The Race for Gallium Nitride Blue Lasers: a Tribute to Shuji Nakamura

The Race for Gallium Nitride Blue Lasers: A Tribute to Shuji Nakamura

Scott Corzine October 24, 2014

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 1 Outline

• Motivation • Challenges • Accomplishments • What’s Happened Recently

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 2 Key Markets for Blue Lasers DVDs Laser Printers Color Displays

Advantages: 3-Fold Increase in Lower NA allows Efficient, Compact, High Storage Density Simpler Optics Power Blue Light Source Requirements:

Read: 1-2 mW 5-10 mW 1-10 W Write: 15-30 mW

410 nm or less 450 nm, 520 nm

Good Beam Quality High EfficiencyScott Corzine

The Race for GaN Blue Lasers Scott Corzine 3 Basic Components of a Semiconductor Laser

Optical Cavity • Lateral Processing • Mirror Facets

Electrical Connection Epi Layers • P Contact • P Cladding • N Contact • I Active • N Cladding Substrate

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 4 Epi Material Requirements

• Active Layer: direct bandgap semiconductor in the desired wavelength range • Cladding Layers: compatible higher-bandgap semiconductors – large bandgap differences to confine electrons – large index differences to confine photons • Substrate: must be suitable for epitaxial growth – lattice-matched to desired epi materials – compatible crystal structure (zinc blende, wurtzite, etc.)

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 5 Epi Material Requirements

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 6 Periodic Table VIII

III IV V VI VII He 5 7 6 8 9 10

B N C O F Ne

13 15 14 16 17 18 Al P I II Si S Cl Ar

31 33 29 30 32 34 35 36 Ga As Cu Zn Ge Se Br Kr 49 51 47 48 50 52 53 54 In Sb • • • Ag Cd Sn Te I Xe 81 83

80 80 82 84 85 86

• Smaller Atom Smaller • Constant Lattice Smaller • Wavelength Shorter • Au Hg Tl Pb Bi Po At Rn Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 7 III-V and II-VI Compounds

Short III-V Materials Wavelength BN AlN GaN InN BP AlP GaP InP BAs AlAs GaAs InAs BSb AlSb GaSb InSb Long Wavelength II-VI Materials MgO ZnO CdO HgO MgS ZnS CdS HgS MgSe ZnSe CdSe HgSe

MgTe ZnTe CdTe HgTe Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 8 Lasing Wavelengths of Common Semiconductor Materials

InP 1200-1600 nm InGaAs • Telecom, Datacom InGaAsP InP AlGaAs 700-1100 nm InGaAs • CDs, Laser Printers, Datacom GaAs AlGaAs InGaP 620-690 nm InGaP • DVDs, Laser Printers AlInGaP AlInP

400 600 800 1000 1200 1400 1600 1800 Wavelength (nm) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 9 Different Options for Blue Lasers

2f-GaAs 400-500 nm InGaAs • Bulky, Complex External Optics GaAs AlGaAs ZnSe 480-550 nm • Short Lifetimes (<1000 hrs) ZnCdSe ZnSSe • Not Blue Enough ZnMgSSe GaN 390-440 nm InGaN • Lattice-Mismatched System GaN AlGaN GaN InN

350 400 450 500 550 600 650

Wavelength (nm) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 10 Epi Material Requirements

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 11 Role of Cladding Layers Electron Confinement e– N Ileak ~ exp[-ΔEc /kT ]

ΔEc

 want large ΔEc

active barrier cladding • smaller Ith • better over T P h+

energy in active Γ = mode profile total energy Optical Confinement

 want large Δn Δn • maximize Γ Scott Corzine index profile • reduce substrate leakage

The Race for GaN Blue Lasers Scott Corzine 12 Common Lattice-Matched Systems

2.5 AlP AlInGaP

2 GaP AlAs AlGaAs 1.5 InP GaAs

1 InGaAsP Bandgap (eV) Bandgap 0.5 InAs 0 5.4 5.5 5.6 5.7 5.8 5.9 6 6.1

Lattice Constant (Å) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 13 AlInGaN Material System

Strain (%) -4 -2 0 2 4 6 8 10 12 7

6 AlN Lattice mismatch limits: • Al and In compositions 5 • Epi layer thickness ? 4 AlGaN (Al < ~20%)

3 GaN Bandgap(eV) 2 InGaN (In < ~20%) InN 1 3 3.1 3.2 3.3 3.4 3.5 3.6 Lattice Constant (Å) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 14 Conduction Band Offsets

