1. Auger Electron Spectroscopy of In 2 O on GaAs(001)-(2x4) As, Ga In O Ga As In:O = 2:1 In 2 O 3(s)  In 2 O (g) +O 2(g) Scanning Tunneling Microscopy and Spectroscopy of Gallium Oxide and Indium Oxide Deposition on GaAs(001)-(2x4) Clean GaAs(001)-(2x4) Surface Clean STM ImageClean Ball & Stick Diagram 16Å In 2 O on GaAs(001)-(2x4) 410°C Dose/Low Coverage 050Å In 2 O Bonding in the Trough Ball and Stick Diagram Line Spacing of In 2 O Vs. Ga 2 O at Monolayer Coverage Row Spacing (Å) Percentage of Spacing Approximation of the Density of States for Both Clean and O Adsorbed GaAs(001)-(2x4) 0 Fermi Level -0.75 -1.5 Clean GaAs(001)-(2x4) Unpinned After O Adsorption Pinned Sample Bias (eV) dI/dV/(I/V) (a.u.) 1.5eV 0.75eV Approximation of the Density of States for Ga 2 O on Both n- and p-type GaAs(001)-(2x4) Sample Bias (eV) Fermi Level dI/dV/(I/V) (a.u.) n-type Ga 2 O/GaAs p-type Ga 2 O/GaAs Fermi Level VB CB Electronic Measurements of In 2 O on GaAs(001)-(2x4) Fermi Level 0 -1.4 Sample Bias (V) In 2 O on n-type GaAs(001)-(2x4) 0 Clean p-type GaAs(001)-(2x4) Fermi Level -0.3 1.2 0 In 2 O/p-type GaAs(001)-(2x4) Fermi Level 0.3 Sample Bias (V) dI/dV/(I/V) (a.u.) Clean n-type GaAs(001)-(2x4) 0 -1.4 dI/dV/(I/V) (a.u.) Main Chamber Equipped With: LEED AES QMS STM Filaments Al 2 O 3 Crucible Ta Flag Water Cooled Cu Collimator Gate Valve Experimental Setup In 2 O 3 In 2 O In 2 O 3(s)  In 2 O (g) +O 2(g) Ga 2 O 3(s)  Ga 2 O (g) +O 2(g) GaAs(001)-(2x4)Ga 2 O on GaAs(001)-(2x4)In 2 O on GaAs(001)-(2x4) 122 eV 122 ev Low Energy Electron Diffraction Images Calculating Domain Sizes: ex. Ga 2 O ‡ ‡ a b ‡‡ b a Average Domain Size= (b/a)(4Å) b= distance between (1x1) spots a=full width half maximum of the spot diameter [110]8.2 Å 19.2 Å [110] Ave. Domain Sizes Ga 2 O and In 2 O on GaAs(001)-(2x4) 410°C Dose/Monolayer Coverages Ga 2 O/GaAs(001)-(2x4) In 2 O/GaAs(001)-(2x4) 16Å 0 300Å 300Å 0 300Å 300Å 8Å8Å ABSTRACT The surface structures formed upon deposition of Ga 2 O and In 2 O onto the technologically important As- rich GaAs(001)-(2x4) surface have been studied using scanning tunneling microscopy (STM) and spectroscopy (STS) and Low Energy Electron Diffraction (LEED), and the results are compared with density functional theory (DFT) calculations. At sub-monolayer coverage, the initial bonding sites are different for Ga 2 O and In 2 O adsorptions due to the ability of the incident species to surmount different activation barriers for chemisorption. In 2 O first bonds in the trough between the arsenic dimer rows, whereas Ga 2 O first inserts into the dimer rows. Although the initial bonding for both species is distinctly different, at elevated surface temperatures, a (2x1) surface reconstruction is seen with LEED for both Ga 2 O and In 2 O adsorptions. Although both oxides show (2x1) periodicity, Ga 2 O induces a larger step density while In 2 O has much larger row spacing. Both oxides form crystalline charge balanced surface reconstructions that are electronically unpinned: there are no states within the band gap. The surfaces are unpinned because the oxides restore the Ga and As surface atoms to near bulk charge. Michael Hale, Jonathan Sexton, Sang Yi, Darby Winn, and Andrew Kummel University of California, San Diego 9500 Gilman Dr. La Jolla, Ca. 92093-0358 Ga 2 O on GaAs(001)-(2x4) 410°C Dose/Low Coverage As Ga O 8Å8Å [110] Ga 2 O Inserts into Arsenic Dimer Pairs