Monolithically Coupled Photo Diode - HBT or a Photo - HBT : A Modeled Comparison BENNY SHEINMAN, DAN RITTER MICROELECTRONIC RESEARCH CENTER ELECTRICAL

Monolithically Coupled Monolithically Coupled Photo Diode - HBT Photo Diode - HBT or a Photo - HBT : or a Photo - HBT :

A Modeled Comparison A Modeled Comparison BENNY SHEINMAN, DAN RITTER

MICROELECTRONIC RESEARCH CENTER

ELECTRICAL ENGINEERING DEPARTMENT

TECHNION – ISRAEL INSTITUTE OF TECHNOLOGY

Confidential

2Technion—Israel Institute of Technology

Workshop outlineWorkshop outline Introduction. Phototransistor electrical configurations. General bandwidth / efficiency limitations

in a photo-detector. Additional limitation in a top illuminated

PIN diode / phototransistor. Electrical modeling of the top illuminated

PIN diode / phototransistor.

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Phototransistor structurePhototransistor structure

Emitter

Optical window coated by AR silicon nitride

Collector

Base

Subcollector

Semiinsulating InP substrate

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Photo-diode, HBT structurePhoto-diode, HBT structure

Emitter

Optical window coated by AR silicon nitride

Semiinsulating InP substrate

Subcollector = n-type contact

Base = p-type contact

Collector = i-region

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Photo-diode and HBT or Photo-diode and HBT or PhotoHBT ?PhotoHBT ?

Photo HBTHBT+photodiodesame layers

HBT+photodiodedifferent layers

Transistor performance

Compromised:1. Miller effect2. Collector transit

time

Compromised1. Collector transit time

Optimal

ResponsivityCompromisedCompromisedMaximal

Optical windowSmall ?Large ?Large

TechnologyStandardStandardDifficult

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Phototransistor Phototransistor configurationconfiguration

Common Base

Hole current flows to ground no current gain

mg v r

Emitter

Base Collector

opticalI

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Common Collector

High current gainLow output resistance limits performance.

er opticalI LoadR

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Common Emitter

High current gain.Bandwidth limited by Miller

effect:

5020

50C

C

BCmiller m C BC BCRI mA

C g R C C

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Miller EffectMiller Effect

Le

Re

RbeCbe

Rbi

Cbcx

RcLcRb

Cbci

'I'E

Rbc CollectorBase

Emitter

I'EIE

CP

iP

iP

Le

Re

RbeCbe

Rbi

Cbcx

RcLcRb

Cbci

'I'E

Rbc CollectorBase

Emitter

I'EIE

CP

LB

Phototransistor Integrated PIN HBT

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Cascode ConfigurationCascode Configuration

1m C BCmiller BCg R C C

Performance comparable to that of a PIN + HBT

??

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Kirk effectKirk effect

0 50 100 150 200 250 3000

50

100

150

200

250

Current Density [KA/cm2]F

req

ue

nc

y

[GH

z]

150nm Collector

Fmax

Ft

0 50 100 150 2000

50

100

150

200

250

Current Density [KA/cm2]

Fre

qu

en

cy

[G

Hz]

650nm Collector

Ft

Fmax

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Kirk effect (cont.)Kirk effect (cont.)

2

2 ( )CB bikirk s C

V Vj v qN

D

Associated time constant for a 1*10Associated time constant for a 1*10 emitter emitter and a 10and a 10 diameter optical window: diameter optical window:

Collector Thickness

2[ / ]kirkJ KA cm min [ ]er [ ]BCC fF [ sec]p

150nm 200 1.5 60 0.09 300nm 100 3 30 0.09 450nm 50 6 20 0.12 600nm 20 15 15 0.225

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Photodetectors Photodetectors bandwidth limitationsbandwidth limitations

Carrier transit time:

RC of detector capacitance and amplifier input resistance:

7

2h

o

vf

D

oload

Df

A R

M. Agethen et al. IPRM 2002M. Agethen et al. IPRM 2002

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Photodetectors quantum Photodetectors quantum efficiencyefficiency2

22

100 (1 ) (1 )

,

.

( ).

.

