Growth issues and optical properties of nonpolar …Shigefusa F. Chichibu Center for Advanced...

Shigefusa F. Chichibu

Center for Advanced Nitride TechnologyInstitute of Multidisciplinary Research for Advanced MaterialsTohoku University

Growth issues and optical properties of nonpolar (Al,In,Ga)N films and quantum wells

Koji Hazu and Takeyoshi Onuma as Assistant Professors

Chichibu Laboratory (IMRAM, Tohoku Univ.)

Quantum well laser structure

Optoelectronic devices

Epitaxial growth Material Science

Wide bandgap semiconductor quantum nanostructures

GaN, ZnO etc

New functional and planet conscious semiconductor optoelectronic devices, material growth, and material engineering

MOVPE

NH3-MBE Femtosecond Ti:sapphire laser

HWPSE forZnO/MgZnOheterostructures

SEM / CL

HR XRD Bruker D8

Contributors & Acknowledgments

Laboratory membersMOVPE Growth and Characterization:T. Onuma, K. Hazu, T. Koyama, T. Koida, M. Kubota, L. Zhao, H. Yamaguchi

Samplesm-plane GaN substrate : K. Fujito, H. Namita, T. Nagao (Mitsubishi Chemical)Quantum wells and Devices :

S. Nakamura, S. P. DenBaars, J. S. Speck, U. K. Mishra, S. Keller, P. Fini,B. Haskell, A. Chakraborty, H. Masui (UCSB & ERATO-JST),H. Ohta, K. Okamoto, H. Takasu (RHOM)

BudgetsNakamura Inhomogeneous Crystal Project-ERATO-JST, Grant-in-Aid forScientific Research in Priority Areas No. 18069001 under MEXT,AOARD/AFOSR, ROHM, Mitsubishi Chemical, NGK etc.

Outline

1. Introduction

2. Issues on heteroepitaxial nonpolar (Al,In,Ga)N [UCSB samples]√ Planar growth and lateral epitaxial overgrowth of GaN√ Optical properties of InGaN/GaN and AlGaN/GaN quantum wells

3. Homoepitaxial nonpolar (In,Ga)N [Tohoku-films ROHM-devices]√ Low defect density freestanding (FS) m-plane GaN substrate√ GaN and InGaN growth by MOVPE√ Device performance Digest -- m-plane LEDs and LDs

4. Summary

papers available from http://www.tagen.tohoku.ac.jp/labo/chichibu/SHIGEFUSA/paper/GaN.html

Group-III Nitride Semiconductors

400

800600500

300

200

250

(nm)

0.30 0.34 0.3801234567

BA

ND

GA

P EN

ERG

YE g

(eV)

LATTICE PARAMETER a (nm)

IR

UV

DE

EP

UV

InN

GaN

AlN Group-III Nitride Semiconductors(Al, Ga, In)N

Wide Direct Bandgap range√ AlN 6.01 eV√ GaN 3.43 eV√ InN 0.67 eV

From deep UV to IR

Hard material

High-power, high-frequencyElectronic Devices

Blue, green, white LEDs and 400nm LDs

Group-III Nitride Semiconductors

400

800600500

300

200

250

(nm)

0.30 0.34 0.3801234567

BA

ND

GA

P EN

ERG

YE g

(eV)

LATTICE PARAMETER a (nm)

IR

UV

DE

EP

UV

InN

GaN

AlN

Practical devices exclusively use c-plane (0001) InGaNquantum well active region

Issues on EQE vs wavelength (c-plane)

200 300 400 500 600

AlInGaP

~ 54% maximum value forAllnGaP LEDs

Increase in InNmolar fraction(1) point defects

(low Tg of InGaN)

Blue

AlGaN InGaN-base

Green

GaN

te

mpl

ate

GaN

-free

etc

.

AlN

~ 63%4)

10-6 %6)

EQE of (Al, In, Ga)N QW LEDs1-6)

10-6

10-5

10-2

10-1

EQE

(%)

10-4

10-3

5)

1) Khan et al., Nat. Photon. 2, 77 (2008).2) Shur et al., Proc. SPIE 6894, 689419 (2008).3) Yasan et al., APL 83, 4701 (2003).4) Narukawa et al., JJAP 45, L1084 (2006).5) Hirayama et al., APEX 1, 051101 (2008).6) Taniyasu et al., Nature 441, 325 (2006).

√ Substrate absorption√ Increase in TDD and point defects

WAVELENGTH (nm) -10 -5 0 5 10Z (nm)

ENER

GY

(arb

. uni

ts)

[0001]

c-plane

polarization fields

[0001][0001]

(2) polarization effects(increased latticemismatch →increased QCSEs)Chichibu et al.

