Twinning Superlattices in Semiconducting Nanowires

We report the first observation of quasi-periodic twinning superlattices (TSLs) in semiconducting nanowires. The periodicity of the superlattice appears to be controlled by $\Delta $T=T$_{m }$- T, i.e., the degree of undercooling of the liquid phase in contact with the solid phase during VLS growth, where T$_{m}$ is the melting point of the solid phase. We present results from two III-V systems (GaP, InP) in which the superlattice is generated by the periodic 180\r{ } flipping of the $<$112$>$ direction relative to the $<$111$>$ growth direction of the nanowire. We suspect that our observations mean that a TSL structure can be grown in many compound semiconducting nanowire systems. Control of the superlattice period should allow significant design possibilities for thermoelectric, electronic and electro-optic applications. This work was supported, in part, by NSF-NIRT DMR-0304178