iii-nitride quantum materials and nano-structures for new ... · • blue led 1997 (nakamura &...

Zhe Chuan Feng, White LED, 2007 July

III-Nitride Quantum Materials and Nano-structures for New

Generation Light Emitting Devices

Zhe Chuan Feng (馮哲川)Professor, National Taiwan University

Graduate Institute of Electro-Optical Engineering & Department of Electrical Engineering, Taipei, Taiwan, ROC

{國立台灣大學光電工程學研究所暨電機工程學系}Tel: +886-2-3366-3543; E-mail: [email protected]

Web: http://eoe.ntu.edu.tw/; http://ee.ntu.edu.tw/


Blue and White Light Emitting Devices

- New Era of Solid-State Lighting

Part-I :


• General– Historical Developments in Lighting for human being -

• News & information from Blue 2005• Semiconductor LED & Lighting in Taiwan• R&D from LumiLEDs• Basis of LED and Technology

– Semiconductor LED, MQW LEDs, Resonance Cavity LEDs– Phosphor Technology - Organic LED

• Fabrication Technology - Semiconductor LED – MOCVD growth of III-Ns, Characterization, Processing– LED Fabrication Technology

• Marketing and further Development for LEDs– LED advantages in comparison with others– More applications & future development


GENERAL GENERAL -- Lighting HistoryLighting History

• Burning wood ~50,000 years ago• Gas Lighting ~1772• Electric Lighting ~1876• Incandescent Filament Lamp ~1879 (Swan & Edison) • First LED 1907 SiC (H.J. Round)• Fluorescent Lamps 1938• Red LED 1962 (Holonyak & Bevacqua) - AlInGaP 1990’s• Blue LED 1997 (Nakamura & Fasol)


Revolutions in Solid State Electronics andRevolutions in Solid State Electronics and OptoelectronicsOptoelectronics

1940-1950

1980-2000

1990-2020+

Vacuum tubes Transistors

CRTTV

Flat PanelTV /

Displays

Solid State Lighting

Light bulbs


0.01

0.1

1

10

400 450 500 550 600 650 700Wavelength (nm)

InGaN AlInGaP

AlGaAs

GaAsP GaAsPGaP:N

SiC

Color: Ultra-violet Blue Green Yellow Orange Red Infra-Red

Better

Worse

Luminous

IntensityLow PerformanceCommodity LEDs

LEDS LEDS –– Material Systems, Colors and BrightnessMaterial Systems, Colors and Brightness

LightLight EmittingEmitting DiodesDiodes ((LEDsLEDs))

Materials – High Birght & White LED - OLED


Applications ofApplications of LEDsLEDs

After Compound Semiconductor Magzine


Human EyeHuman Eye

Based on empirical data of human

vision


Semiconductor LEDand

Semiconductor Lighting in Taiwan


People interested in LED show


Some technical issues in Semiconductor LED & Lighting


Lattice Constant Lattice Constant vsvsBandgapBandgap


InGaNInGaN//GaNGaN MQW LED on MQW LED on sapphiresapphire


Resonant Cavity Nitride-LED


AlGaInP LEDsAlGaInP LEDs


Blue/UV LED Pump Source for PhosphorsBlue/UV LED Pump Source for Phosphors

• GaN based LEDsgenerate UV light

• UV light is absorbed by appropriate phosphor(s)

• Phosphor converts UV radiation to light of desired colors

• White light generation by phosphor mixing

Contacts

(InAlGa)N

n-GaNUV/Blue

Phosphor Layer

VISIBLE EMISSION

p-GaN


LED Strings, Drive Circuits, AssemblyLED Strings, Drive Circuits, Assembly


• Epitaxy of materials• Characterization of epitaxy

structural materials

• Processing• Packaging• Device Tests

LED Fabrication TechnologyLED Fabrication Technology


Crystal Growth Techniques

•Liquid Phase Epitaxy (LPE) (no GaN or InGaAlP)In LEDs - used mostly for IR and AlGaAs red LEDs

•Vapor Phase Epitaxy (VPE) (hydride VPE or HVPE)

