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Microelectronic Engineering 15 (1991) 275-278
Elsevier
275
10 Gbit/s Monolithic Integrated Optoelectronic Receiver using an MSM Photodiode and AIGaAs/GaAs HEMTs
Y. Hurm, J. Rosenzweig, M. Ludwig, A. Axmann, W. Benz, M. Berroth, R. Osorio,
A. Hillsmann, G. Kaufel, K. Kohler, B. Raynor, and Jo. Schneider
Fraunhofer-Institut fUr Angewandte Festkorperphysik ,
Tullastr. 72, D-7800 Freiburg, Germany
Abstract
A 10 Gbit/s monolithic integrated optoelectronic receive r has been fabricated with a metalsemiconductor-metal (MSM) pholodiode and enhancement/de pletion 0.5 f.1.m recessed-gate AIGaAs/GaAs HEMTs. A -3 dB bandwidth of 11.3 GHz has bee n achieved.
1. DESIGN AND FABRICATION
Several research g roups have reported on the technology of monolithic in tegration of MESFETs on GaAs with photodetectors for light of wavelength 0.85 ~m [1,2]. ln this paper we present
the firs t pholoreceiver which is based on an MSM pholodiode and A1GaAs/GaAs HEMTs (3].
The photoreceiver was fabricated using our es tablished 0.5 ~lm recessed-ga te process for double
delta-doped qua ntum well HEMTs [4,5]. Now Ihis standard process includes MSM photodiodes .
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depletion AIGaAs/GaAs HEMTs.
0167·9317/91/$3.50 © 199 1 - Elsevier Science Publishers BY All rights reserved.
276
V Hunn et al. /10 Gbit/s m onolithic integrated optoelectronic receiver
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Fieure 2. Circuit diagram of the photOreceiver. The receiver consists of
an MSM photOdiode, a transimpedance amplifier with fWe enhancement transistors and three NiCr thin
film resistors, and an output buffer
with two deplet io n transistors.
-,~ ,
Fieure 3. Photograph of the
fabricated pholoreceiver. The
depicted chip area measures
500x350 flm 2. The MSM
photodiode at the left side has
an active area of 25x25 flm 2.
Figure 1 shows a cross-section of an MSM photodiode integrated with enhancement and depletion type transistors. The vertical structure was grown on the semi-insulating GaAs substrate
by molecular beam epitaxy [4]. The AlAs mole fraction of the A1GaAs layers was 0.3. By means
of etch SlOps and a selective reactive ion etch process, exact control of the transistor threshold
voltages was obtained [SJ. The site of the MSM photodiode was etched down to the undoped
buffer layerby a wet etch prior to the fabrication of the photodiode fingers. The 1 lAm wide fingers
with a 1.5 lAm separation were defined by electron beam lithography and subsequent evaporation
and lifl-Qff of Ti/Pt/Au metal.
As shown in Figures 2 and 3 the pholoreceiver consists of an MSM photodiode, a transimpedance amplifier with a 500 Q feedback resistor, and an output buffer. Airbridges connect the pho·
todiode to the electric circuit. The layout also includes blocking ca pacitors for the supply voltages.
2. DEV ICE AND CIRCUIT PERFORMANCE
Figure 4 shows the curren t-voltage characteristics of an MSM photodiode irradiated by light
of various intensities at a wavelength of 0.84 ~m. The DC responsivities of the photodiode were
V Hu nn et al. /10 Gbit/s monolithic integrated opLOelectronic receiver
277
RG32-68 2582
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Figure 4. Current- voltage characteristics of an MSM photod iode
for different intensity of the laser
diode irradiation .
OptIcal
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Fi gure 5. Measured frequency response of the photorece ive r. The
measured - 3 d B bandwidth lies at
8.2 GHz.
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Fi2ure 6. Eye diagrams of
the laser d iode current and
the pholorece iver output
voltage for a 10 Gbit/s N RZ
pseudora ndom da ta stream
(same photo receiver as that
in Fig. 5).