APL 69, 4188 (1996).Takeuchi et al.

JJAP 36, L382 (1997).

102

101

100

Polarization discontinuity at heterointerfaces

E. Hellman, MRS Internet J. Nitride Semicond. Res. 3,11 (1998).

Low crystal symmetry : No inversion symmetry along the c-axis→spontaneous polarization (PSP)

Lattice mismatched STRAINED heterostructures→piezoelectric polarization (PPZ)

C6v4: uniaxial anisotropy

(0001) Ga-polar case

0C/m2

strain

Spontaneouspolarization

Piezoelectricpolarization

relaxed

PSPPSP

PSP

PPZ

relaxed

compressive PSPPSP

PSP

PPZ+σ

+σ-σ

-σ

F. Bernardini, V. Fiorentini, and D. Vanderbilt,Phys. Rev. B 56, R10024 (1997).

tensile

Polarization discontinuity produces immobile charges (±σ)at the interfaces

Wurtzite lattice

no inversion symmetry along the c-axis

* T. Takeuchi et al., Jpn. J. Appl. Phys. 39, L413 (2000).and U. Schwarz and M. Kneissl, PSS (PRL) 1, A44 (2007).

*

(1013)

Avoid polarization fields - off c-axis semipolar -

(1011)

[0001][1120]

[1010]

[0001][1010]

[1120]

m-planea-planenonpolar planes

m-plane GaN and AlGaN/GaN / γ-LiAlO2

P. Waltereit et al., Nature 406, 865 (2000).

Nonpolar m- and a-plane InGaN/GaN

<0001>

PPZ

InG

aN Q

W

GaN

bar

rier

GaN

bar

rier

PSP PSP PSP

Fpol

polar (0001) In0.15Ga0.85N (3nm)/GaN(15nm)

-10 -5 0 5 10-4.5-4.0-3.5-3.0

-1.0-0.50.00.5

2.60eV

1.74MV/cm

Z (nm)

Ene

rgy

(eV

)

ΔEC:ΔEV=5:1

<1120>

<000

1>

InG

aN Q

W

GaN

ba

rrie

r

GaN

ba

rrie

r

P SP

P SP

P SP

P PZ

-10 -5 0 5 10-3.5-3.0-2.5-2.00.00.51.01.5

ΔEC:ΔEV=5:1

2.81eVE

nerg

y (e

V)

Z (nm)

Nonpolar (1120), (1100), (001)In0.15Ga0.85N (3nm)/GaN(15nm)

[0001][1120]

[1010]

[0001][1010]

[1120]

SFC et al., Nat. Mater. 5, 810 (2006)

Nonpolar light-emitting diodes (LEDs)

C. Q. Chen, V. C. Q. Chen, V. AdivarahanAdivarahan, J. W. Yang, M. , J. W. Yang, M. ShatalovShatalov, E. , E. KuokstisKuokstis and M. A. Khan: and M. A. Khan: JpnJpn. J. Appl. Phys. 42, L1039 (2003).. J. Appl. Phys. 42, L1039 (2003).

a-plane

MOCVD, GaN / Al0.12Ga0.88N (3x), on r-plane Al2O3

MOCVD, In0.17Ga0.83N / GaN (5x), on HVPE LEO a-plane GaN template

A. Chakraborty, B. Haskell, S. Keller, J. S. Speck, S. P. DenBaars, S. Nakamura andU. K. Mishra: Appl. Phys. Lett. 85, 5143 (2004).

UCSB

University of South Carolina

MOCVD, In0.15Ga0.85N / GaN (3x), on r-plane Al2O3

A. A. ChitnisChitnis, C. Chen, V. , C. Chen, V. AdivarahanAdivarahan, M. , M. ShatalovShatalov, E. , E. KuokstisKuokstis, V. , V. MandavilliMandavilli, J. Yang and , J. Yang and M. A. Khan: Appl. Phys. Lett. 84, 3663 (2004).M. A. Khan: Appl. Phys. Lett. 84, 3663 (2004).