In LEDs - used mostly for low brightness GaP and GaAsP LEDsAlso used by HP for GaP window growth on HB AlInGaP LEDsStarting to be used in GaN for “substrate” growth

•Metal Organic Chemical Vapor Deposition (MOCVD)(OMVPE, MOVPE: Metal Organic Vapor Phase Epitaxy) - Most widely used technique for High Brightness LEDs

•Molecular Beam Epitaxy (MBE)


MOCVD System


Flow Patterns During MOCVD GrowthFlow Patterns During MOCVD Growth

Computer Generated Flow Patterns in Rotating Disc System

Smoke Flow Patternsin Rotating Disc System

Data Courtesy of Sandia National Laboratories


LED processingLED processing


General Blue LED Process General Blue LED Process FlowFlow

N-GaNIn-GaNP-GaN

PR Strip

N-GaNIn-GaNP-GaNNi/Au

Metal Lift-off

N-GaN

In-GaNP-GaNNi/Au

Al/Ti/Pt/Au

Ni/Au

Metal Lift-off

N-GaN

In-GaNP-GaNNi/Au

Al/Ti/Pt/Au

Resist Resist

Photo Level 4N-GaN

In-GaNP-GaNNi/Au

Al/Ti/Pt/Au

Resist Resist

Ni/Au

Evaporation

N-GaNIn-GaN

ResistP-GaN

Photo Level 1

Oxidation

Contact Alloy

Native Oxide Removal

N-GaN

In-GaNP-GaNNi/Au

Al/Ti/Pt/Au

Metal Lift-off

ContactAlloy

P-metal Alloy

Photo Level 2

N-GaN

In-GaNP-GaNNi/Au

Resist

Mesa Etch :

Transparent Contact:

N-layer Metal:

P-bonding Pad:

N-GaN

In-GaNP-GaNNi/Au

Resist

Evaporation

Al/Ti/Pt/Au

N-GaNIn-GaN

ResistP-GaN

RIE

Resist

Photo Level 3

N-GaNIn-GaNP-GaN

Resist Resist

N-GaNIn-GaNP-GaN

Resist Resist

Evaporation

Ni/Au


Standard GaN LED Fab ProcessesStandardStandard GaNGaN LEDLED FabFab ProcessesProcesses

p GaN

SUBSTRATE

Active Region

n GaN

Semi-transparent contact formation

p GaN

SUBSTRATE

Active Region

n GaN

Semi-transparent contact

Mesa and isolation etch

p GaN

SUBSTRATE

Active Region

n GaN

Passivation formation


p GaN

SAPPHIRE SUBSTRATE

Active Region

n GaN

SiO2Semi-Transparent

Contact

P-pad

N-padGaN:Mg (p-doping)

(Ga,In)N Active Layer

Nucleation Layer

Contract geometry

P-type contact

A Standard GaN Blue LED Chip


White LED Technology: Binary complementaryWhite LED Technology: Binary complementary

• Wavelength– Blue GaN 470nm– YAG 572nm

400 500 600 7000.0

0.5

1.0

1.5

T=4500 KRa=90K=330 lm/W

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)


New Packaging (New Packaging (LuxeonLuxeon//LumiledsLumileds))

Emitter

Star

Line

Ring


LED PackagingLED Packaging


Imperative forLighting

Applications

High-Power LED

LED Output Power Improvement

High Internal Efficiency Material

Efficient Light ExtractionChip

High Operating Current

High Current Density

Large Chip

Theoretical limit is 30 Lm at 20mA!

1000 Lm


Organic LightOrganic Light--Emitting Diode (OLED)Emitting Diode (OLED)

(from IBM Almaden)

Organic light-emitting devices (OLEDs) operate on the principle of converting electrical energy into light, a phenomenon known as electroluminescence. In its simplest form, an OLED consists of a layer of this luminescent material sandwiched between two electrodes. When an electric current is passed between the electrodes, through the organic layer, light is emitted with a color that depends on the particular material used.