Material ΔEc GaAs/AlAs 440 meV InGaAsP/InP (1.55µm) 220 meV InGaAsP/InP (1.3µm) 160 meV InGaP/AlInP 260 meV

InGaN/GaN (xIn=10%) 100 meV

InGaN/GaN (xIn=20%) 200 meV

GaN/AlGaN (xAl=10%) 100 meV

GaN/AlGaN (xAl=20%) 200 meV Scott Corzine

(GaN numbers assume 50% conduction band offset) (estimates do not take into account strain and quantum effects) The Race for GaN Blue Lasers Scott Corzine 15 One Method to Reduce Leakage

P e– N P e– N

active active

barrier barrier

cladding cladding

Electron Blocking Layer Example P-AlGaN (x=0.05) 5000 Å Epi Design P-GaN 1000 Å AlGaN (x=0.2) 200 Å InGaN(x=0.2) MQW 360 Å

N-GaN 1000 Å AfterScott Corzine N-AlGaN (x=0.05) 5000 Å Shuji Nakamura

The Race for GaN Blue Lasers Scott Corzine 16 Index Differences

Material Δn GaAs/AlAs 0.6 InGaAsP/InP (1.55µm) 0.4 InGaAsP/InP (1.3µm) 0.3 InGaP/AlInP 0.4

GaN/AlGaN (xAl=10%) 0.06

GaN/AlGaN (xAl=20%) 0.12 GaN/AlN 0.44

AlxGa1-xN index @ 400nm, x < 0.3 ~ 2.54 - 0.6x (from Brunner et. al., JAP, 82 (10), p5090, 1997) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 17 GaN/AlGaN Waveguide Modes: Effect of Cladding Composition

0.005 GaN

AlGaN AlGaN Index Profile 2.54 0.004 x = 0.05 /nm) 2.5 G x = 0.1 0.003 x = 0.15 2.46 0.002  Typical Cladding: x = 0.07-0.1 0.001 Guide =

0.25µm d = 0.4-0.6 mm Mode Shape ( Shape Mode

0 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 Scott Corzine z (mm) l= 410 nm

The Race for GaN Blue Lasers Scott Corzine 18 Epi Material Requirements

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 19 Common Material Systems

2.5 AlP AlInGaP InP Substrate 2 GaP AlAs AlGaAs 1.5 InP GaAs

1 InGaAsP Bandgap (eV) Bandgap 0.5 GaAs Substrate InAs 0 5.4 5.5 5.6 5.7 5.8 5.9 6 6.1

Lattice Constant (Å) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 20 Substrate Options for GaN

Strain (%) -15 -10 -5 0 5 10 7

6 AlN  Buffer Layer Required 5

4 GaN

3 Bandgap(eV) 2 Sapphire SiC InN

1 2.6 2.8 3 3.2 3.4 3.6 Lattice Constant (Å) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 21 GaN on Sapphire

GaN (High Temp) GaN or AlN Buffer Layer (Low Temp) Sapphire Substrate  Dislocation Density  Carrier Recombination, 9 10 -2 ~ 10 - 10 cm Scattering, Reliability? TEMScott Corzineimage from D. Basile, HP Labs

The Race for GaN Blue Lasers Scott Corzine 22 SiC vs Sapphire GaN Laser on SiC GaN Laser on Sapphire

• Conductive Substrate Allows: • Insulating Substrate Requires:   Vertical Current Flow  Two Top Contacts   Single Top Contact • Poor Thermal Conductivity • 10x Better Thermal Conductivity • Poor Cleaved Facets • High Quality Cleaved Facets • But, Best Devices Still Made Scott Corzine • But, Substrates are Expensive on Cheap Sapphire Substrates     The Race for GaN Blue Lasers Scott Corzine 23 Cavity Requirements • Vertical Waveguiding: large index differences • Lateral Waveguiding: must be able to process the epi materials – gain-guided (metal patterning) – stripe and ridge waveguides (etching) • Low Scattering Losses: smooth surfaces/interfaces • Optical Feedback: crystal facets or distributed reflectors – smooth cleaved facets – smooth etched facets – etched periodic gratings (regrowth) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 24 Cavity Requirements • Vertical Waveguiding: large index differences • Lateral Waveguiding: must be able to process the epi materials – gain-guided (metal patterning) – stripe and ridge waveguides (etching) • Low Scattering Losses: smooth surfaces/interfaces • Optical Feedback: crystal facets or distributed reflectors – smooth cleaved facets – smooth etched facets – etched periodic gratings (regrowth) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 25 Types of Lateral Guides

