Self-assembled Zn/ZnO dots on silicon by RF magnetron sputter

Summary form given only. ZnO possesses superior semiconductor properties and chemical stability and thus has attracted much attention for potential applications in piezoelectric and optoelectronic devices. With the trend toward nanoscale object fabrication for better carrier confinement, research on ZnO quantum dots becomes more active. Up to now, high quality ZnO quantum dots have only been demonstrated by pulsed laser deposition (PLD) assisted with anodic aluminum oxide templates [i], metal-organic chemical vapor deposition (MOCVD) [ii,iii] or molecular beam epitaxy (MBE) [iv , v]. While some of the processes were complicate, all of them require delicate design and controls. Thus, we attempt to provide an easier method to fabricate high crystalline ZnO nanodots by RF magnetron sputter. We demonstrated that self-assembled Zn or ZnO nanodots could be fabricated only by oblique-angle RF magnetron sputter on a rotating Si substrate at 470degC where the sputtering gas is Ar and hydrogen and the target is pure ZnO. When a large substrate bias of -400 V was applied, the resulting dots are pure Zn. Scanning electron microscopy (SEM) results show that the nanodots grown on Si (100) substrate for the growth time of 30 min and 60 min are semispherical shape as shown in Fig.l, with the average dot size of 30 nm and 50 nm and the dot density of 3 x 1010/cm2 and 1.8 x 1010/cm2, respectively. However, the nanodots are composed of Zn rather than ZnO, determined by scanning transmission electron microscopy (STEM) analysis as shown in Fig.2. High-resolution transmission electron microscopy (TEM) results in Fig.3 show that the as-prepared Zn nanodots are of single crystalline. The dots nucleated from surface pits resulting from ion bombardment during sputtering, and the side walls of the nanodots appear to be Si (111) facets. The as-synthesized rectangular nanodots seem to be well aligned with silicon substrate from the plan-view TEM bright-field image (Fig. 4 (a) and (b)), with Zn <2110> // Si <002>. When no substrate bias was applied, hexagonal pyramidal ZnO dots result faceted with <10-11> as shown in Fig. 5. The composition is confirmed by STEM energy dispersive spectroscopy (EDS) and the pyramidal dots emitted a UV light at 385 nm"1 from cathodeluminescence measurements. Compared with others, this novel method could provide advantages on higher uniformity, low cost, and more controls, which renders this to be useful for industrial applications in many optoelectronic devices.