Fascinated Journeys into Blue Light Isamu AKASAKI Meijo University - - PowerPoint PPT Presentation

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Fascinated Journeys into Blue Light Isamu AKASAKI Meijo University - - PowerPoint PPT Presentation

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Fascinated Journeys into Blue Light Isamu AKASAKI Meijo University and Nagoya University CONTENTS 1. Introduction 2. Creation of GaN single crystal with excellent quality 3. Development of GaN p-n junction Blue LEDs and Laser diodes 4.

slide-1
SLIDE 1

Fascinated Journeys into Blue Light

CONTENTS

  • 1. Introduction
  • 2. Creation of GaN single crystal with excellent quality
  • 3. Development of GaN p-n junction Blue LEDs and Laser diodes
  • 4. Summary

Isamu AKASAKI

Meijo University and Nagoya University

1/20

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SLIDE 2

2/20

Electron energy

(Internal) photo-electric effect spontaneous emission Valence band Light

Conduction band electron

(Positive)

hole

Energy bandgap Eg Excitation light

Conservation of energy

［A］ Energy bandgap Eg：

>2.6 eV (< 480 nm) (Wide bandgap semiconductors)

［B］ Energy band structure：

Direct-transition type for conservation of electron momentum

Blue Light-Emitting Devices (LED, Laser diode)

(radiative recombination)

  • 1. Introduction
slide-3
SLIDE 3

[1] High-quality single crystal [2] p-n junction

+ +

  • +

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

  • +

+ + +

n type p type

Depletion layer

electron hole

High-performance Blue LED and Laser diode

Light emission

Eg

＋ －

（~3V）

Electric current p-n junction hole Electron energy

Applied forward voltage

  • 1. Introduction

3/20

p-n junction LED

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SLIDE 4

Candidate materials for Blue Light-Emitters

in 1960s-’70s

  • 1. Introduction

4/20

ZnSe GaN

[A] Energy gap (Eg) 2.7 eV 3.4 eV [B] Energy band structure direct direct [1] Crystal growth straightforward too difficult Substrate GaAs sapphire Lattice mismatch 0.26 % 16 % [2] p-n junction not realized at that time Number of researchers many few Physical & chemical stability low high

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SLIDE 5

Chose GaN in 1973 at Matsushita Research Institute Tokyo (MRIT)

because of toughness, wider direct Eg, and non-toxicity

Candidate materials for Blue Light-Emitters

in 1960s-’70s

  • 1. Introduction

5/20

ZnSe GaN

[A] Energy gap (Eg) 2.7 eV 3.4 eV [B] Energy band structure direct direct [1] Crystal growth straightforward too difficult Substrate GaAs sapphire Lattice mismatch 0.26 % 16 % [2] p-n junction not realized at that time Number of researchers many few Physical & chemical stability low high

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SLIDE 6

GaN MIS Blue LED by HVPE

MIS Blue LED

1978 MIS Blue LED, not p-n junction LED

  • 1. Introduction

at MRIT sapphire

SiO2 film n-GaN i-GaN Ohmic electrode n-GaN (30 μm) i-GaN (~1μm)

Epoxy dome

hν

The brightest Blue LED at that time, however, still weak and high operating voltage First as-grown highly n-type cathode

6/20

Started growth of GaN by MBE in 1973, and by HVPE in 1975

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SLIDE 7

Tiny but high-quality crystallites embedded in HVPE-grown crystals Recognized the great potential of GaN

Made up my mind to go back to the beginning; i.e. Crystal Growth in 1978

High-quality tiny crystallites

Potential of GaN

100μm

  • 1. Introduction

Surface of GaN grown on sapphire by HVPE (1975-78)

7/20

at MRIT

slide-8
SLIDE 8

Crystal growth methods for GaN

Hydride Vapor Phase Epitaxy (HVPE) H. P. Maruska and J. J. Tietjen: (1969).

GaCl (g) + NH3 (g) = GaN (s) + HCl (g) + H2 (g)

Issues: Susceptible to reverse reactions, Too fast growth rate Molecular Beam Epitaxy (MBE) I. Akasaki: (1974) (unpublished).

Ga (g) + NH3 (g) = GaN (s) + H2 (g)

Issues: Prone to nitrogen deficiency, Slow growth rate (at that time) Metalorganic Vapor Phase Epitaxy (MOVPE), (MOCVD) H. M. Manasevit et al: (1971).

