| Summary: | 博士 === 國立中央大學 === 機械工程研究所 === 97 === When the chip size of light emitting diodes (LEDs) and the input power become larger, current spreading in the active layer will obviously affect the optical, electrical, and thermal packaging performances of the LED chip. To further understand the current spreading behavior in the active layer, we use a three-dimensional numerical simulation to analyze the electrical characteristic and current distribution of a GaN LEDs device. The results and trends found could serve as useful references for researchers focusing on the design of an LED chip.
Employing two-dimensional analysis, in lateral configuration LEDs, the current flows vertically in the p-GaN and active layers, and horizontally in the spreading and n-GaN layers. Therefore, that the current crowding in the active layer would be generated at p- or n-electrodes is mainly dependent on the effect of resistance match between the spreading and n-GaN layers. In addition, the current distribution in the active layer can also obviously affect light extraction efficiency (LEE) and driving voltage.
Using three-dimensional analysis, for real cases of side-view LEDs, the driving voltage for the well-designed p- and n-electrode patterns considered in our study can be markedly reduced to around 0.45 V, which corresponds to about 13% decrease in magnitude. The influence of the change in p-electrode pattern on current spreading and voltage drop is more significant than that made by altering the n-electrode pattern for this type of LED. On the other hand, the vertical LEDs with a current blocking layer are also analyzed, it shows that thermal effect in the LED chip should be taken into account and is more obvious in such cases.
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