unusual compositional dependence of the exciton reddduced ...mctp/sciprgpgs/events/2011/bcs/talk...
TRANSCRIPT
Unusual compositional dependence of the it d d
Unusual compositional dependence of the it d dexciton reduced mass
in GaAs1 xBix (x=0‐10%)exciton reduced massin GaAs1 xBix (x=0‐10%)1‐x x ( )1‐x x ( )
G Pettinari1 A Polimeni2 J H Blokland1 R Trotta2G. Pettinari1, A. Polimeni2, J. H. Blokland1, R. Trotta2,P. C. M. Christianen1, M. Capizzi2, J. C. Maan1,
X Lu3 E C Young3 and T Tiedje3X. Lu , E. C. Young and T. Tiedje
1High Field Magnet Laboratory,Radboud University Nijmegen, The Netherlands
2Dipartimento di Fisica,Sapienza Università di Roma, Italy
Radboud University Nijmegen, The Netherlands
3Department of Physics and Astronomy,University of British Columbia, Vancouver, Canada
Ann Arbor, July 16th
Outline
Bismuth in GaAs:
‐ electronic properties
‐magneto‐photoluminescence (0‐30 T) andexciton reduced mass determinationexciton reduced mass determination
‐ evidence for a largely perturbed band structure‐ evidence for a largely perturbed band structure
Ga(As,Bi) expected trendselectronegativityatomic
electron
electronegativity
first ionization potential V
6p Bi4p As
CBs
Bi is expected to
number
III B V Bconfiguration
2s N4s Ga
p s
VBs
influence thevalence bandB N
3.0414.5
1s22s2p3
Al P2.181.81
Large relativistic corrections are expected due to Z →
Ga As9.81
[Ar]3d104s2p3
.86.00
[Ar]3d104s2p1
expected due to ZBi →large SO splitting ∆0 of VB anion p‐states
∆ (G Bi) 2 15 V
In Sb
Tl Bi2.027.29
∆0(GaBi)=2.15 eVTl Bi[Xe]4f145d106s2p3
P. Carrier and S.‐H. Wei, Phys. Rev. B 70, 035212 (2004)
Ga(As,Bi) expected trends
Predicted E = ‐1 45 eV for GaBi
A. Janotti, S.‐H. Wei, and S. B. Zhang, Phys. Rev. B 65, 115203 (2002)
GaBi
Predicted Eg= ‐1.45 eV for GaBidensity functional formalism and LDA (64‐atom cell calculation)
Expected band gap reduction following (heavier anion)‐(smaller gap) rule
L XΓ
(heavier anion) (smaller gap) rule
EBiVBM
Y. Zhang, A. Mascarenhas, and L. –W. Wang, Phys. Rev. B 71, 155201 (2005)
L li ti f l b d t t t BiEBiVBM • Localization of valence band states at Bi atoms• Bi generates an impurity state (EBi) 80 meVbelow the VBM• Pressure coefficient of EBi similar to GaAs, no Bi state emerging from the VBdensity functional formalism and LDA
Ga(As,Bi) observed trends
1.20
1.40
(eV
)
GaAs1-x
Bix
T=290 K4.10eV5.9eV36.0)1()(
)1()1(
GaBi
GaAsGaBiBiGaAs1
==−=+=
−−−+=−
βαβα Exxb
xxExExExx
b
Kunishige Oe and Hiroshi Okamoto, Jpn. J. Appl. Phys. 37, L1283 (1998)X. Lu et al., Appl. Phys. Lett. 95, 41903 (2009)
1.00Ener
gy
experiment (PL)
x=(0‐5)% ∆Eg≈‐80 meV/%Bi(GaAs1‐xNx; ∆Eg≈-100 meV/%N; b~16-20 eV)
X. Lu et al., Appl. Phys. Lett. 95, 41903 (2009)
0.8000 2 4 6 8 10 12
x (%)
experiment (PL)
1.44
A larger band gap reduction is observed for the same increase in lattice constant
1.28
y (e
V) In
zGa
1-zAs
GaAs N
Potential for0 96
1.12
nd g
ap E
nerg GaAs
1-yNy z =24%
y=5%GaAs
1-wSb
ww=22%
GaAs Bi1 31 µm• Heterojunction bipolar transistors• Solar cells• Telecom
0.8
0.96
5 6 5 65 5 7 5 75
Ban
x=10%GaAs
GaAs1-x
Bix
1.31 µm
1.55 µm
5.6 5.65 5.7 5.75a (Å)
Ga(As,Bi) observed trendsB. Fluegel et al., Phys. Rev. Lett. 97, 067205 (2006)
eV340eV152
)1()1()BiGaAs(GaAs0
GaBi0
GaAs0
GaBi010
=∆=∆
−−∆−+∆=∆ − xxxxxx b
eV34.0eV15.2 00 ∆∆
b = ‐6.0 eV(GaAs1‐xNx; ∆0 constant)
Potential for spintronics
Bi‐related states form with pressure coefficient similar to GaAs
Ultrafast photoresponse in the NIR for emitters and detectors of pulsed THz radiationK. Bertulis et al., Appl. Phys. Lett. 88, 201112 (2006)
S. Francoeur et al., Phys. Rev. B 77, 085209 (2008)
Ga(As,Bi): what about the carrier mass?
