Growth and structure of chemically vapor deposited Ge nanowires on Si substrates

Chemical vapor deposition by Au-catalyzed decomposition of GeH4 has been used to grow Ge nanowires on single-crystal silicon. The nanowires grow over the temperature range similar to320-380 degreesC under the conditions used, probably by the vapor-liquid-solid (VLS) process. The lowtemperature growth aids integration with conventional electronic devices. At the optimum temperature near 320 degreesC, many of the nanowires are epitaxially oriented with the substrate crystal structure, growing in (111) directions-at an oblique angle on (001)-oriented Si substrates and nearly vertically on Si(111). High-resolution transmission electron microscopy confirms that the nanowires grow in the (111) directions and that the crystal lattice continues from the substrate into the nanowires. Transmission electron microscopy also shows that the nanowires contain very few crystalline defects. Au-containing nanoparticles (possibly V-phase Au0.6Ge0.4) are found at the tips of the nanowires, but no Au can be detected within the nanowires themselves.