Growth of Si and Ge nanostructures on Si substrates using ultrathin SiO2 technology

Using scanning reflection electron microscopy and a high-temperature scanning tunneling microscopy (STM), we study the growth processes of Si and Ge nanostructures on Si substrates covered with ultrathin SiO₂ films. Si windows are formed in the ultrathin SiO₂ films by irradiating focused electron beams used for SREM or field emission electron beams from STM tips before or during heating samples. Ge nanoislands are grown only at the Si window positions by depositing Ge on the samples and by subsequent annealing of them. Moreover, Ge nanoislands about 7 nm in size and ultrahigh density (>10¹²/cm²) are grown on the ultrathin SiO₂ films. These nanoislands can be manipulated by STM when they are separated from Si substrates by the ultrathin SiO₂ films. Si, Ge, Ge/Si and Si/Ge/Si nanoislands can also be grown on the Si windows by selective growth using Si₂H₆ and GeH₄ gases. These nanoislands are found to be stable on the Si windows during high-temperature annealing. These results indicate that ultrathin SiO₂ technology is useful for growing Si and Ge nanostructures on given areas.