| Summary: | 博士 === 國立成功大學 === 光電科學與工程學系 === 100 === In this dissertation, we have demonstrated that ion implantation technologies can be applied to the GaN-based LEDs. The aim of this study is to increase LED light extraction efficiency by selectively implanted substrate. Ion implantation cause lattice disorder, thus, GaN has different growth rate at two different regions. Finally, a selective area growth (SAG) phenomenon can be created.
In the first phase of this dissertation, ions were implanted on a selective area of a GaN template. When GaN is regrown, they initially form a V-shape, and inverted Al0.27Ga0.83N pyramidal shells were embedded to create index steps within a GaN layer. An increased angular randomization of photons is emitted from the active layer of the LED. Under a 20 mA current injection, the output power was enhanced by 10% then conventional LED was formed. In addition, this dissertation modified GaN growth conditions to form air gaps above the implanted regions, which can achieve the scattering of photons around the embedded GaN/air interfaces. With a 20 mA current injection, the output power was enhanced by 36%, and then conventional LED was formed. The increased photons escape probability was evidenced by the Tracepro simulation program.
Implantation techniques applied to sapphire substrate is the secondary focus of this dissertation. No matter whether implanted or not, a low temperature GaN (LT-GaN) nucleation layer can be deposited, and random nucleation existed during the recrystallization step. The nuclei provided a chance to follow GaN molecule adhesive; therefore, periodic air gaps were not formed using LT-GaN as the nucleation layer. In view of this, a high temperature AlN (HT-AlN) nucleation layer with crystallization is suitable for selectively implanted sapphire. After GaN growth, periodic air gaps were formed on the implanted sapphire under 15%output power enhancement, as compared with the conventional LED. However, high quality AlN is very difficult to grow due to a narrow growth window. The greater leakage current and broad FWHM of XRD revealed poor GaN quality influenced by a non-optimal HT-AlN nucleation layer. Finally, selective implantation was applied on a sputtered AlN nucleation layer, which successfully formed air gaps above the implanted regions. With a 20 mA current injection, the output power was enhanced by 26% more than conventional LED.
Moreover, selective area growth was carried out on the three dimensional GaN shapes. InGaN multi quantum well (MQW), grown on a truncated pyramid microstructure, can achieve multiple wavelength LEDs. The LED colors include green, blue, and red corresponding emissions from the mesa/valley plan, inclined plane, and mesa edge regions, respectively. Furthermore, this dissertation clarifies that the red emission was from InGaN quantum dots.
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