Sub-bandgap photoluminescence in
InGaAs/InAsP heterostructures
lattice-mismatched to InP substrates
J. Peter Campbell and Tim Gfroerer
Davidson College, Davidson, NC
Mark Wanlass
National Renewable Energy Laboratory
Project supported by Research Corporation and the
American Chemical Society – Petroleum Research Fund
Previous Work
• Previous work
provides indirect
evidence that
increasing lattice
mismatch changes
the distribution of
defect levels.
Increasing Mismatch
Motivation
• Can we find direct
evidence for these
defect levels?
• Sub-bandgap PL
spectra may reveal
the states.
Increasing Mismatch
Phonons (Heat)
Photons (Light)
Fourier Transform IR Spectroscopy
1.00E-03
1.00E-02
0.00E+00
1.00E-03
-1.00E-03
Fourier
-2.00E-03
1.00E-04
-3.00E-03
1.00E-05
-4.00E-03
Transform
-5.00E-03
-6.00E-03
-200.00
-150.00
-100.00
-50.00
0.00
50.00
100.00
150.00
Interferogram
200.00
1.00E-06
1.00E-07
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
Spectrum
1.20
1.30
1.40
Sample Structure
• Bandgap Series:
Increased [In] in
active layer increases
lattice mismatch
relative to substrate.
• Buffer Series:
Varying [As] in InAsP
buffer layer optimizes
active/buffer layer
interface.
InGaAs
Substrate
(InP)
DEFECT
Bandgap Series Spectra
1.E+16
1.E+14
T = 77K
[In] = 0.53
0% MM
Intensity (arb. units)
1.E+12
1.E+10
[In] = 0.60
0.46% MM
1.E+08
1.E+06
[In] = 0.66
0.87% MM
1.E+04
1.E+02
[In] = 0.72
1.28% MM
1.E+00
1.E-02
1.E-04
[In] = 0.78
1.69% MM
1.E-06
0.30
0.40
0.50
0.60
Energy (eV)
0.70
0.80
0.90
Temperature Dependence
Arrhenius Plot for Bandgap-Series 0.53 eV peak
-15.00
PL Intensity = eEa / kT
-15.50
LN (PL Intensity)
-16.00
-16.50
[In]=0.53
-17.00
[In]=0.60
-17.50
Thermal Activation Energies
-18.00
[In] = 0.53, Ea = 24 +/- 6 meV
[In] = 0.60, Ea = 24 +/- 3 meV
-18.50
-19.00
50
70
90
110
1 / kT (eV)
130
150
170
Conclusions and Future Work
• Nonradiative transition from mid-gap states
appear to be phonon-assisted (phonon
energy ~ 30 meV)
• Shallow states can result when the
buffer/active interface is mismatched.
• Transient Capacitance Spectroscopy will be
used to further characterize sub-bandgap
energy levels. (Summer 2003)
Buffer Series Spectra
1.00E+07
T = 77K
[As] = .43
Intensity (arb. units)
1.00E+04
[As] = .52
1.00E+01
[As] = .59
1.00E-02
[As] = .62
1.00E-05
[As] = .70
1.00E-08
0.20
0.30
0.40
0.50
Energy (eV)
0.60
0.70
Buffer Series Results
[As] in InAsP Lum Intensity Lum Intensity
.35 eV Peak .45 eV Peak
(arb. units)
(arb. units)
0.43
0.52
0.59
0.62
0.7
2
3
7
8
6
0
6
26
686
0
• All samples have an unidentified peak near
0.35 eV.
• Peak B is strongly [As] dependent.
• Other studies show that [As] = 0.52, 0.59
have the highest radiative efficiency.
Temperature Dependence
Arrhenius Plot for Bandgap-Series .53 eV peak
-15.00
y = 2.43E-02x - 1.91E+01
2
R = 8.99E-01
-15.50
-16.00
y = 2.40E-02x - 1.92E+01
R2 = 9.75E-01
LN (Lum)
-16.50
Ea/kT
Lum = e^
LN (Lum) = Ea (1/kT)
-17.00
-17.50
[In] = .53
[In] = .60
The slope of this plot is a measure of the
thermal activation energy of the defect state
causing this luminescence.
-18.00
[In] = .53 Ea = 24 +/- 6 meV
[In] = .60 Ea = 24 +/- 3 meV
-18.50
-19.00
50
70
90
110
1/kT (eV)
130
150
170
Bandgap Series Spectra
1.E+16
1.E+14
[In] = .53
1.E+12
0% MM
Intensity (arb. units)
1.E+10
[In] = .60
.46% MM
1.E+08
1.E+06
[In] = .66
.87% MM
1.E+04
1.E+02
1.E+00
[In] = .72
1.28% MM
1.E-02
1.E-04
[In] = .78
1.69% MM
1.E-06
0.30
0.40
0.50
0.60
Energy (eV)
0.70
0.80
0.90