Selective Area Growth Of GaN Nanowires Research Articles

Selective-area growth and optical properties of GaN nanowires on patterned SiOx/Si substrates

We present the results of selective-area growth of GaN nanowires by molecular beam epitaxy on patterned SiOx/Si substrates without using seed layers. The morphological and optical properties of selectively grown GaN nanowires are compared to the properties of GaN nanowires grown on the amorphous SiOx layer. The experimental results show that the selectivity of GaN nanowires is achieved at a substrate temperature of 825 °C which is the lower limit for the selective-area growth of GaN nanowires on SiOx/Si substrates. The study of the photoluminescence spectra of the grown nanowires, measured at 77 K show an emission line at 3.47 eV, which corresponds to strain-free GaN.

Selective-Area Growth of GaN Nanowires on Patterned SiOx/Si Substrates by Molecular Beam Epitaxy

We demonstrate the possibility of selective-area growth of ordered arrays of GaN nanowires by molecular beam epitaxy on SiOx/Si substrates patterned by photolithography with microspherical lenses without the preliminary formation of seed layers. The effect of the substrate temperature on the morphological properties of the obtained arrays of nanowitres is studied. The optimal growth parameters ensuring the selective-area growth of GaN nanowires are experimentally found.

Селективный рост методом молекулярно-пучковой эпитаксии массивов нитевидных нанокристаллов GaN на процессированных SiO-=SUB=-x-=/SUB=-/Si-подложках

We present the results on the selective-area growth of GaN nanowires using a molecular beam epitaxy technique on patterned SiOx/Si substrates without any seed layers. The patterned SiOx/Si substrates were prepared by the simple microlens photolithography method. The influence of the substrate temperature on the morphological properties of GaN nanowires was investigated. The optimal growth parameters for the selective-area growth of GaN nanowires were experimentally determined.

Selective-area growth of GaN nanowires on SiO2-masked Si (111) substrates by molecular beam epitaxy

We analyze a method to selectively grow straight, vertical gallium nitride nanowires by plasma-assisted molecular beam epitaxy (MBE) at sites specified by a silicon oxide mask, which is thermally grown on silicon (111) substrates and patterned by electron-beam lithography and reactive-ion etching. The investigated method requires only one single molecular beam epitaxy MBE growth process, i.e., the SiO2 mask is formed on silicon instead of on a previously grown GaN or AlN buffer layer. We present a systematic and analytical study involving various mask patterns, characterization by scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy, as well as numerical simulations, to evaluate how the dimensions (window diameter and spacing) of the mask affect the distribution of the nanowires, their morphology, and alignment, as well as their photonic properties. Capabilities and limitations for this method of selective-area growth of nanowires have been identified. A window diameter less than 50 nm and a window spacing larger than 500 nm can provide single nanowire nucleation in nearly all mask windows. The results are consistent with a Ga diffusion length on the silicon dioxide surface in the order of approximately 1 μm.

Compatibility of the selective area growth of GaN nanowires on AlN-buffered Si substrates with the operation of light emitting diodes

AlN layers with thicknesses between 2 and 14 nm were grown on Si(111) substrates by molecular beam epitaxy. The effect of the AlN layer thickness on the morphology and nucleation time of spontaneously formed GaN nanowires (NWs) was investigated by scanning electron microscopy and line-of-sight quadrupole mass spectrometry, respectively. We observed that the alignment of the NWs grown on these layers improves with increasing layer thickness while their nucleation time decreases. Our results show that 4 nm is the smallest thickness of the AlN layer that allows the growth of well-aligned NWs with short nucleation time. Such an AlN buffer layer was successfully employed, together with a patterned SiOx mask, for the selective-area growth (SAG) of vertical GaN NWs. In addition, we fabricated light-emitting diodes (LEDs) from NW ensembles that were grown by means of self-organization phenomena on bare and on AlN-buffered Si substrates. A careful characterization of the optoelectronic properties of the two devices showed that the performance of NW-LEDs on bare and AlN-buffered Si is similar. Electrical conduction across the AlN buffer is facilitated by a high number of grain boundaries that were revealed by transmission electron microscopy. These results demonstrate that grainy AlN buffer layers on Si are compatible both with the SAG of GaN NWs and LED operation. Therefore, this study is a first step towards the fabrication of LEDs on Si substrates based on homogeneous NW ensembles.