Post on 13-Mar-2020
SPRITE Workshop 1
Channelling Theory and Simulation
• Channelling Applications
• The FLUX Code
Katharina Lorenz1, Andrés Redondo-Cubero1,2,
Peter Smulders3
1Instituto Superior Técnico, Portugal
2Universidad Autónoma Madrid, Spain
3Groningen University, The Netherlands
SPRITE Workshop, IST, 18. May 2015
SPRITE Workshop 2
Outline
• Introduction:
- Rutherford Backscattering and Channelling (RBS/C)
- III-Nitrides
• Characterisation of III-N structures from 3D to 0D:
- 3D Thin films (crystal quality, strain, ion implantation damage,
lattice site location of dopants)
- 2D Quantum wells (crystal quality, strain)
- 1D Nanowires (mosaicity)
- 0D Quantum dots (crystal quality, strain)
• The FLUX Code
• Summary
SPRITE Workshop 3
RBS
Concept
+ Mass perception (kinematic factor)
+ Concentration (x-section)
+ Depth resolution (stopping force)
SPRITE Workshop 4
Ion-Channelling
Reduction of yield up to 98%
Lattice position of impurities
(interstitial or substitutional)
Sensitive to disorder,
lattice mismatch, strain, defects
etc.
“Channelling of energetic ions
occurs when the beam is carefully
aligned with a major symmetry
direction of a single crystal.”
[Lindhard 1965]
SPRITE Workshop 5
Schematic of particle trajectories undergoing scattering at the
surface and channeling within the crystal. The depth scale is
compressed relative to the width of the channel in order to
display the trajectories.
Ion-Channelling
SPRITE Workshop 6
Channelled ion
Ion backscattered at surface
Backscattering or dechannelling takes place when the
incident angle is higher than the critical angle for channelling.
Ion-Channelling – Critical Angle
SPRITE Workshop 7
RBS-Channelling
3 0 0 4 0 0 5 0 0 6 0 0
0
5 0 0 0
1 0 0 0 0
1 5 0 0 01 .8
o
1 .4o
1 .0o
0 .8o
0 .6o
0 .4o
0 .2o
0 .0o
c h a n n e l b
ac
ks
ca
tte
rin
g y
ield
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
0.2
0.4
0.6
0.8
1.0
min
no
rmaliz
ed y
ield
angle [deg.]
• Minimum yield: related with the crystal quality (blocked area).
• Half-width angle: related with the critical angle for channeling.
SPRITE Workshop 8
Rutherford Backscattering /Channelling
Elemental depth profile
Compositional quantification
Interface and growth problems
No standards, non-destructive
Damage profile
Lattice defects
Amorphous layers
Strain in epitaxial films
SPRITE Workshop 9
Shadowed fraction
substitutional
interstitial
interstitial
RBS/C Lattice Site Location
SPRITE Workshop 10
Group-III Nitrides
3.1 3.2 3.3 3.4 3.5 3.60
1
2
3
4
5
6
7
AlGaN
InGaN
Ba
nd
ga
p (
eV
)
a Lattice Constant (Å)
AlN
GaN
InN
Al1-x
InxN x~17-18 %
Al1-x
InxN
InGaN:
LEDs, LASERS
AlGaN:
UV emitters/
Detectors
HEMTS
AlInN: - Widest energy range
- Lattice-match to GaN
SPRITE Workshop 11
Samples
Al1-xInxN
- Growth by MOCVD
- Substrate: GaN on (0001) sapphire
- Thickness: ~100 nm
sapphire
GaN (1-6 mm)
Al1-xInxN
Biaxial strain
a
c
SPRITE Workshop 12
Crystal Quality of thin films
300 400 500 600 7000
500
1000
1500
2000Al
Ga
random
fit
<0001> aligned
cou
nts
channel
In
min(In)=3%
Composition, thickness and crystal quality
Good crystal quality for InN contents < ~20% (Minimum yields 3-6%)
}
}
SPRITE Workshop 13
Example AlInN/GaN bi-layers
350 400 450 500 550 600 650 7000
500
1000
1500
2000
25001000 1200 1400 1600 1800
Ga
In random
fit
<0001> aligned
min
(In)=0.04
co
un
ts
channel
Al
energy [keV]
400 6000
500
1000
1500
2000
1000 1200 1400 1600 1800
min
(In)=0.40
24%In random
Fit
<0001> aligned
cou
nts
channel
19%In
energy [keV]
w
w
Good crystalline quality Worse crystalline quality
Growth at 840 ºC Growth at 760 ºC
SPRITE Workshop 14
Measuring Strain by RBS/C
cossin
||
rel
relepi
c
cc
rel
relepi
a
aa
||
Tetragonal distortion:
c
atan
Lorenz et al. PRL 97 (2006) 85501
Lorenz et al. JCG 310 (2008) 4058
SPRITE Workshop 15
Strain Relaxation: Compressive Strain
400 500 600 7000
500
1000
1500
2000
1000 1200 1400 1600 1800
min
(In)=0.40
24%In random
Fit
<0001> aligned
co
un
ts
channel
19%In
energy [keV]
w
w
30.5 31.0 31.5 32.0 32.5 33.0
0.6
0.7
0.8
0.9
1.0
1.1
Ga
In interface
In surface
no
rmalis
ed y
ield
angle (deg.)
