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 )
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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+
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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 :
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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.
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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.