In-situ monitoring of InGaAsN MQW structures - Laytec

MICRONOVA
In-situ monitoring of InGaAsN MQW
structures
Outi Reentilä
Micro and Nanosciences Laboratory
Micronova
Helsinki University of Technology (TKK)
Finland
LayTec in-situ seminar in Bratislava
June 3rd 2007
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MICRONOVA
http://www.micronova.fi/
OUTLINE
1. MOVPE growth of dilute nitrides
2. In-situ monitoring of thin layer growth
Slope method
QW composition using matrix method
3. Summary
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MICRONOVA
MOVPE GROWTH
Growth of dilute nitride MQW samples by low pressure Thomas Swan MOVPE
system, ex-situ characterization by HR-XRD, PL, AFM...
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MICRONOVA
Example, SESAM
structure:
Fabry-Perot oscillations
are observed during
growth of thick layers,
fine structure seen for
growth of thin InGaAsN
QWs (7 nm thick).
IN-SITU REFLECTANCE MONITORING
In-situ monitoring by LayTec’s EpiTT at 635 nm.
In-situ reflectance (632 nm)
0.50
0.45
0.40
0.35
0.30
0.25
In-situ monitoring of an absorber structure
on GaAs/AlAs Bragg mirror
growth of GaAs spacing layers
growth of MQW region
1000 2000 3000 4000 5000 6000 7000 8000
Time of growth (s)
fine structure
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MICRONOVA
SLOPE METHOD
• no complete Fabry-Perot oscillations
• increasing (decreasing) reflectance during QW (barrier) growth
Reflectance
0.309
0.305
0.301
0.297
0.293
QW
barrier
slope ∆R/∆ /∆ /∆t /∆
QW
barrier
QW
QW
barrier
barrier
1400 1500 1600 1700
Time (s)
T(setpoint)=575C
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MICRONOVA
SLOPE METHOD
Rough analysis of the QW composition using a slope method:
Slope of the 1st QW (10 -4 x1/nm)
12
9
6
3
0
15 %
17 %
12 %
7 %
In 0.18 Ga 0.82 As on GaAs
InGaAsN on GaAs
-1 0 1 2 3 4 5 6
QW nitrogen content (%)
GaAsN on GaAs
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MICRONOVA
Reflectance
MATRIX METHOD
For more sophisticated MQW in-situ analysis:
use of matrix method to calculate theoretical reflectance curves.
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
GaAs on GaAs
AlGaAs layer
GaAs layer
Temperature ramp
690 o C - 670 o C
measured
calculated
0 200 400 600 800 1000
Time of structure growth (s)
From simulation:
GaAs at 670°C
n = 4.2-0.3i
AlGaAs at 690°C:
n = 3.3-0.03i
(growth rates
determined by XRD)
O. Reentilä et al., J. Appl. Phys.
101 033533 (2007)
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MICRONOVA
Measured real and imaginary parts of refractive index of In xGa 1-xAs
QW as a function of In content x:
Imaginary part κ
-0.28
-0.30
-0.32
-0.34
-0.36
-0.38
-0.40
-0.42
InGaAs QWs AND THE MATRIX METHOD
GaAs
GaAs
0 5 10 15 20 25 30
InGaAs indium content (%)
Indium content more accurately from imaginary part (κ).
4.08
4.06
4.04
4.02
4.00
3.98
3.96
Real part n
O. Reentilä et al., J. Appl. Phys. 101 033533 (2007)
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MICRONOVA
Calculated curves for InGaAs/GaAs MQW structures (different indium
contents) using n and κ obtained by fitting to measured curves.
Reflectance change (%)
2.0
1.5
1.0
0.5
0.0
-0.5
InGaAs QWs AND THE MATRIX METHOD
50 100 150 200
Time (s)
25 %
20 %
15 %
10 %
5 %
O. Reentilä et al., J. Appl. Phys. 101 033533 (2007)
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MICRONOVA
Real part n
For (In)GaAsN:
• linear dependency between the imaginary part and [N]
• no dependency was found in the real part when [N] was varied
4.08
4.05
4.02
3.99
4.08
4.05
4.02
3.99
4.08
4.05
4.02
3.99
0 1 2 3 4 5 6
0 1 2 3 4 5 6
0 1 2 3 4 5 6
Nitrogen content (%)
InGaAsN QWs AND THE MATRIX METHOD
0 % In
12 % In
17 % In
Imaginary part
-0.30
-0.35
-0.40
-0.45
-0.50
GaAs
In 0.12 GaAs
In 0.17 GaAs
0 % In
12 % In
17 % In
C(0) = -1.078
C(0.12) = -1.62
C(0.17) = -2.44
0 1 2 3 4 5
InGaAsN nitrogen content (%)
O. Reentilä et al., Appl. Phys. Lett. 89, 231919 (2006)
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MICRONOVA
SUMMARY
• Dilute nitride samples fabricated by low-pressure MOVPE
system were studied by in-situ reflectometry and several exsitu
measurements
• Growth of MQW structures can be monitored and the layers
(at least partially) analysed during growth
• More work is needed to resolve
• the effect of strain on the refractive index
• in-situ monitoring of the growth rate AND the refractive index
at the same time, i.e., full in-situ characterization of the MQW
structures
• the reason why n is not changing when the nitrogen content is
varied
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MICRONOVA
RELATED PUBLICATIONS
O. Reentilä, M. Mattila, M. Sopanen, H. Lipsanen, Nitrogen content of GaAsN quantum
wells by in-situ monitoring during MOVPE growth, Journal of Crystal Growth, 290 345-349
(2006)
O. Reentilä, M. Mattila, L. Knuuttila, T. Hakkarainen, M. Sopanen, H. Lipsanen, In situ
determination of nitrogen content in InGaAsN quantum wells, Journal of Applied Physics,
100 013509 (2006)
O. Reentilä, M. Mattila, L. Knuuttila, T. Hakkarainen, M. Sopanen, H. Lipsanen, Comparison
of H2 and N2 as carrier gas in MOVPE growth of InGaAsN quantum wells, Journal of Crystal
Growth, 298 536-539 (2007)
O. Reentilä, M. Mattila, M. Sopanen, H. Lipsanen, In-situ determination of InGaAs and
GaAsN composition in multi-quantum-well structures, Journal of Applied Physics, 101
033533 (2007)
O. Reentilä, M. Mattila, M. Sopanen, H. Lipsanen, Simultaneous determination of indium
and nitrogen contents of InGaAsN quantum wells by optical in-situ monitoring, Applied
Physics Letters, 89 231919 (2006)
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MICRONOVA
ACKNOWLEDGEMENTS
M. Sc. Marco Mattila
Dr. Teppo Hakkarainen
Dr. Lauri Knuuttila
Docent Markku Sopanen
Prof. Harri Lipsanen
Micro and Nanosciences Laboratory, Micronova
Helsinki University of Technology
Finland
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