Catalyst free self‐organized grown high‐quality GaN nanorods

Abstract

AbstractHighly ordered GaN nanorods were grown self‐organized and without catalyst on r‐plane sapphire by molecular beam epitaxy while the AlN nucleation sites for the nanorods were provided by a nitridation process using a metal‐organic vapor‐phase epitaxy system. The growth window for the nanorod formation was analysed in detail and turned out to be very sensitive with respect to the growth temperature. The nanorods are symmetrically tilted with an inclination angle of 62° between the substrate and the nanorods. The mirror axis is the c‐direction of the compact GaN layer surrounding the roots of the nanocolumns. Methods for the control of the nanorod density and the suppression of one nanorod growth direction are presented. The results indicate a diffusion based growth mechanism. Transmission electron microscopy studies and high resolution X‐ray diffraction (HRXRD) polar plots reveal the epitaxial relationship between substrate, compact GaN layer and nanorods. The nanorods grow in c‐direction and the side facets are m‐planes. Transmission electron microscopic and optical analysis of the nanorods reveal the good structural and optical properties, respectively. A full width at half maximum (FWHM) of 1.2 meV of the donor‐bound exciton emission was measured for both the ensemble and single free‐standing nanorods. Successful n‐ and Mg‐doping of nanorods was verified by a strong increase of the micro‐photoluminescence intensity of the respective donor‐bound and acceptor‐bound exciton emission peak in comparison to an undoped sample. magnified imageThe background shows a secondary electron microscope image (angle of 10° between sample surface and electron beam) of the nanorods. Superimposed to the SEM image, a typical micro‐photoluminescence spectrum of the excitonic emission of an ensemble at 25 K is presented. The donor‐bound, acceptor‐bound and free exciton lines are labelled with D0X, A0X and FX, respectively.