Quantum Well Infrared Photodetectors: From Laboratory ...€¦ · Quantum Well Infrared Detectors:...

Research & Technology

Quantum Well Infrared Photodetectors: From Laboratory Objects to Products

P. Bois6th Rencontres du Vietnam: Hanoi 2006

Nanophysics: from fundamental to applications

Research & Technology Hanoi 2006/Nanophysics/PS 2.8 / P. Bois2

QWIP history: from laboratory objects to products

late 80's : first QWIP Bell Labs (B. Levine)90's : Focal Plane Arrays Demonstrators00's : equipment, systems and programs

FPAs: ACREO, AIM/IAF, BAE-US, QWIPTech, QmagiQ, Thales, ...Imagers: AIM, FLIR Systems, Indigo Systems, Thales, ...

QWIPs : attractive physics and devices ...

but Thales is an industrial group (⇒ products : yield, costs, ...)

How introduce an emergent technology (QWIP) in an unfavourable context due to other IR technologies (MCT, InSb, µbolometers, ...)?


INTRODUCTION: Imagery

Reflected Luminance

Ultra-violet Visible "Solar" IR Thermal IR

0.5 µm 3 µm 10 µm

Wavelength

EmittedLuminance


Nature is perfect ...LWIRMWIR

Infrared imaging : passive detection, night, all weather

10-3

10-2

10-1

100

101

102

103

104

Spec

tral

Emitt

ance

(W.m2 µ-1

)2 3 4 5 6 7 8 9

102

Wavelength (µm)

0.8

0.6

0.4

0.2

0.0

Atm

ospheric Transmission

TBB =600 K

TBB =300 K

λλ

dTdRBB ),(

⇒ Defence & Security⇒ Aerospace (Enhanced Vision System) ⇒ Industry (non destructive testing)⇒ Medical (breast cancer, cardiovascular diseases, ...)

With and without IR EVS


IR technologies for LWIR and MWIR

Thermal detectorsMicrobolometers (→ 640x512)Advantage = uncooled (low cost)Drawback = low performance

Quantum DetectorsAdvantage = high sensitivityDrawback = cryogenics (cost and reliability)Eligibles semiconductors for 8-12 µm range (LWIR) :

HgCdTe (MCT) : linear arrays, small staring arrays 128x128 (→ 10000 pixels)QWIP (GaAs): large staring arrays 640x512 (330000 pixels) → 1 Mpixel

Eligibles semiconductors for 3-5 µm range (MWIR) :HgCdTe (MCT) : staring arrays 320x240 → 640x512InSb: large staring arraysQWIP (GaAs): large staring arrays 640x512 → 1 Mpixel


EVOLUTION OF IR IMAGERS

3rd gen thermal imagers: high sensitivity & high resolution

General trend : from mono-detector to 2D array

easier opto-mechanics better sensitivity / resolution / reliabilityA mastered processing technology is required for large formats :small pitch, uniformity, production yield ⇒⇒ availability and cost

Catherine FC

Catherine QW

Catherine GP

Castor

300 mK 60 mK 180 mK 60 mK

1rst gen | 2ndgen | 3rst gen

ΝΕ∆Τ :

Medium range IR cameras

(1-3 km)Thales Optronics


THALES OBJECTIVES

Build an alternative technology for moderate costLWIR Thermal Imagers

• cost reduction of IR imagers :

- active layer for staring arrays → QWIPs- cryogenics- optics- read-out circuits

• performance improvement

• integration of advanced functions


Quantum Well Infrared Detectors: Basics

Ga As1-xxAl Ga As1-xxAl Ga As

d

∆Ec

+++

hν

MBE growth•GaAs substrate •GaAs well•AlXGa1-XAs barrier

Silicon doped⇒ carriers = electrons

TEM picture Modulated conduction band

⇓

Quantum levels in wells

•Thermal stability

•Uniformity

•3", 4", … 6" substrates

hν

SC heterostructureSC heterostructuren type dopantn type dopant

Unipolar devicesSilicon

Intraband transitions


QWIP: customized spectral detection range

200

50

100

150

400

10060 80 120

20 %

X = 5 %

10 %

E LIE2

40 %

E ETENDU2

Al Ga Asx 1-x GaAs

E

E 2

1

15

20

10

5

E

- E

(

meV

)2

1

d ( Å )