<-2113>
relaxed AlInN
Depth dependent strain measurement
Energy windows (W) select different depths
Surface layer is relaxed
Deeper region under compressive strain
Relaxation via change of composition
SPRITE Workshop 16
Strain Relaxation: Compressive Strain
600 800 1000 1200 14000
500
1000
1500
Random
Fit
<0001> alignedco
un
ts
energy (keV)
min
(In)= 0.3
Al0.78
In0.22
N
W1 W2
-1.0 -0.5 0.0 0.5 1.0 1.50.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
W1 (interface)
W2 (surface)
no
rma
lise
d y
ield
angle (deg.)
<2113>
Relaxation towards the surface
Relaxation via change of c/a ratio (constant composition)
Depth dependent strain measurement
Energy windows (W) select different depths
SPRITE Workshop 17
Morphology Change
Pseudomorphic
x=.16
Partly relaxed
x=0.22
Relaxed
x=0.240.19
RMS=0.6 nm RMS=2.1 nm RMS=6.2 nm
Roughening/3D growth
SPRITE Workshop 18
“Anomalous” features like double-dips
InN content 15%
30.5 31.0 31.5 32.0 32.5 33.0 33.50.0
0.2
0.4
0.6
0.8
1.0 <2113>
31.7º
Ga
In
no
rmaliz
ed y
ield
angle (deg.)
32.4ºR
100 200 300 400 500 600 7000
500
1000
1500
2000
2500
3000
random
aligned
min(In)=0.06
co
un
ts
channel
Al
Ga
In
R: angle for relaxed AlInN
determined from Vegard´s law
SPRITE Workshop 19
Steering effects in the interface
Angular scan of GaN substrate distorted when kink angle ≤ critical angle
a-energy
kink angle (InN content)
InN content 19%
30.5 31.0 31.5 32.0 32.5 33.0 33.50.0
0.2
0.4
0.6
0.8
1.0
Ga
In
no
rmaliz
ed y
ield
angle (deg.)
<2113>
SPRITE Workshop 20
Steering effects: FLUX Simulations
→ Increasing beam energy
→ Comparison with simulations
Different kink angles
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.50.0
0.2
0.4
0.6 In 1 MeV
Ga 1 MeV
Ga 2 MeV
Yie
ldAngle (deg.)
º
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.50.0
0.2
0.4
0.6
0.8
Yie
ld
Angle (deg.)
AlInN
Ga =0.7º
Ga =0.4º
Ga =0.2º
Different energies
Redondo-Cubero, Lorenz et al. APL 95 (2009) 051921
Redondo-Cubero, Lorenz et al. JPD 42 (2009) 065420
SPRITE Workshop 21
GaN Scans and FLUX Simulations
<-2113>
-1.5 -1.0 -0.5 0.0 0.5 1.00.2
0.4
0.6
0.8
1.0<10-11>
Angle [deg.]
