Growth issues and optical properties of nonpolar (Al,In,Ga)N films - - PowerPoint PPT Presentation

Shigefusa F. Chichibu

Center for Advanced Nitride Technology Institute of Multidisciplinary Research for Advanced Materials Tohoku 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 for ZnO/MgZnO heterostructures SEM / CL HR XRD Bruker D8

Contributors & Acknowledgments

Laboratory members MOVPE Growth and Characterization:

• T. Onuma, K. Hazu, T. Koyama, T. Koida, M. Kubota, L. Zhao, H. Yamaguchi

Samples m-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)

Budgets Nakamura Inhomogeneous Crystal Project-ERATO-JST, Grant-in-Aid for Scientific 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

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

400 800 600 500 300 200 250 (nm)

0.30 0.34 0.38 1 2 3 4 5 6 7 BANDGAP ENERGY Eg (eV)

LATTICE PARAMETER a (nm)

IR UV DEEP 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-frequency Electronic Devices

Blue, green, white LEDs and 400nm LDs

Group-III Nitride Semiconductors

400 800 600 500 300 200 250 (nm)

0.30 0.34 0.38 1 2 3 4 5 6 7 BANDGAP ENERGY Eg (eV)

LATTICE PARAMETER a (nm)

IR UV DEEP UV InN GaN AlN

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

Issues on EQE vs wavelength (c-plane)

200 300 400 500 600 AlInGaP

~ 54% maximum value for AllnGaP LEDs Increase in InN molar fraction (1) point defects (low Tg of InGaN)

Blue AlGaN InGaN-base Green

G a N t e m p l a t e G a N

• f

r e e e t c .

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

5 10 Z (nm) ENERGY (arb. units) [0001]

c-plane polarization fields [0001] [0001]

(2) polarization effects (increased lattice mismatch → 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)

C6v

4: uniaxial anisotropy

(0001) Ga-polar case

C/m2 strain Spontaneous polarization Piezoelectric polarization relaxed PSP PSP PSP PPZ relaxed

compressive

PSP PSP 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-plane a-plane nonpolar 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

InGaN QW

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

• 10
• 5

5 10

• 4.5
• 4.0
• 3.5
• 3.0
• 1.0
• 0.5

0.0 0.5 2.60eV 1.74MV/cm Z (nm) Energy (eV) ΔEC:ΔEV=5:1 <1120> <0001>

InGaN QW

GaN barrier GaN barrier PSP PSP PSP PPZ

• 10
• 5

5 10

• 3.5
• 3.0
• 2.5
• 2.0

0.0 0.5 1.0 1.5 ΔEC:ΔEV=5:1 2.81eV Energy (eV) 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. Adivarahan

Adivarahan, J. W. Yang, M. , J. W. Yang, M. Shatalov Shatalov, E. , E. Kuokstis Kuokstis and M. A. Khan: and M. A. Khan: Jpn

• Jpn. 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 and
• U. 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. Chitnis

Chitnis, C. Chen, V. , C. Chen, V. Adivarahan Adivarahan, M. , M. Shatalov Shatalov, E. , E. Kuokstis Kuokstis, V. , V. Mandavilli Mandavilli, 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
• 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

Issues in nonpolar GaN heteroepitaxy

SFs

PV-TEM 200nm SF density 3.8x105cm-1 g=1010

TDs

1μm g=0002 TDD 2.6x1010cm-2 X-TEM r r-

• plane Al

plane Al2

2O

O3

3

NL NL-

• GaN

GaN a a-

• plane GaN

plane GaN

MOVPE MOVPE

GaN 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

HVPE HVPE

m-plane 6H-SiC

LEO LEO-

• GaN

GaN GaN GaN SiO2mask

asymmetric LEO asymmetric LEO

m-plane GaN template

[0001] [1100] [1120]

SiO2mask Ga-polar Wing N-polar Wing Window

4×109 1×105 5×106 1×105 >> >> << << >> =

m-plane InGaN QWs grown on LEO GaN base

Plan-view SEM image

Ga-polar wing N-polar wing Window

2.6 2.8 3.0 3.2 3.4 450 400 WAVELENGTH (nm) INTENSITY (arb. units) PHOTON ENERGY (eV) PL 300K 8K B UV InN molar fraction: depends on the base structure CL (300K) wide B V spot UV P 10μm

5kV x2,000

In0.08Ga0.92N(3.1nm) / GaN(6.9nm) Ga-polar wing window N-polar [1100] [1120] [0001]

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

ΔEc ΔEv Eg(AlxGa1-xN) =6.138x+3.412(1-x)-0.82x(1-x) 3) ΔEc:ΔEv=3:1 me=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) 2 4 6 8 10 3.40 3.44 3.48 3.52 3.56 3.60 PL PEAK ENERGY (eV) 293K

• n (1120) GaN
• n (1120) LEO-GaN

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

• n (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 INTENSITY (arb. units) 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

1 2

L=4.1nm L=9.3nm

• n GaN

8K

system

PL INTENSITY (arb. units) TIME (ns)

L=2.4nm L=6.2nm

• n LEO-GaN

2 4 6 8 10 100 103 8K PL lifetime (ns) GaN WELL WIDTH (nm)

• n GaN
• n LEO-GaN

τPL independent of L no polarization fields

Ti:sapphire 242nm 2mW

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

τPL ～ τR (L.T.) short τR comparable 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
• 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

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> 2

nm

1µm

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

407.4 Wavelength (nm) 435 Output power (mW) 23.7 EQE (%) 38.9

Schmidt et al., JJAP 46, L126 (2007).