J. Wu et al., J. Appl. Phys. 105, 011101 (2009)R. N. Kini et al., J. Appl. Phys., 106, 043705 (2009)
Bi incorporation affects the electron mobility
We address the carrier effective mass in Ga(As,Bi)b t h t l iby magneto‐photoluminescence
The samplesGrown on (100) GaAs by molecular beam epitaxyGrown on (100) GaAs by molecular beam epitaxy
x =0, 0.6, 1.3, 1.7, 1.9, 3.0, 3.8,4 5 5 6 8 5 and 10 6%
GaAs1-x
Bix
T = 200 K
FE
8 %
x = 10.6%
4.5, 5.6, 8.5 and 10.6%
TG=(270 – 380) °C, thickness t=(40‐350) nm
x = 8.5%
x = 5.6%
X. Lu et al., Appl. Phys. Lett. 92, 192110 (2008)
b. u
nits)
x = 3 8%
x = 4.5%
ensi
ty (a
rb
x = 3%
x = 3.8%
PL In
te
x = 1.9%
x = 1.7%
d l
x = 1.3%
x = 0.6%LE
Good structural properties 0.8 1.0 1.2 1.4Energy (eV)
The samplesGrown on (100) GaAs by molecular beam epitaxyGrown on (100) GaAs by molecular beam epitaxy
x =0, 0.6, 1.3, 1.7, 1.9, 3.0, 3.8,4 5 5 6 8 5 and 10 6%
GaAs1-x
Bix
T = 200 K
FE
8 %
x = 10.6%
4.5, 5.6, 8.5 and 10.6%
TG=(270 – 380) °C, thickness t=(40‐350) nm
x = 8.5%
x = 5.6%
b. u
nits)
x = 3 8%
x = 4.5%
110
ensi
ty (a
rb
x = 3%
x = 3.8%
90
110
M (m
eV)
T=200 K
PL In
te
x = 1.9%
x = 1.7%
70FWH
M
x = 1.3%
x = 0.6%LE
500 2 4 6 8 10
x (%)
Unusual compositional linewidth dependence 0.8 1.0 1.2 1.4Energy (eV)
Unusual compositional linewidth dependence
High‐magnetic field measurements NijmegenThe Netherlands
B = 0 – 33 T
‐ Powered by 2×10 MW at 500 V (4⋅104 A)
‐ Chilled by 104 l/min deionised water at 30 atm at 10 °C.
1 hour magnet time costs 1,000 €
Why 200 K?
GaAs1-x
Bix
x=1.9%T=210 KFE GaAs
1-xBix
x=8.5%FE
nits
)
x 1.9%
P=12 P0 ni
ts)
x 8.5%T = 200 K
P=20 P
nsity
(arb
. un
P=P0
P= 4 P0
0
nsity
(arb
. un
LEP= PP= 2 P
0
P= 10 P0
P=20 P0
PL In
ten LE
P 12 P
T=10 K
PL In
ten T = 10 K
P=20 P0
0
P= 4 P0
P=12 P0
P= P0 P= P
0
P= 2 P0
P= 10 P0
0
1.15 1.2 1.25 1.3 1.35 1.4Energy (eV)
0.8 0.85 0.9 0.95 1 1.05Energy (eV)
Localized excitons dominate low‐T photoluminescencep
G. Pettinari et al., Appl. Phys. Lett. 92, 262105 (2008)
Why 200 K?un
its) GaAs
1-xBi
x - x = 0.6%
P0
= 8 W/cm2(a) GaAs
1-xBi
x - x = 5%
P0
= 8 W/cm2(c)(3.6%)GaAs
1-xBi
x - x = 1.9%
P0
= 8 W/cm2(b) 4.5%
ensi
ty (a
rb.