N
orm
alis
ed Y
ield
-1.5 -1.0 -0.5 0.0 0.5 1.0
<10-11>
<-2113>
-1.5 -1.0 -0.5 0.0 0.5 1.0
<10-11>
0.2
0.4
0.6
0.8
1.0
1.2
experiment
simulation
13% InN15% InN
<-2113>
19% InN
=0.3º =0.5º =0.66º
SPRITE Workshop 22
Strain Analysis XRD - RBS
||
XRD
RBS
cossin
0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
compressive
te
trag
on
al dis
tort
ion
T
[%]
RBS InN content x
XRD
RBS/C+MC
raw RBS/C
weighted linear fit
tensile
Lorenz et al. PRL 97 (2006) 85501 Perfect Lattice matching for x=0.171
SPRITE Workshop 23
Implantation damage in GaN
31015 at/cm2 Eu implantation 300 keV at RT
2 damage regions (surface / bulk)
500 520 540 560 580 600 620 640 660 680 700 720
200
400
600
800
1000
1200
1400
1600
18001400 1500 1600 1700 1800
random
<0001> aligned
<0001> aligned virgin
channel
yie
ld (
coun
ts)
Eu
x10B
energy (keV)
S
SPRITE Workshop 24
0 100 200 300 4000.00
0.02
0.04
0.06
0.08
min
depth (nm)
exp. min
1x1014
Ar/cm2
SRIM Argon profile
SRIM defect profile
0 100 200 300 4000.00
0.02
0.04
0.06
0.08
rel. d
efe
ct co
nce
ntr
atio
n
depth (nm)
exp. defect profile 1x1014
Ar/cm2
SRIM Argon profile
SRIM defect profile
Implantation damage in GaN
200 220 240 260 280 300 320 340 360 380 400
10
100
1000 aligned as-grown
aligned implanted
random
RB
S Y
ield
(coun
ts)
channel
RBS/C aligned spectra need correction
for dechannelling (in this case using the DICADA program, Gärtner
et al. NIMB 216 (1983) 275; 227 (2005) 522)
1x1014 Ar/cm2
∆𝜒𝑚𝑖𝑛=𝑌𝑎𝑠−𝑖𝑚𝑝𝑙𝑎𝑛𝑡𝑒𝑑𝑎𝑙𝑖𝑔𝑛𝑒𝑑
− 𝑌𝑎𝑠−𝑔𝑟𝑜𝑤𝑛𝑎𝑙𝑖𝑔𝑛𝑒𝑑
𝑌𝑟𝑎𝑛𝑑𝑜𝑚
Correction for
dechannelling
SPRITE Workshop 25
→ Homogeneous Eu distribution
with depth ~0.1at%
→ Excellent crystal quality
(Minimum yield <3%)
GaN:Eu grown by MOCVD at 1000ºC
400 500 600 7000
1000
2000
3000
40001000 1200 1400 1600 1800
random
fit
<0001> aligned
co
un
ts
channel
Eu
x10
Ga
energy (keV)
Lattice site location of Eu in GaN
SPRITE Workshop 26
→ Eu incorporated to ~100% on Ga-sites
→ Eu displaced (0.2Å) for sample grown at 900ºC
→ Eu clusters
Lattice site location of Eu in GaN
0.0
0.2
0.4
0.6
0.8
1.0
1.2
-2 -1 0 1 20.0
0.2
0.4
0.6
0.8
1.0
-0.8 0.0 0.8
Eu
Eu sim
Ga
Ga sim
norm
aliz
ed y
ield
900ºC
<1011>
<0001>
angle [deg.]
1000ºC
616 618 620 622 624 626 628 630
1E-4
1E-3
0.01
0.1
PL inte
nsity (
arb
. units)
wavelength (nm)
1000 ºC
950ºC
900ºC
PL exc. 348 nm at low T
Lorenz et al. APL 97 (2010) 111911
SPRITE Workshop 27
Group-III Nitride Nanostructures
2D
InGaN/GaN quantum wells (QW)
LED
1D
GaN nanowires (NW)
Nano-LEDs, sensors
0D
GaN quantum dots (QD)
2-3 nm
InGaN QW
SPRITE Workshop 28
Problems when going to nano-scale
Limited depth resolution
in conventional RBS (~20nm)
Problems:
Besides thickness and composition
is the width of the peak dependent on
- Energy resolution
- Intermixing of layers
- Roughness
In case of ambiguities need of
complementary experimental
techniques (TEM, AFM...)
