1 properties of gan films grown by atomic layer deposition using low-temperature iii-nitride...
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Properties of GaN Films Grown by Atomic Layer Deposition Using Low-temperature III
-nitride Interlayers
J. R. Gong
Department of Materials Science and Engineering
Feng Chia University
June 4, 2004
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Co-workers
C. L. Wang B. H. Shih
Y. L. Tsai I. H. Chien
W. T. Liao S. W. Lin
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OUTLINE
Applications of III-nitrides
Fundamental aspects of ALD
LT-III-nitride interlayers
— LT-GaN interlayer
— LT-AlN interlayer
— Ternary LT-AlGaN interlayer
Conclusions
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Elemental and compound semiconductors
Column IV: Si, Ge, SiGe, SiC
Column III and V: GaAs, InP, InAs, InSb, GaN and alloys
Column II and VI: ZnSe, CdS, HgTe and alloys
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Semiconductor bandgaps
UV-wide bandgap (GaN, ZnSe)
IR-narrow bandgap (InSb, HgTe)
Direct (mostly III-V):
light emission possible LEDs, Lasers
Indirect (mostly Si):
light emission forbidden transistors, ICs
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Bandgap engineeringUV region
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Research and development history of GaN
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Direct band gap
The adjustability of band gap from 1.9eV (InN)
to 6.2eV (AlN)
Good radiation hardness
High temperature resistance
Advantages of III-nitrides
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Applications of III-nitride devices
HBLEDs
— traffic signal
— full-color outdoor display
— back light for LCD
LDs
— DVDs
High Power Electronics
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Markets for nitride-based LEDsMarkets for nitride-based LEDs
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Reacting speed of LEDs is 20 times faster than traditional light bulbs.
LED traffic signal
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Outdoor full-color LED display
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LCD backlight
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LED car indicators
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LED general lighting
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LED Chip
substrate
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Atomic Layer Deposition
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Photographs of the home-made ALD growth system
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R.F. Coil
Quartz
Exhaust
SusceptorTMG
NH
N
H
HydrogenPurifier
Three-wayValve
RegulatorValveMass FlowController
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2
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TMA
A schematic diagram of the ALD system for the growth of III-nitride films
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A schematic diagram of the rotating susceptor for ALD process
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Fundamental aspect of atomic layer deposition (ALD)
An ideal ALE growth cycle produces a monolayer AB compound.
(B)(A)
AX
(C)
BY
(D)
AB (monolayer)
AB(sub.)
AB(sub.)
AB(sub.)
AX
AB(sub.)
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Influence of low temperature GaN intermediate layers on the
properties of GaN films
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A schematic structure of HT-GaN films without LT-GaN interlayer
sapphire
AlN buffer layer
HT-GaN 150, 380, 600 nm
HT: 1000 ℃
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(a) (c)(b)
SEM micrographs of the surface morphologies of
HT-GaN films grown on (0001) sapphire substrates
150 nm 380 nm 600 nm
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Schematics of HT-GaN films inserted with LT-GaN interlayers
sapphire
AlN buffer layer
HT-GaN(150 nm)
LT-GaN interlayer (7 nm)
HT-GaN(230 nm)
sapphire
AlN buffer layer
HT-GaN(150 nm)
sapphire
AlN buffer layer
HT-GaN(150 nm)
LT-GaN interlayer (20 nm)
HT-GaN(230 nm)
LT-GaN interlayer (70 nm)
HT-GaN(230 nm)
sapphire
AlN buffer layer
HT-GaN(380 nm)
(a) (b) (c) (d)
LT: 500 ℃
HT: 1000 ℃
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(a) (b)
(c) (d)
SEM surface morphologies of HT-GaN films
inserted with a LT-GaN interlayer
0 nm
20 nm
7 nm
70 nm
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The role of LT-GaN interlayer on the growth of HT-GaN film
The arrangement of Ga adatoms is merited by the suppression of surface kinetics at low growth temperatures, which is believed to stop the extension of mosaic structure from the underlying 150 nm-thick HT-GaN film during the growth of LT-GaN interlayer.
A LT-GaN interlayer thickness deviated away from its optimised value was observed to deteriorate the quality of the subsequently grown HT-GaN film.
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RT PL spectra of HT-GaN films inserted with different LT-GaN interlayer thicknesses
(The inset shows the effect of interlayer thickness on the PL emission energy)
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(0002) DCXRD curve of a HT-GaN film inserted
with a 20-nm-thick LT-GaN interlayer
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Cross-sectional TEM image of a HT-GaN film
inserted with a 20-nm-thick LT-GaN interlayer
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A schematic structure of GaN films having various LT-GaN interlayer thicknesses
sapphire
AlN buffer
LT-GaN
HT-GaN0.9 m
HT-GaN0.6 m
25Å<d<300Å
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RT PL spectra of GaN films inserted with LT-GaN interlayers having different thicknesses
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PL linewidth of GaN films inserted with LT-GaN interlayers having various thicknesses
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Influence of low temperature AlN intermediate layers on the p
roperties of GaN films
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A schematic structure of GaN films having various LT-AlN interlayer thicknesses
sapphire
AlN buffer
LT-AlN interlayer
HT-GaN0.9 m
HT-GaN0.6 m
25Å<d<125Å
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RT PL spectra of GaN films inserted with AlN interlayers having different thicknesses
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PL linewidth of GaN films inserted with LT-AlN interlayers having various thicknesses
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Influence of low temperature AlGaN intermediate layers on th
e properties of GaN films
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A schematic structure of GaN films having various LT-AlxGa1-xN interlayer thicknesses
sapphire
AlN buffer
LT-AlxGa1-xN
HT-GaN0.9 m
HT-GaN0.6 m
25Å~200Å
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RT PL spectra of GaN films having 2.5 nm-thick LT-AlGaN interlayers with different Al contents
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RT PL spectra of GaN films having 5 nm-thick LT-AlGaN interlayers with different Al contents
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RT PL spectra of GaN films having 7.5 nm-thick LT-AlGaN interlayers with different Al contents
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RT PL spectra of GaN films having 10 nm-thick LT-AlGaN interlayers with different Al contents
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PL linewidth of the GaN films versus the Al content of the 2.5 nm-thick LT-AlGaN interlayer
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PL linewidth of the GaN films versus the Al content of the 5nm thick LT-AlGaN interlayer
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PL linewidth of the GaN films versus the Al content of the 7.5nm thick LT-AlGaN interlayer
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PL linewidth of the GaN films versus the Al content of the 10nm thick LT-AlGaN interlayer
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RT PL spectra of GaN films inserted with different Al0.6Ga0.4N interlayers thicknesses
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PL linewidth of GaN films inserted with LT-Al0.6
Ga0.4N interlayers having various thicknesses
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Conclusions
HT-GaN films inserted with LT-GaN interlayers having optimized thickness show improved surface morphology and enhanced near band-edge PL intensity when compared with that of a HT-GaN film without any LT-GaN interlayer.
The insertion of LT-GaN interlayers in HT-GaN films was found to reduce the compressive strain in HT-GaN films.
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Conclusions
The insertion of a LT-AlxGa1-xN interlayer in a HT-GaN film was found to improve the optical properties of the film considerably when the thickness of interlayer is below a certain value.
It appears that the optimized interlayer thickness for the HT-GaN films having LT-AlxGa1-xN interlayers with a specific Al-content decreases as the Al composition in the interlayer increases.
The high Al-content LT-AlxGa1-xN interlayer was observed to block some of the threading dislocations (TDs) originated from the underlying GaN layer based on the studies of cross-sectional TEM.
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