University of South Carolina

m-plane

MOCVD, InGaN / GaN, on m-plane 4H-SiC

N. F. Gardner, J. C. Kim, J. J. Wierer, Y. C. Shen, and M. R. Krames:Appl. Phys. Lett. 86, 111101 (2005).

A. Chakraborty, B. Haskell, S. Keller, J. S. Speck, S. P. DenBaars, S. Nakamura and U. K. Mishra: Jpn. J. Appl. Phys. 44, L173 (2004).MOCVD, In0.17Ga0.83N / GaN (5x), on free-standing m-plane GaN template UCSB

Lumileds Lighting

A. Chakraborty, B. Haskell, H. Masui, S. Keller, J. S. Speck, S. P. DenBaars, S. Nakamura and U. K. Mishra: Jpn. J. Appl. Phys. 45, 739 (2006).MOCVD, In0.16Ga0.84N / GaN (5x), on free-standing m-plane GaN template UCSB

Outline

1. Introduction



4. Summary


Issues in nonpolar GaN heteroepitaxySFs PV-TEM

200nm

SF density3.8x105cm-1

g=1010

TDs

1μmg=0002

TDD 2.6x1010cm-2

X-TEM

rr--plane Alplane Al22OO33

NLNL--GaNGaNaa--plane GaNplane GaN

MOVPEMOVPEGaN 1100°C

NL-GaN 600°C

1) Craven et al., APL 81, 469 (2002).

TDD (cm-2)

SFD (cm-1)

m-plane GaN template

2×109

1×105

5×106

3×103

2) Haskell et al., APL 86, 111917 (2005).

MBE

HVPEHVPE

m-plane 6H-SiC

LEOLEO--GaNGaNGaNGaN

SiO2mask

asymmetric LEOasymmetric LEO

m-plane GaN template

[0001]

[1100]

[1120]SiO2mask

Ga-polar Wing N-polar WingWindow

4×109

1×105

5×106

1×105

>>>>

<<<<

>>=

m-plane InGaN QWs grown on LEO GaN basePlan-view SEM image

Ga-polar wingN-polar wing

Window

2.6 2.8 3.0 3.2 3.4

450 400WAVELENGTH (nm)

INTE

NSI

TY (a

rb. u

nits

)

PHOTON ENERGY (eV)

PL

300K

8KB UV

InN molar fraction:depends on the base structure

CL (300K)wide

B

V

spot

UVP

10μm

5kV x2,000

In0.08Ga0.92N(3.1nm) / GaN(6.9nm)

Ga-

pola

r

wing

win

dow

N-p

olar

[1100]

[112

0]

[0001]

Onuma et al., JVST B 25, 1524 (2007).

ΔEc

ΔEvEg(AlxGa1-xN)=6.138x+3.412(1-x)-0.82x(1-x) 3)

ΔEc:ΔEv=3:1me=0.18m0, mh=1.52m0

2)

2) M. Suzuki et al., PRB 52, 8132 (1995) .3) T. Onuma et al., JAP 95, 2495 (2004).

Schrödinger eq.GaN WELL WIDTH (nm)

0 2 4 6 8 103.40

3.44

3.48

3.52

3.56

3.60

PL

PE

AK

EN

ER

GY

(eV

)

293K

on (1120) GaN

on (1120) LEO-GaN

Al0.16Ga0.84N/GaNAl0.2Ga0.8N/GaN

on (1120) LEO-GaN

no QCSE !

PHOTON ENERGY (eV)

3.40 3.50 3.60

293K

L=6.2nm

L=5.3nm

L=3.4nm

L=2.4nm

PL

INTE

NS

ITY

(arb

. uni

ts)

PHOTON ENERGY (eV)strain-free

(0001)LEO-GaN

Koida et al., APL 84, 3768 (2004).

Nonpolar a-plane AlGaN/GaN QWs

Nonpolar a-plane AlGaN/GaN QWs

0 1 2

L=4.1nmL=9.3nm on GaN

8K

system

PL

INTE

NS

ITY

(a

rb. u

nits

)

TIME (ns)

L=2.4nmL=6.2nm on LEO-GaN

0 2 4 6 8 10

100

103 8K

PL

lifet

ime

(ns)

GaN WELL WIDTH (nm)

on GaNon LEO-GaN

τPLindependent of L

no polarization fields

Ti:sapphire 242nm 2mW

1) Im et al., PRB 57, R9435 (1998).

τPL ～ τR (L.T.)

short τRcomparable to (0001)AlGaN/GaN QW

(L=1.3, 2.5nm)

AlGaN AlGaN

GaN

nonpolar

AlGaN AlGaN

GaN

polar

(0001)Al0.15Ga0.85N/GaN QW 1)

F=350kV/cm

APL 84, 3768 (2004).

Outline

1. Introduction



4. Summary


m-plane free-standing (FS)-GaN substrates

cut from 10-mm-thick c-plane GaN grown by HVPE

(Mitsubishi Chemical Co.)

Fujito et al., pss(a) 205, 1056 (2008).