Ga(CH3)3 (g) + NH3 (g) GaN (s) + 3CH4 (g) Advantages:

  • No reverse reactions
  • Easy to control growth rate, alloy (AlGaN, GaInN) composition,

and impurity-doping

Decided to adopt MOVPE (1979)

2 3

  • 2. Creation of GaN single crystal with excellent quality

at MRIT

8/20

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SLIDE 9

Mixing TMG (TMA) with NH3 just before the reactor inlet, and (1) High speed gas flow (2) Substrate inclined at a 45-degree angle

110 cm/sec (1) Inclined substrate (2)

sapphire

  • Y. Koide

(1985) First MOVPE system (Handmade)

  • 2. Creation of GaN single crystal with excellent quality

Exhaust

Uniform growth, but not specular surface, still poor material quality

Improvements in MOVPE reactor and growth condition (1) (2)

Started anew to MOVPE since 1981 at Nagoya University

0.7~20cm/sec substrate susceptor RF coil guide NH3+H2 TMG+TMA+H2 delivery tube TMG+(TMA)+H2 NH3+H2

Exhaust Reactor

Bird-view SEM image

Suppressed the convective gas stream, and the adduct formation GaN

sapphire

9/20 Reactor design changed

10 μm

by H. Amano

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SLIDE 10

Growth on a highly-mismatched substrate

Homoepitaxy Heteroepitaxy

defects Lattice matching Huge lattice-mismatch

Interfacial energy σ

Growth on the same substrate

GaN GaN

but

not available A A A B

For epitaxial growth, it is considered to be gospel to have a lattice matching: (e. g. Si on Si, GaAs on GaAs)

GaN sapphire

mismatch ~ 16%

  • 2. Creation of GaN single crystal with excellent quality

Lattice

10/20

slide-11
SLIDE 11

TMG(TMA)+H2 NH3+H2 delivery tube substrate susceptor Exhaust RF coil

Direct growth

(Common method)

newly- developed

LT-buffer layer

425 cm/sec Key technologies: (1) Much higher-speed gas flow (425 cm/sec) (2) Substrate inclined at a 45-degree angle (3) Deposition of thin AlN buffer layer at about 500 oC, before the growth of GaN single crystal at about 1000 oC (1) (3)

(3) Innovation in MOVPE growth method (1985)

Low-temperature (LT-) buffer layer

Sapphire(0001) LT-buffer LT-buffer (20~50 nm) ~500 oC

GaN

High-quality GaN ~ 1000 oC

  • H. Amano
  • 2. Creation of GaN single crystal with excellent quality

(2)

11/20

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SLIDE 12

Creation of high-quality GaN (1985)

Until 1985

(b)

GaN grown by HVPE

GaN grown by MOVPE using LT-buffer

Since the late 1985

Many cracks, pits Crack-free, pit-free Rough surface Specular surface Dislocations: > 1011 cm-2 Dislocations: 108-109 cm-2 Free electron conc. >1019 cm-3 Free electron conc. < 1016 cm-3 Electron mobility: ~20 cm2/V･s Electron mobility: ~700 cm2/V･s Weak luminescence Intense luminescence

Crystal quality, electrical property, and luminescence property were dramatically improved at the same time

GaN grown by MOVPE

100μm

  • 2. Creation of GaN single crystal with excellent quality

GaN island crystal Sapphire 2mm

12/20

slide-13
SLIDE 13
  • 2. Creation of GaN single crystal with excellent quality

Increase GaN thickness

LT-buffer layer

Sapphire

Mixture both amorphous & fine crystallites of AlN GaN LT-buffer layer

Sapphire

Lateral growth of GaN dominates

Surface (SEM) images Growth model Growth model of GaN using LT-buffer layer

(1) As-deposited LT-AlN buffer layer (2) 5 min GaN growth (3) 10 min GaN growth (4) 20 min GaN growth (5) 60 min GaN growth

GaN island

Growth model GaN island Sapphire

  • K. Hiramatsu

Direct growth for 60 min. (No LT-buffer)

Surface (SEM) images

13/20

LT-buffer layer

Sapphire

GaN layer of excellent quality

1μm

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SLIDE 14

Realization of p-type GaN, AlGaN, and GaInN

1988 Found greatly enhanced blue emission of Zn doped GaN by electron irradiation (LEEBI)

Achieved the first p-type GaN

1989 Doped Mg using CP2Mg and electron irradiation

High-quality Mg-doped GaN subjected to LEEBI

1991 p-type AlGaN 1995 p-type GaInN

  • M. Kito
  • H. Amano

1986 High-quality GaN using LT-buffer layer (Low residual impurities)

Basic Technology

(C5H5)2Mg

  • 3. Development of GaN p-n junction Blue LEDs and Laser diodes

14/20

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SLIDE 15

The world’s first GaN p-n junction blue LED (1989) I-V curves

p-n LED MIS LED

GaN p-n junction Blue LED

Voltage Current

  • H. Amano
  • M. Kito
  • 3. Development of GaN p-n junction Blue LEDs and Laser diodes

