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Workshop « Phototransistors » September 9, 2003 Budapest Hungary

Workshop « Phototransistors » September 9, 2003 Budapest Hungary. InP-based Phototransistors and comparison of performances to those of PIN and UTC photodiodes Carmen Gonzalez Alcatel R&I - Laboratoire OPTO+ Carmen. Gonzalez@alcatel.fr. Outline. InP/InGaAs-based bipolar phototransistor

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Workshop « Phototransistors » September 9, 2003 Budapest Hungary

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  1. Workshop « Phototransistors »September 9, 2003 Budapest Hungary InP-based Phototransistors and comparison of performances to those of PIN and UTC photodiodes Carmen Gonzalez Alcatel R&I - Laboratoire OPTO+ Carmen. Gonzalez@alcatel.fr

  2. Outline InP/InGaAs-based bipolar phototransistor Photo-HBT performances as a direct photodetector Optoelectronic integrated circuits OEIC: - O/E narrow band amplifier - O/E upconverting mixers Performances of: - Top illuminated PIN photodiode - Back illuminated UTC photodiode Summary

  3. Photo-HBT developed at OPTO+ Choice of material to maximize carrier velocities Material System : InP (despite of cost) vs GaAs InP, InGaAs : Higher electron velocities and lower surface recombination velocities than GaAs InGaAs : Narrow band gap Eg = 0.75 eV, compatible with the detection of 1.30 and 1.55 µm wavelength light

  4. Vertical structure Key technology : epitaxy · Layer Growth : Chemical Beam Epitaxy · Base Layer : Carbon doped Low diffusion coefficient · Compositionally graded -base In Ga As x 1- X •no antireflection layer Photo-HBT developed at OPTO+

  5. Photo-HBT as a direct photodetector Emitter area : 9 µm2 Base area : 44 µm2 Optical window area : 16 µm2 RDC = 0.2 A/W

  6. Saturation characteristics @ -1dB: -21 dBm

  7. Analog noise characteristics Input noise current spectral density <Iin> (pA/Hz^0.5) photo-HBT CHAIN Spectrum b-tee 2 3 Analyser LNA C < I > in G = 50 dB P (dBm/Hz) NF < 5 dB 1 sys_noise B RBW = 2 MHz ­ E I b _ tot I =I + I b _ tot b_ elec ph

  8. Analog noise characteristics Input noise current spectral density @ 40 GHz: Ic <Iin> (mA) (pA/Hz^0.5) 2 50 10 66

  9. Digital noise characteristics BER at 10-9: C/N = 24.3 dB

  10. CB VCE Photo HBT /4 line h Out In RBpol IB OEIC using photo-HBTs An O/E narrow-band amplifier at 28 GHz: 2 cascode cells with 1 photo-HBT+3HBTs Transimpedance Gain = 50 dB @ 28 GHz BER at 10-9: 24.3 dB

  11. Cascode cells + P (LO IF) = out circuit G 28 GHz 42 GHz conv P (IF ) B B B B B B - out PDmode photo HBT PLO PRF PRF PLO Photo-HBT Chip size : 1634 x 1300 µm2 Chip size : 2850 x 1600 µm2 Optoelectronic mixers using photo-HBTs Upconversion mixer from 2 GHz to 28 GHz and to 42 GHz Mixer G conv 28 GHz 17.8 dB 42 GHz 9.2 dB

  12. P I N Top illuminated PIN photodiode The main attraction of this device is its compatibility for integration with SHBTs. For example, this photoreceiver realized by D. Huber et al., IEEE JLT 2000 P+:InGaAs InGaAs N+:InGaAs Trade-off between efficiency and speed (bandwidth) The better performances with a Photoabsorption layer of 400nm: Bandwidth = 30 GHz  R = 0.30 A/W PIN photodiode SHBT-based preamplifier SHBT Base-collector homojunction = PIN homojunction  Bandwidth = 53 GHz  Transimpedance gain = 44.3 dB Photoabsorption layer

  13. PIN photodiode For higher-speed operations, waveguide or travelling-wave photodiodes are proposed. TW-PD with bandwidth of 100 GHz has been reported. However, photoreceivers based on edge-coupled PIN PDs exhibit similar characteristics to those obtained with top-illuminated PIN-PD Top-illuminated phototransistors, which offer internal gain, could greatly reduce the need for preamplification, with circuits less complicated than those associated to PIN PD, in particular at millimeter wave frequencies.

  14. Optical absorption region Barrier p+ Base p+ p+ - + Collector n CB p-Contact Sub collector n+ Space-charge region VB Back illuminated UTC photodiode In high-speed optical systems  optical pre-amplifier can be installed directly in front of the photoreceiver Need of photodiodes with  broad bandwidth, high responsivity and high output power Uni-traveling-carrier photodiode principle Separate absorption and space-charge region: high carrier density Electrons only contribute to drift current:  transit time improved Proposed by T. Ishibashi et al., NTT, 1997

  15. Back illuminated UTC photodiode p+ : Base contact p+ : Barrier p+ : Base absorption layer Shimizu et al. IEEE PTL, vol 10, pp. 412, 1998 Composite collector Since UTCs require a thin absorption layer:  Responsivity is relatively low* < 0.2 A/W  Need of edge-illumination for improving R Sub-collector InP-Substrate *The responsivity is generally the same as that of a PIN-PD for the same absorption layer thickness

  16. Light UTC refracting-faced photodiode To achieve higher responsivity in edge illuminated configuration Output power dependance on input light UTC photo-HBT 20 GHz 19 GHz Popt 2.5 dBm 2.5 dBm PRF -30 dBm -21 dBm Fukushima et al. EL, vol 37, pp 780-781, 2001

  17. Summary - Future prospect High speed photo-SHBT based on InP technology Frequency performances up to the mm-wave band Compatible with SHBT technology for monolithically integrated photoreceivers (amplifiers, mixers, oscillators) It is well suited for performing more complex O/E functions, as mixing or selft-oscillation, at high frequency and high bit rates

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