Nanostructures withquantum wells

and quantum dots

Prof. Dr. Alexander L. Gurskii

B.I.Stepanov Institute of Physics,National Academy of Sciences of

Belarus

Contents1. Introduction

- some application areas- optoelectronic devices: historical view

2. Theoretical background- basic definitions- quantum confinement and the density of states- heterostructure design- different types of heterostruc- tures- recombination mechanisms

3. Device examples4. Conclusion.

BASIC APPLICATION AREASOF QUANTUM CONFINED

STRUCTURES

1. NANOELECTRONICS- 2DEG-based devices (HEMT)- nanotube transistors-logical gates

2. NANOOPTOELECTRONICS- LASERS- LEDs

Blu-ray Disc FoundersHitachi, Ltd.LG Electronics Inc.Matsushita Electric Industrial Co., Ltd.Pioneer CorporationRoyal Philips ElectronicsSamsung Electronics Co., Ltd.Sharp CorporationSony CorporationThomson

http ://optics.org/artic les/new s/9/3/4/1Sony p lans to re lease the first D VD recorder based on a v io le t d iode laser next m onth.The new m achine w ill be ava ilab le in Japan from m id-April, priced at 450 000 yen ( .D isc capacity: 27 G b (up to 50 G b)

about $3800)

Some applications of laser diodes and LEDs based onwide-band gap semiconductors (AlInGaN-based system)

Both USA and Japanalready haveNational programs ofsolid state lighting

The replacement of incandescent bulbsby LEDs allow to save up to 1 TW h/year ofelectric power, or $ 100 billion each year

The use of Si substrates instead of sapphire will allow to produce low cost devices

HETEROSTRUCTURES: HISTORY AND PROGRESS

GaAs BASED HETEROSTRUCTURES

1963 conception of double heterostructure lasers:double injection, c&o confinement

Alferov, KazarinovKroemer

19661967

GaAsP-lattice mismatched DH LDs, 77KAlGaAs-lattice matched heterostructures

Alferov et al.Rupprecht et al.

1969 AlGaAs-DH LD: Jthr=4300 A/cm2, RT, pulse,770 nm, LED, transistors, solar sell elements

Alferov et al.

1970 AlGaAs LDs, CW, RT, Jthr=940 A/cm2

InGaAsP: from IR to visible

Alferov et al.Hayashi, PanishAlferov et al.Antipas et al.

1974 Quantum sized effect in GaAs/AlGaAs(multi) graded structure of kabs, h = F(dw)

Resonance tunneling

Dingle et al.Esaki, Chang, Tsuet al.

1975 First AlGaAs/GaAs MQW optically pumpedlaser, T = 15 K, h = 1.53 eV

Van der Ziel,Dingle et al.

1978 AlGaAs/GaAs LD, RT, QUANTUM WELLJthr=3*103 A/cm2, nm

Dupius, Dapcus,Holonyak et al.

1980 QW heterostructures: transistors,Quantum Hall effect

Mimura et al.Klitzing et al.

1982 AlGaAs/GaAs GRINSH, Jthr=160 A/cm2 Tsang et al.1983 GaAs/InGaAs strained LD, RT, CW Holonyak et al.19961997

InGaAs/GaAs QDs LDs, RT, CWJthr=97 A/cm2, P = 160 mW, h = 1.3 eV

Bimberg, Park,Alferov et al,.

2000 InGaAs/GaAs QD transverse&VCSEL,m, J<100 A/cm2, P = 2.7 W

Ustinov et al.

19942000

Quantum engineering quantum cascadelasers: 4 – 11 m, T = 320 K

Faist, Capasso,Sirtory, Cho

2000 Nobel Prize "for developing semiconductorHeterostructures used in high-speed- andopto-electronics"

Zhores I.Alferov,Herbert Kroemer

ZnSe BASED HETEROSTRUCTURES

1990 p-ZnSe:N Park et al.

1991 ZnSe/ZnCdSe QW SCH LD, T = 77 Knm

Qiu et al.Haase et al.

