A. Molina-Sánchez*, J. Segura-Ruiz, N. Garro, A. …III-N Nanowires InN: Properties and...
Transcript of A. Molina-Sánchez*, J. Segura-Ruiz, N. Garro, A. …III-N Nanowires InN: Properties and...
A. Molina-Sánchez*, J. Segura-Ruiz, N. Garro, A. Garcia-Cristobal, A. Cantarero, F. Iikawa,
C. Denker, J. Malindretos, and A. Rizzi
Niza, 9 de Mayo de 2011
III-N NanowiresInN: Properties and accumulation layer
Electronaccumulation at the surface(films)
Reassigned bangap around 0.67 eV
Transport experiments point theexistence of the electron
accumulation layer
rrgDD 2
2
3
2
conductance g vs the radius r
6.1rg measured
Nano Letters B 9, 1567 (2009)
III-N NanowiresInN NWs: Photoluminescence experiments
Courtesy of J. Segura-Ruiz & C. Denker
0.6 0.7 0.8 0.9 1.0
PL,
PLE
yie
ld (a
rb. u
nits
)
Energy (eV)
InN NWs samples grown under differentconditions
Photoluminescence
Blue‐shift of the emission energy (differentelectron concentration?)
Broadening increases with the emissionenergy.
Photoluminescence excitation
Blue‐shift and slope are different for eachsample. Higuer slopes for samples with higherabsorption edges.No exciton related peaks .
III-N NanowiresSelf-consistent modeling
Schrödinger eq.
Wave functions : Poisson eq.
n(r)= f (EF)||2
Fermi level and electron density
V(r)Potential energy
Until convergence
Donor surface statesrelease electronsinside the NW
n(r)
InN nanowire Nss+
Uniform distribution of donors in the volume
+ND+ Electrons occupy the
energetic levelsdetermined by thepotential energy
EFermi
n(r)
V(r) Nss+
radius
energy
Calculation of conduction and valence band states
Optical absorption (comparisonwith experiments)
0 10 20 30 40
-1.0
-0.5
0.0
1017
1018
1019
V -
E c (eV
)
r (nm)
EF-Ec
n (c
m-3
)
(2,0)
(1,0)
III-N NanowiresPotential profile and electron distribution
Electron density. Highconcentration near to the NW surface
The potential energy fallsat the NW surface. Itdetermines the electronicstates
The potential energyconfines the electronwave functions near tothe NW surface
ND = 31017 cm-3
Nss = 11013 cm-2
++
III-N NanowiresOptical absorption of InN NWs. Influence of size
Blue‐shift of the absorption edge fordecreasing NW size
0.6 0.7 0.8 0.9 1.0 1.1
15 30 45
0.7
0.8
0.9
-bulk
(a
rb. u
nits
)
Energy (eV)
Ene
rgy
(meV
)R (nm)
50
40
20
10
ND = 31017 cm-3
Nss = 11013 cm-2
++
Reduction of the absorption intensitywith respect to the non‐degeneratebulk spectrum
Confinements effects are onlyAppreciable for radius < 15 nm
III-N NanowiresOptical absorption of InN NWs. Influence of doping
0.65 0.70 0.75 0.80 0.85
(a
rb. u
nits
)
Energy (eV)
ND = 1017 cm-3
Nss = 1012 cm-2
Nss = 1013 cm-2
+
++
ND = 51017 cm-3
Nss = 1012 cm-2
Nss = 1013 cm-2
+
++
Different effects of ND and Nss on the absorption profile+ +
The increase of ND blue‐shifts theabsorption edge
+
The increase of Nss reduces theabsorption intensity
+
0
EFEc V(r)
Ev V(r)
III-N NanowiresComparison with PL and PLE experiments
0.6 0.7 0.8 0.9 1.0
PL,
PLE
yie
ld (a
rb. u
nits
)
Energy (eV)
G532
G041
G136
G044
(i) Excitation and relaxation(ii) Emission
Eemission
Pem
Prel
EexcitationPabs
The PLE spectra exhibit a blue‐shift Agreement of theoretical absorption with PLE spectra for excitation energy < 0.9 eVThe PL broadening increases with the increasing of the absorption edge
PLE experiment
InN NWs grown under different conditions
III-N NanowiresComparison with PL and PLE experiments
The determined doping concentrations are in the range of the reported experimental values
Sample ND (1017 cm‐3) Nss (1013 cm‐2)
G532 0.8 2.5
G041 2.0 2.4
G136 5.0 1.7
G044 7.5 1.4
Doping level is associated to the growth conditions
Broadening increases with the Fermi energy
EFEc V(r)
Ev V(r)
Small Fermi energy
EF
Ec V(r)
Ev V(r)
High Fermi energy
Eemission Eemission
III-N NanowiresConclusions
• Effective‐mass approximation is an alternative to solveself‐consistent problems. For instance, the determination of the electron distribution in InN NWs.
• Optical absorption of InN NWs with electron accumulationlayer exhibits a blue‐shift that depends on:
• NW size.• Doping concentration.
• Agreement of the theoretical absorption spectra with thePLE spectra (deduction of the doping level).
THANK YOU FOR YOUR ATTENTION
III-N NanowiresQuestions
01 ii ?
noyesEND
Initial Potential EnergyV(r)
eEV c
1
2
3
4
Schrödinger Eq.
electronic structure
charge density&
Fermi energy
Poisson Eq.electrostatic potential i(r)
Check convergence