Grazing incidence
400 450 500 550 600 650 7000
500
1000
1500
2000
25001200 1400 1600 1800
Ga
In random
fit
<0001> aligned
simulation
10nm layer
min
(In)=0.06
cou
nts
channel
Al
energy [keV]
AlInN/GaN
SPRITE Workshop 29
GaN QD / AlN Multilayers
Chamard et al. Phys. Rev. B 69 (2004) 125327
150 b
ilay
ers
SiC
AlN (10nm)
AlN spacer: ~8 nm
GaN QD: 6ML
Grown by MBE using the
Stranski-Krastanow growth mode
SPRITE Workshop 30
RBS Normal Incidence
Random and <0001> aligned Scan across <0001>
Excellent crystalline quality along c-axis min=4%!
100 200 300 400 500 6000
200
400
600
800
1000
1200
Al
co
un
ts
channel
<0001>aligned
random
Ga
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.00.0
0.2
0.4
0.6
0.8
1.0
Ga
Al
No
rma
lize
d Y
ield
Angle
<0001>
SPRITE Workshop 31
Crystal Quality of QDs
450 500 550 600 6500
100
200
300
400
random
<0001> aligned86%
17%14%13%11%11%
co
un
ts
channel
7 GaN QD planes
min 12%
Crystal quality of each QD plane can be assessed
and does not change with depth
QD at surface show reduced channelling
probably due to strain relaxation and oxidation
7 Q
D p
lanes
SiC
AlN (10nm)
AlN spacer: ~40 nm
GaN QD: 3.5ML
200nm
SPRITE Workshop 32
Buried SQW / SQD-plane
SiC
GaN SQW
AlN
AlN
10 nm
3.5 ML
26 nm
AlN
AlN
SiC
10 nm
3.5 ML
26 nm
GaN QD 100 200 300
0
300
600
900 =65º
=80º
=5º
cou
nts
channel
RBS XRR
AlN cap QD 8.9 (1.0) nm 9.4 nm
QD 2.6 nm (Vf=27%) 0.46 nm
AlN cap SQW 8.1(1.0) nm 8.8 nm
SQW 0.6 (1) nm 0.54 nm
Ga
Al
SPRITE Workshop 33
Quality Buried SQW / SQD-plane
SQW QD-plane
-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.50.0
0.2
0.4
0.6
0.8
1.0
Ga SQW
Al cap
Al buffer
angle (deg.)
no
rmaliz
ed y
ield
-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.50.0
0.2
0.4
0.6
0.8
1.0
Ga QD
Al cap
Al buffer
angle (deg.)no
rmaliz
ed y
ield
<0001>
Crystal quality better in QD than in QW
Formation of misfit defects?
- misfit (GaN-AlN 2.5%) can lead to fomation of dislocations and stacking faults
as evidenced by TEM analysis (Kandaswamy et al. JAP 106 (2009) 013526)
min=15% min=5%
SPRITE Workshop 34
Strain measurement: thin film
30.5 31.0 31.5 32.0 32.5 33.0 33.50.0
0.2
0.4
0.6
0.8
1.0 <2113>
31.7º
Ga
In
no
rmaliz
ed y
ield
angle (deg.)
32.4ºR
sapphire
GaN (1000 nm)
Al1-xInxN
cossin
Lorenz et al. PRL 97 (2006) 85501; JCG 310 (2008) 4058
SPRITE Workshop 35
Problems when going to nano-scale
For example a buried GaN single quantum well (SQW) in AlN
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.00.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Al
Ga
angle (deg.)
no
rma
lize
d y
ield
<-2113>
SiC
GaN SQW
AlN
AlN
10 nm
3.5 ML
26 nm
The GaN SQW is too thin to exhibit channelling effects on the beam
Ga-atoms act like an impurity
Scans do not shift but show asymmetries and flux peaking
SPRITE Workshop 36
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
Experiment
Simulation
no
rma
lize
d y
ield
angle (deg.)
Strain in Buried SQW / SQD-plane
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6 Experiment
Simulation
no
rma
lize
d y
ield
angle (deg.)