Gain-Guided Stripe Ridge

Metal Stripe Deep Mesa etched Shallow Mesa etched • No Etching past Active into Upper Cladding  Simple to Make • Good Confinement • Controlled Confinement • Poor Confinement  Low Threshold  Low Threshold  High Threshold  Multi-Mode  Single-Mode  Low Efficiency • Poor Heat Flow • Good HeatScott Flow Corzine

The Race for GaN Blue Lasers Scott Corzine 26 Sidewall Etching Examples

2 µm 2 µm

Dry Etching Using Wet (PEC) Etching Using

Cl2/H2/Ar ICP KOH under UV light (~ 0.7 µm/min) (~ 0.3 µm/min)

Shul, et al. Youtsey, et al. Scott Corzine Appl. Phys. Lett. 69, 1119 (1996) Appl. Phys. Lett. 71, 2151 (1997)

The Race for GaN Blue Lasers Scott Corzine 27 Ridge Laser for Single-Mode Nakamura, et al. n Appl. Phys. Lett. 73, 832 (1998) n eff1 n eff2 eff2 70 mW Etched Mesa contact cladding  Effective Index Step guide 100 mW  Current Confinement active guide cladding contact 3 µm 2 µm

Mesa Height and Width Control Lateral Mode Structure  Etched sidewalls can be Scott Corzine  typical width ~ 3-5µm a source of scattering

The Race for GaN Blue Lasers Scott Corzine 28 Cavity Requirements • Vertical Waveguiding: large index differences • Lateral Waveguiding: must be able to process the epi materials – gain-guided (metal patterning) – stripe and ridge waveguides (etching) • Low Scattering Losses: smooth surfaces/interfaces • Optical Feedback: crystal facets or distributed reflectors – smooth cleaved facets – smooth etched facets – etched periodic gratings (regrowth) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 29 Cavity Loss Mechanisms

Internal Losses: •Absorption • Scattering

P ~ ei x

-1 L i (cm )  Internal Loss

Mirror Losses 1 1   ln m L R Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 30 Internal Cavity Losses

Material i GaAs/AlAs 3-10 cm-1 InGaAsP/InP InGaN/AlGaN 35-50 cm-1

Sources of Internal Loss • Absorption  Free Carriers in Doped Layers  Absorption Tails in “Transparent” Layers • Scattering  Dislocations  Rough Sidewalls Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 31 Measured AlGaN Absorption Curves

Large Absorption Tails

Brunner, et al. Scott Corzine J. Appl. Phys. 82, 5090 (1997)

The Race for GaN Blue Lasers Scott Corzine 32 Cavity Requirements • Vertical Waveguiding: large index differences • Lateral Waveguiding: must be able to process the epi materials – gain-guided (metal patterning) – stripe and ridge waveguides (etching) • Low Scattering Losses: smooth surfaces/interfaces • Optical Feedback: crystal facets or distributed reflectors – smooth cleaved facets – smooth etched facets – etched periodic gratings (regrowth) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 33 Cleaving GaN on Sapphire GaN

Sapphire

~2.4° 3 µm

16 nm roughness (1100) Cleavage Planes  R ~ 4% Scott Corzine m-face of Sapphire Stocker, et al. (1210) Appl. Phys. Lett. 73, 1925 (1998)

The Race for GaN Blue Lasers Scott Corzine 34 Cleaving GaN on SiC

High Quality Cleaved Facets Are Readily Obtained

1 µm Doverspike,Scott Corzine et al. SPIE ’98, 3284, 82 (1998)

The Race for GaN Blue Lasers Scott Corzine 35 Other Types of Mirrors

Dry-Etched Facets 3rd-Order Gratings

Abare, et al. Hofstetter, et al. Appl. Phys. Lett. 73, 3887 (1998) Appl. Phys. Lett. 73, 2158Scott (1998) Corzine

