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Production of GaN Thin Films by Metalorganic CVD and Modelculer Beam Epitaxy

Emre Alan Suat Öner Işık Kübra Çelik Övgü Gençer A. Damla Serarslan Engin Hünder

İSTANBUL TEKNİK ÜNİVERSİTESİ

MBM511E – MODERN SURFACE MOD. TECH.

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Gallium Nitride

Properties of GaN

Structure of GaN

Applications

Processing Techniques

Metalorganic CVD

An Introduction to MOCVD

Application Example

Moleculer Beam Epitaxy

An Introduction to MBE

Application Example

Contents

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Gallium Nitride

GaN is semiconductor commonly used

in bright light emitting diodes (LEDs)

since 1990s.

Properties

GaN Crystalhttp://en.wikipedia.org/wiki/File:GaNcrystal.jpg

Wide and direct energy gap,

High heat capacity,

Environmentally friendly compared to Arsenic,

Resistance to effects of radiation.

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Gallium Nitride

Cubic (Beta) GaN

Zinc Blende

Meta Stable

Direct Energy Gap

(~3.2 eV)

Structure of GaN

Hexagonal (Alpha) GaN

Wurtzite

Stable

Direct Energy Gap

(~3.4 eV)

a

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Gallium Nitride

LED white lambs, Traffic lambs,

Full-color printers and scanners,

Key material for high frequency and high power transistors,

Blue-Ray Disc’s laser diode readers,

Nano scale electronics,

Solar cell arrays for satellites,

Microwave radio-frequency power amplifiers.

Applications

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Gallium Nitride

Metalorganic CVD (MOCVD)

Moleculer Beam Epitaxy (MBE)

Processing Techniques

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Metalorganic CVD

»A. Damla Serarslan, 521111001

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Metalorganic CVD

A chemical vapour deposition method of epitaxial growth of materials, especially compound semiconductors

The surface reaction: organic compounds or metalorganics + metal hydrides containing the required chemical elements

Formation of the epitaxial layer: pyrolysis of the constituent chemicals at the substrate surface

The growth of crystals is by chemical reaction

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Metalorganic CVD

Principle of operation: transport of precursor molecules (group-III metalorganics + group-V hydrides or alkyls) by a carrier gas (H2, N2) onto a heated substrate; surface chemical reactions.

The process takes place not in a vacuum, but from the gas phase at moderate pressures (2 to 100 kPa).

Wide application for devices such lasers, LEDs, solar cells, photodetectors

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Metalorganic CVD

(CH3)3In + PH3 = InP + 4CH4

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Metalorganic CVD

Reactors Chamber material must be nonreactive with

the chemicals being used. It must also withstand high temperatures. (stainless steel or quartz)

Components:• Gas handling system• Pressure maintenance system• Gas exhaust and cleaning system

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Metalorganic CVD

Gas Handling System

Carrier Gas

Material Sources

ReactorExhaust System

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Gas Handling System Gas is introduced via 'bubblers'. In a bubbler a carrier gas is bubbled through

the metalorganic liquid, which picks up some metalorganic vapour and transports it to the reactor.

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Metalorganic CVD

Material Sources Volatile precursor molecules transported by

the carrier gas Growth of III-V semiconductors:

• Group III: generally metalorganic molecules (trimethyl- or triethyl- species)

• Group V: generally toxic hydrides (AsH3; PH3 flammable as well); alternative: alkyls (TBAs, TBP).

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Application Example

Suat Öner Işık

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LOGOHigh Quality GaN Nanowires

Synthesized Using a CVD Approach

Blue light emitting diodes

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GaN is a new generation of semi conductors .

The growth of GaN nanowires over large area substrate is very important for the application of nanowires and need to be optimized.Control of morphology is also important because surface roughness will affect the near band-gap emissions.

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How can it be produced? High quality GaN nanowires are syntesized on a large

area Si substrate by direct reaction of gallium with ammonia using InCl3 as a catalyst.

A polished Si wafer of 10x20mm2 was cleaned in %80 HCl solution for 30 min and rinsed with distilled water.Thin layer of gallium melt is deposited on the surface of Sİ wafer and several drops of InCl3 ethanol solution are spread over the surface of the gallium layer.

The Si substrate is placed in a quartz boat in a tube furnace which evacuated to about 20mTorr and purged with argon.

The temperature of the furnace was increased to 920C at a rate of 30C/min under a constant flow of argon.Kept 920C for 20 min. under constant flow of ammonia.Then the furnace is cooled to room temperature,a layer of light yellow products can be visible on the surface of Si in the quartz boat.

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The sharp diffraction peaks reveal that GaN nanowires synthesized in high quality.

The products are first characterized by X-ray diffraction.

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It is visible that the GaN nanowires are grown over a large on the substrate.Very densed GaN nanowires.

The nanowires have a very smooth and straight morpology .

These GaN nanowires have extreme uniformity in diameter around 80nm,smooth morphology which is obviously advantageous in nanodevice applications.