700 .

spot A

r Dr L

spot

A

e e

where

r radiusof thediode

r optical spot size radius

D thicknessof absorbing layer

L absorbtionlength nm

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Ideal AmplifierIdeal Amplifier

Only transit time limits performanceOnly transit time limits performance

0inr

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Base-collector junction in a Base-collector junction in a phototransistorphototransistor

GaInAs active layers:

Base layer highly resistive -

Base 19 35 10p cm 30-50nm

Collector 15 17 35 10 2 10n cm 150-700nm

Sub-collector 19 33 10n cm 400nm

500 1000BasesR

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A top illuminated PIN as a A top illuminated PIN as a notch filternotch filter

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Additional RC filter Additional RC filter bandwidth limitation in a top bandwidth limitation in a top

illuminated PIN diode / illuminated PIN diode / phototransistor.phototransistor.

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RC network in a PIN RC network in a PIN detectordetector

r0

dr

r

Io1

R1

C1Io2

R2

C2Io3

R3

C3IoN

RN

CN

I1I2 I3 I4

Physical structure

Electrical equivalent circuit

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0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Frequency [GHz]

Qu

an

tum

eff

icie

nc

y [

%]

rd=12.5 R

sBase

=900

D=150nmD=300nmD=450nmD=600nm

Spot size radius =12.5Spot size radius =12.5

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0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Frequency [GHz]

Qu

an

tum

eff

icie

nc

y [

%]

rd=12.5 R

sBase

=500



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0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Frequency [GHz]

Qu

an

tum

eff

icie

nc

y [

%]

rd=6 R

sBase

=900



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0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Frequency [GHz]

Qu

an

tum

eff

icie

nc

y [

%]

rd=6 R

sBase

=500



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0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Frequency [GHz]

Qu

an

tum

eff

icie

nc

y [

%]

rd=6 R

sBase

=900


Spot size radius =6Spot size radius =6

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0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Frequency [GHz]

Qu

an

tum

eff

icie

nc

y [

%]

rd=6 R

sBase

=500


Spot size radius =6Spot size radius =6

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Top illuminated photo-Top illuminated photo-transistortransistoroption 1option 1

Emitter

Base Metal

Base Mesa

Optical windowContactTo base

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Top illuminated photo-Top illuminated photo-transistortransistoroption 2option 2

Emitter

Base Metal

Base Mesa

Optical windowContactTo base

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0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Frequency [GHz]

No

rma

lize

d f

ilte

red

cu

rre

nt

[%]

rd=12.5 R

sBase

=900



12.5

Internalcontact

2

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Model of top illuminated Model of top illuminated detector detector

4848

0.2pF0.2pF

0

2

2

BaseS

S

Rv

r ri v

r i Cr t

0i

Solution of current equations is difficult:Solution of current equations is difficult:

Yet for a known capacitance value,Yet for a known capacitance value, a single pole fit gives good resultsa single pole fit gives good results

SC

- distributed photocurrent- distributed photocurrent

-Photodiode capacitance / areaPhotodiode capacitance / area

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0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Frequency [GHz]

No

rma

lize

d c

urr

en

t [%

]

rd=12.5 , R

sBase

=900 , D=300nm

AccurateSingle pole

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High efficiency High efficiency phototransistors phototransistors

Cover optical window with conducting transparent ITO (Indium Tin Oxide) layer.

Place internal and external contact to the diode:

Backside illumination.

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Overcoming the limitationsOvercoming the limitations

Incorporating novel structures in photo-transistors:

Wave guide photodetectors Distributed phototransistors Resonant-cavity-enhanced photodetector. Uni-traveling-carrier photodiode.

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ConclusionsConclusions In the cascode configuration, photo-HBT have

comparable performance to PIN detector + HBT processed from the same layers.

PIN detector + HBT processed from different layers will have superior performance.

The highly resistive base layer produces an internal filter in the top illuminated PIN detector.

The influence of the filter should be included in the model of the detector.

Documents

Monolithically Coupled Photo Diode - HBT or a Photo - HBT : A Modeled Comparison BENNY SHEINMAN, DAN RITTER MICROELECTRONIC RESEARCH CENTER ELECTRICAL