OLED: Physics and FabricationOLED: Physics and Fabrication

(from Univ. of Arizona)

An electric field is applied to the device. On the ITO layer, holes are induced into the hole-conducting polymer layer At the same time, electrons from the cathode are injected in the electron-conducting layer.

OLEDs: on a transparent substrate, the first electrode deposited (~100nm), one or more organic layers coated by either thermal evaporation or spin coating of polymers (~100 nm), metal cathode (such as magnesium-silver alloy, lithium- aluminum or calcium) evaporated on top (~100 nm).


LED Markets, Advantages & FuturesLED Markets, Advantages & Futures


LED Efficiency LED Efficiency SummarySummary


More More Fascinating Fascinating

Applications of Applications of Semiconductor Semiconductor & White& White LEDsLEDs


High-Brightness LEDs – Some New Applications


The World’s First Operation under only LED Lighting

Junichi Shimada Department of Thoracic Surgery, Kyoto Prefectural University of Medicine and Division of Surgery, Kyoto Prefectural Yosanoumi Hospital, Japan


LEDs in Cars - 2


LEDs in Car - 3


LEDs in Cars - 1


White & Blue Light Devices will

be quickly and widely developed

and applied in Science,

Technology and Human Life


Part-II

InGaN/GaN Multiple Quantum Well Light Emitting Diodes:

Basic Mechanisms of

Energy-Efficient Luminescence


2.5 3.0 3.5

M O C V D

Q W 8a

PL

Inte

nsity

(a.u

.)

Energy (eV)

Tem p. : 9K 16K 20K 30K 40K 50K 70K 90K 110K 140K 170K 200K 250K 300K

14.09m W

InGaN/GaN 8QW s(W) 1.2nm (B) 3nm 8-QWs x(In)=17.8%

Left:Emissions- QW

Right:Emissions- GaN barriers

InGaN/GaN 8QWs: Temperature dependent PL

Temperature dependent PL


0 50 100 150 200 250 3002.6

2.7

3.4

3.5

Peak

Ene

rgy

(eV)

Temperature (K)

InGaN/GaN 8QWsQW8a

GaN band

MQW emission

0 20 40 60 80 100

0.3

0.4

0.5

0.6

0.7

0.80.9

11.1

InGaN/GaN 8QWs

Internal quantum efficiency (IQE)at 300K = 34.8%

Inte

grat

ed P

L In

tens

ity (a

.u.)

1000 / T (K-1)

PL peak position versus T (9–300 K)

η(Internal Quantum Efficiency):The time integrated photoluminescence intensity at room temperature normalized to a low temperature (9K) value

(W) 1.2nm / (B) 3nm x 8 x(In) : 17.8%Varshni Eq. for Eg(GaN) – T:E(T)=E(0)-αT2/(β+T)E(0) =2.7015 eV

α = 0.368 meV/K, β = 618 K

Anomalous T-behavior of MQW PL peak is attributed to band-tail states due to inhomogeneities in the InGaN-based material.

InGaN/GaN 8QWs: Peak position & Arrhenius plot


2.0 2.5 3.0 3.50.0

0.5

1.0 InGaN/GaN 8QWs

PL

PL

Inte

nsity

(a.u

.)

Energy (eV)

PLE

216meV

QW 8a

Comparison of RT PL and PLE spectra from a MOCVD-grown InGaN-GaNMQW (8-QWs) sample – Quantum confined Stark effect (QCSE).

InGaN/GaN 8QWs: PL & PLE spectra

Photoluminescence excitation (PLE)


TRPL of InGaN/GaN QWs

TRPL Dependences on Excitation power variation Detection λ

M. Pophristic, F.H. Long, C.A. Tran, R.F. Karlicek, Z.C. Feng & I. Ferguson, “Time-resolved spectroscopy of InxGa1-xN multiple quantum wells at room temperature”, Appl. Phys. Lett. 73, 815-817 (1998).


