Nano-optoelecrtronics based on III-V Semiconductor Quantum ... · Jungil Lee Nano Device Research...
Transcript of Nano-optoelecrtronics based on III-V Semiconductor Quantum ... · Jungil Lee Nano Device Research...
Jungil LeeNano Device Research Center, KIST
3rd Korea-USA NanoForum, Tower Hotel Seoul, April 3-4, 2006
Nano-optoelecrtronics based on III-V Semiconductor Quantum Dots
KIST
- Founded 1966, gouv. affilliated- 4 Res. Div.s & 1 Res. HQ(future technol.)
Materials, Systems, Environ., Bio-sci- 654 (422(306 Ph.D.)researchers)- 130MU$/yr, ‘04- Future Technol. HQ
Micro Systems Res. Ct.Nano Device Res. Ct.Simulation (supercom., cluster type)team
Nano Device Res. Ct.- Mag. Mater. group + Semicon. Group
(Spintronics)- Semicon. group.
Joo Sang Lee, Young Ju Park (MIT lab)Jin Dong Song (MBE)Won Jun Choi (QD LD, QDIP)Ilki Han (Hi pwr LD, SLD, QCL) (NRL)Woon Jo Cho (nc Si)Jung Il Lee (electrical charac.)~ 20 studs & 1 PD
Collaborators- domesticSRC: - QSRC (TWKang, Dongguk U.), GaN- QPSI (YPLee, Hanyang U.), polymer PC
NRL: - VCSEL (YHLee, KAIST)- QD Technol (SKNoh, KRISS)- Ultrafast Phenom (DSKim, SNU)- Compound Semi Epi (EJYoon, SNU)- QD Opt Dev (DHLee, CNU)1.5QD, SOA- QD PL (YHCho, Chungbuk NU)
Collaborators- international
Germany: WuerzburgUK: Sheffield France: CNRS(IEF, LPN, LSP, LEOM, IMEP,
LAAS)China: CAS-SITP, -IoSemiJapan: U.Tokyo, NICTUSA:
Programs
Dual: QCL –’07Nano R&D (QM D/Wr Technol, 7U+KIST+3Co):
- QD(LD, SOA, Mod)- PC(passive, active) -’11
ETRI: 1.55 um QD LDABITD: QSIP (KIST, KRISS, KAIST) -’04Frontier(TND): Opt Interconnect (YTLee,
GIST)Growth Engin: GaN LED (KOPTI)
Contents
I. QD vs. QWII. QD growth (ALE)III. QD LDIV. QD SLDV. QD IPVI. SummaryVII.Prospects
I. QD vs. QW
Carrier localization & Discrete DOS: - Low leakage currents of LDs- Small active volume ; low transparent current density of LDs- Large activation (thermalization) energy ;
High temperature operation of LDs and IR-PDsStable operation of high power laser at high temp.
- Low refractive index change by injection current ;Small α-parameter -> low chirping (high speed operation)
small filamentation (high power LD)Inhomogeneous broadening due to size fluctuation:
- Large gain bandwidth ; SOA, ECL, SLD
II. QD Growth (ALMBE)
ALMBE mode (ALE mode)ALE:Atomic Layer epitaxy
• Wetting layer is ignorable• Relatively large dot size(> ~30 x ~10 nm)• Wavelength ( more than 1500 nm is possible)
GaAs
n
As In
Dots
GaAsGaAs
n
As In
Dots
GaAs
7.5 nm In0.2Ga0.8As
1.2 nm In0.2Ga0.8As
DWELL 구조 900 1000 1100 1200 1300 14000.0
0.2
0.4
0.6 650 mW
400 mW
200 mW
100 mW50 mW
T = 300 K
PL In
tens
ity (a
.u.)
Wavelength (nm)
34 meV
64 meV
900 1000 1100 1200 1300 14000.0
0.2
0.4
0.6 650 mW
400 mW
200 mW
100 mW50 mW
T = 300 K
PL In
tens
ity (a
.u.)