FELE
T = 180 K16×P
0
3×P0
P0
FET = 180
16×P0
3×P0
P0
FET = 180 K
16×P0
3×P0
P0
K
16×P0ized
PL
Inte FE GaAs
16×P0
16×P0
Nor
mal
i
FELE
T = 150 K 3×P0
P0
0.25×P0
FELE
T = 150 3×P0
P0
0.25×P0
FELE
T = 150 K 3×P0
P0
0.05×P0
K
1.2 1.3 1.4 1.5Energy (eV)
0
1.0 1.1 1.2 1.3Energy (eV)
0
1.0 1.1 1.2 1.3 1.4Energy (eV)
0
Accurate choice of measurement power and temperaturep p
Why 200 K?
S I h f l A l Ph L 96 131115 (2010)R K d i l J A l Ph 106 023518 (2009) S. Imhof et al., Appl. Phys. Lett. 96, 131115 (2010)R. Kudrawiec et al., J. Appl. Phys. 106, 023518 (2009)
x=3%x=4.5%
Magneto‐PL: data
30 T
GaAs1-xBixx=8.5% T=190 K
P=10 W/cm2
30 T
GaAs1-xBixx=8.5% T=190 K
P=70 W/cm2
At high power carrier scattering disrupts
30 T
b. u
n.)
30 Tg p
the coherence of the electron/hole cyclotron orbit
nten
sity
(arb cyclotron orbit
PL In
0.80 0.85 0.90 0.95 1.00 1.050 T
Energy (eV)0.80 0.85 0.90 0.95 1.00 1.05
0 T
Energ (eV)Energy (eV) Energy (eV)
G Pettinari et al Phys Rev B 81 235211 (2010)G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)
Magneto‐PL: data
0.95P
0 = ~10 W/cm2
3×P0
At high power carrier scattering disrupts
0.94En
ergy
(eV
) 0
7×P0
15×P0
g pthe coherence of the electron/hole cyclotron orbit
0.93
PL P
eak
E
T = 190 K
cyclotron orbit
0.92 0 6 12 18 24 30B (T)
T 190 KGaAs
1-xBi
x- x = 8.5%
B (T)
G Pettinari et al Phys Rev B 81 235211 (2010)G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)
Magneto‐PL: data
At high power carrier scattering disrupts
T=5 KGaAs:Si
nSi
=1018 cm-3(e,A)
bbg p
the coherence of the electron/hole cyclotron orbit22T
24T26T28T30T
units
)
cyclotron orbitas found in degenerate GaAsand InN14T
16T18T20T22T
tens
ity (a
rb. u
and InN
06T08T10T12T
PL In
t
1.54µ = 0.049 m
0
1.42 1.46 1.5 1.54 1.58Energy (eV)
00T02T04T
1.52
1.53
ergy
(eV
) LL0
(e,A)Energy (eV)
1.51
Ene
me = 0.069 m
0 G Pettinari et al Phys Rev B 79 165207 (2009) 0 10 20 30
B (T)G. Pettinari et al., Phys. Rev. B 79, 165207 (2009)
Magneto‐PL: data
At high power carrier scattering disrupts
30TInN n=4×1017 cm-3
T = 5K
g pthe coherence of the electron/hole cyclotron orbitcyclotron orbitas found in degenerate GaAsand InNand InN
08T10T
682
02T04T06T
678er
gy (m
eV)
µ = 0.093 m0
600 620 640 660 680 700 720Energy(meV)
00T
670
674Ene
G. Pettinari et al., Phys. Rev. B 79, 165207 (2009) 0 8 16 24 32B (T)
Magneto‐PL: data
GaAs1-x
Bix - x = 0.6% T = 200 K 15 GaAs
1Bi
. . . back to GaAsBiun
its)
B = 30 T 10
15 1-x x
x = 0.6%
T = 200 Kfreeexciton
sity
(arb
. u 27 T24 T21 T18 T 5
10
E d (meV
)
PL In
ten
FE
15 T12 T09 T06 T 0
5
∆E
localizedexciton
1.2 1.3 1.4 1.5E ( V)
FE
FE GaAs
LE 03 T00 T 0 6 12 18 24 30
B (T)Energy (eV)
Localized excitons behave differently
Magneto‐PL: analysis
B i d d hif f i b
2
B‐induced shift of given by(see D. Cabib, E. Fabri, and G. Fiorio, Il Nuovo Cimento 10B, 185 (1972))
