IEEE National Distinguished Lecture Program, India

Lecture

Advances in

Semiconductor Photonic

Devices – Part IIN. R. Das

Institute of Radio Physics and ElectronicsUniversity of Calcutta, India

IEEE National Distinguished Lecture Program, India

Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 2

N. R. D

as

INRAPHEL

C.U.

Topics In Part-I (discussed previously)

Introduction: Photonic Device, Nanostructure

Photon emission process

Optical Source (LED, LASER), Modulator

In Part-II (present)Optical amplification

Photon absorption process

Optical Detector (photodetector)


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Optical AmplifierErbium-doped Fiber Amplifier

(EDFA)

Level 1

Level 2

Level 3 tsp~1ms

tsp~10msFast decay

1480nm

1460nm1540nm

Spontaneous emission (1500-1600nm)

Stimulated emission (1500-1600nm)

WDM coupler

Erbium-doped FiberTransmission fiber

Pump laser

Outputamplified signal

Input signal (optical)


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Optical Amplifier

Semiconductor Optical AmplifierInput signal (Light)

Population inversion

Stimulation by input

Amplified light output

n+

Active layer

P+ (confining layer)

p+

N+ (confining layer)

I

Input Output


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Absorbing Photons

CB

VB

Conduction Band

Valence Band

CB

VB

Continuous bands Discrete States

Subbands

Inter-band (VB CB)

Intra-band (Inter subband)(subband subband)

n=±1

n=±0

Eg Eg '

h≥Eg h≥Eg'

Light (radiation) incident on semiconductor


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C.U.

PhotodetectorAbsorption of light

Electrical current in the external circuit

Classifications byNo. of junctions, wavelength range, transition

states, internal gainPhotodetector (PD)

No internal gain Internal gain

Photoconductor,APD, Phototransistor, …

pn, p-i-n, Schottky, MSM, …


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C.U.

Junction Photodiodepn photodiode

Electrons and holes separated by built-in field

– Large region undepleted– Non-uniform field, Bias-dependent

depletion

• Solutionp+n, pn+ structures

Non-uniform field

p-i-n structure (next)

p+ n

- +

+ + + + + + + + + +

- - - - - - - - - -P N

W

- +

E

0 x

DriftDiffusion Diffusion


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C.U.

pin Photodiode

p n- +

W

i

E

x

Uniform field in i-region, Depletion at Low bias W~ i-layer thickness (~ Bias-independent) Large bandwidth, low noise No gain


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INRAPHEL

C.U.

Avalanche Photodiode (APD)

p-n junction

Large Gain Large noise Low BW at high gain

P N- +

E

0 x

crE

Hole

Electron

Ionization region

Ionizing electron

Avalanche Multiplication

Gain

Bias


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C.U.

Schottky, M-S-M PDsSchottky

Easy to fabricate, High speed No gain, Undesirable spectral response

M-S-M (Metal-Semiconductor-Metal)

Ultra-low capacitance, Large bandwidth

Good Integrability with HEMT, HBTManufacturing limitation

Metal

n

- +n-

VR

Semiconductor

Semiconductor

Metal (+)

Metal (-)


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Phototransistor

n p n

E B C• Light incident on base• Reverse biased B-C junction separates carriers• Gain: Transistor action• Uniform gain with bias• Large dark current, moderate BW


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INRAPHEL

C.U.

Photodetector Performance

)exp(1)1( WR

– conversion efficiency (Eg~h)

R– Reflection coeff. (AR coating) – Abs. Coeff. (Material/band-gap)

Quantum efficiency (QE)

W

drift diffusiondiffusion

-

+ + + + + + + + + +

- - - - - - - - - -

p n

e

+

h

RI0

V


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INRAPHEL

C.U.

Photodetector Performance

Bandwidth (BW)Transit-time delay, RC delay

W

drift diffusiondiffusion

-

+ + + + + + + + + +

- - - - - - - - - -

p n

e

+

h

RI0

V

d

Ban

dw

idt

h

Transit-time limited

RC limited

Overall

(APD)

Gain

BW


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INRAPHEL

C.U.

PD Performance

1/f GR Johnson

frequencyN

oise

NoiseThermal/Johnson Noise

Material, structure

Shot Noise / Generation-recombination (GR) Noise

Flicker (1/f) Noise

Excess Noise factor (APD)


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Advanced Structures

RCE PD Multiple reflections

QE improvedThin layer (d)

Large BWFree space optical interconnect

Dielectric Stack (R1)

InGaAs

p InP

n InPInP/InGaAsPDBR (R2)

d

n Contact

p Contact

BW (tr.-time) ↓ as d ↑ QE ↑ as d ↑

Trade-off

Conventional structure:

Solution !


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C.U.

Advanced Structures

EC PDsLengths (QE, BW) decoupled

High QE = f(L)Large BW= f(d)

Good coupling (Integrated circuit) Absorption layer d

L

P

N

+

-

Waveguide PD, Waveguide-fed PD, Travelling wave PD


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C.U.

Heterostructure PIN PD

Absorption only in i-layerReduced diffusion

transparent

P+ InP i - InGaAs N+ InP

d

absorbing

h~Eg

EgEGEG


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Heterostructure APD

SAGCM APD

i-InGaAlAs Grading

n+-InAlAs Charge

i-InAlAs Multiplication

InP

i-InGaAs Absorption

InP contact

-

+

• Reduced tunneling• Reduced hetero-interface trapping• To use undoped multiple layer

Separate Absorption, Grading, Charge and Multiplication


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INRAPHEL

C.U.