Wavelength (nm)
34 meV
64 meV
12000 13000 14000 15000 16000-200
0
200
400
600
800
1000
1200
1400
94.3meV
14860AInAs/GaAs ALE QDRT
PL
inte
nsity
(A.U
.)
wavelength(A)
Bandgap engineering of QD : 1150 ~ 1500 nm
Detection wavelength tuning possible
In0.5Ga0.5As QDλ= 1150 nm
InAs QDλ= 1250 nm
D: 1.02 x 1011 /cm2
QD Growth
SK mode dot ALE mode dots
GaAs
• Wetting layer is inevitable• Relatively small dot size(≤ ~30 x ~10 nm)• Wavelength (1000 ~ 1300 nm + α)
• Wetting layer is not necessary• Relatively large dot size(≤ ~60 x ~10 nm)• Wavelength ( more than 1500 nm is possible)
GaAs
N periods of layers
Weting layer
Dots
In As
Dots
GaAs
Sample #A(ALE) Sample #B(S-K)
Dot density, width and height of the sample #A are ~4.1x1010/cm2, ~40.8 nm, and ~7.2 nm, respectively,In the case of the sample #B, 13.4x1010/cm2, ~31.0 nm, ~2.6 nm, respectively.
AFM images
3 3 nmnm
3 3 nmnm
~32~32oo
{136} facet formation We can observe indium diffusion into GaAs below the QDs
Indium can diffuse into GaAs matrix below the QDs during growth interruptions, andthis helps the QDs
HR-TEM images (ALE dot)
HR-TEM images(SK dot)
~ 23 o
The QDs have flat bottom-shape
Sample #A(ALE) Sample #B(S-K)
Thickness of WL : ~ 2.1 nm Thickness of WL : ~ 4 nm
Reduced thickness of wetting layers in the QDs grown by ALMBE was predicted by Guryanov et al. Surf. Sci. 352-354, 651 (1996).
Wetting layer thickness
0.9 1.0 1.1 1.2 1.30.0
0.2
0.4
0.6
0.8
1.0
1.2 T = 300 KSample #A
Sample #B
Nor
mal
ized
PL
inte
nsity
(arb
. uni
ts)
Wavelength (µm)
(x ~20)
Sample #A has a 2 peaks. (Ground and 1st excited level)
Sample #B has only 1 level.
FWHM of sample #A (~29 meV)is ~ half of that of sample #B(~64 meV).
This implies that size distributionof sample #A is more uniformThan sample #B.
~29 meV~64 meV
PL spectra
Temp. depen’t PL spectra
0 50 100 150 200 250 300
1.00
1.02
1.04
1.06
1.08
Temperature (K)
PL p
eak
ener
gy (e
V)
22242628303234363840
Ground level
PL p
eak
FWH
M (m
eV)
0 50 100 150 200 250 300
1.10
1.12
1.14
1.16
1.18
1.20
1.22
Temperature (K)
PL p
eak
ener
gy (e
V)
586062646668707274
PL p
eak
FWH
M (m
eV)
(a) (b)
0 50 100 150 200 250 300
1.00
1.02
1.04
1.06
1.08
Temperature (K)
PL p
eak
ener
gy (e
V)
22242628303234363840
Ground level
PL p
eak
FWH
M (m
eV)
0 50 100 150 200 250 300
1.10
1.12
1.14
1.16
1.18
1.20
1.22
Temperature (K)
PL p
eak
ener
gy (e
V)
586062646668707274
PL p
eak
FWH
M (m
eV)
(a) (b)
0 50 100 150 200 250 300
1.00
1.02
1.04
1.06
1.08
Temperature (K)
PL p
eak
ener
gy (e
V)
22242628303234363840
Ground level
PL p
eak
FWH
M (m
eV)
0 50 100 150 200 250 300
1.10
1.12
1.14
1.16
1.18
1.20
1.22
Temperature (K)
PL p
eak
ener
gy (e
V)
586062646668707274
PL p
eak
FWH
M (m
eV)
(a) (b)Sample #A(ALE) Sample #B(S-K)
Temperature dependence of PL peak energy and PL peak linewidth of (a) the sample #A, and (b) the sample #B. In the case of the sample #A, only ground level is considered.