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0.25 NW for 4 V and 0.27 NW for 10 V bias. The da rk current at 4 V was 2 nA for an active area
of25x2S f1 m2 . T he following mean values for the enhancement and depletion HEMT parameters, respectively, have been Obtained: threshold voltage::: 0.1 and -0.5 V, tra nsconductance =
500 and 390 mS/mm, source resistance =0.7 and 0.6 Qmm, transit frequency::: 35 and 30 GHz.
AJI high frequency measu rements of the receiver were performed on-wafer using CASCADE probes . The photodiode was irradiated by 0.84 f1m light from a highspeed ORTEL laser diode
via a single mode fiber. The current driving the laser diode was modulated to obtain up to 0.8 m W
peak-ta-peak modula ted optical signa!s. The relative response versus frequency, measured al
278
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et al. f 10 Gbitfs monolithic illtegrated optoelectronic receiver
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Fiiure 7. Measured frequency response of a photoreceiver from a
different wafer (RG32--68). The
measured -3 dB bandwidth lies at
11.3 GHz.
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the output of a photoreceiver (wafer RG31-1 05), is shown in Figure 5. The -3 dB bandwidth o f
the pholoreceiver for sinuso idal modu lated incident light lies at 8.2 GHz. The frequency response of the ORTEL laser diode itself was determined using a calibrated GEe photodiode. The circuit response to pulse-modulated non-relum-to-zero (NRZ) optical signals was tes ted at data
ra les up to 10 GBitls by means of an ANR ITSU pulse pattern genera tor. The eye diagrams of the
laser diode current and the photo receiver outpu t voltage demo nstrate (Figure 6) that the optoelectron ic receiver operates successfully for a 10 Gbills NRZ pseudorandom data stream of length
27_1 bits. Eye diagrams of the same quality were observed for the data stream length 2 31 _ 1 bits.
Figure 7 shows the relative response versus frequency of a photoreceiver from a different wafer (RG 32--68) from that in Figures 5 and 6. For this wafer the threshold vo ltages are 0 and -0.7 V
fo r the enhancement and depletion HEMTs, respec tively. Due 10 the different opera ting point of
the transimpedance amplifier the effective transimpedance of the photoreceiver was 330 Q instead of 440 n, i.e. the output voltage was 25 % lowe r. Furthermore, the freque ncy response is not
as flat as that of the firs t photoreceiver, however, the - 3 dB bandwidth lies a t 11.3 GH z.
ACKNOWLEDGEMENT
The financial support of the Bundesministerium flir Forschung und Technologie through the
CAE-project NT2778A is gratefully acknowledged. Spec ial thanks go to H. S. Rupprecht for hi s
continuous encouragement.
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[2]
[3]
[4]
C.S. Harder, B. Van Zeghbroeck, H. Meier, W. Patrick, and P. Vetliger,
IEEE Electron Device Let!. , vol. EDL-9, pp. 171 - 173, 1988.
H. Hamaguchi, M. Makiuc hi , T. Kumai, and O. Wada,
IEEE Electron Device Let!. , vo l. EDL--8, pp. 39-41, 1987.
V. Hurm, J. Rosenzweig, M. Ludwig, W. Benz, M. Berroth, A. Hulsmann,
G. Kaufel , K. Kohler, B. Raynor, and J. Schneider,
Electron. Leu., vol. 27, pp. 734-735,1991.
K. Kohler, P. Ganser, K. H. Ba chem, M. Mai er, J . Hornung, and A. Hulsmann,
Proc. l nt. Symp. CaAs and Related Compounds , Jersey, 1990, Ins!. Phys. Co nf. S er. ,
vol. 112, pp. 521 - 526, 1990.
[5]
A. Hlilsmann, G. Kaufel , K. Koh ler, B. Raynor, 1. Sc hne ider, and T. lakobus,
lpn. l . Appl. Phys. , vol. 29, pp. 23 17-2320,1990.