TDD<5×106 cm-2, SFD<1×103 cm-1

c-plane FS-GaN boule

m-plane FS-GaN wafers

<0001>

<1120><1010>

2nm

01µm

ML step 0.26nmRMS ≅0.072nm SFC et al., APL 92, 091912 (2008).

407.4Wavelength (nm) 435

Output power (mW) 23.7

EQE (%) 38.9Schmidt et al., JJAP 46, L126 (2007).

1.79

3.1Okamoto et al., JJAP 45, L1197 (2006).

Drivingcurrent20mA

m-planeInGaN LEDs

Progress of m-plane InGaN devices using low defect density FS-GaN substrates

m-planeInGaN LDs

APEX 1, 011102 (2008).

405.5

Jth (kA/cm2)

Lasing wavelength (nm) 404

7.5 4.0

Pulsed CW

Schmidt et al., JJAP 46, L190 (2007).JJAP 46, L187; L820 (2007).

451.8

22.3

Pulsed459

5.0

CW481

APEX 1, 072201 (2008).6.1

CW

Issues in (In,Ga)N growth on m-plane substrate

√ Is the m-plane substrate ready for homoepitaxy ?√ Are the growth conditions similar to c-plane growth ?√ Are InGaN alloys grown coherently ?√ Are the optical properties promising ?√ .... etc.

Labor the issues in (In,Ga)N growth by MOVPE on the low DD m-plane FS-GaN substrates

Outline

1. Introduction



4. Summary


Growth conditionsHorizontal MOVPE (Tohoku Univ.)

c-plane FS-GaN (TDD < 107 cm-2)and c-plane GaN/(0001)Al2O3 for comparison

TDD < 5x106 cm-2, SFD < 103 cm-1, Δω(10-10)≅90 arcsec

m-plane GaNsubstrate

325μm

m-plane GaN cut from 10mm-thick c-planeGaN substrate (Mitsubishi)

GaN 1.5μm

Pgrowth : 5.3×104 PaH2 carrierTMGa+NH3

Rg=1.5 μm/hTg=1090 °CV/III =5000

GaN

APL 92, 091912 (2008);erratum 93, 129901 (2008).

InGaN 200-250nm

InGaNPgrowth : 6.6×104 PaN2 carrierTMGa+TMIn+NH3

Rg=0.1 μm/hTg=750-820 °CV/III =40000-1000000

APL 93, 151908 (2008).

MOVPE m-plane GaN homoepitaxy (1.5μm)

V/III RATIO

3000 5000 10000

Tg (°C)

1100

1090

1050

2nm

0 1µm

3nm

0

3nm

0

nm

2

0

nm

3

0

<0001>

<1120><1010>

substrate

2nm

01µm

APL 92, 091912 (2008);erratum 93, 129901 (2008).

ML step 0.26nmRMS ≅0.072nm

XRCs of GaN substrate and epilayer

INTE

NSI

TY (a

rb. u

nits

)

Δω (°)0 0.10.05 -0.1 -0.05

azimuth<0001>

31″

azimuth<11-20>

91″

(1-100)GaN

Tg=1050°CV/III=5000<(1010)XRC>

INTE

NSI

TY (a

rb. u

nits

)

Δω (°)0 0.10.05 -0.1 -0.05

azimuth<11-20>

122″

azimuth<0001>

36″

substrate epilayer

SFC et al., APL 92, 091912 (2008);erratum 93, 129901 (2008).

m-plane GaN : Polarized low temp. NBE PLP

L IN

TEN

SIT

Y (a

rb. u

nits

)

PHOTON ENERGY (eV)3.45 3.50

on GaN/Al2O3

E//c

E⊥c

I2 FXAFXB

FXA,Bn=2

on m-plane FS-GaN

I2

FXA

FXB

FXA,Bn=2,C

on c-plane FS-GaN

A,Bn=2

I1

He-Cd 325.0 nm 38W/cm2 10K

α-polarization (k//c)σ-polarization (k⊥c, E⊥c)π-polarization (k⊥c, E//c)

Paskov PR B 64, 115201(2001)

m-plane GaN homoepitaxy (1.5μm) - TRPL -

SFC et al., APL 92, 091912 (2008);erratum 93, 129901 (2008).

