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

Growth issues and optical properties of nonpolar (Al,In,Ga)N films and quantum wells Shigefusa F. Chichibu Center for Advanced Nitride Technology Institute of Multidisciplinary Research for Advanced Materials Tohoku University Koji Hazu and Takeyoshi Onuma as Assistant Professors

Chichibu Laboratory (IMRAM, Tohoku Univ.) Optoelectronic devices Wide bandgap semiconductor quantum nanostructures GaN, ZnO etc Epitaxial growth Material Science New functional and planet conscious semiconductor optoelectronic devices, material growth, and material engineering HWPSE for ZnO/MgZnO heterostructures SEM / CL MOVPE Quantum well laser structure Femtosecond Ti:sapphire laser NH 3 -MBE 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 BANDGAP ENERGY E g (eV) 7 (nm) AlN Group-III Nitride Semiconductors 200 DEEP UV 6 (Al, Ga, In)N 5 250 Wide Direct Bandgap range √ 300 AlN 6.01 eV 4 UV √ GaN 3.43 eV √ GaN 3 400 InN 0.67 eV 500 From deep UV to IR 2 600 800 Hard material IR 1 InN High-power, high-frequency 0 Electronic Devices 0.30 0.34 0.38 LATTICE PARAMETER a (nm)

Blue, green, white LEDs and 400nm LDs

Group-III Nitride Semiconductors BANDGAP ENERGY E g (eV) 7 (nm) AlN 200 DEEP UV 6 5 250 300 4 UV GaN 3 400 500 2 600 800 IR 1 Practical devices exclusively InN 0 use c-plane (0001) InGaN 0.30 0.34 0.38 quantum well active region LATTICE PARAMETER a (nm)

Issues on EQE vs wavelength ( c -plane) EQE of (Al, In, Ga)N QW LEDs 1-6) ~ 54% maximum value for 10 2 ~ 63% 4) AllnGaP LEDs 10 1 Blue . c 10 0 Green 5) t e e t c -plane ENERGY (arb. units) EQE (%) e a 10 -1 e l Increase in InN N p r f a m - G molar fraction N 10 -2 e a t G (1) point defects 10 -3 AlN AlGaN InGaN-base AlInGaP (low T g of InGaN) 10 -4 (2) polarization effects 10 -5 6) (increased lattice 10 -6 % 10 -6 mismatch → [0001] 200 300 400 500 600 increased QCSEs) -10 -5 0 5 10 WAVELENGTH (nm) Z (nm) Chichibu et al . √ Substrate absorption APL 69, 4188 (1996). [0001] [0001] √ Increase in TDD and point defects Takeuchi et al. JJAP 36, L382 (1997). 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). polarization fields 6) Taniyasu et al ., Nature 441 , 325 (2006).

Polarization discontinuity at heterointerfaces Low crystal symmetry : Wurtzite lattice No inversion symmetry along the c -axis C 6v 4 : uniaxial anisotropy → spontaneous polarization ( P SP ) Lattice mismatched STRAINED heterostructures no inversion symmetry → piezoelectric polarization ( P PZ ) along the c -axis Polarization discontinuity produces immobile charges ( ±σ )at the interfaces (0001) Ga-polar case Piezoelectric P SP compressive + σ polarization P SP P PZ - σ Spontaneous P SP 0 polarization relaxed C/m 2 P SP - σ E. Hellman, MRS Internet J. P SP P PZ + σ tensile strain Nitride Semicond. Res. 3 ,11 (1998). P SP relaxed F. Bernardini, V. Fiorentini, and D. Vanderbilt, Phys. Rev. B 56, R10024 (1997).

Avoid polarization fields - off c -axis semipolar - (1011) (1013) nonpolar planes a -plane m -plane [1010] [ 1120 ] [0001] [0001] * * T. Takeuchi et al ., Jpn. J. Appl. Phys. 39, L413 (2000). and U. Schwarz and M. Kneissl, PSS (PRL) 1, A44 (2007). [1010] [ 1120 ]

m -plane GaN and AlGaN/GaN / γ -LiAlO 2 P. Waltereit et al ., Nature 406, 865 (2000).

