| Summary: | 碩士 === 國立成功大學 === 化學工程學系 === 104 === Owing to the significant optoelectronic property, GaN is used for light emitting diodes, laser diodes, sensors and high mobility transistor. Since 1-D nano-structure has the advantage of high aspect ratio and high specific surface area which help releases the stress comparing to film structure, 1-D structure seems like the choice for light emitting diode devices. We combined the two elements mentioned above, GaN and 1-D nano-structure, and fabricated GaN nano-rods for light emitting diode devices with the self-developed PECVD reactor. However, 1-D nano-structure is having the disadvantage of high surface defect density and low recombination efficiency due to its high specific surface area. We hope to avoid the unwanted surface defect by fabricating the nano-rods into core-shell structure.
Due to the experience from our former team members, we are able to fabricate high quality GaN nano-rods on silicon substrates. We chose silane and Magnesium nitride as the doping source, dope silicon and magnesium in respect into n-type and p-type GaN. Focusing on the doping concentration in p-type GaN, we controlled the amount of magnesium by adjusting the Magnesium nitride vapor pressure so that we can achieve different concentrations of Magnesium being brought into the reacting area. Then we make use of the relationship between Photoluminescence intensity and doping concentration to get the relatively higher doping concentration for p-type GaN.
In second stage of growth, we want the n-type GaN to grow along the crystal of pre-grown p-type GaN. We lowered the opportunity of re-nucleation which usually took place on top of the pre-grown sample by rising the temperature of the reacting area, lowering the amount of Gallium source and lowering the reacting pressure. We observed through SEM image and found that the re-nucleation situation gradually disappeared, and the n-type from second stage of growth had started to grow along the pre-grown sample.
The samples with p-n junction were made into light emitting devices, and the rectifying I-V curves confirmed the existence of p-n junction. Once the current density reached 80mA/mm2, electroluminescence is observed. As the current density increase, the violet light became brighter. Core-shell structure did helped improved the efficiency in fabricating light emitting diodes, and led to electroluminescence.
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