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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. Introduction.

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

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  1. 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

  2. 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.

  3. Phototransistor structure

  4. Photo-diode, HBT structure

  5. Photo-diode and HBT or PhotoHBT ?

  6. Phototransistor configuration Common Base Hole current flows to ground  no current gain

  7. Phototransistor configuration Common Collector High current gain Low output resistance limits performance.

  8. Phototransistor configuration Common Emitter High current gain. Bandwidth limited by Miller effect:

  9. Miller Effect Integrated PIN HBT Phototransistor

  10. Cascode Configuration Performance comparable to that of a PIN + HBT ?

  11. 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

  12. Kirk effect (cont.) Associated time constant for a 1*10 emitter and a 10 diameter optical window:

  13. Photodetectors bandwidth limitations • Carrier transit time: • RC of detector capacitance and amplifier input resistance: M. Agethen et al. IPRM 2002

  14. Photodetectors quantum efficiency

  15. Ideal Amplifier Only transit time limits performance

  16. Base-collector junction in a phototransistor GaInAs active layers: Base layer highly resistive -

  17. A top illuminated PIN as a notch filter

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

  19. 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

  20. Spot size radius =12.5

  21. Spot size radius =12.5

  22. Spot size radius =12.5

  23. Spot size radius =12.5

  24. Spot size radius =6

  25. Spot size radius =6

  26. Top illuminated photo-transistoroption 1 Optical window Emitter Contact To base Base Metal Base Mesa

  27. Emitter Base Metal Base Mesa Top illuminated photo-transistoroption 2 Optical window Contact To base

  28. Spot size radius =12.5 2 12.5 Internal contact

  29. 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

  30. High efficiency phototransistors • Cover optical window with conducting transparent ITO (Indium Tin Oxide) layer. • Place internal and external contact to the diode: • Backside illumination.

  31. Overcoming the limitations Incorporating novel structures in photo-transistors: • Wave guide photodetectors • Distributed phototransistors • Resonant-cavity-enhanced photodetector. • Uni-traveling-carrier photodiode.

  32. 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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