( m)

λp

µd

30

Example for detection around 8.5 µm: d = 5.2 nm ; x = 26 %


QWIP Advantages and Drawback: 1990'sADVANTAGES :

III-V TECHNOLOGY (DUALITY)⇓

Large FPAs→ 640 x 512 → …

BAND GAP ENGINEERING

DRAWBACK :OPERATING TEMPERATURE

SPECIFICITY :

- Large substrates (3", 4", …)- Process and metallurgy mature- Uniformity ⇒ Performances- Production yield ⇒ Cost- Resistance to CMO

- Versatility (3 µm → 20 µm)- Advanced functions

Tunability, Multispectrality- LWIR : ∆T ≈ - 15 K vs MCT PV

(MCT FPAs<128x128)

- Optical coupling (gratings)

SO WHAT ? ⇒ APPLICATIONS, MARKET !


TRT APPROACH

Analyze, understand : 1988 - 1994ADVANTAGES

DRAWBACKS

Modelize, optimize : 1993 - 1998OPERATING TEMPERATURE

Realize : 1997 - 2000LABORATORY DEVICES

Develop : 2000 - 2002FPA DEMONSTRATORS

Produce : 2002 -FPAs


QWIP: Principle of operation

• steady state operation ⇒ current is conserved

F0 Fi-1

Fi

Injected current at emitter contact

Capture probability

Optical current

Thermioniccurrent

pcJ Jth + Jop

A

+ + +

+ + +

+ + + + + +

hν

Rq gh

=αν

η(

g exc

trt= τ

QWIPs are "extrinsic" photoconductors


Optical coupling

Polarization selection rule forbids normal incidence⇓

artificial way is required for realizing FPAs:prisms, antennas, slope edges, diffraction gratings, ...

Standard QWIPs : diffraction gratings : reference• are now modeled, optimized, mastered with "standard III-V recipes"

rkii eEx̂ ⋅−

Incident field

grating

n2λ

a)

b)

2

yE

2 µm

LWIR


These are not diffraction gratings: near field optics!

iy

EE

ix

EE

Near field

rkii eEx̂ ⋅− Incident field

At resonance

QWIP pixel scheme

h λ⎫⎪⎪⎬⎪⎪⎭

<

IR Flux


QWIP PARAMETERS

Gratings : Period, Aspect ratio, depth

Contact layers : Thickness, doping

Active layer : Number of wells,

Barrier thicknessAl contentWell doping and width.

A.R. coating : Thickness

Substrate : Residual Thickness

IR

• QWIP optimization implies a global modeling of the structure

• including operating conditions (temperature, optical flux)


TBB = 300K

F/1.6

D*(70K, peak)cm.Hz1/2/W



D*(110 K, peak) cm.Hz1/2/W

λp = 10.6 µm, ∆λ = 0.9 µm 3.5 1010 1.2 1010 9 109 λp = 8.8 µm, ∆λ = 1 µm 1011 8 1010 5 1010 109

λp = 4.6 µm, ∆λ = 0.5 µm 2 1012 2 1012 8 1011 2 1011 0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

Spe

ctra

l res

pons

e (A

/W)

1816141210864Wavelength (µm)

D*(100 K) = 2.5 1011 cm.Hz1/2/W

D*(77 K) = 8 1010 cm.Hz1/2/W

D*(50 K) = 1.4 1010 cm.Hz1/2/W

D*(77 K) = 1.6 1010 cm.Hz1/2/W

Spectral Response and D* for QWIP


QWIP TECHNOLOGY

⇒ Avoid degradation of intrinsic performancesWarning: uniformity has to be preserved for each new QWIP quantum design or processing step

⇒ Prefer ascendant compatibility technologiesStandard III-V processing

Cheap fabrication processing : •Contact photolithography (5 to 9 steps)

•Dry etch

•Sputtering metal deposition

⇒ Large format FPAs (640x512 and above)

⇒ Bispectral FPAsPitch= 25 µm


Thinning: required for thermal cycling reliabilityOnly 1 chemical step (100% yield)

