Role of surface pre-nitridation of molybdenum foil on growth of GaN nanorods using laser MBE

Abstract

We have grown GaN nanorods on thin Mo metal foil using laser molecular beam epitaxy (LMBE) at growth temperature of 700 °C and studied the effect of pre-nitridation parameters of Mo surface on GaN nanorods structural and optical properties. It has been found that the tapering of GaN nanorods grown on Mo foil critically depends on the nitrogen plasma condition for pre-nitridation of Mo foil. The well-aligned and inverse-taper GaN nanorods were grown on nitridated Mo foil underlow nitrogen plasma flux condition. The grown GaN nanorods are having porosity at the top side and tapered at the bottom side. The density and length of inverse-taper GaN nanorodsare ∼2.9 ×109cm-2 and 280-400 nm, respectively. In case of GaN growth on pre-nitridated Mo foil under high nitrogen plasma flux condition, the tapered GaN nanorods inclined with respect to the Mo foil surface normal were obtained on Mo foil. The tapered GaN nanorods density (3.47×109 cm−2) and length (340-670 nm) are higher than the inverse-taper GaN nanorods. The Raman spectroscopy measurements revealed that the GaN nanorods possess nearly stress-free wurtzite GaN structure. The room temperature photo luminescence spectroscopy measurements disclosed that the near band edge emission luminescence intensity is 3.9 times higher for the inverse-taper GaN nanorods than the tapered GaN nanorods. The prominent defect-related luminescence peak maxima of 2.28 eV was obtained for tapered GaN nanorods whereas no defect related peak was observed for inverse-taper GaN nanorods. These observations revealed that the well-aligned inverse-tapered GaN nanorods possesses excellent optical properties compared to inclined dense tapered GaN nanorods.