InGaN MQW LEDRE26461 nm 10kt1 = 23.02 ns

fitting begins at 1ns(a)

0 40 80 120 160

fitting begins at 1ns

461 nm 240Kt1 = 3.81 ns

time (ns)

0 50 100 150 200 250 300

InGaN MQW LEDRE26T

ime

Con

stan

t (ns

)

Temperature (K)

• T-dependence of lifetime (10-300 K), measured at PL peak -462 nm.

• Typical TRPL data and fittings at two temperatures of 10 and 240 K.• A single-exponential fit - determine the lifetime.

TRPL on newly MOCVDTRPL on newly MOCVD--growngrown InGaNInGaN//GaN MQWsGaN MQWs


2.0 2.5 3.0

fitInGaN MQW LEDRE26

PL

lifet

ime

(ns)

Photon Energy (eV)

PL

inte

nsity

(a.u

.)

2

3

4

5

6

0 10 20 30 40

----- laser----- fit

InGaN MQW LEDRE26440 nm (2.817 eV)t1 = 2.51 ns

PL

inte

nsity

(a.u

.)

(a)

time (ns)

• TRPL data and fittings atλ=440 nm. Fittingbegins at about 1.5 ns in order to avoid the laser response.

• The RT TRPL was measured from 436nm to 492nm, with 15 points. The t PL values increase with decreasing photon energy.

• This is characteristic of the localized system. The depth of localization can be evaluated by assuming the exponential distribution of the density of tail states and by fitting the photon energy dependence of the t PL values using the equation:

(A pulsed laser 374 nm)

TRPL ofTRPL of InGaNInGaN//GaN MQWsGaN MQWs: dependence on photon energy: dependence on photon energy


TRPLTRPL

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.00.0

200.0

400.0

600.0

800.0

1.0k

1.2k

He-Cd laser: 372.5nm

InGaN MQW25-re35TRPL: 446nmSlit: 0.5mmTime: 60s

Time(ns)

TRP

L In

tens

ity(a

.u.)

0

100

200

300

400

500

600

700

Laser TRP

L Intensity(a.u.)

0

exp1)(

EEE

Eme

radPL −

+=

ττ

2.0 2.5 3.0

535

540

545

InGaN MQW25-re35PLSlit: 0.5mmTime: 0.1s

Energy(eV)

TRP

L In

tens

ity

fit

4

6Data: re35f4d1_CModel: user2 Equation: y=p1/(1+exp((x-p2)/p3)) Weighting:y No weighting Chi^2/DoF = 0.00091R^2 = 0.9984 p1 6.4214 ? .03199p2 3.05437 ? .00317p3 0.12909 ? .00445

DecayTim

e(ns)

RE35τrad =6.42 nsEme =3.05 eVE0 =129 meV

RN37τrad =5.92 nsEme =2.94 eVE0 =104 meV


InGaNInGaN//GaNGaN 55--QWsQWs: TEM : TEM bright field imagebright field image & & HighHigh--angle annular dark fieldangle annular dark field (HAADF) (HAADF) imageimage

TEM bright field image from a MOCVD InGaN-GaN MQW LED on sapphire. Structural features of five QWs are clearly seen. The widths of the well and barrier are determined to be 4 nm and 40 nm, respectively. The TEM image shows no threading dislocation at this area, but some strain field around the well, which sometimes may induce V-shape defects and high density of stacking faults.

High resolution transmission electron microscopy


InGaNInGaN//GaNGaN 55--QWsQWs: TEM : TEM bright field imagebright field image & & HighHigh--angle annular dark fieldangle annular dark field (HAADF) (HAADF) imageimage

100 nm

HAADF Detector

HAADF STEM contrast is mainly due to thermal diffuse scattering, whose intensity is almost proportional to the square of atomic number. Five bright stripes parallel to the basal plane are InGaN layers and dark ones are GaN layers.

High resolution transmission electron microscopy


VV--defects & defects & HAADF STEM HAADF STEM images of theimages of the InGaNInGaN//GaNGaN MQWMQW

(G978)

Threading dislocation originating from GaN/sapphire interface to disrupt the InGaN/GaN MQW, and to initiate the V-defect, which have inverted the hexagonal pyramid-shaped ｛10-10｝side walls.

