In this paper, a new equivalent circuit model of GaN-based light emitting diodes(LEDs) is established. The impact of the series resistance to luminous efficacy is simulated using the MATLAB software. GaN-based LEDs with different ncontact electrode materials(LEDs with Ni/Au and LEDs with Cr/Au) are fabricated. By comparing and analyzing the results of performances, we concluded that both the series resistance and the carrier loss could affect the luminous efficacy severely.LEDs with lower series resistance have higher luminous efficacy and its efficiency droop is alleviated simultaneously. To improve luminous efficacy, the fabrication process should be optimized for lower series resistance.
A new epitaxial structure of AlGaInP-based light-emitting diode(LED) with a 0.5-μm GaP window layer was fabricated. In addition, indium tin oxide(ITO) and localized Cr deposition beneath the p-pad electrode were used as the current spreading layer and the Schottky current blocking layer(CBL), respectively. The results indicated that ITO and the Schottky CBL improve the total light extraction efficiency by relieving the current density crowding beneath the p-pad electrode. At the current of 20 mA, the light output power of the novel LED was 40% and 19% higher than those of the traditional LED and the new epitaxial LED without CBL. It was also found that the novel LED with ITO and CBL shows better thermal characteristics.
Fabrication temperature is an important factor affecting the manufacturability of electronic devices,especially for the bottom-up self-assembled nano-device.In this study,we used a lateral-bridged zinc oxide(ZnO)nanowire array UV sensor as a model to investigate the influence of temperature on device performance over the entire manufacturing process,from sensor fabrication to packaging.We found that annealing of the SiO2 substrate would make ZnO seed layer on top of it more compact and uniform,and hence improve the lateral orientation and uniformity of ZnO nanowires grown from the seed layer.With the annealed substrate,the light-to-dark current ratio increased by two orders of magnitude.On the contrary,annealing the ZnO seed layer would deteriorate the light-to-dark current ratio of the sensor,because annealing caused most of the grains in the seed layer to become vertically aligned,which in turn affected the lateral growth of ZnO nanowire arrays.During the packaging process,the surface structure of ZnO nanowires would change if the chip welded at a temperature of 230℃for 2 min,resulting in a decrease of light-to-dark current ratio by three orders of magnitude.