SQW QD-plane
0.9 nm QD =0.12º T= -3.1%
1.7 nm QD =0.7º T= -1.6%
2.6 nm QD =0.5º T= -0.4%
0.9 nm QW =0.14º T=-3.9%
0.6 nm QW =0.22º T= -7%
QD partly relaxed but error in current
data anlysis is extremely high
MC simulations need to include sample imperfections and QD
T (fully strained)=-3.6% T (Raman, XRD)= -2.4% (Cros et al. PRB 76 (2007) 165403)
SPRITE Workshop 37
High resolution RBS or MEIS
Electrostatic
analyzer
Position sensitive
detector
RBS HR-RBS / MEIS
Energy ~ 1-5 MeV (a, p) ~ 50-500 keV (a, p)
Detector system Si surface barrier detector Electrostatic analyser or magnetic spectrometer:
Resolution of detector system ~ 15 keV < 1 keV
Depth resolution ~10 nm < 1 nm
Probing depth ~1 mm ~20 nm
MEIS
SPRITE Workshop 38
MEIS: Strain distribution in GaN QDs
Blocking
QD relax towards
the top of the pyramid
Jalabert et al. PRB 72 (2005) 115301
Relaxed c/a
QDs top
SPRITE Workshop 39
RBS/C on nanowires?
- Vertically aligned NW grown by MBE on 111 Si
SPRITE Workshop 40
Alignment of Nanowires
-2 -1 0 1 20.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
-2 -1 0 1 2
norm
aliz
ed y
ield
<0001>
Si
Ga
<-2113>
angle [deg.]
-2 -1 0 1 2
<10-11>
- Preferential orientation of
nanowires:
[111] Si || [0001] GaN
[11-2] Si || [10-10] GaN
Si
Ga/N
250 300 350 400 450 500 550 600 6500
500
1000
1500
2000
random
aligned
cou
nts
channel
GaN NW
Si
SPRITE Workshop 41
Mosaicity of Nanowires
-1 0 10.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
-1 0 1
no
rma
lize
d y
ield
<0001>
to plane
<2113>
to plane
angle [deg.]
-1 0 1
data
0.4º tilt
0.3º tilt
0.5º tilt
data
0.5º twist
0.4º twist
0.6º twist
<2113>
to plane
Ion channelling in NWs
allows determination of
orientation, tilt and twist
via Monte Carlo
simulations:
- Tilt: 0.4º
- Twist: 0.5º
SPRITE Workshop 42
Implantation damage in GaN
Eu implantation 300 keV at RT
Sigmoidal shaped damage build-up curve
Efficient dynamic annealing
0.1 1 100.0
0.2
0.4
0.6
0.8
1.0
IV
IIIregime I
ma
x.
de
fect le
ve
l
fluence (1015
at/cm2)
bulk peak
surface peak
II
Lorenz et al. J. Phys. D
42 (2009) 165103
SPRITE Workshop 43
Implantation damage in GaN
0.1 1 100.0
0.2
0.4
0.6
0.8
1.0
IV
IIIregime I
max. defe
ct le
vel
fluence (1015
at/cm2)
bulk peak
surface peak
II
HRTEM
TEM
0002
dark field
- Point defect clusters
- Low concentration of stacking faults
SPRITE Workshop 44
Implantation damage in GaN
0.1 1 100.0
0.2
0.4
0.6
0.8
1.0
IV
IIIregime I
max. defe
ct le
vel
fluence (1015
at/cm2)
bulk peak
surface peak
IIHRTEM
- Increasing number of stacking faults
SPRITE Workshop 45
Implantation damage in GaN
0.1 1 100.0
0.2
0.4
0.6
0.8
1.0
IV
IIIregime I
max. defe
ct le
vel
fluence (1015
at/cm2)
bulk peak
surface peak
II
- Nanocrystalline surface layer with voids
- Stacking fault density in bulk saturates
0 20 40 60 80 100 120 1400.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
defect distribution
Eu-profile at-%
rel. c
on
c. p
oin
t d
efe
cts
Eu
co
nc
en
tra
tio
n (
at-
%)
depth (nm)
SPRITE Workshop 46
InxGa1-xN/GaN: Thin film
200 250 300 350 400 450 500 550 600 650 7000
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500 experimental data
fit
co
un
ts
channel
In
Ga
N
Fit results:
50 nm In15.9Ga84.1N sapphire
GaN (1-6 mm)
InxGa1-xN
A fit (e.g. using the NDF code) gives the thickness and composition of the film
and can give information on compositional gradients, roughness, contaminations
etc.
