1. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 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. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 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. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 3 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 E g = 0.75 eV, compatible with the detection of 1.30 and 1.55 µm wavelength light Photo-HBT developed at OPTO+

4. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 4 Photo-HBT developed at OPTO+  Layer Growth : Chemical Beam Epitaxy  Base Layer : Carbon doped Low diffusion coefficient  Compositionally graded-base In x Ga 1-X As Vertical structure Key technology : epitaxy no antireflection layer

5. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 5 Emitter area : 9 µm 2 Base area : 44 µm 2 Optical window area : 16 µm 2 Photo-HBT as a direct photodetector R DC = 0.2 A/W

6. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 6 Saturation characteristics @ -1dB: -21 dBm

7. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 7 photo-HBT CHAIN Spectrum Analyser 32 C E B 1 <I in >  I b_tot I b_ =I b_elec +I ph LNA b-tee G = 50 dB NF < 5 dB P sys_noise (dBm/Hz) RBW = 2MHz Analog noise characteristics Input noise current spectral density (pA/Hz^0.5)

8. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 8 Analog noise characteristics Input noise current spectral density @ 40 GHz: Ic (mA) (pA/Hz^0.5) 2 50 10 66

9. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 9 Digital noise characteristics BER at 10 -9 : C/N = 24.3 dB

10. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 10 OEIC using photo-HBTs Photo HBT /4 line CBCB V CE Out In I B h R B pol 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. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 11 B B P LO P RF Cascode cells 28 GHz Photo-HBT BB P LO P RF Chip size : 1634 x 1300 µm 2 42 GHz Chip size : 2850 x 1600 µm 2 Optoelectronic mixers using photo-HBTs Upconversion mixer from 2 GHz to 28 GHz and to 42 GHz HBTphotoPDmodeout circuitout conv )(IFP IF)(LOP G    G conv 28 GHz 17.8 dB 42 GHz 9.2 dB Mixer

12. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 12 Top illuminated PIN photodiode P I N Trade-off between efficiency and speed (bandwidth) The better performances with a Photoabsorption layer of 400nm: Bandwidth = 30 GHz R = 0.30 A/W Photoabsorption layer 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 SHBT Base-collector homojunction = PIN homojunction Bandwidth = 53 GHz Transimpedance gain = 44.3 dB PIN photodiode SHBT-based preamplifier

13. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 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. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 14 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 Back illuminated UTC photodiode p-Contact Sub collector Barrier Base p+ Collector n n+ Optical absorption region Space-charge region CB VB + - 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. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 15 Back illuminated UTC photodiode p + : Base contact p + : Barrier p + : Base absorption layer Composite collector Sub-collector InP-Substrate Since UTCs require a thin absorption layer:  Responsivity is relatively low* < 0.2 A/W  Need of edge-illumination for improving R *The responsivity is generally the same as that of a PIN-PD for the same absorption layer thickness Shimizu et al. IEEE PTL, vol 10, pp. 412, 1998

16. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 16 L ight Output power dependance on input light UTC photo-HBT 20 GHz 19 GHz P opt 2.5 dBm 2.5 dBm P RF -30 dBm -21 dBm UTC refracting-faced photodiode To achieve higher responsivity in edge illuminated configuration Fukushima et al. EL, vol 37, pp 780-781, 2001

17. Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 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