The Race for GaN Blue Lasers Scott Corzine 36 Performance Requirements • High Optical Gain: small effective masses – low threshold current – high differential gain • High P- and N-Doping: shallow donor and acceptor levels – low voltage operation • low series resistance • good ohmic contacts • Robust, Reliable Materials: low impurity and defect concentrations – long lifetime Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 37 Performance Requirements • High Optical Gain: small effective masses – low threshold current – high differential gain • High P- and N-Doping: shallow donor and acceptor levels – low voltage operation • low series resistance • good ohmic contacts • Robust, Reliable Materials: low impurity and defect concentrations – long lifetime Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 38 Relevant Gain Parameters

Material mC mHH GaAs/AlAs 0.04-0.07 0.35-0.6 InGaAsP/InP Large Effective Masses  Takes Lots of InGaN/AlGaN 0.15-0.2 0.8-1.6 Carriers to Get Gain

-3 2 2 Material Ntr (cm ) Jtr (A/cm ) dg/dN (cm ) tr (ns) GaAs/AlAs 1-2 x 1018 50-100 2-5 x 10-16 2-3 InGaAsP/InP InGaN/AlGaN ~1019 200-500 0.5-2 x 10-16 2-3 Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 39 Gain vs Current Density (Theory) Example Design: 140 In0.2Ga0.8N/GaN MQW (50Å) If R = 18%, L= 500µm

120 ) n = 4 -1 1 w   ~ 35 cm - m 100 nw = 3 -1 g (cm g If i = 0 cm G 80 nw = 2 J ~ 1 kA/cm2  th n = 1 60 w nw ~ 1 or 2

40 -1

If i = 40 cm Modal Gain, Gain, Modal 20  J ~ 2 kA/cm2  th n ~ 2, 3, or 4 0 w 0 0.5 1 1.5 2 2.5 3 Yeo, et al. Scott Corzine 2 Current Density (kA/cm ) J. Appl. Phys. 84, 1813 (1998)

The Race for GaN Blue Lasers Scott Corzine 40 Other Issues for Gain in InGaN QWs

• Indium Clustering? – localized transitions? – quantum dot effects? • Free Electron-Hole Pair or Exciton Transitions? • Piezoelectric Field is Strong in Strained InGaN – is gain affected?

Very Unusual: Broad Low Energy Gain Spectrum Song, et al. Scott Corzine Appl. Phys. Lett. 72, 1418 (1998)

The Race for GaN Blue Lasers Scott Corzine 41 Performance Requirements • High Optical Gain: small effective masses – low threshold current – high differential gain • High P- and N-Doping: shallow donor and acceptor levels – low voltage operation • low series resistance • good ohmic contacts • Robust, Reliable Materials: low impurity and defect concentrations – long lifetime Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 42 Voltage Drops in Laser Structure

Vlaser = Vdiode + I ( R) Rp-contact

Rp-AlGaN/GaN

R n-contact Rn-AlGaN/GaN

Active

GaN

AlGaN Rspread (n-GaN) Scott Corzine Metal

The Race for GaN Blue Lasers Scott Corzine 43 Dopant Materials

Material P-Type Dopants N-Type Dopants -3 -3 Element Eact (meV) Cmax (cm ) Element Eact (meV) Cmax (cm )

GaAs C 26 ~1020 Si 5.8 ~3x1018 Zn 30.7 ~1019 Se 5.8 ~1019 Mg 28.4 ~1019 Be 28 ~1019

GaN Mg 170-200 ~1018 Si 12-17 ~1019 AlGaN Mg + 4·x[%] ~1017 Si 15-20 ~1019 r (n-GaN/AlGaN) < 0.01 Wcm r (p-GaN) ~ 1-2 Wcm 0.1-0.2 V/µm @ 1 kA/cm2  r (p-AlGaN) ~ 10-20 Wcm 1-2 V/µm @ 1 ScottkA/cm Corzine2

The Race for GaN Blue Lasers Scott Corzine 44 Ohmic Contacts

Material P-Contacts N-Contacts 2 2 Metal rc (W-cm ) Metal rc (W-cm ) GaAs AuZn 10-5-10-6 Au/Ge/Ni 10-5-10-6

