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
Auger Electron Spectroscopy of In2O
on GaAs(001)-(2x4)
Experimental Setup
ABSTRACT
The surface structures formed upon deposition of Ga2O and In2O onto the technologically important Asrich GaAs(001)-(2x4) surface have been studied using scanning tunneling microscopy (STM) and
In2O3(s)In2O(g)+O2(g)
Ga2O3(s)Ga2O(g)+O2(g)
In2O3(s)In2O(g)+O2(g)
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,
In2O
In2O3
whereas Ga2O first inserts into the dimer rows. Although the initial bonding for both species is distinctly
In2O
In2O
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
Main Chamber Equipped With:
Al2O3 Crucible
In:O = 2:1
2.5
2
1.5
As, Ga
In
1
Water Cooled Cu
Collimator
As
O
0
-1
0
200
400
800
1000
1200
16Å
16Å
Ga2O and In2O on GaAs(001)-(2x4)
410°C Dose/Monolayer Coverages
Low Energy Electron Diffraction Images
GaAs(001)-(2x4)
In2O Bonding in the Trough
600
Electron Energy (eV)
In2O on GaAs(001)-(2x4)
410°C Dose/Low Coverage
Ga2O on GaAs(001)-(2x4)
410°C Dose/Low Coverage
Ga2O Inserts into Arsenic Dimer Pairs
Ga
0.5
LEED
AES
QMS
STM
Ta Flag
unpinned because the oxides restore the Ga and As surface atoms to near bulk charge.
Clean Ball & Stick Diagram
-0.5
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
Auger Signal (a.u.)
3
Gate Valve
Filaments
Clean STM Image
3.5
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
Clean GaAs(001)-(2x4) Surface
Ga2O on GaAs(001)-(2x4)
In2O on GaAs(001)-(2x4)
Ga2O/GaAs(001)-(2x4)
In2O/GaAs(001)-(2x4)
300Å
Ball and Stick Diagram
300Å
[110]
[110]
122 ev
122 eV
122 eV
Calculating Domain Sizes:
ex. Ga2O
Ave. Domain Sizes
b= distance between (1x1) spots
a
a
‡
Approximation of the Density of States for Both
Clean and O Adsorbed GaAs(001)-(2x4)
60
1.5eV
5
Fermi Level
4
3
30
20
10
0
8
10
12
14
16
18
Row Spacing (Å)
20
22 >24
8
After O Adsorption
6.5
Pinned
5
3.5
2
0.75eV
0.5
-1
-0.75
-1.5 -1.3
-1.0 -0.8 -0.5 -0.3
0 -0.1 0.2 0.4 0.7 0.9 1.1 1.4 1.6 1.9 2.1 2.3
Sample Bias (eV)
Clean n-type GaAs(001)-(2x4)
3
[110]
8.2 Å
16Å
Approximation of the Density of States for Ga2O
on Both n- and p-type GaAs(001)-(2x4)
Clean p-type GaAs(001)-(2x4)
Fermi Level
0
-2.0
2.3
2.1
1.9
1.7
1.4
1.2
1.0
0.7
0.5
0.3
0.1
-0.2
-0.4
-0.6
-0.9
-1.1
-1.5
-1.3
-1.5
-2.0
40
-1.8
2
50
19.2 Å
8Å
0
-3.2
-1.4
-0.7
0
In2O on n-type GaAs(001)-(2x4)
Fermi Level
-1.0
1.2
3.4
-1.4 0
Sample Bias (V)
5.6
-0.3 0
1.2
In2O/p-type GaAs(001)-(2x4)
Fermi Level
0
-1.5
-1.0
0 0.3
Sample Bias (V)
10
n-type Ga2O/GaAs
9
8
7
6
Fermi Level
5
4
CB
VB
3
2
-2.5
dI/dV/(I/V) (a.u.)
Ga2O
70
6
dI/dV/(I/V) (a.u.)
Percentage of Spacing
80
7
[110]
Electronic Measurements of In2O
on GaAs(001)-(2x4)
Clean GaAs(001)-(2x4)
Unpinned
8
300Å
b
dI/dV/(I/V) (a.u.)
In2O
dI/dV/(I/V) (a.u.)
90
b
50Å
Line Spacing of In2O Vs. Ga2O
at Monolayer Coverage
‡
dI/dV/(I/V) (a.u.)
0
dI/dV/(I/V) (a.u.)
O
0
‡
‡
dI/dV/(I/V) (a.u.)
Ga
300Å
Average Domain Size= (b/a)(4Å)
a=full width half maximum of the spot diameter
As
0
dI/dV/(I/V) (a.u.)
8Å
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
p-type Ga2O/GaAs
9
7
Fermi Level
5
3
1
-1
VB
-1.2 -0.9 -0.6 -0.3
CB
0.0
0.3
0.6
0.9
Sample Bias (eV)
1.2
1.5
1.8