Zhe Chuan Feng, White LED, 2007 July (G978)

(b)(a) QW1

Digital Analysis of Lattice image techniqueDigital Analysis of Lattice image technique-- showing QDshowing QD--like structureslike structures

The color-coded map of the local In concentration in anInGaN/GaN QW structure, which contains 5 InGaN layers. (a) is QW1 just next to the capping layer and (e) is QW5 at the bottom

of the active layer.

(e) QW5

Zhe Chuan Feng, White LED, 2007 July (G978)

HRHR--TEM images from a greenTEM images from a green InGaNInGaN MQW LEDMQW LED

HRTEM images from a green InGaN MQW LED (scale: 20-nm & 2-nm). The In-clustering is seen clearly. These nano-structural or QDs features are closely correlated with results from HRXRD, PL/PLE.


Fig. HRTEM images from an InGaN-GaN MQW LED (scale: 50-nm)

HRHR--TEM images from a blueTEM images from a blue InGaNInGaN MQW LEDMQW LED

Fig. HRTEM image from an InGaNMQW LED (scale: 2-nm).

HRTEM from another LED on a QW area, with the In-clustering seen clearly. These nano-structural or QDs features are closely correlated with results from HRXRD, PL/PLE


Figure 3 exhibits a HRTEM from another LED on a QW area, with the In-clustering seen clearly. These nano-structural or QDsfeatures are closely correlated with results from HRXRD, PL/PLE

Fig. 3. HRTEM image from an InGaNMQW LED (scale: 2-nm).


MonolayerMonolayer fluctuations influctuations in InGaN QWsInGaN QWs

From Humphries et al.

Upper interface(rough)

lower interface(abrupt)

InGaN QWs are not atomically flat


InGaN-GaN MQW: HR-XRD & Simulation


32 .5 33 .0 33 .5 34 .0 34 .5 35 .0 35 .5

1 0 0

1 0 0 0

1 0 0 0 0

1 0 0 0 0 0

1 0 0 0 0 0 0

34 .3 34 .4 34 .5 34 .6

+ 6+ 5

+ 4

+ 3

+ 2

+ 1

-10 -9-8 -7

-6 -5 -4-3 -2

-1

0

G aN (0002 )

M O C V D

InG aN -G aN M Q W LE D

HR

XR

D In

tens

ity (C

ount

s/se

c)

2 θ (o)

5 -w e lls

G 436

+ 1-1

n= 0

G a N (0 0 0 2 )

InGaN-GaN MQW: excellent characteristic HR-XRD

• GaN peak is very sharp and all satellite bands, which are narrow, up to 10-thorder are obtained. • More fine structures are seen between satellite peaks, indicating the excellent layer crystalline perfection and sharp interfaces between all multiple layers.• Such a nice XRD pattern is reported for the first time in the literature.

(G978)


• The computer simulation leads to the precise determination of layer parameters of the thickness and composition

• GaN peak is very sharp and all satellite bands, which are narrow, with high orders obtained.

• Fine structure seen between satellite peaks, indicate the excellent layer crystalline perfection and sharp interfaces between all multiple layers.

InGaN-GaN MQW: HR-XRD Simulation Results


Al0.15Ga0.85N/GaN on Al2O3

RSM of (1 0 1) reflection

-0.1

0

0.1

0.2

-0.2-0.1 0 0.20.1 0.3

GaNAlGa

N

0-0.1 0.1

0

-0.1

0.1

GaNAlGaN

HR-XRD Reciprocal Spatial Mapping on AlGaN/GaN

RSM of (004) reflection

AlGaN

5950

5900

6000

2750 2800 2850

Qx*10000

Qy*

1000

0GaN

AlGaN

5950

5900

6000

2750 2800 2850

Qx*10000

Qy*

1000

0GaN

RSM of (1 0 4) asymmetric reflection


Raman scattering of a MOCVD undoped GaN/sapphire, (a) normal incidence and (b) cross-section incidence,. (c) and (d) expansions in 500-600 and 700-800 cm-1.

