Jungil LeeNano Device Research Center, KIST

jil@kist.re.kr

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