It is noteworthy that the PL linewidth of the sample #A is insensitive to cryostat temperature due to lack of wetting effect, that is, reduced thickness of wetting layers and/or uniform formation of QDs in ALMBE APL 88, 133104(2006)
Hi quality QD
S-K dot vs ALE dot
500 1000 1500 2000e2
e3
e4
e5
e6
e7
SK(G.S): 800ps
SK 1105D00 ST 1080D15 DWELL 1085D15 SK 1095D15 ST 1125D20 DWELL 1150D15
Nor
mal
ized
PL
Inte
nsity
Delay Time(ps)
ALE(G.S) : 2.2ns
1.1 1.2 1.3 1.4 1.5
Photon Energy (eV)
1100 1000 900 800
WL (HH, LH) GaAs
GaAs 500 A3 stack InAs ALE dot15 K
PL In
tens
ity (a
rb. u
ints
)
Wavelength (nm)
TR-PLPLE
ALE dot: longer lifetime, thinner wetting layer
P+ GaAs 200 nm
P- GaAs 200 nm
P- Al0.70Ga0.30As 1.5 m
P-Al0.15Ga0.85As 40 nm
GaAs 50 nm
P- GaAs 3 nm
GaAs 12 nm
GaAs 65 nm
n+ GaAs Substrate
n- GaAs 200 nm
n- Al0.70Ga0.30As 1.5 m
n-Al0.15Ga0.85As 40 nm
X 3
Contact Layer
Cladding Layer
Waveguide Layer
Contact Layer
InAs DWELL
III. QD LD - Modulation doping
GaAs
Al0.7GaAs
InAs QDN+ P+
P+ GaAs 200 nm
P- GaAs 200 nm
P- Al0.70Ga0.30As 1.5 m
P-Al0.15Ga0.85As 40 nm
GaAs 50 nm
P- GaAs 3 nm
GaAs 12 nm
GaAs 65 nm
n+ GaAs Substrate
n- GaAs 200 nm
n- Al0.70Ga0.30As 1.5 m
n-Al0.15Ga0.85As 40 nm
X 3
Contact Layer
Cladding Layer
Waveguide Layer
Contact Layer
InAs DWELL
Hi T. grown spacer layer
HGTSL (High Growth Temperature Spacer Layer)1
subo
o
1 H.Y. Liu et al., JAP, 96, 1988, (2004) [Sheffield]
QDLD PL Spectrum
1000 1050 1100 1150 1200 1250 1300 1350 14000.00
0.02
0.04
0.06
0.08
0.10
0.12
1st E.S.1206 nm(1028 meV)
PL In
tens
ity [a
. u.]
Wave length [nm]
QDLD #1612RT-PL
G.S.1302nm(952 meV)
76 meV
FWHM= ~32 meV
Large Energy separation : 76 meV improvement in the T sensitivity1
Narrow FWHM : 32 meV uniform size distribution of QDs
1 O.B. Shchekin et al., APL, 77, 466, (2000) [Deppe]
QDLD lasing cgaract. I
0 100 200 3000
10
20
30 L=1200 µm L=2000 µm
QDLDW=15 µm, 1.1xIth@25oC, 0.1% pulseAs cleaved
Opt
ical
Pow
er [m
W]
Current [mA]
0 100 200 300
10
20
30
L=500 µm L=700 µm L=1000 µm L=1500 µm
QDLDW=50 µm, 1.1xIth@25oC, 0.1% pulseOne-sided HR
Opt
ical
Pow
er [m
W]
Current [mA]
< L-I characteristics of L= 1200 µm & L= 2000 µm As-cleaved QDLD>
< L-I characteristics of L= 1200 µm & L= 2000 µm As-cleaved QDLD>
< L-I characteristics of L= 500 ~ 1500 µm HR-coated QDLD. >
< L-I characteristics of L= 500 ~ 1500 µm HR-coated QDLD. >
AS-cleaved QDLD :Jth= 493, 155 [A/cm2]HR-coated QDLD : Jth= 634, 452, 163, 95 [A/cm2]
QDLD lasing charact. II
1000 2000 30001200
1300
AS-cleadved HR-coated
QDLD@25oC, 0.1% pulse1.1xIth
Lasi
ng w
avel
engt
h [n
m]
Cavity length [µm]
G.S.
E.S.
< Characteristics of lasing λ vs. cavity length L >< Characteristics of lasing λ vs. cavity length L >
~ 750 µm~ 750 ~ 750 µµmm
1200 13000.0
0.5
1.0
1206 nm(1028 meV)
(ii)
Nor
mal
ized
Inte
nsut
y [a
. u.]
