| Summary: | 博士 === 國立成功大學 === 微電子工程研究所碩博士班 === 101 === In this dissertation, the luminous efficiency and electrostatic discharge protection ability on GaN-based light emitting diodes (LEDs) were investigated and fabricated.
We can enhance the current spreading ability on LEDs using epitaxial and process technologies. In epitaxial design, we inserted a light-doping n-GaN layer between active region and n-GaN layer. In process design, we used different ways to fabricate the current blocking layer and modulated p-extension electrode thickness. The light output power measured from the LEDs with best current spreading ability is 47 % larger than that of conventional LEDs. In contrast, light output power is much more uniform across the whole chip. Although the optical property can be improved by process technology, the electrostatic discharge (ESD) cannot be enhanced oppositely.
In second section, we observed the quantum-confined stark effect (QCSE) within the active region by doping Si atom in quantum barriers and modulated the un-doped GaN layer thickness. During the optical experiment, it is found that doping Si atom in quantum barriers cannot affect the QCSE in each quantum well. But, the internal capacitance value decreased as increasing the un-doped GaN layer thickness. Thus, the ESD protection ability decayed. In general, the LED with large leakage will result in low internal capacitance. Therefore, we consider that the variation of internal capacitance could be attributed to an increase in built-in electric field induced by stronger spontaneous polarization field.
Finally, we investigated the piezoelectric polarization field within each quantum well using different pre-strain interlayer and different quantum barrier thickness. According to the results, the LED with strong piezoelectric polarization field will emit long wavelength. In emission wavelength as a function of injection current characteristic, the strong piezoelectric polarization field also results in severe blue-shift. In order to differentiate the piezoelectric polarization field for the fabricated LEDs, the temperature-dependent EL characteristics were measured and achieved. It is worthy noted that the value of injection current, at which the wavelength of blue-shift changed to red-shift, shifted to larger injection current when the temperature increased. This is because that the carriers would be excited by the higher ambient temperature. Thus, it would escape from the MQWs, and the energy band-gap of MQW caused by QCSE cannot be screened and filled effectively. In other words, it needs higher injection current to provide more carriers which can complete the screening of QCSE of LEDs.
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