Sanjay Nayak

Surface modification induced photoluminescence enhancement of GaN nanowall network grown on c-sapphire

Surface nitridation of the c-sapphire substrate is used to improve the optical and structural quality of a GaN nanowall network film grown by plasma assisted molecular beam epitaxy. The nitridation results in the formation of a thin AlN layer on the sapphire surface. Several in-situ and ex-situ characterization are complementarily used to probe the changes in epitaxial growth, band edge emission and strain in the films. The GaN nanowall network layer formed on the pre-nitrided substrate shows a two order higher intensity of band edge luminescence than that of a GaN epilayer, demonstrating its potential for light-emission applications.

Edge enhanced growth induced shape transition in the formation of GaN nanowall network

We address the mechanism of early stages of growth and shape transition of the unique nanowall network (NwN) nanostructure of GaN by experimentally monitoring its controlled growth using PA-MBE and complementing it by \textit{first-principles} calculations. Using electron microscopy, we observe the formation of tetrahedron shaped (3 faced pyramid) islands at early stages of growth, which later grows anisotropically along their edges of the (20

Structural, optical and electronic properties of a Mg incorporated GaN nanowall network

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Enhanced radial growth of Mg doped GaN nanorods: A combined experimental and first-principles study

1) facets, to form the wall like structure. The mechanism of this crystal growth is discussed in light of surface free energies of the different surfaces, adsorption energy and diffusion barrier of Ga ad-atoms on the (20

Nanostructuring GaN thin film for enhanced light emission and extraction

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Spectroscopic signatures of native charge compensation in Mg doped GaN Nanorods.

1) facets. By \textit{first-principles} calculations, we find that the diffusion barrier of ad-atoms decreases with decreasing width of facets, and is responsible for the anisotropic growth and formation of the nanowall network. This study suggest that formation of NwN is a archetype example of structure dependent attachment kinetic (SDAK) instability induced shape transition in thin film growth.

Raman signature of compensation effect in Mg doped GaN Nanorods

We report the growth of a Mg incorporated GaN nanowall network (NwN) by using a plasma assisted molecular beam epitaxy (PA-MBE) system that was characterized by photoluminescence (PL) spectroscopy, Raman spectroscopy, high-resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). We record a PL enhancement (≈3.2 times) in nominally and moderately Mg incorporated GaN compared to that of an undoped NwN. Two distinct (and broad) blue luminescence peaks appear at 2.95 and 2.70 eV for the heavily Mg incorporated (1020 atoms per cm3) GaN, of which the 2.95 eV peak is sensitive to annealing. The incorporated Mg concentration is estimated to be 1020 atoms per cm3 while retaining its band edge emission at ≈3.4 eV. XPS valence band spectra shows a shift in the Fermi level towards Valence Band Maximum (VBM) and the increase in Mg flux confirms the formation of p-type GaN. Mg accumulation at the nanowall surface and the GaN/Al2O3 interface was observed from SIMS measurements.

On the origin of Blue Luminescence in Mg doped GaN

We discuss the microstructural origin of enhanced radial growth in magnesium (Mg) doped single crystalline wurtzite gallium nitride (w-GaN) nanorods (NRs) grown by MBE, using electron microscopy and first-principles Density Functional Theory calculations. Experimentally, we observe that Mg incorporation increases the surface coverage of the grown samples as a consequence of an increase in the radial growth rate of the NRs. We also observe that the coalescence of NRs becomes prominent and the height at which coalescence between proximal rods occurs decreases with increase in Mg concentration. From first-principles calculations, we find that the surface free energy of the Mg doped surface reduces with increasing Mg concentration in the samples. The calculations further suggest a reduction in the adsorption energy and the diffusion barrier of Ga adatoms along [ 11 2 ¯ 0 ] on the side wall surface of the NRs as the underlying mechanism for the observed enhancement in the radial growth rate of GaN NRs. The physics and chemistry behind reduction of the adsorption energy of Ga ad-atoms on the doped surface are explained in the light of electronic structure of the relevant surfaces.We discuss the microstructural origin of enhanced radial growth in magnesium (Mg) doped single crystalline wurtzite gallium nitride (w-GaN) nanorods (NRs) grown by MBE, using electron microscopy and first-principles Density Functional Theory calculations. Experimentally, we observe that Mg incorporation increases the surface coverage of the grown samples as a consequence of an increase in the radial growth rate of the NRs. We also observe that the coalescence of NRs becomes prominent and the height at which coalescence between proximal rods occurs decreases with increase in Mg concentration. From first-principles calculations, we find that the surface free energy of the Mg doped surface reduces with increasing Mg concentration in the samples. The calculations further suggest a reduction in the adsorption energy and the diffusion barrier of Ga adatoms along [ 11 2 ¯ 0 ] on the side wall surface of the NRs as the underlying mechanism for the observed enhancement in the radial growth rate of GaN NRs. Th...