| Summary: | 博士 === 長庚大學 === 電子工程學系 === 99 === Abstract
The luminescence of Ⅲ-Ⅴ based light emitting diodes was investigated through three kinds of selective circuit region confinement techniques. To increase the external quantum efficiency of a light-emitting diode while limiting its forward voltage, we prepared both (AlxGa1-x)0.5In0.5P LED and the buried oxides through selective wet oxidation of the AlAs layers of AlAs–GaAs distributed Bragg reflectors. The wet oxidation process forms a stable AlOx material that acts as an insulation layer and affects both the carrier and optical confinements. To determine the tradeoff conditions for LED oxidation, we used the Taguchi method which is a robust technique that is often used to analyze significant trends that occur under a set of the oxidation conditions. In this study, we used an L9 orthogonal array to measure the effects that a series of factors have upon the of the LED in an effort to limit the values of Vf. Relative to the as-grown LED, the oxidized LEDs that had been treated under the tradeoff wet-oxidation conditions displayed a sharply enhanced brightness (62.4% increase) with only a slightly increased value of Vf (only a 24.5% increase).
Next, we used the selective ring-region activation technique to restrain the surface leakage current and to monitor the luminescence characteristics of InGaN–GaN MQW blue light-emitting diodes. To access the current blocking region after forming a periphery high-resistance ring-region of the Mg-doped GaN layer and to reduce the degree of carrier trapping by the surface recombination centers, we deposited a Ti film onto the Mg-doped GaN epitaxial layer to form a high-resistance current blocking region. Furthermore, the luminescence characteristics could be improved by varying the width of the highly resistive region of the ; in our best result, the relative electroluminescence intensity was 30% (＠20 mA) higher than that of the as-grown blue LEDs.
Finally, we also investigated the improvement of the light extraction efficiency of InGaN/GaN MQW blue light-emitting diodes via the sidewall wet etching method. Meanwhile, the relationship between the FWHM of the (102)-rocking curve and the wet etching time was also studied. The etching time is longer as the FWHM of the (102)-rocking curve increased. That means the etching conditions could be controlled without ant over-etching phenomena. Compare with the standard LED, the output power was enhance 11.4% from the SWE LED under a 20 mA operating current.
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