Transcript Auger Electron Spectroscopy of InN

Electron Spectroscopies
of InN grown by HPCVD
Rudra P. Bhatta
Solid State Physics (Physics - 8510)
Fall 2005
Department of Physics and Astronomy
Georgia State University
Atlanta, Georgia
Outline
 Motivation: InN and its application
 InN sample grown by HPCVD
 Auger Electron Spectroscopy
Data Analysis to Determine Composition
Composition vs. Treatment and Position
 Low energy electron diffraction
 High Resolution Electron Energy Loss Spectroscopy
Surface Structure and Bonding
Film Polarity
 Summary
 Future work
Application of InN & In rich group III-Nitides
 High-efficient energy conversion system
solid state lighting (high-efficient light emitting diodes)
 High speed opto-electronics for optical communication systems
 Solid state lasers operating in the blue and ultraviolet regions
 Terahertz device structures (emitters and detectors)
 Nonlinear optical switching elements.
 Spintronic device structures.
Motivation for studying indium nitride
 Research on indium nitride growth and characterizarion has
increased tremendously in recent years.
 Controversy in the measurement of fundamental properties
such as band gap, lattice constant, and effective mass.
 Difficulty of InN growth due to its low dissociation temperature
and the high vapor pressure of nitrogen over InN.
 Potential of high pressure chemical vapor deposition (HPCVD):
- stabilizes InN to higher temperature, and
- allows growth of InN, GaN, and AlN at similar conditions.
HPCVD grown Indium Nitride
Reactor pressure
15 bar
Gas flow velocity
41 cm /s
Ammonia:TMI ratio
240
Substrate
HPCVD GaN buffer
on sapphire (0001)
Flow Direction
HPCVD Growth: N. Dietz and coworkers, JVST B 23, 1790 (2005) or phys. stat. sol. latest issue
Auger Electron Spectroscopy (AES)
AES is a surface-sensitive spectroscopic technique used for
elemental analysis of surfaces; it offers:
 High sensitivity (nearly 1% monolayer) for all elements
except H and He.
 Quantitative compositional analysis of the surface region.
 A means of monitoring surface cleanliness of samples.
Auger electrons are the secondary ionized electrons
Nitrogen and Indium AES peaks (dN/dE)
N
Nitrogen
Si0.54N0.46
In
Indium
Metal
InN
388
402
409
300
Hand book of Auger Electron Spectroscopy, 2nd Edition, L.E.Davis et al., Physical Electronics Division, 1978
350
400
450
Energy (eV)
500
AES Lineshapes for InN and In
N
N
In
In
InN
as received
InN
as received
N(E)
dN/dE
InN
sputtered
InN
sputtered
Indium
native oxide
Indium
native oxide
Metallic
Indium
Metallic
Indium
350
375
400
425
Energy (eV)
450
475
350
375
400
425
Energy (eV)
450
475
Peak fitting of InN Auger Spectra
carbon
nitrogen
N(E)
indium
oxygen
200
250
300
350 400 450
Energy (eV)
500
550
Peak fitting of InN Auger Spectra
Assumed linear background
Integrated area under peaks
carbon
nitrogen
N(E)
carbon: 220 – 285 eV
nitrogen: 358 – 392 eV
indium: 392 – 418 eV
oxygen: 500 – 522 eV
indium
oxygen
200
250
300
350 400 450
Energy (eV)
500
550
O/In calibrated from
native oxide of metallic
indium (In2O3)
N/In calibrated from
highest nitrogen content
InN (assumed 1:1)
Atomic Fraction vs. Sample Treatment
0.6
C
N
In
O
Atomic Fraction
0.5
0.4
0.3
0.2
Argon
Sputtered
Region
0.1
0
0
40
220
840
2
Argon Sputtering (A s/cm )
Atomic Fraction vs. Sample Treatment
0.6
C
N
In
O
1000 L H2 over
1800 K Tungsten
filament with
sample at 350 K
+
1000 L H2 over
1800 K Tungsten
filament with
sample at 600 K.
0.5
Atomic Fraction
Atomic Hydrogen
Cleaning (AHC)
0.4
0.3
0.2
1 L= 1x10-6 torr s
0.1
0
0
40
220
840
2
Argon Sputtering (A s/cm )
AHC
AHC
McConville and
coworkers,
Univ. of Warwick
Piper et al., JVST A
23, 617 (2005).
Atomic Fraction vs. Position
0.6
N
In
O
After Atomic
Hydrogen Cleaning
Atomic Fraction
0.5
0.4
0.3
0.2
0.1
0
2
3
4
Flow Direction
5
6
7
8
Position from edge (mm)
9
10
Schematic of LEED optics operated as RFA
LEED: A technique used for the determination of surface structure
 Sample sits at
the center of the grids.
 Grid 1&4 are grounded.
 Grids 2 &3 are at
potential slightly
less than that of
electron gun.
