ZnO 나노막대 및 나노막대-그래핀 하이브리드 기반 삼차원 나노구조 성장과 광소자 응용

Abstract

Despite the potential of three-dimensional (3D) nanostructures in the fields of integrated optics, bio-chips, and nanoelectromechanical systems, it is still challenging to fabricate 3D structures with the nanoscale precision, especially in cost-effective manner. Solution-based chemical synthesis is a promising alternative to the conventional vapor-phase method owing to its advantages in commercial-scale production at low cost. In especial, selective and vertical growth of 1D nanocrystal arrays in solution can allow us to construct sophisticated nanostructures with artificially-regulated 3D height profiles. However, crystal growth in solution, several issues still remain, including the control of position and morphology. Moreover, a deeper understanding of the crystals growth and systematic study of the diverse relationships between diameter and axial growth velocity is required. In this dissertation, we systematically studied the strong interactive growth behaviors among the neighboring nanocrystals found in ZnO hexagonal nanorod arrays with precisely defined positions and diameters. During anisotropic growth of ZnO hexagonal nanorods arrays, strong interactive growth behaviors were observed. In particular, there are multiple growth regimes demonstrating that the diameter of the rod is dependent on its height. Local interactions among the growing rods result in cases where height is (i) irrelevant to the diameter, (ii) increased with increasing diameter or (iii) inversely proportional to the diameter. These phenomena originate from material diffusion and the size-dependent Gibbs-Thomson effect that are universally applicable to a variety of material systems, thereby providing bottom-up strategies for diverse 3D nanofabrication. The hybridization of different types of materials grown by bottom up approach enables versatile and tailor-made properties with performances far beyond those of the individual materials. This dissertation presents that 1D and 2D hybrid structures composed of vertical ZnO nanorods grown on large-area graphene, are integrated onto the GaN/InGaN light emitting diodes (LEDs). Compared with GaN LED without transparent conducting electrode, both current injection and light emission increased almost 2~3 times by the introduction of graphene based conducting electrode. Additional ~66 % increase in light emission was achieved by growing the ZnO nanorods on the graphene, which is consistent with the finite-difference-time-domain modeling result. Furthermore, electroluminescence intensity profiles confirm the uniform light emission with high brightness in GaN LED with the ZnO nanorods-graphene hybrid electrode.