Nonpolar m - and a -plane InGaN/GaN polar (0001) Nonpolar (1120), (1100), (001) In 0.15 Ga 0.85 N (3nm)/GaN(15nm) In 0.15 Ga 0.85 N (3nm)/GaN(15nm) P SP <1120> <0001> P SP P SP P SP P SP <0001> P SP P PZ P PZ GaN barrier GaN barrier InGaN QW InGaN QW barrier barrier [0001] [1120] GaN GaN 0.5 1.5 1.74MV/cm 1.0 0.0 [1010] F pol Energy (eV) Energy (eV) 0.5 -0.5 [1010] [0001] -1.0 0.0 2.60eV 2.81eV -3.0 -2.0 -3.5 -2.5 -4.0 -3.0 Δ E C : Δ E V =5:1 Δ E C : Δ E V =5:1 -4.5 -3.5 [1120] -10 -5 0 5 10 -10 -5 0 5 10 Z (nm) Z (nm) SFC et al ., Nat. Mater. 5, 810 (2006)

Nonpolar light-emitting diodes (LEDs) a -plane C. Q. Chen, V. Adivarahan C. Q. Chen, V. 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). MOCVD, GaN / Al 0.12 Ga 0.88 N (3x), on r -plane Al 2 O 3 University of South Carolina 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 A. M. A. Khan: Appl. Phys. Lett. 84, 3663 (2004). M. A. Khan: Appl. Phys. Lett. 84, 3663 (2004). MOCVD, In 0.15 Ga 0.85 N / GaN (3x), on r -plane Al 2 O 3 University of South Carolina A. Chakraborty, B. Haskell, S. Keller, J. S. Speck, S. P. DenBaars, S. Nakamura and U. K. Mishra: Appl. Phys. Lett. 85, 5143 (2004). MOCVD, In 0.17 Ga 0.83 N / GaN (5x), on HVPE LEO a -plane GaN template UCSB m -plane 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, In 0.17 Ga 0.83 N / GaN (5x), on free-standing m -plane GaN template UCSB N. F. Gardner, J. C. Kim, J. J. Wierer, Y. C. Shen, and M. R. Krames: Appl. Phys. Lett. 86, 111101 (2005). MOCVD, InGaN / GaN, on m -plane 4H-SiC 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, In 0.16 Ga 0.84 N / 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 TDs X-TEM PV-TEM SF density MOVPE MOVPE TDD 2.6x10 10 cm -2 3.8x10 5 cm -1 GaN 1100 ° C a - a -plane GaN plane GaN NL-GaN 600 ° C NL- -GaN GaN NL r - r -plane Al plane Al 2 2 O O 3 3 1) Craven et al ., APL 81, 469 (2002). 1 μ m g=1010 g=0002 200nm SiO 2 mask asymmetric LEO asymmetric LEO [1120] HVPE HVPE LEO- -GaN GaN LEO SiO 2 mask [0001] MBE GaN GaN m -plane 6H-SiC [1100] m -plane GaN template 2) Haskell et al., APL 86, 111917 (2005). m -plane GaN template Ga-polar Wing Window N-polar Wing 2 × 10 9 5 × 10 6 4 × 10 9 5 × 10 6 << >> >> TDD (cm -2 ) << = 1 × 10 5 >> 3 × 10 3 1 × 10 5 1 × 10 5 SFD (cm -1 )

m -plane InGaN QWs grown on LEO GaN base Plan-view SEM image WAVELENGTH (nm) 450 400 10 μ m 8K PL Ga-polar wing B UV INTENSITY (arb. units) 300K N-polar wing Window CL (300K) wide UV 5kV x2,000 P spot Ga-polar N-polar window V [1120] B wing 2.6 2.8 3.0 3.2 3.4 [0001] [1100] PHOTON ENERGY (eV) In 0.08 Ga 0.92 N(3.1nm) / GaN(6.9nm) InN molar fraction: Onuma et al ., JVST B 25, 1524 (2007). depends on the base structure