GaN Ni/Au 10-2-10-3 Ti/Al 10-5-10-6 Pt/Ni/Au 5x10-4 Pd/Al 10-5 recently Pd/Au 4x10-4 Ti/Ag 5x10-5 reported Ta/Ti 3x10-5 Ti/TiN 4x10-6

-3 2 2 rc = 10 W-cm  1 V @ 1 kA/cm

- 4 2 Scott Corzine Want rc < 10 W-cm

The Race for GaN Blue Lasers Scott Corzine 45 Example: Voltage Drops @ 10kA/cm2

Vlaser = 3V + 16.15V 10-3 W-cm2  10V ~ 19V 10 Wcm (0.5µm)  5V

(assuming current crowding comparable to laser stripe width) 10-5 W-cm2  0.1V 0.1 Wcm (0.5µm)  0.05V

Active

GaN 0.01 Wcm (100µm)  1V AlGaN Scott Corzine (assuming conduction x-section comparable Metal to laser stripe dimensions)

The Race for GaN Blue Lasers Scott Corzine 46 Performance Requirements • High Optical Gain: small effective masses – low threshold current – high differential gain • High P- and N-Doping: shallow donor and acceptor levels – low voltage operation • low series resistance • good ohmic contacts • Robust, Reliable Materials: low impurity and defect concentrations – long lifetime Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 47 Reliability Issues

Material Degradation Mechanisms AlGaAs • Oxygen Contamination is a Source of Nonradiative Recombination which can Limit Device Lifetimes

• Laser Facet Damage GaN • High Dislocation Densities are a Major Concern. However: (1) Defect Propagation is Slower than in GaAs (but more temperature dependent) (2) Defect Recombination Rates are Slow • Laser Facet Damage? For Long Lifetime, Still Desirable to Minimize DefectScott Density Corzine

The Race for GaN Blue Lasers Scott Corzine 48 Epitaxial Lateral Overgrowth (ELOG)

Vertical Dislocation Threads Can’t Follow Lateral Growth

Lateral Growth

The Result: Nearly Defect-Free Material!

Nam, et al. Scott Corzine Appl. Phys. Lett. 71, 2638 (1997)

The Race for GaN Blue Lasers Scott Corzine 49 Highlights of Challenges for GaN Laser Research • Lattice Mismatched System – limits range of cladding layer compositions and thicknesses – difficult to create good electron and photon confinement • Lack of Suitable Substrate – high dislocation densities • reliability concerns • large scattering losses – high quality cleaved facets are difficult to make • Large Effective Masses (in Both Conduction and Valence Bands) – high carrier and current densities required for optical gain – low differential gain (due to asymmetry in band structure) • Large Acceptor Activation Energy – high p-type doping difficult (especially in AlGaN) • high series resistance • hard to make good p-ohmic contacts Scott Corzine – high voltage operation

The Race for GaN Blue Lasers Scott Corzine 50 First GaN Blue Laser - Dec‘95 (Nichia)

1μs pulse width 1ms rep rate

Nakamura, et al. Jpn. J. Appl. Phys., 35, L74 (1996) Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 51 Nichia’s Early Laser Structure

Ridge Waveguide InGaN MQW Active

c-face Sapphire Substrate

Nakamura, et al. IEEE J. STQE, 3, 712 (1997) RIE-Etched Facets Nakamura,Scott et al. Corzine Jpn. J. Appl. Phys., 35, L74 (1996)

The Race for GaN Blue Lasers Scott Corzine 52 Who’s Got Blue? (circa 1998)

Company Operation Entry Date (CW) Nichia RT, CW: 6000 hr Dec-95 (Nov-96) Meijo University RT, Pulsed Jun-96 Toshiba RT, Pulsed Sep-96 Cree RT, quasi-CW: 30 sec Jun-97 (Jan-98) Fujitsu 250K, quasi-CW: 1 sec Jul-97 (Oct-98) UCSB RT, Pulsed Sep-97 Sony RT, quasi-CW: 1 sec Oct-97 (Jul-98) Xerox RT, Pulsed Oct-97 Hewlett Packard RT, Pulsed Nov-97 SDL RT, Pulsed Feb-98 Pioneer RT, Pulsed Aug-98 Scott Corzine RT = Room Temperature CW = Continuous Wave The Race for GaN Blue Lasers Scott Corzine 53 Typical Commercial Laser Performance

