Fascinated Journeys into Blue Light · Fascinated Journeys into Blue Light . CONTENTS 1....
Transcript of Fascinated Journeys into Blue Light · Fascinated Journeys into Blue Light . CONTENTS 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
2/20
Elec
tron
ener
gy
(Internal) photo-electric effect spontaneous emission
Valence band
Light
Conduction band electron
(Positive)
hole Ene
rgy
band
gap
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
[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 Elec
tron
ener
gy
Applied forward voltage
1. Introduction 3/20
p-n junction LED
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
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
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
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
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)
23
2. Creation of GaN single crystal with excellent quality
at MRIT
8/20
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
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
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
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
2. Creation of GaN single crystal with excellent quality
Incr
ease
GaN
thic
knes
s
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 layerSapphire
GaN layer of excellent quality
1μm
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
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
Cur
rent
H. Amano M. Kito
3. Development of GaN p-n junction Blue LEDs and Laser diodes 15/20
Achieved conductivity control of n-type GaN
SiH4 flow rate [sccm]
Elec
tron
con
cent
ratio
n [c
m-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
UV (376 nm) Laser diode (1996)
Stimulated emission by optical pumping (1990)
EL in
tens
ity
AlGaN/GaN/GaInN
・
・
Wavelength (nm)3600
0
370 380 390
1.5kA/cm2
~ x 50
Current (mA)
Inte
grat
ed li
ght i
nten
sity
(arb
. uni
ts)
3.0kA/cm2
GaN-based laser
EL in
tens
ity (a
rb. u
nits
)
Stimulated emission by current injection (1995)
By current injection
3.43.3 3.5Photon energy (eV)
Emis
sion
inte
nsity
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
Number of Papers Related to Nitrides (1965-2012)
1970 1980 1990 2000 20100
1000
2000
3000
Num
ber o
f Pap
ers
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)
While many researchers abandoned the development of 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
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)
Supported by