In the recent years fabrication of semiconductor nano-pillars or -wires has received considerable attention due to their potential for optoelectronic and electronic applications.
Growth of III-V nanowires by the vapour-liquid-solid mechanism has been very promising [1,2]. Recently a very new method, quite different from epitaxy, has been reported wherein the formation of ordered III-V quantum dots [3,4] and whiskers [5] by high energy (a few keV) ion sputtering was demonstrated. However, generation of self-organized nano-pillars of controlled size and uniformity by preferential sputtering of group V species at lower ion energies has hitherto not been investigated. This method could be attractive since it is simple, cost-effective and does not require any patterning.
This work presents a detailed experimental and theoretical investigation of self-organized InP nanopillars formed during bombardment of InP by low energy (200 to 400 eV) nitrogen ions. The formation of self-organized InP nano-pillars by ion-sputtering is experimentally demonstrated. For an ion-energy of 400 eV and sample temperature of 250oC, the obtained pillars have a ball-like feature at the top and are fairly uniform in diameter (~100 nm); their density is in the range of 1010 cm-2. By increasing the sputtering time, the pillar-height can be increased up to about 1 micron. Transmission electron microscopy investigations show that the stem of the pillars is mono-crystalline InP. The material composition in the top portion (100-200 nm) as determined by X-ray micro-analysis is strikingly different - the ball-like feature contains predominantly In and the region just below is phosphorous rich. Finally, InP pillar formation by ion sputtering is explained using a physical model for generation of stable In-nuclei taking into account the preferential sputtering of P, and the diffusion (thermal and ion-assisted) of the excess In atoms on the surface.
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