19972000

RT, CW, t = 400 h, Jthr = 500 A/cm2, Ithr = 25-30 A, P = 20 mW

SONYOkuyama et alLandwehr

2000 ZnSe/CdSe QD lasers, RT, Ithr = 4 kW/cm2 Kopjev, IvanovAlferov, Usikovet al.

2000 ZnSe “white” LED: blue LED+orange PLBlue-green-orange Mixed-Colour LEDsI = 20 mA – 2 mW, U = 2.7 V, t > 800 hBlue-red ZnSe/BeTe LEDs: - 1000 h

Sumimoto Ltd

Reusher, Ivanovet al.

19941996

ZnSe based QWHs: Stark effect, self-electro-optics effects, bistable switchers, modulators

Ebeling,Gutovskii et al.,Marquardt,Heuken et al.Cavenett et al.

19992001

ZnMgSSe/ZnSe. Theory: 2D e-h plasmaband gap renormalisation, Auger effect intrions.

Poklonski et al.

1997

2000

ZnMgSSe/ZnSe SCH MQW OPL: Tmax=612K, 440–490 nm, Ithr=20 kW/cm2

Effect of inherent laser annealing

Yablonskii,Gurskii, Kalish,Heuken, Heimeet al.

2003 ZnMgSSe/ZnCdSe quantum dot laserpumped by the GaN blue laser

Yablonskii, Gur-skii, Lutsenko,Ivanov, Heukenet al.

GaN BASED HETEROSTRUCTURES

1992 p-GaN:Mg e-beam annealing thermal annealing

Akasaki et al.Nakamura et al.

199419952000

InGaN/GaN QW LED, T = 300 KT ~ 5*104 h, T = 325 K, 16%Al(In)GaN/Al(In)GaN QW LED: V=2-8V, 340 – 540 nm, I=0.2-20 A, P = 10 mW

Nakamura et al.Nichia, HP, CreeEMCOR,XEROXOtsuka et al.

1996 InGaN/GaN LD, T = 300 K, pulsed,nm, U = 28 V, Jthr = 13 kA/cm2

Nakamura et al.

1998

2000

InGaN/GaN SCH LD, CW, RT, nm,P = 2 mW (104 h), P=30 mW (150 h, 320 K)Jthr=3.6 kA/cm2, Ithr = 43 mA, Uthr= 4.3 V.10 (30) mW, 60oC 2000 (500) h; P=40mW

Nakamura et al.

2000 InGaN/GaN QW LD, T = 300 K,nm (4.6 kA cm-2, 6.1 V), t = 200 h,P = 5 mW

Nakamura et al.

1997

2000

Al(In)Ga/AlGaN QD OPLT = 20 K, h3.48 eV, Ithr = 0.75 MW/cm2

QD VCSE OPL (16 K, 3.02 eV, 1 MW/cm2)Tanaka et al.Krestnikov et al.

AlGaN/GaN transistors: HEMT, MESFET,BJT, Eg = 3.4 eV, Ebd = 5 MV/cm, = 2000cm2/Vs, fpgf=100 GHz, Tm =673 K, t>1000 h

19992001

Pt-GaN, Pt-AlGaN-HEMT transistors Gas (H2, CO, NO) sensing devices

Luther et al,Schalving et al.

19962000

Piezoelectric field up to 1 MV/cm2 inIn(Al)GaN/GaN QWs, nscr > 1018 cm-3

Hangleiter et al.Bernardini et al.Chichibu et al.

19982000

InGaN/GaN QWs: UV laser assistedannealing, OPL –470 nm, T > 300 K

Yablonskii,Lutsenko,Schineller,Heuken et al.