1.79 3.1

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

Driving current 20mA

m-plane InGaN LEDs Progress of m-plane InGaN devices using low defect density FS-GaN substrates m-plane InGaN 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 Pulsed 459 5.0 CW

481

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
• 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

Growth conditions

Horizontal 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 GaN substrate

325μm

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

GaN 1.5μm Pgrowth : 5.3×104 Pa H2 carrier TMGa+NH3 Rg=1.5 μm/h Tg=1090 °C V/III =5000 GaN

APL 92, 091912 (2008); erratum 93, 129901 (2008). InGaN 200-250nm

InGaN Pgrowth : 6.6×104 Pa N2 carrier TMGa+TMIn+NH3 Rg=0.1 μm/h Tg=750-820 °C V/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 2

nm

1µm 3

nm

3

nm nm

2

nm

3 <0001> <1120> <1010>

substrate

2

nm

1µm

APL 92, 091912 (2008); erratum 93, 129901 (2008). ML step 0.26nm RMS ≅0.072nm

XRCs of GaN substrate and epilayer

INTENSITY (arb. units) Δω (°) 0.1 0.05

• 0.1
• 0.05

azimuth <0001> 31″ azimuth <11-20> 91″ (1-100)GaN Tg=1050°C V/III=5000

<(1010)XRC>

INTENSITY (arb. units) Δω (°) 0.1 0.05

• 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 PL

PL INTENSITY (arb. units) PHOTON ENERGY (eV) 3.45 3.50

• n GaN/Al2O3

E//c E⊥c I2

FXA FXB FXA,Bn=2

• n m-plane FS-GaN

I2

FXA FXB FXA,Bn=2,C

• n 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

• n m-plane FS-GaN,

τPL,eff=302ps

• n GaN/Al2O3, 92ps
• n c-plane FS-GaN, 33ps

system PL INTENSITY (arb. units) TIME (ns) 1 2 3 4

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 // [1100] (nm-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°C V/III : 76000

<XRD>

XRD INTENSITY (arb. units)

30 31 32 33 34 35 (1010) GaN (1010) InxGa1-xN

2θ (°) 0.08 0.03 0.03 0.06 0.02

x=

11 zz xx yy

C C C ε ε ε

13 12

− − =

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

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

0.05 0.10 0.15 200 400

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)GaN

XRD/XRC FWHM (") 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 INTENSITY (arb. units)

400 350 InxGa1-xN x= 0.08 0.027 0.032 0.06 0.02 164meV 107meV 118meV 159meV 162meV FWHM 37meV 293 K He-Cd 325nm GaN 450

2.8 3.2 3.6 3.0 3.4 2.6

0.14 310meV 1) SFC et al., Nat. Mater. 6, 810 (2006). IPL(300K)/IPL(8K) (%) (b) InN MOLAR FRACTION x

• n m-plane FS-GaN

0.00 0.05 0.10 0.15 0.20 0.1 1 10 100

• n c-plane FS-GaN

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

• n c-plane GaN/Al2O3

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

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

1 2 3 4 5

2ω-Ti:Al

2O3

(361nm, 120nJ/cm2)

system

250K 200K 300K 150K 100K 50K 6K TIME (ns) PL INTENSITY (arb. units)

m-plane In0.06Ga0.94N film

20 40 10

• 3

10

• 2

10

• 1

10

He-Cd 325.0nm 38W/cm2

ηint(300K)=11% 1000/T (K-1) PL INTENSITY (arb. units)

Low temperature Radiative lifetime = 600 ps (nearly constant below 100 K) Room temperature Nonradiative lifetime 150 ps Radiative lifetime 1.2 ns

0.1 1 10 TEMPERATURE (K) LIFETIME (ns) 100 200 300 τPL,eff (c) τNR,eff τR,eff

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

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

Summary of Device Characteristics

300 400 500 600 5 10 0.01 0.1 1 10 100 Jth (kA/cm2) Wavelength (nm) CW nonpolar / semipolar GaN c-plane MCC m-plane GaN substrate Defective materials EQE (%) c-plane m-plane (Rohm) (b) (a) AlInGaP

EQE of LEDs Threshold current density

• f LDs

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 LED and LD wafers

• 4. Summary

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

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 radiative lifetime / polarized emission). √ m-plane growths on free-standing GaN substrates TD and SF densities -- nearly equal to the underlayer value Reasonable IQE as bulk InGaN films (11% for x=0.06) -- similar to c-plane Improved radiative lifetime (at room temperature) √ m-plane LEDs and LDs on free-standing GaN substrates Coming up to overtake c-plane devices.