Transcript Document

Displacement of Surface As Atoms by Insertion of Oxygen Atoms into As-Ga Backbonds
Experimental: Sang I. Yi, Michael Hale, Peter Kruse
Calculations: Jonathan Sexton
Advisor: A. Kummel
Introduction
•
GaAs is used in wireless communication, high-speed
microelectronics, and optoelectronics
•We have shown the chemical dynamics for As atom displacement
from the surface lattice sites during the onset of oxidation:
University of California, San Diego
Department of Chemistry, 0358
9500 Gilman Drive
La Jolla, CA 92093
• The native oxide of GaAs is poor in quality and is not
able to make a practical MOSFET
Conclusions
• As is liberated at the onset of oxidation with O atoms.
• The number of Single sites increases with O exposure.
• It is believed that excess As at the interface, is the cause
of the poor electronic properties
• Double sites increasingly dominate the surface sites because they
are charge balanced.
3.97 Å
• We explore the chemical dynamics for As atom displacement
from the surface lattice sites during the onset of oxidation
• The number of metastable sites formed is limited by charge
balance.
Clean GaAs(001)-c(2x8)
• In the search for a practical MOSFET oxygen should not be used
at the initial stage of processing.
Clean + O
Site I
Site I + O
16 Å
Site A
1
2
1
0.46q
Single
Site II
[110]
The Chemical
Dynamics of an O
Atom Reacting with
GaAs(001)
Double
2
[110]
DFT Calculations
5 minute exposure to atomic O
5 minute exposure to atomic O
Double + Single
Site 
[1 1 0 ]
[1 1 0 ]
4.40 Å
Ga20As20H32 Cluster
Single
Top View
Clean (0)
Site I (-4.48)
Site I +II
3.97 Å
[110]
[110]
4.28 Å
16 Å
16 Å
Double (-3.26)
5 minute exposure to atomic O
Site II (-4.56)
4.00 Å
20 minute exposure to atomic O
4.40 Å
4.28 Å
Site  (-1.98)
Single (-3.26)
4.45 Å
Site A (-2.60)
Site B (-1.98)
[110]
Site I
[110]
16 Å
Disorder
[110]
4.44 Å
[110]