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The catalysts play an important role in the synthesis of the nanowires.Eutectic liquid droplets’ (under proper temperature with the reactants ) diameter is very important for final diameter of nanowires.

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Introduction and Background

What is epitaxy?

Molecular Beam Epitaxy

MBE

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Experimental Methods

• Vacuum consideration• Growth chamber details• Growth characterization

and rate monitors• Beam flux, stoichiometry

A commercial MBE system delivered by VG Semicon

MBE

Illustration of the deposition chamber

MBE

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Diagnostic instruments for MBE

Auger Electron Spectroscopy(AES, SEM)

Ellipsometry Laser interferometric method Reflection High-Energy Electron

Diffraction (RHEED)Surface Acoustic Wave Devices

(Quartz Crystal Microbalances)

MBE

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Advantages of MBE Technique

Clean growth environmentPrecise control of the beam fluxes

and growth conditionEasy implementation of in situ

diagnostic instrumentsCompatibility with other high vacuum

thin-film processing methods (metal evaporation, ion beam milling, ion implantation)

MBE

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Molecular Beam Epitaxy in Industry

• Research & prototypes• High-frequency receivers – Portable phones – DIRECTV• Optoelectronics – DVD – Digital cameras• Superconductors – YBa2Cu3O7-d

MBE

Application Examples of GaN with MOCVD and Molecular Beam Epitaxy methods

Kübra ÇelikMalzeme Bilimi Ve Mühendisliği

521112003

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Ga2O3 Pulsed Laser Deposition on Conventional Sapphire Substrate

GaN Metalorganic Chemical Vapor Deposition (MOCVD) on Ga2O3

InGaN Light-Emitting Diode (LED) structure was successfully fabricated on the GaN/Ga2O3/sapphire

GaN-based semiconductors have been studied for their use in high-brightness green, blue, and white light-emitting diodes (LEDs); laser diodes; ultraviolet photo-detectors; and high power or high temperature microelectronic devices.

GaN heteroepitaxy; the growth of GaN on foreign substrates, is still a standard process in the optoelectronic industry.

The relatively low price and availability of sapphire make it one of the most suitable substrates for GaN heteroepitaxy

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The growth atmosphere played a more important role in the crystallinity of GaN on Ga2O3 thin film

N2 atmosphere and H2 atmosphere has been studied

The Ga2O3 interlayer completely decomposed within the surrounding H2 at the elevated temperature

Reduction reaction of Ga2O3 by H2 gas at high temperature

GaN formed as grains, not as a layer30

SEM micrograph of GaN grown on a Ga2O3 interlayer in an H2 ambient

It is clear that GaN formed as grains, not as a layer

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The light emitting images of the InGaN LED fabricated on the GaN/Ga2O3/sapphire with a 50 mA operating current are shown

High brightness blue emitting

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The growth of heavily Mg-doped GaN thin film on Si substrate by Molecular Beam Epitaxy

The wide band gap semiconductors of III-nitrides such as GaN, AlN and their alloys, have received considerable attention as ideal materials for optoelectronic and high-temperature/high-power devices due to their unique properties, such as large direct band gap, high breakdown field and high thermal conductivity

Mg-doped GaN could be converted into conductive p-type material by low-energy electronbeam irradiation (LEEBI)

The growth of GaN thin film on Silicon substrate has a number of advantages as compared to other substrates including lower cost, excellent wafer quality, and more design flexibility with current silicon

electronic circuit system33

The growth of heavily Mg-doped GaN thin film on Si substrate by Molecular Beam Epitaxy

P-type GaN on Si was normally grown by using molecular beam epitaxy (MBE) or metalorganic chemical vapor deposition (MOCVD).

MBE and MOCVD have been demonstrated and reported to be two of the advanced growth techniques for fabricating III-nitrides compound semiconductors with high crystal quality for device applications.

However, MBE offers a number of potential advantages over MOCVD for the growth of IIInitride materials.

For instances, more efficient use of source materials, higher accuracy in controlling the epilayers, as well as no requirement for post-growth annealing for the

activation of p-type dopant

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The growth of heavily Mg-doped GaN thin film on Si substrate by Molecular Beam Epitaxy

The growth of heavily Mg doped GaN on Si (111) by Plasma-assisted Molecular Beam Epitaxy (PAMBE) has been done.

The structural and optical characteristics of the grown p-GaN were analyzed

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References The growth of heavily Mg-doped GaN thin film on Si

substrate by Molecular Beam Epitaxy Thin Solid Film 2011 756-760

MOCVD growth of GaN on sapphire usingGa2O3 interlayer J. Of Electrochemical society 158 H1172 2011

R. L. Moon and Y.-M. Houng, in Chemical vapor deposition - Principles and applications, edited by M. L. Hitchman and K. F. Jensen, Academic Press, London, 1993

G. B. Stringfellow, Organometallic vapor phase epitaxy: theory and practice, Academic Press, Boston, 1989

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