2002 InGaN/GaN true blue laser Yablonskii,Lutsenko, Gurskii,Heuken et al.

2002 InGaN/GaN/Si blue laser Yablonskii,Lutsenko, Gurskii,Heuken et al.

SOME BASIC DEFINITIONS:

Heterostructure:Crystal consisted of one ore more junctionsbetween different semiconductors with differentEg, lattice constants, layer thiknessEg > 2 eV wide band-gap semiconductors

Design:Substrate + a sequence of thin layers

Potential well:

Active layer Ega < Eg

c of claddings (barriers)Band offset: Ev > 0, Ec < 0

Classical:Lx

a «Ly, Lz, Lxa » h/p,

Lxa » aB

? is the de Broglie wavelength of the carriersaB is the Bohr exciton radius

Quantum well:Lx

a « Ly, Lz and Lxa ~ aB

Quantum size effect:

the carrier movement in the x directionis quantizedthe carrier energy becomes definite discrete

Optical and carrier confinement due to Eg and nr

Heterostructure types:

Single heterostructuresDouble heterostructuresSingle, double and multiple QWHsSeparate confinement QWHsGraded-Index SCH

D E N S I T Y O F S T A T E S A N D C A R R I E R D I S T R I B U T I O N

S c h e m a t i c d r a w i n g o f d e n s i t y o f s t a t e s f u n c t i o n s o f s t r u c t u r e s w i t hd i f f e r e n t d i m e n s i o n a l i t y f o r e l e c t r o n s ( b l a c k l i n e s ) . S c h e m a t i c d r a w i n g

o f o c c u p i e d e l e c t r o n s t a t e s u n d e r e x c i t a t i o n ( r e d l i n e s )

Em

E vcvc 2

232 ,)0(

, 2

)2()(

n

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L

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)( 2

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E , ,

)3( , )]()()([

1 )( [ 1 ]

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xhen L

n

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[ 2 ]

1 Y . A r a k a w a a n d H . S a k a k i / A p p l . P h y s . L e t t . 4 0 ( 1 1 ) , 1 9 8 22 B . M r o z i e w i c z e t a l . / P h y s i c s o f S e m i c o n d u c t o r L a s e r s ( b y P W N – P o l i s h S c i e n t i f i cP u b l i s h e r s – W a r s z a w a , 1 9 9 1 ) p . 1 8 0

GAIN FORMATION

Schematic drawing of the gain formation in 3D bulkDH active material (top) and in a 2D QW material(bottom). Due to the smaller density of states in 2D thetransparency current I0 is diminished. Due to thesquare density of states, a given number of injectedcarriers is more efficient to create gain in the 2D QW(center), which translates into a steeper gain-currentcurve (right)[1].

1 С. Weisbuch / Journal of Crystal Growth 138 pp.776-785, 1994

STRUCTURE DESIGN AND CARRIERDISTRIBUTION

Schematic drawings of several QW laser structuresand associated energy levels and occupied electronstates under carrier injection[1].

1 С. Weisbuch / Journal of Crystal Growth 138 p.776-785, 1994

p n+

+++_

____

+

E

E

x

FE

C

EV

+x

EC

EV

Fe F

h

Energy diagram

Main weak pointsS trong tem pera ture dependence o f laser thresho ldH igh th reshold current density (J>25x10 A /cmat Т=300 К)Low to ta l quantum y ie ld (2 -3% at T=300 К );C oo ling by liqu id gases is necessaryS hort life tim e (several hours a t Т=300 К)

3 2

CLASSICAL HETEROSTRUCTURES

Fundamental physical phenomena:

a) - one-sided injection andsuperinjection;

b) - diffusion in built-inelectrcal field;

c) - electrical and opticalconfinement;

d) - effect of wide-gapwindow;

e) - diagonal tunneling overthe heterointerface.

Important features for technology: In principle, lattice-matched structures are necessary; For lattice matching, multicomponent solid solutions should be

used; In principle, epitaxial growth technology is necessary

Important consequences for application insemiconductor light emitting devices

Low threshold semiconductor laser diodes operating in CW regimeat room temperature (Jth

103 A/сm2); High-efficient LEDs

But: Threshold current is still high enough; Strong temperature dependence of threshold current

Zh.I.Alferov. Sov. Phys. Semicond, 1998, Vol. 32, №1, p.3-18.

