Site - Controlled VLS Growth of Planar Nanowires : Yield and 2 Mechanism

7 ABSTRACT: The recently emerged selective lateral epitaxy 8 of semiconductor planar nanowires (NWs) via the vapor− 9 liquid−solid (VLS) mechanism has redefined the long10 standing symbolic image of VLS NW growthvertical NWs 11 extending out of the substrate. The in-plane geometry and self12 aligned nature make these planar NWs completely compatible 13 with large scale manufacturing of NW-based integrated 14 nanoelectronics. Here, we report on the realization of perfectly 15 site-controlled growth of GaAs planar NW arrays with unity 16 yield using lithographically defined gold (Au) seed dots. The 17 growth rate of the planar NWs is found to decrease with the NW width when spacings are fixed, which is consistent with the 18 conventional model where the Gibbs−Thomson effect is considered. It is found that in general, the planar and out-of-plane NW 19 growth modes are both present. The yield of planar NWs decreases as their lateral dimension shrinks, and 100% yield of planar 20 NWs can be achieved at moderate V/III ratio. Based on a study of the shape of seed particles, it is proposed that the adhesion 21 between the liquid-phase seed particle and the substrate surface is important in determining the choice of growth mode. These 22 studies represent advances in the fundamental understanding of the VLS planar NW growth mechanism and in the precise 23 control of the planar NW site, density, width, and length for practical applications. In addition, high quality planar InAs NWs on 24 GaAs (100) substrates is realized, verifying that the planar VLS growth mode can be extended to heteroepitaxy. 25