SPRITE Workshop 47
InxGa1-xN/GaN: Manual Analysis
200 250 300 350 400 450 500 550 600 650 7000
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500 experimental data
fit
co
un
ts
channel
In
Ga
N
16.0
)1(1
191.0/221996.62550
/482264.21220
)(
)(
Ga
In
Ga
In
Ga
In
rGa
rIn
Ga
In
iri
N
N
N
N
xx
x
N
N
strbarn
strbarn
InY
GaY
N
N
NY
Fit results:
50 nm In0.159Ga0.841N
2550 cnts
1220 cnts
2
cm
atN
i
Composition from fit and manual analysis match perfectly
sapphire
GaN (1-6 mm)
InxGa1-xN
SPRITE Workshop 48
200 250 300 350 400 450 500 550 600 650 7000
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500 experimental data
fit (50 nm)
simulation 10nm
thicknessco
un
ts
channel
In
Ga
N
InxGa1-xN/GaN: Going to Nanoscale
For very thin layers the height of the In-peak depends not only on composition
but also on the thickness of the layer due to the limited depth resolution.
sapphire
GaN (1-6 mm)
InxGa1-xN
x=0.16
SPRITE Workshop 49
InxGa1-xN/GaN: Multi Quantum Well (MQW)
QW thickness and QW composition difficult to measure with most techniques
- XRD measured the period and average composition
- PIXE, WDX measures the total In-content; QW thickness needs to be known
- SIMS suffers from artefacts due to contaminations from the sides
- TEM+EDX possible but very time consuming
5 samples with different InN content
InxGa1-xN/GaN MQW
5 periods
Nominal QW thickness 3nm
Grown by Metal Organic Chemical
Vapour Deposition (MOCVD) sapphire
GaN (1-6 mm)
sapphire
GaN (1-6 mm)
InGaN 3 nm
GaN 21 nm
SPRITE Workshop 50
InxGa1-xN/GaN: Multi Quantum Well (MQW)
Composition and thickness cannot be determined unambiguously
(complementary measurements necessary e.g. TEM).
Period, total InN content and “product” thickness × composition.
Assuming the nominal thickness of 3 nm, x was determined to vary from 2 to 14 %
350 400 450 500 550 600 650 7000
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
=60º=70º
=5º
cou
nts
channel
=40º
RPI198A fit using ~5nm QW
350 400 450 500 550 600 650 7000
200
400
600
800
1000
1200
1400
1600
1800
2000
=60º
=70º
=5º
cou
nts
channel
=40º
RPI198A fit using ~3nm QWFit using ~3nm QW, x=0.11 Fit using ~5nm QW, x=0.07
sapphire
GaN
(1-6
mm
)
sapphire
GaN
(1-6
mm
)
SPRITE Workshop 51
Crystal Quality in QWs
300 400 5000
500
1000
1500
2000
2500
3000
3500
4000
4500
460 480 500 520 5400
100
200
300
400
500
co
un
ts
channel
RPI198A
Ga
In
random
aligned
channel
four QW
min
=4%
Minimum yield for Ga: < 2% in all samples
Minimum yield for In: 2-10% (better for thinner GaN barrier layers)
SPRITE Workshop 52
Grazing Incidence
Layer Material Thickness
[nm]
1 GaN/AlN 3.435
2 AlN 4.558
3 GaN/AlN 2.669
4 AlN 5.202
5 GaN/AlN 2.642
6 AlN 5.082
7 GaN/AlN 2.557
8 AlN 5.037
9 GaN/AlN 2.663
160 180 200 220 240 260 2800
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
Fit
Experimental Data
channel
cou
nts
GaAlTilt 86º
Input:
Cylindrical QD: Height 2.6 nm
Radius 8.5 nm
QD volume fraction 40%
SPRITE Workshop 53
Simulating QD with NDF
1N. Barradas et al. APL 71 (1997) 291. 2J.P. Stoquert et al. Phys. Rev. B 66 (2002) 144108. 3N. Barradas et al. unpublished
- NDF1 (IBA Data Furnace) spherical2 and cylindrical3 QD
→ cylindrical QD: Height 2.6 nm
Radius 8.5 nm
NDF calculates:
- Quantity of material crossed
- Energy spread due to
difference in stopping power
→ volume fraction
SPRITE Workshop 54
Volume fraction of GaN QD
Volume-fraction of GaN QD: 0.4
Good agreement with TEM
Uncovered QDs at surface are bigger
(confirmed by TEM, Gogneau et al. JAP 96 (2004) 1104)
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1000
2000
3000
4000
V = 0.30
V = 0.40
V = 0.45
Experimental Data
channel
co
un
ts
GaTilt 86º