Abstract ▼ AI-Helper

Gallium nitride (GaN) based semiconductors have been under intense research focus in recent years largely due to their electronic and optoelectronic applications. In comparison to large area devices, GaN nanowires (NWs) based devices provide unique opportunity to dramatically improve device efficien...

Gallium nitride (GaN) based semiconductors have been under intense research focus in recent years largely due to their electronic and optoelectronic applications. In comparison to large area devices, GaN nanowires (NWs) based devices provide unique opportunity to dramatically improve device efficiency and scope of integration. In this study, we have studied the growth behaviors and characterizations of GaN NWs on nano-patterned Si(111) substrate by MOCVD. GaN NW arrays were grown on a nano-patterned Si(111) substrate by MOCVD technique through a self-assembly process. The GaN NWs growth method has been a considerable interest in the metal catalytic method to initiate vapor-liquid-solid (VLS) mechanism and selective-area growth (SAG) using nano-mask. The metal catalytic-assisted VLS growth mechanism and SAG method are still the most widely exploited approach for fabricating a variety of one-dimensional NWs. On SAG method, the fabrication of nano-pattern using nano-mask by lithography takes long time and is very expensive. However, in our study, the nano-pattern was fabricated by etching process of Au nano-droplets. Therefore we can reduce the time to fabricate nano-patterns. In this study, we analyze the effect of nano-pattern size and Al pre-deposition process prior to growth of NWs for growth behavior of GaN NWs. The size of nano-pattern was controlled by controlling of Au nano-droplet size which was increased by increasing Au sputtering time. The size of nano-pattern synthesized on Si(111) substrate was corresponding to size of Au nano-droplet, and the diameter of GaN NWs grown on nano-patterns was similar to the size of nano-pattern. When the GaN NWs were grown using Al pre-deposition, we can observe the high-density, vertically aligned, high-quality GaN NWs. These studies were analyzed by varying one experimental parameter at a time while keeping all the other growth conditions as constant. This thesis precisely explained the experimental results and the detailed characterization of the GaN NWs grown on nano-patterned Si(111) substrate by MOCVD. We characterized a best sample of our experiment samples by several characteristic measurements. The grown samples were characterized by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), photoluminescence (PL), cathodeluminescence (CL) and high-resolution transmission electron microscopy (HR-TEM). We observed Au nano-droplets, nano-patterns and GaN NWs grown on substrate using FE-SEM. As a result, the size of Au nano-droplets 20±10, 30±15, 45±10, 60±15, 70±15 and 100±15 nm with different Au sputtering time, and the size of nano-patterns and the diameter of GaN NWs were increased in accordance with Au sputtering time increase. And the site which GaN NWs was not grown has clean surface without any particles and GaN bulks. The PL and CL results of the NWs indicated that the grown GaN NWs with high optical qualities. From the XRD pattern, the peak corresponding to wurtzite-type hexagonal GaN was observed. The HR-TEM image in combined with SAED pattern revealed that the GaN NWs grown on nano-patterned Si(111) substrate were crystalline with a single-crystal wurtzite structure and preferentially oriented in the [0001] direction. These results suggest that GaN NWs can be utilized for fabrication of nano scale optoelectronic devices.

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