ieee national distinguished lecture program, india
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A slide on Advances in Semiconductor Photonic Devices..Part IITRANSCRIPT
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)
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 3
N. R. D
as
INRAPHEL
C.U.
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)
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 4
N. R. D
as
INRAPHEL
C.U.
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 5
N. R. D
as
INRAPHEL
C.U.
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 6
N. R. D
as
INRAPHEL
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, …
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 7
N. R. D
as
INRAPHEL
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 8
N. R. D
as
INRAPHEL
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 9
N. R. D
as
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 10
N. R. D
as
INRAPHEL
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 (-)
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 11
N. R. D
as
INRAPHEL
C.U.
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 12
N. R. D
as
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 13
N. R. D
as
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 14
N. R. D
as
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)
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 15
N. R. D
as
INRAPHEL
C.U.
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 !
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 16
N. R. D
as
INRAPHEL
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 17
N. R. D
as
INRAPHEL
C.U.
Heterostructure PIN PD
Absorption only in i-layerReduced diffusion
transparent
P+ InP i - InGaAs N+ InP
d
absorbing
h~Eg
EgEGEG
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 18
N. R. D
as
INRAPHEL
C.U.
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 19
N. R. D
as
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 20
N. R. D
as
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 21
N. R. D
as
INRAPHEL
C.U.
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 22
N. R. D
as
INRAPHEL
C.U.
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]
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 23
N. R. D
as
INRAPHEL
C.U.
QWIP in UseIR Camera
LWIR Handheld QWIP Camera:GaAs/AlGaAs MQW
QWIP-LED with CCD
[IEEE PTL 2002, 182]
Thermal Imaging
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 24
N. R. D
as
INRAPHEL
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 25
N. R. D
as
INRAPHEL
C.U.
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 26
N. R. D
as
INRAPHEL
C.U.
QRIP
Schematic Structure
Emitter
Collector
Quantum Wire (QR)
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 27
N. R. D
as
INRAPHEL
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]
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 28
N. R. D
as
INRAPHEL
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 29
N. R. D
as
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 30
N. R. D
as
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 31
N. R. D
as
INRAPHEL
C.U.
SimulatorsRSOFT Design Group
OptSIMCAD for Optical Communication
BeamPROPWaveguide & Fiber Application
LaserMODActive Devic Application
FemSIM, Cavity mode solver
...
"FIBER OPTIC SERVICES" , Mumbai
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 32
N. R. D
as
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”
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 33
N. R. D
as
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
Aug 7-9, 2009 IEEE NDLP Lecture (NERIST) / NRD(RPE/CU) 34
N. R. D
as
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.