No abstract

The crystallization of amorphous Si induced by Al during heat treatment has been investigated by cross section and plan view transmission electron microscopy. The lowest temperature of Al induced crystallization of amorphous Si was found to be 440 K. The crystallization temperature, however, depends on the thickness of Al layers in layered structures and on the concentration of Al in co-deposited layers below 1-nm-layer thickness and 15 at.% of Al concentration, respectively. Al-induced crystallization in layered structures starts at the Al/amorphous Si interfaces and is located close to them. The amount of crystallized Si depends on the quantity of Al and on the temperature and increases with them. The mechanism of crystallization involves intermixing of Al with Si and the formation of an alloy of high metal concentration in the amorphous/crystalline interface. When the formation of this alloy is not assured due to low Al concentration, then crystallization does not start or the process of crystallization stops. In Al induced crystallization the nucleation of polycrystalline Si grains rather than their crystal growth is affected.

X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), and reflection high-energy electron diffraction (RHEED) have been used to show that 30 min exposures of a degreased and deionized-water-rinsed Ge(001) wafer to ultraviolet (UV)–ozone in laboratory air is sufficient to remove C contamination and form a nonpermeable passive amorphous GeO2 layer with a thickness of ≂1.8 nm. Subsequent annealing in ultrahigh vacuum (UHV) at ≥390 °C for ≥30 min resulted in desorption of the oxide layer and the exposure of a clean well-ordered Ge(001)2×1 surface. No impurities, including C and O, were detected by either XPS or AES. EELS spectra from the clean surface showed well-defined peaks corresponding to transitions involving dangling bonds, surface states, and surface plasmons. Shorter UV–ozone exposures (i.e., <30 min) often resulted in residual C contamination while incomplete oxide removal was obtained at lower oxide desorption temperatures. Ge overlayers deposited by molecular beam epitaxy at temperatures between 200 and 450 °C on UV–ozone processed substrates were found by a combination of plan-view and cross-sectional transmission electron microscopy to be highly perfect single crystals with abrupt film/substrate interfaces and no detectable dislocations or extended defects.

We have studied the influence of matrix materials on the self-organization of InAs nanostructures grown on InP substrates by molecular-beam epitaxy. Our results show that InAs quantum dots are formed on InAlGaAs, whereas quantum-wire-like structures are produced on InAlAs and InGaAs. Tuning from vertical anticorrelation in InAs/InAlAs superlattices to vertical correlation in InAs/InGaAs and InAs/InAlGaAs superlattices is observed, which is explained by the size effects in the nanostructure–nanostructure interaction.