 Only elastically
scattered electrons
reach to the
fluorescent screen.
LEED image of InN
Spot positions yield
information on the size,
symmetry and rotational
alignments of surface
unit cell with respect to
substrate unit cell.
Distance between the
spots gives information
about the distances
between the atoms.
Sharpness of the
spots gives insight on how
well ordered the surface
atoms are arranged.
E = 39.5 eV
High Resolution Electron Energy Loss Spectroscopy
HREELS
Surface Vibrational Spectroscopy
eE = 12.5 eV
60o from normal
e E < 500 meV (4000 cm-1)
specular collection
InN
HREELS Normalized Intensity
HREELS of InN after AHC
Atomic
Deuterium
Cleaned
60
cm
-1
x 25
Atomic
Hydrogen
Cleaned
x 25
0
500
1000
1500
2000
-1
Energy Loss (cm )
2500
3000
3500
HREELS Normalized Intensity
HREELS of InN after AHC
N-D stretch
2410
60
cm
Atomic
Deuterium
Cleaned
-1
x 25
N-H stretch
3260
Atomic
Hydrogen
Cleaned
x 25
0
500
1000
1500
2000
-1
Energy Loss (cm )
2500
3000
3500
HREELS Normalized Intensity
HREELS of InN after AHC
N-D stretch
2410
60
cm
Atomic
Deuterium
Cleaned
-1
x 25
-1
No InH stretch (~1700 cm )
-1
No NH bend (~1500 cm )
2
N-H stretch
3260
Atomic
Hydrogen
Cleaned
x 25
0
500
1000
1500
2000
-1
Energy Loss (cm )
2500
3000
3500
HREELS of InN after AHC
HREELS Normalized Intensity
N-D bend
640
N-D stretch
2410
60
cm
Atomic
Deuterium
Cleaned
-1
N-H bend
870
x 25
N-H stretch
3260
Atomic
Hydrogen
Cleaned
x 25
0
500
1000
1500
2000
-1
Energy Loss (cm )
2500
3000
3500
HREELS of InN after AHC
HREELS Normalized Intensity
N-D bend
640
N-D stretch
2410
60
cm
Atomic
Deuterium
Cleaned
-1
N-H bend
870
x 25
N-H stretch
3260
Atomic
Hydrogen
Cleaned
Fuchs-Kliewer
surface phonon
550
x 25
0
500
1000
1500
2000
-1
Energy Loss (cm )
2500
3000
3500
HREELS of InN after AHC
HREELS Normalized Intensity
Surface-NH(ND)
bounce
N-D bend
360
640
InN surface is N-terminated
N-D stretch
2410
60
cm
Atomic
Deuterium
Cleaned
-1
N-H bend
870
x 25
N-H stretch
3260
Atomic
Hydrogen
Cleaned
Fuchs-Kliewer
surface phonon
550
x 25
0
500
1000
1500
2000
-1
Energy Loss (cm )
2500
3000
3500
HREELS of InN after AHC
Surface-NH(ND)
bounce
N-D bend
360
640
* No plasmon due to electron
-1
accumulation (~2000 cm )
-1
HREELS Normalized Intensity
* Small CH stretch (~2950 cm )
-1
* No OH stretch (~3600 cm )
N-D stretch
2410
60
cm
Atomic
Deuterium
Cleaned
-1
N-H bend
870
x 25
N-H stretch
3260
Atomic
Hydrogen
Cleaned
Fuchs-Kliewer
surface phonon
550
x 25
0
500
1000
1500
2000
-1
Energy Loss (cm )
2500
3000
3500
Surface Structure of InN after AHC
Hydrogen terminated InN( 0001)
Growth Direction
H
N
In
N-polar surface consists of
N atoms bonded to three In
atoms in the second layer
and one dangling bond
normal to the surface.
Atomic hydrogen saturates
the dangling bonds to
stabilize the surface.
Summary
 Indium nitride sample grown by high pressure chemical vapor deposition
was investigated by AES, LEED, and HREELS.
 The composition of the InN surface was determined by integrating areas
under peaks in N(E) Auger Electron Spectra.
 Sputtering produces nitrogen deficient surface.
 Atomic hydrogen cleaning (AHC) produces a contaminant-free, wellordered c-plane InN surface with a 1x1 LEED pattern.
 HREELS of InN after atomic hydrogen (deuterium) cleaning shows
NH (ND) stretch, bend and bounce vibrational modes.
 No InH, NH2, or OH vibrational modes are observed.
 InN surface is N-terminated and N-polar, i.e. InN (0001).
Future work
To study the desorption rate of hydrogen from the surface at
different temperature by the process of HREELS and
temperature programmed desorption (TPD).
To study the reaction of ammonia and trimethyl indium (TMI) on
the indium nitride surface in order to understand the surface
reaction during the growth.
Thank you for your attention.