Auger Electron Spectroscopy of In 2 O on GaAs(001)-(2x4)

1. Approximation of the Density of States for Both Clean and O Adsorbed GaAs(001)-(2x4) Approximation of the Density of States for Ga2O on Both n- and p-type GaAs(001)-(2x4) Auger Electron Spectroscopy of In2O on GaAs(001)-(2x4) In2O on GaAs(001)-(2x4) 410°C Dose/Low Coverage Low Energy Electron Diffraction Images Clean GaAs(001)-(2x4) Surface Line Spacing of In2O Vs. Ga2O at Monolayer Coverage Ga2O on GaAs(001)-(2x4) 410°C Dose/Low Coverage Electronic Measurements of In2O on GaAs(001)-(2x4) Experimental Setup In2O3(s)In2O(g)+O2(g) Ga2O3(s)Ga2O(g)+O2(g) GaAs(001)-(2x4) Ga2O on GaAs(001)-(2x4) In2O on GaAs(001)-(2x4) In2O3(s)In2O(g)+O2(g) Clean GaAs(001)-(2x4) Unpinned Clean n-type GaAs(001)-(2x4) Clean p-type GaAs(001)-(2x4) In2O Bonding in the Trough Clean STM Image n-type Ga2O/GaAs 300Å Clean Ball & Stick Diagram Ball and Stick Diagram In:O = 2:1 [110] dI/dV/(I/V) (a.u.) dI/dV/(I/V) (a.u.) Gate Valve 1.5eV Filaments Fermi Level Fermi Level Fermi Level [110] Percentage of Spacing CB VB ‡ ‡ As, Ga In In2O In2O Ga As In2O3 In2O 0 -1.4 -0.3 0 -1.5 1.2 8Å O dI/dV/(I/V) (a.u.) dI/dV/(I/V) (a.u.) dI/dV/(I/V) (a.u.) dI/dV/(I/V) (a.u.) p-type Ga2O/GaAs In2O/p-type GaAs(001)-(2x4) After O Adsorption Pinned In2O on n-type GaAs(001)-(2x4) 122 eV 122 ev Row Spacing (Å) 122 eV a 0 300Å ‡ ‡ Calculating Domain Sizes: Main Chamber Equipped With: LEED AES QMS STM Average Domain Size= (b/a)(4Å) Al2O3 Crucible Fermi Level dI/dV/(I/V) (a.u.) Fermi Level b ex. Ga2O Fermi Level Ave. Domain Sizes dI/dV/(I/V) (a.u.) b= distance between (1x1) spots a=full width half maximum of the spot diameter 8Å 0.75eV a 19.2 Å Ta Flag 0 50Å VB CB 16Å [110] 8.2 Å [110] Water Cooled Cu Collimator As Ga O 0 -1.4 -0.75 0 16Å -1.0 0.3 0 b 16Å 0 300Å Sample Bias (V) Sample Bias (eV) Sample Bias (V) Sample Bias (eV) ABSTRACT The surface structures formed upon deposition of Ga2O and In2O 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 Ga2O and In2O adsorptions due to the ability of the incident species to surmount different activation barriers for chemisorption. In2O first bonds in the trough between the arsenic dimer rows, whereas Ga2O 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 Ga2O and In2O adsorptions. Although both oxides show (2x1) periodicity, Ga2O induces a larger step density while In2O 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. Ga2O and In2O on GaAs(001)-(2x4) 410°C Dose/Monolayer Coverages Ga2O/GaAs(001)-(2x4) In2O/GaAs(001)-(2x4) 300Å Ga2O Inserts into Arsenic Dimer Pairs Scanning Tunneling Microscopy and Spectroscopy of Gallium Oxide and Indium Oxide Deposition on GaAs(001)-(2x4) Michael Hale, Jonathan Sexton, Sang Yi, Darby Winn, and Andrew Kummel University of California, San Diego 9500 Gilman Dr. La Jolla, Ca. 92093-0358