Nanophotonic DetectorQuantum Well PD

RCE Multiple Quantum Well (MQW) Increased absorption

Incident Light

Bottom (front) mirror

P-Si

Top (back) Mirror

i-Si1-xGex (dw)

Metal Contact

N-Sii-Si (dB)

i-Si (dB)

i-Si1-xGex (dw)

(a)N-Si SubstrateM

QW

• 1.3m wavelength

(near-infrared)

• SiGe Technology

• Interband transition


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INRAPHEL

C.U.

Infrared DetectorsApplications:

Medium /Long wavelength IR (MWIR/LWIR)• Thermal imaging, Night vision, Millitary, Security,

Non-invasive Medical diagnosis, Agriculture, Food Industry,Environmental Pollution Monitoring, …

• Materials InSb, InAs (3-5m)

HgCdTe (MCT) (8-14m)High absorption coefficient and low thermal

emission(>75K), Light weightDifficult (low gap) to grow, process, fabricate into devices

Semiconductor Nanostructures (QWIP, …)Inter-subband transition


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Emitter

Collector

GaAs

AlGaAs

Contact

Contact

AlGaAs band-gap

Conduction band offset

Valenceband offset

GaAsBand-gap

n=1n=2

n=3

n=1

n=2

GaAsWell

AlGaAsBarrier

AlGaAsBarrier

Quantum Well Infrared Photodetector (QWIP)

(not to scale)

Transition (Interband)Bound to Bound, Continuum,

Quasi-Continuum


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QWIPInjection Current

Capture

EscapeTotal Current

(Emitter)

(Collector)

Escape: TunnelingThermionic

emission

CurrentThermal excitaion

(dark current)Photoexcitaion

(photo current)Balance:

(capture/escape)

GaAs ~ 4.1 nm, Al0.26Ga0.74As ~ 48 nm [APL, 71 , 1997, p.2011]


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INRAPHEL

C.U.

QWIP in UseIR Camera

LWIR Handheld QWIP Camera:GaAs/AlGaAs MQW

QWIP-LED with CCD

[IEEE PTL 2002, 182]

Thermal Imaging


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C.U.

High uniformityExcellent reproducibilityLow power consumptionHigh resolutionLarge format Fast response timeMulti-color detection No response for normal incidenceLarge dark currentLow operating temperature

QWIP features


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Problems and Solutions

Solving Polarization ProblemManufacturing steps

45º wedgeRoughed mirror on the backGrating on the surface

StructureQuantum Wire Infra-red Photodetector (QRIP)

Quantum Dot Infra-red Photodetector (QDIP)

MQW

450


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QRIP

Schematic Structure

Emitter

Collector

Quantum Wire (QR)


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C.U.

QDIP Structure

Structure N+ - N - N+ diode

structure Undoped InAs QDs (small

band-gap material) Undoped N- GaAs layer

(wide-gap barrier) InGaAs Capping layer

(strain-relieving)

[APL 79, 2001, p.3341]


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C.U.

QDIP Performance

[APL 83, 2003, p752]

Dar

k C

urr

ent

(A)

10-4

10-6

10-8

10-10

10-12

Detectivity: Noise currentNoise current : Dark currentGain: Escape/capture probabilityResponsivity: Quantum efficiency, gain

Ph

oto

curr

ent

(a.u

.) 100

10-1

10-2

10-3


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INRAPHEL

C.U.

QWIP, QRIP and QDIP

Performance QWIP QRIP QDIPSensitivity to normal Incidence

Very low Good Good (/ best among the three)

Photoelectric gain

Moderate

Large Large

Operating Temperature

Low High High

Dark current Large Small Small

Commercial Use(Current Status)

Best Low Low


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INRAPHEL

C.U.

Simulations Mode I:

Obtain Physics-based ModelsSolve analytically / numericallyUse program codes (MATLAB, C, ...) to

simulateGood control, but time consuming

Mode II:Use Commercial SoftwaresQuick solution, but little control


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INRAPHEL

C.U.

SimulatorsRSOFT Design Group

OptSIMCAD for Optical Communication

BeamPROPWaveguide & Fiber Application

LaserMODActive Devic Application

FemSIM, Cavity mode solver

...

"FIBER OPTIC SERVICES" , Mumbai


N. R. D

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INRAPHEL

C.U.

SimulatorsSILVACO Device Simulator

ATLAS2D Simulation Modules

:Luminous (OE Device):LED, Laser: Quantum (quantum structures), …

3D Simulation Modules: Luminous3D: Quantum3D, ...

“Integrated Micro Systems -India”


N. R. D

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INRAPHEL

C.U.

Summary & Conclusion

Interband and Intersubband Absorption

PhotodetectorTypes, Principles, Performance

Heterostructure improves performance

Nanophotonic detectorsTailorable absorption

Infra-red detectors (intersubband transition)

Simulation approach


N. R. D

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INRAPHEL

C.U.

Some References P. Bhattacharya, “Semiconductor Optoelectronic

Devices”, PHI (India), New Delhi, 2002.

B. R. Nag, “Physics of Quantum Well Devices”, Kluwer Academic Publishers, London, 2000.

D. Bimberg, et al, , “Quantum Dot Heterostructures”, John Wiley & Sons, Chichester, England, 1999.

J. M. Senior, “Optical Fiber Communication, PHI (India), 1994.

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