3ω-Al2O3:Ti (267nm, 120nJ/cm2) 293K

on m-plane FS-GaN, τPL,eff=302ps

on GaN/Al2O3, 92ps

on c-plane FS-GaN, 33ps system PL

INTE

NSI

TY (a

rb. u

nits

)

TIME (ns)1 2 3 40

m-plane InGaN (200nm) / GaN : x-ray analyses

q // [0001] (nm-1)-12-12.5 -11.5

45

45.5

46

44.5

44

q //

[110

0] (n

m-1

)

GaN

InGaN

(2201)GaN

InGaN

q // [1120] (nm-1)-40 -39 -38

(1320) GaN

InGaN

<Reciprocal Space Mapping (x=0.08)>

coherent growth(anisotropic strain)

Tg : 750°CV/III : 76000

<XRD>

XRD

INTE

NSI

TY (a

rb. u

nits

)

30 31 32 33 34 35

(1010)GaN

(1010)InxGa1-xN

2θ (°)

0.08

0.03

0.03

0.06

0.02x=

11

zzxxyy C

CC εεε 1312 −−=

SFC et al., APL 93, 151908 (2008).

m-plane InGaN (200nm) / GaN : x-ray analyses

0 0.05 0.10 0.150

200

400 Δ2θ (10-10)Δω (10-10) <0001>Δω (10-10) <11-20>Δω (10-12) <11-20>

59"81"

81"average

InxGa1-xN/GaN//FS-(10-10)GaNX

RD

/XR

C F

WH

M ("

)

InN molar fraction x

Δω : tilt and twist similar to underlayer GaN

Δ2θ-ω :plane distance

inhomogeneity increases

SFC et al., APL 93, 151908 (2008).

m-plane InGaN films -- room temperature PL

WAVELENGTH (nm)

PHOTON ENERGY (eV)

PL IN

TEN

SITY

(arb

. uni

ts)

400 350

InxGa1-xN x=

0.08

0.027

0.032

0.06

0.02 164meV

107meV

118meV

159meV

162meV

FWHM37meV293

K

He-Cd 325nm GaN450

2.8 3.2 3.63.0 3.42.6

0.14310meV

1) SFC et al., Nat. Mater. 6, 810 (2006).

I PL(

300K

)/IPL

(8K

) (%

)

(b)

InN MOLAR FRACTION x

on m-plane FS-GaN

0.00 0.05 0.10 0.15 0.20

0.1

1

10

100

on c-plane FS-GaN

a-plane InGaN(defective planar)after Ref.1

on c-plane GaN/Al2O3

SFC et al., APL 93, 151908 (2008).

m-plane In0.06Ga0.94N film -- TRPL results vs T

0 1 2 3 4 5

2ω-Ti:Al2O3(361nm, 120nJ/cm2)

system

250K

200K

300K

150K

100K50K

6K

TIME (ns)

PL IN

TEN

SITY

(arb

. uni

ts)

m-plane In0.06Ga0.94N film

0 20 4010-3

10-2

10-1

100

He-Cd 325.0nm 38W/cm2

ηint(300K)=11%

1000/T (K-1)

PL IN

TEN

SITY

(arb

. uni

ts)

Low temperatureRadiative lifetime = 600 ps(nearly constant below 100 K)

Room temperatureNonradiative lifetime 150 psRadiative lifetime 1.2 ns

0.1

1

10

TEMPERATURE (K)

LIFE

TIM

E (n

s)

0 100 200 300

τPL,eff

(c) τNR,effτR,eff

SFC et al., APL 93, 151908 (2008).

Outline

1. Introduction



4. Summary


Summary of Device Characteristics

300 400 500 6000

5

100.01

0.1

1

10

100

J th

(kA

/cm

2 )

Wavelength (nm)

CW

nonpolar /semipolar GaN

c-plane

MCC m-planeGaN substrate

Defectivematerials

EQE

(%)

c-plane

m-plane (Rohm)(b)

(a)AlInGaP

EQE of LEDs

Thresholdcurrent densityof LDs

Outline

1. Introduction


3. Homoepitaxial nonpolar (In,Ga)N [Tohoku-films ROHM-devices]√ Low defect density freestanding (FS) m-plane GaN substrate√ GaN and InGaN growth by MOVPE√ Device performance Digest -- m-plane LED and LD wafers

4. Summary


Summary

√ Planar heteroepitaxial nonpolar GaN / TD and SF problems unavoidable. √ LEO does not work finely for nonpolar epitaxy

√ Advantages of nonpolar orientations confirmed (no QCSE, short radiativelifetime / polarized emission).

√ m-plane growths on free-standing GaN substratesTD and SF densities -- nearly equal to the underlayer valueReasonable IQE as bulk InGaN films (11% for x=0.06) -- similar to c-planeImproved radiative lifetime (at room temperature)

√ m-plane LEDs and LDs on free-standing GaN substratesComing up to overtake c-plane devices.

Growth issues and optical properties of nonpolar …Shigefusa F. Chichibu Center for Advanced...

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Transcript of Growth issues and optical properties of nonpolar …Shigefusa F. Chichibu Center for Advanced...