Monolithically coupled photo diode hbt or a photo hbt a modeled comparison
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Monolithically Coupled Photo Diode - HBT or a Photo - HBT : A Modeled Comparison. BENNY SHEINMAN, DAN RITTER MICROELECTRONIC RESEARCH CENTER ELECTRICAL ENGINEERING DEPARTMENT TECHNION – ISRAEL INSTITUTE OF TECHNOLOGY. Workshop outline. Introduction.

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Monolithically Coupled Photo Diode - HBT or a Photo - HBT : A Modeled Comparison

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Monolithically coupled photo diode hbt or a photo hbt a modeled comparison

Monolithically Coupled Photo Diode - HBT or a Photo - HBT : A Modeled Comparison

BENNY SHEINMAN, DAN RITTER

MICROELECTRONIC RESEARCH CENTER

ELECTRICAL ENGINEERING DEPARTMENT

TECHNION – ISRAEL INSTITUTE OF TECHNOLOGY


Workshop outline

Workshop 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 illuminatedPIN diode / phototransistor.


Phototransistor structure

Phototransistor structure


Photo diode hbt structure

Photo-diode, HBT structure


Photo diode and hbt or photohbt

Photo-diode and HBT or PhotoHBT ?


Phototransistor configuration

Phototransistor configuration

Common Base

Hole current flows to ground

 no current gain


Phototransistor configuration1

Phototransistor configuration

Common Collector

High current gain

Low output resistance limits performance.


Phototransistor configuration2

Phototransistor configuration

Common Emitter

High current gain.

Bandwidth limited by Miller effect:


Miller effect

Miller Effect

Integrated PIN HBT

Phototransistor


Cascode configuration

Cascode Configuration

Performance comparable

to that of a PIN + HBT

?


Kirk effect

650nm Collector

150nm Collector

250

250

F

200

200

t

F

150

150

max

F

Frequency [GHz]

Frequency [GHz]

t

100

100

F

50

50

max

0

0

0

0

50

50

100

100

150

200

150

250

200

300

2

2

Current Density [KA/cm

]

Current Density [KA/cm

]

Kirk effect


Kirk effect cont

Kirk effect (cont.)

Associated time constant for a 1*10 emitter

and a 10 diameter optical window:


Photodetectors bandwidth limitations

Photodetectors bandwidth limitations

  • Carrier transit time:

  • RC of detector capacitance and amplifier input resistance:

M. Agethen et al. IPRM 2002


Photodetectors quantum efficiency

Photodetectors quantum efficiency


Ideal amplifier

Ideal Amplifier

Only transit time limits performance


Base collector junction in a phototransistor

Base-collector junction in a phototransistor

GaInAs active layers:

Base layer highly resistive -


A top illuminated pin as a notch filter

A top illuminated PIN as a notch filter


Additional rc filter bandwidth limitation in a top illuminated pin diode phototransistor

Additional RC filter bandwidth limitation in a top illuminated PIN diode / phototransistor.


Rc network in a pin detector

r0

dr

r

R1

R2

R3

RN

C1

C2

C3

CN

Io1

Io2

Io3

IoN

I2

I4

I3

I1

RC network in a PIN detector

Physical structure

Electrical equivalent circuit


Spot size radius 12 5

Spot size radius =12.5


Spot size radius 12 51

Spot size radius =12.5


Spot size radius 12 52

Spot size radius =12.5


Monolithically coupled photo diode hbt or a photo hbt a modeled comparison

Spot size radius =12.5


Monolithically coupled photo diode hbt or a photo hbt a modeled comparison

Spot size radius =6


Monolithically coupled photo diode hbt or a photo hbt a modeled comparison

Spot size radius =6


Top illuminated photo transistor option 1

Top illuminated photo-transistoroption 1

Optical window

Emitter

Contact

To base

Base Metal

Base Mesa


Top illuminated photo transistor option 2

Emitter

Base Metal

Base Mesa

Top illuminated photo-transistoroption 2

Optical window

Contact

To base


Spot size radius 12 53

Spot size radius =12.5

2

12.5

Internal

contact


Model of top illuminated detector

48

0.2pF

Model of top illuminated detector

Solution of current equations is difficult:

- distributed photocurrent

  • Photodiode capacitance / area

Yet for a known capacitance value,

a single pole fit gives good results


High efficiency phototransistors

High efficiency phototransistors

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

  • Place internal and external contact to the diode:

  • Backside illumination.


Overcoming the limitations

Overcoming the limitations

Incorporating novel structures in

photo-transistors:

  • Wave guide photodetectors

  • Distributed phototransistors

  • Resonant-cavity-enhanced photodetector.

  • Uni-traveling-carrier photodiode.


Conclusions

Conclusions

  • 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.


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