CD Players, DVD Players, Laser Printers

Threshold Current, Ith : 20-50 mA

Threshold Voltage, Vth : 2-3 V

Output Power, Pout : 5-30 mW

High Performance/Specialty Applications

Threshold Current, Ith : 0.1-1 mA

Threshold Voltage, Vth : 1.6-2 V

Output Power, Pout : 1-2 W Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 54 Nichia’s Amazing Progress

2000 16 Nichia I (mA) th 14 J (kA/cm2) CW th

1500 12 J

th 10 (kA/cm

1000 8 6

) 500 4

2 Threshold Current (mA) Current Threshold 0 0 Scott Corzine16 mA! 1996 1997 1998 1.2 kA/cm2

The Race for GaN Blue Lasers Scott Corzine 55 Nichia’s Blue Laser (circa 1998)

CW • l : ~ 410 nm

• Ith : ~ 50 mA 2 • Jth : 3-5 kA/cm • V : ~ 5 V Nakamura, et al. th Scott Corzine Jpn. J. Appl. Phys., 37, L1020 (1998) • Pout : > 30 mW

The Race for GaN Blue Lasers Scott Corzine 56 Other “quasi-CW” Players 1600 16 1400 14

1200 12 J

th 1000 10 (kA/cm 800 8 6 600 Sony 2 Fujitsu ) 400 4 200 2

Threshold Current (mA) Current Threshold = CW Cree 0 0 ScottCW Corzine lifetimes 1997 1998 all < 1 min

The Race for GaN Blue Lasers Scott Corzine 57 Pulsed Cree’s Blue Laser (circa 1998)

Bulman, et al. LEOS ‘98, FI2 (1998)

• SiC Substrate

CW • Stripe Waveguide Doverspike, et al. • Cleaved Facets SPIE ‘98, 3284, 82 (1998) Pulsed CW • Wavelength : 408 nm 425 nm

• Lowest Ith : 107 mA 600 mA 2 2 • Lowest Jth : 7.1 kA/cm 25 kA/cm • Lowest Vth : 15.7 V Scott Corzine25 V • Pmax : 2.4 mW 1.2 mW

The Race for GaN Blue Lasers Scott Corzine 58 Fujitsu’s Blue Laser (circa 1998) Pulsed

• SiC Substrate

CW • Ridge Waveguide • Cleaved Facets

Pulsed CW • Wavelength : 406 nm 406 nm

• Lowest Ith : 300 mA 380 mA 2 2 • Lowest Jth : 9.5 kA/cm 12 kA/cm • Lowest Vth : 12.5 V 12.6 V Scott Corzine Soejima, et al. • Pmax : > 20 mW > 0.2 mW Jpn. J. Appl. Phys., 37, L1205 (1998) The Race for GaN Blue Lasers Scott Corzine 59 UCSB’s Blue Laser (circa 1998) Pulsed

• c-face & a-face Sapphire Substrate • Gain-Guided Waveguide • RIE-Etched & Cleaved Facets

Pulsed • Wavelength : 422 nm

• Lowest Ith : 650 mA 2 • Lowest Jth : 9.2 kA/cm • Lowest V : 19 V th Scott Corzine A.C. Abare, M.P. Mack, et al. • P : 67 mW IEEE JSTQE, 4, 505 (1998) max

The Race for GaN Blue Lasers Scott Corzine 60 Sony’s Blue Laser (circa 1998) Pulsed CW

• c-face Sapphire Substrate • Ridge Waveguide • Cleaved Facets

Pulsed CW • Wavelength : 411 nm 411 nm

• Lowest Ith : 280 mA 466 mA 2 2 • Lowest Jth : 7 kA/cm 11.7 kA/cm • Lowest V : 11.8 V 11.5 V Kobayashi, et al. th Scott Corzine Electron. Lett., 34, 1494 (1998) • Pmax : > 5 mW > 5 mW

The Race for GaN Blue Lasers Scott Corzine 61 Xerox’s Blue Laser (circa 1998) Pulsed

• c-face Sapphire Substrate • Gain-Guided Waveguide • CAIBE-Etched Facets

Pulsed • Wavelength : 419 nm

• Lowest Ith : 740 mA 2 • Lowest Jth : 20 kA/cm • Lowest V : 19 V th Scott Corzine David P. Bour, et al. • P : ~ 50 mW IEEE JSTQE, 4, 498 (1998) max

