| Summary: | 碩士 === 國立成功大學 === 光電科學與工程研究所 === 98 === In the study, we first studied the electrical and optical characteristics of light emitting diode(LED) with different heights of cone shaped patterned sapphire substrate(PSS), which is cone-like shape. The heights of the cone-like shape are 1.2μm, 1.4μm and 1.7μm for the study. Adopting the PSS in LEDs, we achieved a smaller reverse leakage current due to the crystal quality improvement. Under 20mA current injection, the output powers are 5.94mW, 6.12mw and 6.25mW for the LEDs with PSS heights of 1.2μm, 1.4μm and 1.7μm, respectively. In other words, the 20mA-output powers of LEDs with 1.2μm, 1.4μm and 1.7μm heights cone shaped PSS could be improved by magnitude of approximately 47.03%, 51.49% and 54.7% respectively, compares with those of the conventional LED.
We demonstrated the also side-wall undercut on the LEDs with different heights of PSS. In our experiment, the etching solution was mixed by H3PO4 and H2SO4 (2:3), and etched LEDs for 5min and 20min. Under 20mA current injection, the LEDs with 5min and 20min undercut etching can be improved by magnitudes of approximately about 3% and 8%, respectively, compared with the non-etching LEDs. As a result, we could get 68% enhancement for combination of PSS and side-wall undercut techniques.
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