∑=∆5
*exc );( i
id cRBE γµ0 048
20P
0 = ~10 W/cm2
3×P0
7×P0
)2()( *exc RBe µγ h=
R* Rydberg
∑=1
exc );(i
id γµ - µ
exc= 0.048 m
0
- µexc
= 0.049 m0
- µexc
= 0.050 m0
10
∆E d (m
eV) 0
15×P0
R Rydberg exc 0
- µexc
= 0.049 m0
0
∆T = 190 K
-100 6 12 18 24 30
B (T)
GaAs1-x
Bix- x = 8.5%
( )
The exciton reduced mass does not depend on excitation power
Magneto‐PL: analysis
High‐temperature PL: free‐exciton or free‐carrier ?
18 T 185 KGaAs Free‐exciton: quadratic‐like
12
18 T = 185 KFree‐carrier: Landau levels form
6
E d (meV
)
µexc
= 0.059 m0
A bl
0
∆E
µ = 0 073 m
A more reasonable carrier reduced mass is found for exciton-like recombination
0 6 12 18 24 30B (T)
µLL
0.073 m0
recombination
Magneto‐PL: analysis
High‐ temperature PL: free‐exciton or free‐carrier ?
15
10
15
meV
)
60×P0 - µ
exc = 0.072 m
0
P0 = 5 mW - µ
exc = 0.071 m
0
(a) 10
15P
0 = 50 mW - µ
exc = 0.079 m
0
2×P0 - µ
exc = 0.080 m
0
(b)
meV
)
5
0
5
∆E d (m
T = 200 KGaAs
1Bi - x = 1.7%
0
5
T = 200 KGaAs Bi - x = 3%
∆E d (m
15 GaAs1 x
Bix
-50 6 12 18 24 30
B (T)
1-x x
0 6 12 18 24 30B (T)
GaAs1-x
Bix
x 3%
10
15
µ = 0.077 m0
(meV
)
1-x x
x = 5.6%T = 200 KP = 150 mW
5
∆Ed
T = 220 Kµ = 0.081 m
0
P = 200 mW
00 6 12 18 24 30
B (T)
Magneto‐PL: results
30 T = 200 Kx = 10.6%
GaAs1-x
Bix
GaAs
8.5%Non monotonic dependence of the
20
d (meV
)
0.6%
1.7%
dependence of the exciton reduced mass on Bi concentration
10
∆E d
4.5%
12 18 24 30B (T)
G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)
Magneto‐PL: results
20
30
GaAsx = 0.6%GaAs1-xBix
T = 200 K
x = 1.3%
x = 1.7%
0
10
30
10
20
30
x = 3.0%
x = 3.8%
x = 4.5%
∆E d (m
eV)
0
20
30x = 5.6%
x = 8.5%
x = 10.6%
∆
12 18 24 300
10
20
12 18 24 30
12 18 24 30
12 18 24 30
12 18 24 30
12 18 24 30 B (T) B (T) B (T)
G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)
Exciton reduced mass
0.08GaAs
1-xBi
x Non conventional compositional dependence
m0 )
compositional dependencek⋅pfollowed by a k⋅p‐like behavior
0.06
µ exc (m
behavior
0.040 2 4 6 8 10
x (%)
me∝m0(1+P2/Eg)‐1E *
e 0( / g)
mhh∝m0(2Q2/E *‐1)‐1
P2=28.9 eV, Q2=8 eV
Eg
, Q
G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)
R. N. Kini et al., J. Appl. Phys., 106, 043705 (2009)
Exciton reduced mass: what we learn
0.08 GaAs1-x
Bix
0 06 (m0 )
0.06
µ exc
0.040 2 4 6 8 10
x (%) 2500x (%)
Consistent with mobility data 1500
2000
2500
m2 V
-1s-1
)Consistent with mobility data
∆µ/µ ≈ ∆m/m ≈ 30%1000
1500
A/µexc
mobility
µ (c
m
5000 0.8 1.6 2.4
mobility
x (%)
Exciton reduced mass: what we learnExciton reduced mass: what we learnThe unexpected increase of the carrier pmass indicates a highly perturbed band structure.0.08 GaAs
1-xBi
x
The plateau value (0.08 m0) is not
0 06 (m0 )
conceivable with a perturbation exerting on the VB only.
