which offers a new idea for studying and solving the efficiency droop problem from the chip level.

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The geometrical structure of clean ZnO(0001) surface and B/ZnO(0001) adsorption system are optimized by using the ultra-soft pseudopotential method of total-energy plane wave based on the density functional theory. Adsorption energy, band structure, density of states and optical properties are calculated and discussed in detail. The results reveal that the T4 site is the most stable adsorption site of ZnO(0001) surface. After a B atom is adsorbed on T4 site, the surface band gap narrows down and the surface state changes a lot, the n-type conduction characteristic is weakened. As for the optical properties, we can find that the absorbing ability of ZnO(0001) surface to ultraviolet light is obviously enhanced after the B atom has been adsorbed on the T4 site of ZnO(0001) surface.