Detail of a 384 x 288 QWIP array after thinning

Si ROIC Si ROIC

QWIP FPA

After substrate removalAfter hybridization


Maturity of QWIP technology: 2000

Physics understanding OKOptical coupling OKProcessing steps OKGood performances achieved at 77K (60-65K in 1995 !) OK

All the building blocks are mastered ⇒ products

US TV format: 640x512 (25 µm)European 1/2 TV format: 288x384 (25 µm)


LWIR QWIP PRODUCTS

Yield on 3” wafer: > 70% (6/8) Yield on 3” wafer: > 80% (25/30)

20022004

ROIC : Indigo ISC 0208 (pitch = 25 µm)½ TV format 384x288

Specifications

ROIC : Indigo ISC 9803 (pitch = 25 µm)TV format 640x512

Specifications for f/2.5 & >70 K: •NETD< 30mK (Tint < 5ms)•Pixel operability : >99.95%•Uniformity > 99.97 % after NUC•no cluster > 6 pixels (central zone)

for f/2.7 & >75 K: •NETD< 40mK (Tint < 5ms)•Dynamic range +/- 50K•Responsivity > 15 mV/K•Operability : >99.5% (all criteria)•no cluster > 5 pixels (central zone)

640x512


CATHERINE XP: LW 384x288 QWIP product•Pupil : 50 mm•FOV : 10°x7,5° and 4°x3° •Electronic zoom : x 2•288x384 LWIR QWIP FPA•Pitch : 25 µm ; f/2.7•Sensitivity : NETD < 60 mK •Dynamics : 100 K (Tbb=300K)•175 mm x 215 mm x 72 mm•2.5 kg•TFPA = 75 K

cooler

Power supplyProximity electronics

Optics

detectorIntegration time < 4ms:

format 768 x 576 using µscan (2x2)

Uniformity and stability:- 2 pts correction in factory……. even for very high performance- 1 pt correction during initialization

4° NFov Version 3° NFov Version10° Wfov 9° WFov


SIRIUS-LW

TRT QWIP Product

640x512 ; pitch 20 µm

16 arrays on 3" wafer

Catherine MP MegaPixelµscanned SXGA format

(1280 x 1024)Thales Optronics (UK)

THALES LW QWIP Camera: CATHERINE-MP

E&O test cell

2005

Largest cluster (5 pixels)Yield on 3” wafer: > 70% (12/16)

Catherine MP


QWIP performance evolutions

Increase operating temperature: lower the cost⇒ more compact systems (cost, volume, consomption)

⇒ more reliable systems

Increase detector format: enhance resolution> 300 000 pixels, pitch reduction⇒ survey applications

Multispectrality, polarimetry: get more informationmultiband or multi-subband spectral detectorspolarimetric detectors ⇒ better identification, multi-weather adaptability


2 color (LW/LW or MW/LW) QWIP arrays

Building blocks validated on+ V1 + V2Signal 256x256 FPA

pitch 25µmIWR mode, 100Hz

Spatial correlation

25 µm

MWIR / LWIR4.6µm / 8.6 µm

NETD: 40mK / 39 mKOperability: 99.5% / 99.9%

LWIR / LWIR8.6µm / 10.8 µm

NETD: 50mK / 59 mKOperability: 99.5% / 99.4%

(details of a 2 color QWIP array)


Polarimetric QWIP FPA : 2006-2007100

90

80

70

60

50

40

30

20

10

0

-10

Pola

rizat

ion

ratio

(%)

10090807060504030

Pixel size (µm)

no diffraction pattern 2D pattern, period 2.6 µm

1D pattern, period 2.6 µm 1D pattern, period 2.7 µm

I0 / I90 = 10

1D pattern1D pattern2D pattern2D pattern 1D pattern1D pattern2D pattern2D pattern

unpolarized "natural" light

polarized light

Polarimetric demonstrator under development- 640 x 512, 20 µm pitch, including microscan

⇒320x256 (x4) polarimetric FPA


CONCLUSIONAfter 15 years of R&D at THALES:

• Physics of QWIP is relatively well understood• Complete modeling is available• Processing is mature (high yield in production)

• still R&D (→FPA level) to increase operating temperature, extend spectral range (4µm-18µm) and implement new functions (multispectrality, polarimetry)

Transition from physics to business is almost achieved, but end-users and equipment manufacturers were hard to convince !

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