electron-channeling-contrast-imaging-for-rapid-iii-v-heteroepitaxial

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging ...

The Ohio State University

Nonresonant multiphoton ionization with time-of-flight mass spectrometry has been used to monitor the desorption of aluminum chloride (Al(x)Cl(y)) etch products from the Al(111) surface at 100 and 500 K during low-coverage (<5% monolayer) monoenergetic Cl(2) (0.11-0.65 eV) dosing. The desorption products in this low-coverage range show predominantly hyperthermal exit velocities under all dosing conditions. For example, with 0.27 eV incident Cl(2), the etch product was found to have a most-probable velocity of 517+/-22 m/s at an Al(111) surface temperature of 100 K. This corresponds to 22 times the expected thermal desorption translational energy for AlCl(3). Cl(2) sticking probability measurements and Al(x)Cl(y) etch rate measurements show etching even at Cl(2) coverages of less than 5% monolayer at surface temperatures between 100 and 500 K. These experimental results are consistent with a combination of fast-time-scale surface diffusion and agglomeration of the adsorbed chlorine to form aluminum chlorides and the presence of activated AlCl(3) chemisorption states having potential energies above the vacuum level. Density functional theory calculations yield results that are consistent with both our experimental findings and mechanistic descriptions.

Low coverage spontaneous etching and hyperthermal desorption of aluminum chlorides from Cl2/Al(111).

The correlation between atomic bonding sites and the electronic structure of SiO on GaAs(001)-c(2x8)/(2x4) was investigated using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and density functional theory (DFT). At low coverage, STM images reveal that SiO molecules bond Si end down; this is consistent with Si being undercoordinated and O being fully coordinated in molecular SiO. At approximately 5% ML (monolayer) coverage, multiple bonding geometries were observed. To confirm the site assignments from STM images, DFT calculations were used to estimate the total adsorption energies of the different bonding geometries as a function of SiO coverage. STS measurements indicated that SiO pins the Fermi level midgap at approximately 5% ML coverage. DFT calculations reveal that the direct causes of Fermi level pinning at the SiO GaAs(001)-(2x4) interface are a result of either local charge buildups or the generation of partially filled dangling bonds on Si atoms.

Direct and indirect causes of Fermi level pinning at the SiO/GaAs interface.

A systematic experimental and theoretical study was performed to determine the causes of oxide-induced Fermi level pinning and unpinning on GaAs(001)-c(2 x 8)/(2 x 4). Scanning tunneling spectroscopy (STS) and density functional theory (DFT) were used to study four different adsorbates' (O(2), In(2)O, Ga(2)O, and SiO) bonding to the GaAs(001)-c(2 x 8)/(2 x 4) surface. The STS results revealed that out of the four adsorbates studied, only one left the Fermi level unpinned, Ga(2)O. DFT calculations were used to elucidate the causes of the Fermi level pinning. Two distinct pinning mechanisms were identified: direct (adsorbate induced states in the band gap region) and indirect pinnings (generation of undimerized As atoms). For O(2) dissociative chemisorption onto GaAs(001)-c(2 x 8)/(2 x 4), the Fermi level pinning was only indirect, while direct Fermi level pinning was observed when In(2)O was deposited on GaAs(001)-c(2 x 8)/(2 x 4). In the case of SiO on GaAs(001)-c(2 x 8)/(2 x 4), the Fermi level pinning was a combination of the two mechanisms.

Article	Year
Low coverage spontaneous etching and hyperthermal desorption of aluminum chlorides from Cl2/Al(111). The Journal of chemical physics\| PubMed ID: 15527367	2004
Direct and indirect causes of Fermi level pinning at the SiO/GaAs interface. The Journal of chemical physics\| PubMed ID: 17343465	2007
Electronic properties of adsorbates on GaAs(001)-c(2x8)/(2x4). The Journal of chemical physics\| PubMed ID: 17919041	2007

Tyler J. Grassman

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