The Race for GaN Blue Lasers Scott Corzine 62 HP’s Blue Laser (circa 1998)

RIE etched wall p-contact (Ni/Au) Pulsed Cleaved facet p-GaN p-AlGaN 50 100 QW(n-GaInN/n-GaInN) p-GaN n-GaN n-contact (Ti/Al) n-AlGaN 40 80 n-GaN Buffer(AlN) Sapphire (0001) 30 60 • c-face Sapphire Substrate 20 40 • Ridge Waveguide • Cleaved Facets

10 20 Forward Voltage (V) Voltage Forward Pulsed 0 0 (mW) facet per Output Light • Wavelength : 415 nm

0 0.2 0.4 0.6 0.8 1 • Lowest Ith : 300 mA 2 Current (A) • Lowest Jth : 16 kA/cm • Lowest V : 14 V th Scott Corzine • Pmax : ~ 100 mW

The Race for GaN Blue Lasers Scott Corzine 63 Nichia’s Amazing Progress II

104 40

Threshold Voltage (V) 1000 stripe ridge 35 LD LD extrapolates to 30 100 > 10 kHrs! 10 25 c-face thick & MD-SLS 1 sapph ELOG cladding 20 V Drop 0.1 15  CW Si-doping 0.01 in MQW 10

0.001 5 RT-CW Lifetime (hours) RT-CWLifetime 0.0001 0 1996 1997 1998 Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 64 Nichia RT-CW Lifetime Data

> 6000 Hrs Lifetime

Nakamura, et al. Scott Corzine Science, 281, 956 (1998)

The Race for GaN Blue Lasers Scott Corzine 65 Evolution of Nichia’s Substrate • Sapphire Substrate • ELOG with Thick Buffer

“Defect-Free” Regions Epi Layers 10-20µm LT + Buffer c-face

ELOG + Sapphire Removal  • Free Standing GaN Substrate

 80-150µm

Polished 80µm LP-MOCVD Off or 150µm HVPE Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 66 Nichia’s Amazing Progress III

500 50 Quantum Efficiency (%) stripe widths = 3 or 4 µm 420 mW! in all cases ELOG 400 AP LP sub 40 growth growth 300 30 RIE etched cleaved mirrors facets 20 200 “GaN” sub 100 10

CW Power/Facet (mW) CW uncoated/HR 0 0 1997 1998 Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 67 Nichia High Power Blue Laser

420 mW with 11% WP Eff.

Nakamura, et al. Scott Corzine Jpn. J. Appl. Phys., 37, L627 (1998)

The Race for GaN Blue Lasers Scott Corzine 68 Summary of Best Results (circa 1998)

2 Company Ith (mA) Jth (kA/cm ) Vth (V) P (mW) ext (%) Lifetime

CW Pulsed CW Pulsed CW Pulsed CW Pulsed RT-CW Nichia 16 1.2 4.3 420 39 6000 hrs Cree 600 107 25 7.1 15.7 1.2 235 0.3 8 30 sec Sony 466 280 11.7 7 11.5 5 280 49 1 sec Fujitsu 380 300 12 9.5 12.5 0.2 80 20 1 sec Toshiba 530 10.6 20 Xerox 600 16 16 50 0.7 HP 300 16 14 100 5 SDL 8.5 150 Pioneer 820 41 35 35 Meijo 290 2.9 16 UCSB 650 9.2 19 67 4.2 Scott Corzine (P and  are per facet)

