R. Navamathavan

Single Nanowire Light-Emitting Diodes Using Uniaxial and Coaxial InGaN/GaN Multiple Quantum Wells Synthesized by Metalorganic Chemical Vapor Deposition

We report the controlled synthesis of InGaN/GaN multiple quantum well (MQW) uniaxial (c-plane) and coaxial (m-plane) nanowire (NW) heterostructures by metalorganic chemical vapor deposition. Two kinds of heterostructure NW light-emitting diodes (LEDs) have been fabricated: (1) 10 pairs of InGaN/GaN MQW layers in the c-plane on the top of n-GaN NWs where Mg-doped p-GaN NW is axially grown (2) p-GaN/10 pairs of InGaN/GaN shell structure were surrounded by n-GaN core. Here, we discuss a comparative analysis based on the m-plane and the c-plane oriented InGaN/GaN MQW NW arrays. High-resolution transmission electron microscopy studies revealed that the barrier and the well structures of MQW were observed to be substantially clear with regular intervals while the interface regions were extremely sharp. The c-plane and m-plane oriented MQW single NW was utilized for the parallel assembly fabrication of the LEDs via a focused ion beam. The polarization induced effects on the c-plane and m-plane oriented MQW NWs were precisely compared via power dependence electroluminescence. The electrical properties of m-plane NWs exhibited superior characteristics than that of c-plane NWs owing to the absence of piezoelectric polarization fields. According to this study, high-quality m-plane coaxial NWs can be utilized for the realization of high-brightness LEDs.

Highly Uniform Characteristics of GaN Nanorods Grown on Si(111) by Metalorganic Chemical Vapor Deposition

Gallium nitride (GaN) nanorod (NR) arrays were grown on a gold-coated Si(111) substrate by metalorganic chemical vapor deposition (MOCVD). The synthesized single GaN NRs were characterized by field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and cathodoluminescence (CL) analysis. The HR-TEM images and selected area electron diffraction (SAED) patterns demonstrated that the GaN NRs were of high quality with a single-crystal wurtzite structure and free from defects. The GaN NRs were observed to have a uniform diameter ranging from 40 to 70 nm, length of up to 1 ?m, and a sharp symmetrical pyramid-like tip at the top. The pyramid-like tip was attributed to the dissociation of nitrogen atoms by the cracking of ammonia (NH3) at the elevated growth temperature. Furthermore, there was no sign of any metal or alloy cluster at the end of the NRs. Thus, the growth of the GaN NRs does not occur by the typical vapor?liquid?solid (VLS) mechanism.

Effect of H2 Carrier Gas on the Growth of GaN Nanowires on Si(111) Substrates by Metalorganic Chemical Vapor Deposition

We report on the morphological changes of GaN nanowires (NWs) induced by varying H2 carrier gas flow rate. The GaN NWs were grown on Au-coated silicon (111) substrates by metalorganic chemical vapor deposition (MOCVD). The surface morphology and optical characterization of the grown GaN NWs were studied by field-emission scanning electron microscopy (FE-SEM) and photoluminescence (PL) and cathodoluminescence (CL) measurements, respectively. The GaN NWs with uniform diameters from bottom to top sizes ranging from 60 to 100 nm and lengths up to 2–3 µm were obtained. Energy-dispersive X-ray spectroscopy (EDX) analysis confirmed the presence of gallium and nitrogen in the grown GaN NWs. It was observed that the lateral growth behavior of the GaN NWs prevailed in the absence of H2 carrier gas. On the other hand, the vertically aligned growth tendency of the GaN NWs was induced by the supply of H2 carrier gas.

Electrical Properties of Low-Dielectric-Constant SiOC(–H) Films Prepared by Plasma-Enhanced Chemical Vapor Deposition from Methyltriethoxysilane and O2

SiOC(–H) films were deposited on a p-type Si(100) substrate by plasma-enhanced chemical vapor deposition (PECVD) from methyltriethoxysilane (MTES) and oxygen precursors. The MTES/O2 flow rate ratio was varied from 40 to 100% to investigate its effect on the properties of the films. Film thickness and refractive index were measured by field-emission scanning electron microscopy (FESEM) and ellipsometry, respectively. The chemical structures of the SiOC(–H) films were characterized by Fourier transform infrared spectroscopy (FTIR) in the absorbance mode. The bonding configurations of the SiOC(–H) films remained the unchanged upon annealing, showing their good thermal stability. The electrical properties of the films were measured using a metal–insulator–semiconductor (MIS) Al/SiOC(–H)/ p-Si structure. The experimental lowest dielectric constant of the SiOC(–H) film was found to be 2.38 at an annealing temperature 500 °C and the film has excellent thermal stability up to 500 °C. The SiOC(–H) films deposited by MTES and O2 precursors are a promising material for next-generation Cu-interconnect technology.

Structural and Mechanical Properties of Low Dielectric Constant SiOC(-H) Films Using MTES/O2 Deposited by PECVD

Low dielectric constant SiOC(-H) films were deposited on p-type Si (100) substrates by plasma enhanced chemical vapor deposition (PECVD) using methyltriethoxysilane (MTES; C7H18O3Si) and oxygen gas as precursors. The SiOC(-H) films were deposited at room temperature and then annealed. Nanoindentation studies were carried out in order to determine the mechanical properties of the SiOC(-H) films. The elastic modulus and hardness of SiOC(-H) films were measured to be in the range of 2.14 – 5.02 and 0.12 – 0.74 GPa, respectively. It was observed that the values of elastic modulus and hardness decreases with increase of flow rate ratio of the precursors. In the SiOC(-H) film, -CH3 group as an end group was introduced into -O-Si-O- chain network, thereby reducing the film density to decrease the values of the mechanical properties.