1/µexc=1/me+1/mh0.06
µ exc
mh→∞, µexc=0.067m0The CB has to be perturbed, tooThe CB has to be perturbed, too
G. Ciatto et al., Phys. Rev. B 78, 035325 (2008)
0.040 2 4 6 8 10
x (%)
, y , ( )
x (%)
Tendency to Bi atom clusteringx=2.4%
Tendency to Bi atom clustering may perturb CB structure
G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)
. . . alternatively
h l l ( ) bl0.08 GaAs
1-xBi
xThe plateau value (0.08 m0) is not conceivable with a perturbation exerting on the VB only.The CB has to be perturbed, too
→ 0 067
0.06
µ exc (m
0 ) mh→∞, µexc=0.067m0
Bi is assumed to substitute As (valence 5)But Bi is usually trivalent due to large
0.040 2 4 6 8 10
But, Bi is usually trivalent due to large separation between 6s2 and 6p3 electrons (A. Zunger, private communication)
A rather strong tendency of Bi to0 2 4 6 8 10x (%)
A rather strong tendency of Bi to substitute for Ga could be expected
G
GaBiGa
AsBi
As
Bi In fact, . . .
Exciton reduced mass: what we learn
Exciton reduced mass: what we learnExciton reduced mass: what we learn
M Kunzer et al Phys Rev B 48 4437 (1993)M. Kunzer et al., Phys. Rev. B 48, 4437 (1993)
GaABi
GaBi Then, what CB structure
is expected forAs As is expected for (GaBi)As?
Exciton reduced mass: what we learn
0.08
k⋅p
GaAs1-x
Bix
The recovery of a conventional‐alloy behaviour above x>8%
i t t d t ti f
0.06
exc (m
0 )
points toward a restoration of a random atomic distribution of Bi atoms
0 04
µ e atoms.
0.040 2 4 6 8 10
x (%)A. Lindsay et al., Phys. Rev. B 77, 165205 (2008)
2
3i=1i=2i=3i=4
m* ho
st
InSbNGaSbN
1
2
m* al
loy/m
00 1 2 3 4x, nitrogen concentration (%) G. Ciatto et al., private communication
Exciton reduced mass: what we learn
0.08
k⋅p
GaAs1-x
Bix
The recovery of a conventional‐alloy behaviour above x>8%
i t t d t ti f
0.06
exc (m
0 )
points toward a restoration of a random atomic distribution of Bi atoms
0 04
µ e atoms.
0.040 2 4 6 8 10
x (%)
90
110
M (m
eV)
PL linewidth
50
70FWH
M
500 2 4 6 8 10
x (%) G. Ciatto et al., private communication
Exciton reduced mass: what we learn
0.08
k⋅p
GaAs1-x
Bix
Alternatively, the formation of Bi antisites is less likely above a
t i Bi t ti
0.06
exc (m
0 )
certain Bi concentration
0 04
µ e
0.040 2 4 6 8 10
x (%)
G
GaBiGa
AsBi
As
Bi
Conclusions
The peculiar dependence of the exciton reduced mass reveals an transition of the nature of the band extrema from impurity like totransition of the nature of the band extrema from impurity‐like to band‐like.
The compositional dependence of the carrier effective mass mirrors major changes occurring in the structural properties of the lattice:‐ disorder to order transition formation of Bi antisites highlighting the competing‐ formation of BiGa antisites highlighting the competing
characteristics of Bi as a metal and a group V element
The decrease in the carrier effective mass for x>8% turns out to be of particular interest in all those applications where carrierof particular interest in all those applications where carrier mobility is a relevant issue.