Wavelength [nm]
(i)
RT-PL
1302 nm(952 meV)
0.0
0.5
1.0
RT-PL
< L-I characteristics of L= 2000 µm. In point (i), only shows G.S. lasing but inpoint (ii), lasing spectrum shows both G.S. & E.S. lasing>
< L-I characteristics of L= 2000 µm. In point (i), only shows G.S. lasing but inpoint (ii), lasing spectrum shows both G.S. & E.S. lasing>
0 100 200 3000
5
10
15
L=1200 µm
QDLDW=15 µm, 1.1xIth@25oC, 0.1% pulseAs cleaved
(ii)
Opt
ical
Pow
er [m
W]
Current [mA]
(i)
QDLD lasing charact. III
T < 50 oC, λ shifted tolonger wavelength
due to thermally inducedband-gap narrowing
T > 55 oC, λ switched toE.S. stateHR-coated QDLD operated
over 65 oC
0 10 20 30 40 50 60 701225
1250
1275
1300
1325
1350As cleaved, LxW= 2000 x 15 µm2
One-sided HR, LxW= 1500 x 50 µm2
QDLD1.1xIth@25oC, 0.1% pulse
Lasi
ng W
avel
engt
h [n
m]
Temperature [oC]
dλ /dT = 0.53 nm/K
QDLD lasing charact. IV
0 50 100 150 200 250 300 3500358
11131619212427293235374043
5 oC 15 oC 25 oC 35 oC 45 oC 55 oC 65 oC
#1612 RWG-HRLxW=1500x50um2 T= var., 0.1 % pulse
Opt
ical
Pow
er [m
W]
Current [mA]
Jth= 89 A/cm2
0 10 20 30 40 50 60 70
4
5As cleaved, LxW= 2000 x 15 µm2(QDLD-A)One-sided HR, LxW= 1500 x 50 µm2(QDLD-B)
To= 55 K
To= 113 K
To= 19 K
ln(It
h[m
A])
Temperature [oC]
To= 108 K
Temperature sensitivity1. Lower growth T of
Al0.7Ga0.3As cladding layer2. non-optimized
p-modulation doping
QDLD lasing charart.V
참고 자료
Sheffield G. λ= 1307 nm @RTJth = 32.5 A/cm2, To= 79 K3-stack, WxL = 20x5000 µm2
Deppe G. λ= 1290 nm @RTJth= 174 A/cm2, To= 200 K5-stack, WxL= 5x650 µm2
λ= 1310 nm @RTJth= 155 A/cm2, To= 113 K3-stack, WxL= 50x1500 µm2
HGTSL P-doping
KISTBhattacharya G. λ= 1240 nm @RTJth = 180 A/cm2, To= infinite5-stack, WxL = 5x800 µm2
Bimberg G. λ= 1280 nm @RTJth = 147 A/cm2, To= 150 K10-stack, WxL = 100x1500 µm2
IV. SLD
0 2 4 6 8
0.0
0.2
0.4
0.6
0.8
1.0QD-SLDL=2mmW=100 µmT=5oCPulse Operation
Pow
er [W
]
Current [A]950 1000 1050 1100 1150
-80
-70
-60
-50
-40
93nm
Inte
nsity
[dB
]Wavelength [nm]
Current [A] 6.5 7.0 7.5 8.0
Max. Power ~ 0.9 W Max. spectral bandwidth ~ 93 nm
Applications : Low coherent broadband light source for OCTWDM-PON
국가지정연구실 (NRL)
SLD epi structure
※NSC (NL Semiconductor)
InAs QD (1.3 µm)
GaAsAlGaAs NSC-1
InAs QD (1.3 µm)
GaAsAlGaAs
InAs QD (1.2 µm)
NSC-2
InAs QD (1.3 µm)
GaAsAlGaAs
InAs QD (1.2 µm)InAs QD (1.25 µm)
NSC-31000 1100 1200 1300 1400 1500
NSC-3
NSC-2
NSC-1
RTOptical power: 15 mW
PL in
tens
ity (a
rb. u
nit)
Wavelength (nm)
Chirped-QD (Quantum Dot) 구조
국가지정연구실 (NRL)
SLD tapered structure
Chirped-QD (Quantum Dot) SLD 제작
l
w
θ
θ θ
mirror
R
Rg = Rg (λ, θ, ∆n)ncore
ncladding
t∆n = ncore-ncladding
Rg
국가지정연구실 (NRL)
SLD 1
QD (NSC-1) SLD
1100 1200 1300 1400-60
-50
-40
-30
-20
-10
0
NSC-1 SLDRidge : 1mm Benting : 1.5mm T : 20CW operating
P
ower
[dB
m]
Wavelength [nm]
50 mA100 mA200 mA
400 mA
800 mA
1000 mA
12851194
1275
1204
0 200 400 600 800 10000
1
2
3
4
5NSC-1 J shape SLDCW operatingCL:Ridge : 1 mm J : 1.5 mmT : 20 oC
Current [mA]
Volta
ge [V
]0
2
4
6
8
10
Pow
er [mW
]
Ground stateExcited state
국가지정연구실 (NRL)
0.0 0.2 0.4 0.6 0.8 1.0 1.20
1
2
3
4
5
NSC-2 QD-SLD(J-shape)- Temp : 20 0C, CW- length : 2mm
Opt
ical
pow
er (m
W)
Current (A)
SLD 2
QD (NSC-2) SLD
1000 1100 1200 1300 1400-70