Q u a n t u m W e l l H e t e r o s t r u c t u r e sF u n d a m e n t a l p h y s ic a l p h e n o m e n a :

3.3 эВ

3.05 эВ

- t w o - d im e n t s io n a l e le c t r o ng a s ( 2 D E G ) ;- s t e p - l i k e f u n c t io n o fd e n s i t y o f s t a t e s ;- in c r e a s in g e x c i t o n b in d in ge n e r g y t h e i r e x c is t e n c e a tr o o m t e m p e r a t u r e isp o s s ib le ;- e f f e c t o f w id e - g a p w in d o w ;- q u a n t u m H a l l e f f e c t ;- c o h e r e n t g r o w t h o fs t r a in e d la y e rh e t e r o s t r u c t u r e s ;

Im p o r t a n t f e a t u r e s f o r t e c h n o lo g y :L a t t ic e - m a t c h e d s t r u c t u r e s a r e n o t a lw a y s n e c e s s a r y ;S u p p r e s s io n o f m is f i t d is lo c a t io n f o r m a t io n d u r in g g r o w t h ;In p r in c ip le , w e l l - c o n t r o l le d e p i t a x ia l g r o w t h t e c h n o lo g y w i t h lo wg r o w t h r a t e s is n e c e s s a r y ( М В Е , M O V P E ) , p o s s ib ly w i t h a t o m ic la y e rg r o w t h m o d e (А L E ) ;

Im p o r t a n t c o n s e q u e n c e s f o r a p p l ic a t io n s ins e m ic o n d u c t o r l ig h t e m i t t in g d e v ic e s :

L o w e r t h r e s h o ld c u r r e n t d e n s i t y a t r o o m t e m p e r a t u r e ( J t h1 0 0 A /с m 2 ) ;

W e a k e r t e m p e r a t u r e d e p e n d e n c e J t h (Т ) ; h ig h e r d i f f e r e n t ia l g a in ;H ig h - e f f i c ie n c y L E D s a n d q u a n t u m c a s c a d e IR la s e r s ;L a s e r s w i t h s u p e r la t t i c e s in g u id in g la y e r ( J t h

4 0 A /с m 2 ) ;

( Z h . I .A l f e r o v . S o v . P h y s . S e m ic o n d , 1 9 9 8 , V o l . 3 2 , № 1 , p .3 - 1 8 ) .

A dvantage: requced therm al dependence o f thethresho ld current dens ity in com parison to thequantum w ell based structures.

It w as show n experim enta lly tha t the structuresw ith quantum w ires have the threshold currentdensity approxim ately 2 tim es low er than thestructures w ith quantum w ells g row n underana logous conditions.

M.Higashiwaki. Compound Semiconductor, 1999, Vol.5, N 6, p.38-39

S Y S T E M S B A S E D O N Q U A N T U M D O T S ( Q D )

B a s e d o n t h e s e l f - o r g a n i z a t i o ne f f e c t o f s e m i c o n d u c t o rn a n o s t r u c t u r e s i n h e t e r o e p i t a x i a ls y s t e m s

M i n i m u m d i m e n s i o n o f Q D D m i n :

)(2

1min

2

*

2

QDEDm

Ee

C

M a x i m u m d i m e n s i o n o f Q D

)(1 QDEkT

F U N D A M E N T A L P H Y S I C A L P H E N O M E N A : Z e r o - d i m e n s i o n a l e l e c t r o n g a s ; D e n s i t y o f s t a t e s i s d e l t a - f u n c t i o n - l i k e ; I n c r e a s i n g e x c i t o n b i n d i n g e n e r g y .

