Growth and density control of GaN nanodots and nanopillars

Abstract

We have fabricated hexagonal pillar like GaN nanostructures on Si (111) substrate. The GaN nanopillars were grown by two step processes, including droplet epitaxy to form GaN nanodots as buffer, and hot wall epitaxy to grow GaN nanopillars. We proposed the growth mechanism of the GaN nanodot by droplet epitaxy. Density of the GaN nanopillars was controlled by changing the density of GaN nanodots. When the nanopillar density was so high as to coalesce with each other, the luminescence efficiency reduced. The deterioration of luminescence is considered to be due to increase of dislocations arising at the nanopillars interface. To obtain the high luminescence efficiency, it is important to increase density of nanopillars with no coalescing. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Heteroepitaxial Growth of Vertically-Aligned GaN Single-Crystalline Microrod Arrays on Silicon Substrates

“…Because the dissociation of N 2 in the reaction region can be weakened by reducing the plasma power to lessen the quantities of nitrogen species, the plasma power was altered from 70 to 40 W. After the growth process, some blocky crystals and microbumps on the surface of the as-grown thin film could be observed, as in Figure 4b, which implies the effective influence of the decreased plasma power on the crystal morphology. When the plasma power was further reduced to 25 in the crystal appearance and the formation of island-like crystals could be discovered, as in Figure 4c. Finally, the vertically aligned microrod arrays were successfully grown on the Si(100) substrate under the condition of plasma power of 15 W, as shown in Figure 4d.…”

“…If the density of GaN microrods is lower, the total luminescence volume becomes smaller, causing poor luminescence efficiency of GaN crystals. 25 On the contrary, when more GaN microrods were grown on the substrate under the condition of a lower growth temperature, as shown in Figure 10, the contact of microrods with one another may produce grain boundaries between the crystals, which further reduces the crystalline quality of GaN as shown in Figure 9. In addition, the generation of the nonradiative recombination, caused by the grain boundaries and the residual defects, during the PL measurement can contribute to the obvious thermal noise appearing on the orange curve in Figure 9.…”

“…As seen in Figure , the density of the vertically aligned GaN microrods was gradually reduced with the raised growth temperature because the temperature gradient between the substrate region and the Ga source region was gradually decreased and the evaporation of Ga to the gas phase was enhanced, leading to fewer Ga atoms precipitating and remaining on the substrate. If the density of GaN microrods is lower, the total luminescence volume becomes smaller, causing poor luminescence efficiency of GaN crystals …”

“…If the density of GaN microrods is lower, the total luminescence volume becomes smaller, causing poor luminescence efficiency of GaN crystals. 25 …”