Structural and Optical Properties of Self-Assembled Epitaxially Grown GaN Nanorods and Nanoporous Film on Sapphire (0001) Using Laser Molecular Beam Epitaxy

The GaN nanoporous-film (NPF) and nanorods (NRs) were grown on sapphire (0001) using laser assisted molecular beam epitaxy (LMBE) technique by laser ablating solid GaN target at different laser energy density. The interconnected GaN NPF was grown at low laser energy density of similar to 4 J/cm(2) whereas vertically aligned GaN NRs was obtained at high laser energy density of 7 J/cm(2). The pore size of the GaN NPF structure is in range of 40-120 nm. The GaN NRs possess hexagonal shape with six sidewall facets and truncated top facet. The length, width and density of GaN NRs are 600-900 nm, 150-250 nm and similar to 2.5 x 10(7) cm(-2), respectively. The X-ray rocking curve full width at half maximum values along GaN (0002) and (1012) planes for GaN NRs obtained to be 0.41 and 0.53 degrees, respectively. The biaxial stress in hetero-epitaxially grown GaN was investigated with Raman spectroscopy and it was found that GaN NRs possesses a very low in-plane compressive biaxial stress of 0.09 GPa. The photoluminescence study exhibits a sharp band-to-band emission at 3.4 eV with a peak line width of 140 meV, signifying the good optical quality of the LMBE grown GaN NRs on sapphire (0001).