I M P O R T A N T F E A T U R E S F O R T E C H N O L O G Y : U s e o f s e l f - o r g a n i z a t i o n e f f e c t s f o r g r o w t h ; L a t t i c e - m i s m a t c h e d l a y e r s o f t h e s t r u c t u r e a r e o f t e n

n e c e s s a r y ; E p i t a x i a l g r o w t h i n V - r i f f l e s ; H i g h - r e s o l u t i o n l i t o g r a p h y i n c o m b i n a t i o n w i t h e t c h i n g o f Q W

s t r u c t u r e s .

I M P O R T A N T C O N S E Q U E N C E S F O R A P P L I A T I O N I NS E M I C O N D U C T O R D E V I C E S

L o v e r t h r e s h o l d c u r r e n t a n d h i g h e r d i f f e r e n t i a l g a i n ; Т e m p e r a t u r e s t a b i l i t y o f t h r e s h o l d c u r r e n t D i s c o n t i n u o u s g a i n s p e c t r a o p e r a t i o n c h a r a c t e r i s t i c s l i k e

t h o s e o f g a s a n d s o l i d - s t a t e l a s e r s a r e p o s s i b l e ; T h e p o s s i b i l i t y o f c r e a t i o n o f “ s i n g l e - e l e c t r o n ” d e v i c e s ; T h e p o s s i b i l i t y o f c r e a t i o n o f “ d e f e c t - f r e e ” d e v i c e s

B u t : T e c h n o l o g y i s p o o r l y d e v e l o p e d , r e p r o d u c i b i l i t y p r o b l e m s

Zh.I.Alferov. Sov. Phys. Semicond. 1998, v.32, N1, pp.3-18.

THRESHOLD CURRENTS OF INJECTION LASERS

Evolution of laser threshold current

Currently, threshold currents have values less than1 mА.

Further decrease of threshold currents is possible in thequantum dot based systems.

Zh.I.Alferov. Sov. Phys. Semicond. 1998, v.32, N1, pp.3-18.

L A S E R T H R E S H O L D

C u r r e n t d e n s i t y a n d g a i n :

)( ,322

2 ,

2

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c

EEdenJ

,

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21imax

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O p t i c a l c o n f i n e m e n t f a c t o r :

d

d

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2

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22 2

, d N d N da a b b , n N d n N d n da a b b b 0

J t h r = f ( T ) :

)()( nsp

nthr edRJ , ]3 0,[n

0

)( ,

)()( )),(,( dETEErR nvc

nsp

nsp

R e s u l t s :

F i g . 1 T h e o r e t i c a l t e m p e r a t u r e s e n s i t i v i t y o f L D s o f t h e a c t i v el a y e r s w i t h v a r i o u s q u a n t u m c o n f i n e m e n td i m e n s i o n a l i t y [ 1 ]

1 Y . A r a k a w a a n d H . S a k a k i A p p l . P h y s . L e t t . 4 0 ( 1 1 ) , 1 9 8 2

E Ee

Eh

x

(E)

n=0transitions

d=10 nm

ZnSe QW

excitons

ZnMgSSeZnMgSSe

0

2

ex E1

2E

0a2d

e3

b hb e k1

k1

2dd

2b

2b

2w

2w

www

m/km/k

m/ka r c s i n2ndk

0

2

ex E1

2E

0a2d

e3

b hb e k1

k1

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2b

2b

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2w

www

m/km/k

m/ka rc s in2ndk

H. M athhieu et a l. Phys. Rev. B , V.46, 4092 (1992)

E

x

y

F. Capasso, J . Faist et al. Solid State Com ., V.102, 231(1997)

Y. Su et al. Optical M aterials, V.14, 205 (2000)

Forward voltage (V)

Y. Arakawa et al. Phys. Stat. Sol. (B), V. 224, 1 (2001)

Conclusions

1. Quantum-dimensional effects allowto create devices based on the newphysical phenomena, with improvedproperties;

2. The creation of such devices is onlypossible using sophisticated technologyusually called «high-technology»

3. The quantum-dimensional nanostruc-tures are the main basis of the scientific-technical progress in such importantareas like solid state lighting, opticalmemory, and nanoelectronics.