-60
-50
-40
-30NSC-2 SLDRidge : 1mm Benting : 1.5mm T : 20CW operating
Pow
er [d
Bm]
Wavelength [nm]
1. 50 mA2. 100 mA3. 200 mA4. 300 mA5. 400 mA6. 500 mA7. 600 mA8. 700 mA9. 800 mA10. 900 mA11. 1000 mA12. 1100 mA
1.2.3
4.5.6.7.
8.9.
10.11.
12.
74 nm76 nm
1.3QD gr1.2QD gr
1.3QD 1st1.2QD 1st
Jpn. J. Appl. Phys. 2005. 8
국가지정연구실 (NRL)
SLD 3
QD (NSC-3) SLD
1000 1100 1200 1300 1400-60
-50
-40
-30
-20
-10
0
98 nm
Wavelength (nm)
Pow
er (d
B)
NSC-3 J-shape SLD- temp : 25 C- length : 2mm- current 200 mA 400 mA 600 mA 800 mA
-100 0 100 200 300 400 500 600 700 8000.0
0.5
1.0
1.5
2.0
2.5
3.0NSC-3 J shape SLDCW operatingCL:Ridge : 1 mm J : 1.5mmT : 20 oC
Current [mA]
Vol
tage
[V]
0
10
20
30
40
Pow
er [mW
]
1.3Q-gr1.3Q-1st
1.25Q-gr
1.25Q-1st
1.2Q-gr
1.2Q-1st
Appl. Phys Lett : submitted
V. QDIP - IR PD Applications
Thermal detector Photon detector
Type - Bolometer type -Ferroelectric type- PN junction
Interband - MCT(HgCdTe) - InSb
Intersubband - Si Schottky - Si QWIP / QDIP - GaAs QWIP / QDIP
- low T opeation ( <77K) - High T. opeation(>77K)
Dis-adv
- low D* - very slow
- non uniform process - low D*
Adv - R.T. operation - high D* - fast response
- uniform and reliable - 2D FPA (easy fab) - fast response
Introduction (Types of IR detector)
Bound-to-Bound
Bound-to-Quasibound
Bound-to-Continuum
hν Continuum band
Quantum Dot instead of Quantum WellNormal incidence operation - Pyramidal shape of QD
Room-temp. operation - Strong confinement by 3-D QDsSmall thermionic dark current - Atomic discrete energy level
Large photoconductive gain - Lack of optical phonon scattering
Bound-to-Continuum Intersubband TransitionD
OS
Energy
WL
∆E ~ 100 meV~ hν > kT
∆E
Quantum Dot for IR detector
R = (e/hc)ηλG ; Responsitivity
D* = A½ R/in ; Detectivity, in ; Noise currentFor high D* and high temperature operation
Low noise(dark) current, high gain are required
Issues in QDIPs
QD : 3-dimensional confinement of electrons-> promising for high temperature operation of IR detector
But grown at low temperature under strained material condition
-> defects and/or misfit dislocation is generated
-> control of defects is crucial for high quality QDIPFor low dark current;
High quality material (growth)Post-growth treatment (Thermal treatment, H-passivation)
1. Operation Wavelength (3-5um, 8-12 um, > 12um): Bandgap engineering by precise growth, post-growth technique
2. Device performance : Operation T, Responsitivity, Detectivity
QDIP의 제작
cleaning
Mesa etching
Metallization
Packaging (1) Mesa etching (2) Metallization and RTA
(3) Fabricated QDIP (4) Packaging
2 mmMetal pattern
(0.5 mm)
2 mmMetal pattern
(0.5 mm)
QD IP
2 mmMetal pattern
(0.5 mm)
2 mmMetal pattern
(0.5 mm)
Quantum Dot instead of Quantum WellNormal incidence operation - Pyramidal shape of QD
Room-temp. operation - Strong confinement by 3-D QDs
2000 4000 6000 8000 10000
1E-5
1E-4
1E-3
Phot
ocur
rent
(Arb
. Uni
ts)
Wavelength (nm)
18 K 60 K 140 K 190 K
Photo-Voltaic QDIP
Al0.3Ga0.7As (28 nm)
GaAs (18 nm)
GaAs (18 nm)
GaAs (18 nm)
GaAs (18 nm)
n+ GaAs (140 nm)
SI (100) GaAs substrate
QDs
n+ GaAs (350 nm)
Direct Si doping ~ 2.0x1018 cm-3
0 100 200 300 400 500 6000.00
0.05
0.10
0.15
Phot
ocur
rent
(a.u
.)