100 200 300 400 500 600 700 800 900 1000

(b) cross-section incidence

(a) normal incidence

sapphire

5145 ? 300 K

MOCVD, GN-d

GaN/sapphire

A1(TO)E1(TO)

E1(LO)

A1(LO)

E2

E2

E2

INTE

NS

ITY

(a.

u.)

RAMAN SHIFT (cm-1)

500 550 600

(c)

A1(TO)

E1(TO)

E2

E2

700 750 800

(d)

RAMAN SHIFT (cm-1)

E1(LO)

A1(LO)

Raman Scattering on Strains-QCSE

200 400 600 800

GaN:

GaN:

x 1

x 1

x 0.03

x 0.03

x 0.3

(h)

(g)

(f)

(e)

(d)

(c)

(b)

(a)

E2

E2

A1(TO)

E1(TO)

E1(LO)

sapphire

sapphire

sufa

cesu

bstra

te

5145 �300 K MOCVD, gn-D

GaN/sapphire

RAMAN SHIFT (cm -1)

700 720 740 760 780 800

x 1

x 1

x 1

x 1

x 0.5

x 0.03

x 0.02

x 0.02

x 0.02(i)

(h)

(g)

(f)

(e)

(d)

(c)

(b)

cross-section incidence

normal incidence

subs

trate

sufa

ce

(a)

E1(LO)

A1(LO)

5145 ? 300 KMOCVD, N71GaN/sapphire

RAMAN SHIFT (cm-1)

Comparative m-Raman spectra of MOCVD-grownGaN/sapphire, with the laser incidence scanning over the film cross-section. The variation of Raman frequency of E1(LO) indicates the strain variation in the film vertical direction.


Raman line shape analysis on E2 & A1(LO) modes

Raman high E2 mode and theoretical fit for GaN/sapphire.

540 550 560 570 580 590 600

E2

567.9 cm-1

n-GaN/Sapphire MOCVD

Theoretical Experimental

Raman Shift (cm-1)

Ram

an In

tens

ity (a

.u.)

[ ] 2023221

0 )2/()()

4exp()(

Γ+−−

∫ qqdLqI

ωωαω

21

22 )]}cos(1[{)( qBAAq πω −−+=

700 720 740 760 780 800

5145 �300 K

sapphire EgA1(LO)

n-GaN/sapphire

Inte

nsity

Raman Shift (cm-1)

Experimental Fitted/separated Overall Fitted

Raman determination of carrier concentration:


ConclusionConclusion

• InGaN/GaN multiple quantum well light emitting diode (LED) structures are attractive and promising for the next generation high efficiency solid state lighting.

• Basic scientific research needed to fully understand the luminescence origins in this materials.

• Materials growth must be closely coupled to advanced characterization techniques to elucidate physical mechanism

• Experienced research team has been assembled which will guarantee the success of the proposed study


Z C Z C FengFeng’’ssbooks,books,

published published in in

19921992--9393--94 :94 :In editing: > 2003:

2006:2004:

GENERAL - Lighting HistoryRevolutions in Solid State Electronics and OptoelectronicsApplications of LEDsHuman EyeInGaN/GaN MQW LED on sapphireAlGaInP LEDsBlue/UV LED Pump Source for PhosphorsLED processingGeneral Blue LED Process FlowStandard GaN LED Fab ProcessesNew Packaging (Luxeon/Lumileds)LED PackagingOrganic Light-Emitting Diode (OLED) OLED: Physics and Fabrication LED Markets, Advantages & FuturesLED Efficiency SummaryTRPL on newly MOCVD-grown InGaN/GaN MQWsTRPL of InGaN/GaN MQWs: dependence on photon energyTRPLDigital Analysis of Lattice image technique �- showing QD-like structuresHR-TEM images from a green InGaN MQW LEDMonolayer fluctuations in InGaN QWsConclusionZ C Feng’s� books,�published in �1992-93-94 :

iii-nitride quantum materials and nano-structures for new ... · • blue led 1997 (nakamura &...

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