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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

2

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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Thanks for your patience!