Optical properties of Ge nanowires grown on silicon (100) and (111) substrates

In this paper, we report Raman Scattering (RS) and photoluminescence (PL) measurements of Ge nanowires (NWs) grown via vapor-liquid-solid (VLS) using chemical vapor deposition silicon substrates consisting of (100) and (111) crystallographic orientations. Ge NWs grown are ∼40 nm in diameter, approximately a micrometer in length, and a sharp narrow Raman peak at ∼300 cm ^-1 indicates single crystal quality. An absence of SiGe peak in the Raman spectra indicates that SiGe interdiffusion is insignificant for the NW volume. Low temperature PL-intensity-dependence spectra indicate that the observed emission originates at the Ge NW - Si substrate interface, where SiGe intermixing has been detected. This interface is formed differently for (111) and (100) oriented Si substrates due to the 〈111〉 preferential growth direction of Ge NWs.