Photon energy (meV)
Vb= 0 V T=10 K T=20 K T=30 K T=40 K T=50 K
-40 -20 0 20 4010.0
12.5
15.0
17.5
20.0
22.5
Res
pons
ivity
(mA
/W)
Bias voltage (mV)
T=10 K
3 stacked-In0.5Ga0.5As/GaAsQD structure
Al0.3Ga0.7AsBlocking layer
Top contactBottom contact
e
• Photo-voltaic effect due to asymmetric band structure induced by direct Si doping, AlGaAs barrier and asymmetric QD shape
• R = 21 mA/W at zero bias at λ∼ 6.2 µm (200 meV)
• Signal detected up to 50 K• No bias -> small dark current -> high detectivity
(MNE2004, Microelectron. Eng., accepted, 2005)
responsivity is 70 times larger than reported value
Post-growth treatment(Thermal annealing)
•Purpose- detection wavelength tuning with post-growth technique
• 300 nm SiO2 capping and annealing (T=700 0C , 1 min )
Al0.3Ga0.7As (28 nm)
GaAs (18 nm)
GaAs (18 nm)
GaAs (18 nm)
GaAs (18 nm)
n+ GaAs (140 nm)
SI (100) GaAs substrate
QDs
n+ GaAs (350 nm)
Direct Si doping ~ 2.0x1018 cm-3
0.9 1.0 1.1 1.2 1.3 1.40.0
0.1
0.2
0.3
T = 30 K
PL
Inte
nsity
(a. u
.)
1.157 eV1.109 eV
Photon energy (eV)
as-grown sample thermally treated sample
- PL peak position : blue-shifted by 48 meV.
(due to intermixing of In/Ga composition)
- PL FWHM : 60 110 meV
- PL intensity : decreased
Post-growth treatment(Thermal annealing)
-0.4 -0.2 0.0 0.2 0.4
1E-5
1E-4
1E-3
0.01
Dar
k cu
rren
t (A
)
Bias Voltage (V)
T = 10 K as-grown sample thermally treated
sample
0 100 200 300 400 5000.00
0.02
0.04
0.06
0.08
0.10
178 meV
200 meV
x 10
Pho
to c
urre
nt (a
. u.)
Photon energy (meV)
Vb=-20 mV, T=10 K as-grown QDIP thermally treated
QDIP
Photo-currentDark current
-Peak position(λ∼ 6.9 µm) : red-shifted by 22 meV.
⇒ due to intermixing In/Ga composition.
-Responsivity : decreased (13.2 6.2 mA/W).
⇒ due to increase of defects.
- Dark current level : 2 times larger.
(due to defects generation )
- Relatively small increase than reported data*.
( might be due to SiO2 dielectric capping layer)
*K. Stewart, et al, J. Appl. Phys. 94, 5283 (2003).1st demonstration of detection wavelength tuning !!
(JJAP, accepted, 2005)
VI. Summary
- QD growth (ALE) more uniform and thinner wetting layer
- QD LD, Ith, T0- QD SLD, wide bandwidth w/ chirping
structure- QD IP, hi T operation, photovotaic
structure, post growth treatment
VII. Prospects
Future Collaboration in:- Optical Commun devices- Intersubband devices, far-IR, THz- Sensors- LED- Bio-photonics