The Race for GaN Blue Lasers Scott Corzine 69 Nichia Announces Commercial Sampling of Blue Laser Diodes - Jan 12, 1999 Nichia’s Web Page: E-mail sent out by Nakamura: VI OL E T LA S E R DI O D E Date Wed, 13 Jan 1999 103425 +1728 From shuji NAKAMURA Subject commercialization of violet laser diodes Ni c h i a a n no u nc es t o r el ea s e s a m pl e s hi p m e nt o f VI OL E T L A SE R DI O DE . Announcement of a start of sample shipments of InGaN-based violet laser diodes S PE C I F I C A T I O N We announced a commercilization of first InGaN-based violet laser diodes through Japanese Nikkei Sangyo news paper T yp e No . NL HV 5 00 yesterday on January 12, 1999. The charactersistics of the violet laser diodes are an output power of 5 mW, an emission Wa v e Le n g t h 40 0 (n m ) wavelength of 400 nm, an operating current of 40 mA and an Ou t p u t Po w e r 5 (m W ) operating voltage of 5V. The lifetime of the laser diodes is more than10,000 hours at room temperature. If you were Pa c k a g e si ze &p h i ;5 .6 ca n ty p e interested in testing our laser diodes, please check URL http//www1a.mesh.ne.jp/nichia/index-e.htm. Just for your information. Sincerely yours, CO N T A C T Shuji Nakamura ------TO K Y O TE C H N I C A L C EN T ER Shuji Nakamura R & D Department NI C H I A CH E M I C A L IN D U S T R I E S , L TD . Nichia Chemical Industries Ltd. TE L : +8 1- 3 -3 45 6 - 3 7 4 6 FA X : +8 1- 3- 5 44 0 - 75 16 491, Oka, Kaminaka, Anan E -m ai l : hs h i mi zu @t o k yo . n i ch i a. co . j p Tokushima 774, Japan Phone +81-884-23-7787 Fax +81-884-23-1802 e-mail (Office) [email protected] [H O M E ] [ C O M P A N Y P R O FI L E ] [H I G H BR I G H T N E S S L E D s ] [ U L T R A G L O W ] [I R VI C O N ] [ R E FE R E N C E ] ------Scott Corzine C op y r i gh t © 1 9 9 8 ,1 99 9 Ni ch i a Ch e m i ca l In d us t ri es , Lt d .

The Race for GaN Blue Lasers Scott Corzine 70 Fast-Forward 5 Years… Sony At Photonics West 2004:

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 71 Progress in the U.S.

Xerox Blue Laser in 2001

M. Kneissl et al., IEEE Jour. Sel. Topics in Quantum Electronics 7, 188 (2001).

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 72 DVD Market

“Blu-ray Disc” Standard 27GB 12 cm disc single-sided single-layer

(conventional DVDs = 4.7GB)

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 73 What Happened to Nakamura?

January 30, 2004…the Japanese court ruled in favor of Nakamura over Nichia in a lawsuit quoting that:

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 74 Fast-Forward 10 Years…

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 75 Shuji wins the Nobel Prize in 2014…

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 76 Isamu Akasaki Hiroshi Amano Shuji Nakamura

share the Nobel Prize

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 77 Isamu Akasaki

Tetsuya Takeuchi In 1973, Professor Akasaki embarked upon the Part of Agilent Labs Blue Laser Team (led by Rick Schneider) Now a Professor at Meijo University previously unexplored challenge of using nitride semiconductors to create a p-n junction-type high- performance blue luminescent device.

However, the issues were even more difficult than predicted, resulting in many challenges and setbacks. In the last half of the 1970s, many researchers abandoned the "unexplored semiconductor" research.

Feeling like he was "walking alone in a wasteland", Professor Akasaki worked on gallium nitride (GaN) crystal growth day and night.

One day, he saw a tiny crystal under his fluorescent microscope that gave off cobalt blue light, and became convinced of theScott major Corzine possibilities of GaN.

The Race for GaN Blue Lasers Scott Corzine 78 Hiroshi Amano

I joined Professor Isamu Akasaki's group in 1982 as an undergraduate student.

In 1985, I developed low-temperature deposited buffer layers for the growth of group III nitride semiconductor films on a sapphire substrate, which led to the realization of group-III-nitride semiconductor based light-emitting diodes and laser diodes.

In 1989, I succeeded in growing p-type GaN and fabricating a p-n-junction-type GaN-based UV/blue light-emitting diode for the first time in the world.

Scott Corzine

The Race for GaN Blue Lasers Scott Corzine 79 Shuji Nakamura

“It also makes me happy to see that my dream of LED lighting has become a reality,” Nakamura said in a statement a press conference this morning.

Nakamura also said he did not anticipate developing the blue LED from the outset of his research but rather started with the goal of simply getting a Ph.D.

“My dream was to get a Ph.D. At that time, in Japan, by submitting several scientific papers, you can get a Ph.D… you don’t have to go to university … so at the time, my dream was to publish five scientific papers,Scott not blue Corzine LED, ” Nakamura said.

The Race for GaN Blue Lasers Scott Corzine 80