15/20

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SLIDE 16

Achieved conductivity control of n-type GaN

SiH4 flow rate [sccm] Electron concentration [cm-3]

1016 1017 1018 1019 1 10 100

1989 Doped Si into high-quality GaN using SiH4

n-type AlGaN

1991

Conductivity control of n-type GaN, AlGaN

1986 High-quality GaN using LT-buffer layer (Low residual impurities)

Basic Technology

  • 3. Development of GaN p-n junction Blue LEDs and Laser diodes

Allowed the use of heterostructure and quantum well in the design of more efficient p-n junction light- emitting structures

16/20

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SLIDE 17

UV (376 nm) Laser diode (1996)

Stimulated emission by

  • ptical pumping (1990)

EL intensity

AlGaN/GaN/GaInN

・ ・

Wavelength (nm)

360 370 380 390 1.5kA/cm2 ~ x 50

Current (mA)

Integrated light intensity (arb. units)

3.0kA/cm2

GaN-based laser

EL intensity (arb. units)

Stimulated emission by current injection (1995) By current injection

3.4 3.3 3.5 Photon energy (eV)

Emission intensity Room temp.

  • 3. Development of GaN p-n junction Blue LEDs and Laser diodes

On the basis of the technologies of LT-buffer layer and p-n junction heterostructures, GaN-based lasers were achieved

Wavelength (nm)

300 400 500 600 700 AlGaN/GaN/GaInN quantum well

Room temp. 17/20

388 nm

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SLIDE 18

Number of Papers Related to Nitrides (1965-2012) 1970 1980 1990 2000 2010 1000 2000 3000

Number of Papers Year

Web of Science Keywords; AlN, GaN,InN, AlGaN, InGaN

High-quality GaN using LT-buffer (1986)

Distinguished Important Achievements

1969

Single crystal GaN (H. P. Maruska et al.)

1971

MIS-type Blue LED (J. I. Pankove et al.)

1986 High-quality GaN single crystal grown with LT-buffer layer by MOVPE 1989 GaN p-n junction Blue LED 1989 Conductivity control of p- and n-type GaN 1990

Room temperature UV stimulated emission from GaN by optical pumping

1990

Growth of GaInN (T. Matsuoka et al.)

1991 p-type GaN by thermal annealing (S. Nakamura et al.) 1993 GaInN double hetero-junction Blue LED (S. Nakamura et al.) 1995 Stimulated emission from GaInN/GaN quantum wells by current injection 1996 Violet laser diode (S. Nakamura et al.) 1996 UV laser diode

3409 papers(2012)

Red characters: Akasaki and Amano group

  • 4. Summary

18/20

p-n junction Blue LED (1989)

slide-19
SLIDE 19

While many researchers abandoned the development

  • f GaN Blue LED, I have been fascinated with the

research on GaN-based semiconductors, since 1973. Through persistent efforts, with the collaboration of Hiroshi Amano, Yasuo Koide, and many students/ coresearchers over many years, we invented high- quality GaN single crystal in 1986, and GaN p-n junction Blue LED in 1989. GaN-based photonic & electronic devices are environmentally-sound, robust, and energy-saving, which benefit humanity.

  • 4. Summary

19/20

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SLIDE 20

20/20

Acknowledgements

With the most generous cooperation of

 M. Hashimoto, Y. Ohki, H. Kobayasi, Y. Toyoda, M. Ohshima, N. Mazda Matsushita Research Institute Tokyo, Inc. (1964−1981)  N. Sawaki, K. Hiramatsu, Y. Koide, H. Amano, M. Kito, T. Kozawa Nagoya University (1981−1992)  H. Amano, S. Kamiyama, T. Takeuchi, M. Iwaya Meijo University (1992− )  B. Monemar Linköping and Lund University  TOYODA GOSEI CO., LTD, & TOYOTA CENTRAL R&D LABS.,INC. (1987 − )  MITI Project (Blue LED,1975−1978)  Grants-in-Aid for Scientific Research (MEXT, JSPS) (1981− )  JST Project (Blue LED,1987−1990) (Violet laser diode,1993−1999)  JSPS Research for the Future Program (1996−2001)  MEXT High-Tech Research Center Project (1996−2004)

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