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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. [email protected]
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
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 Eg = 0.75 eV, compatible with the detection of 1.30 and 1.55 µm wavelength light
Photo-HBT developed at OPTO+
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 InxGa1-XAs
Vertical structure Key technology : epitaxy
• no antireflection layer
Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 5
Emitter area : 9 µm2
Base area : 44 µm2
Optical window area : 16 µm2
-20
-15
-10
-5
0
5
10
15
20
25
1,00E+08 1,00E+09 1,00E+10 1,00E+11 1,00E+12
Frequency (Hz)
Ph
oto
resp
on
se (
dB
)
20 dB/decade
FC = 110 GHz
FCPD-mode
Tr-mode
Gopt = 32 dB
Photo-HBT as a direct photodetector
1A/W
R(A/W)20.LogR(dB)
RDC = 0.2 A/W
Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 6
Saturation characteristics
Photo-HBT saturation at 19 GHz
-60
-55
-50
-45
-40
-35
-30
-25
-20
-15 -10 -5 0 5
Pavg (dBm)
RF
ou
tpu
t p
ow
er
(dB
m)
-1 dBTr-mode
@ -1dB: -21 dBm
Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 7
photo-HBT CHAIN
Spectrum
Analyser
32C
E
B1
<Iin
>
Ib_ tot
Ib_ tot =I b_ elec + Iph
LNAb-tee
G = 50 dB
NF < 5 dB Psys_noise
(dBm/Hz)
RBW = 2 MHz
Analog noise characteristics
Input noise current spectral density <Iin> (pA/Hz^0.5)
Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 8
Analog noise characteristics
Input noise current spectral density
@ 40 GHz: Ic <Iin> (mA) (pA/Hz^0.5)
2 50 10 66
0
10
20
30
40
50
60
70
80
1,00E+09 1,00E+10 1,00E+11
Frequency (Hz)
<Ii
n>
(p
A/H
z^0.
5)
36 pA/Hz 0̂.5@28 GHz
51 pA/Hz 0̂.5@28 GHz
28 GHz
Ic = 10 mA
Ic = 2 mA
Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 9
Data signal : 25 Mb/s, 16 QAM
1,E-11
1,E-10
1,E-09
1,E-08
1,E-07
1,E-06
1,E-05
1,E-04
1,E-03
1,E-02
10 15 20 25 30C/N (dB)
BE
R
@ 27.875 GHz
@ 800 MHz
photo-HBT at 27.875 GHz
Pavg = -5,5 dBm
R = 0.35 A/WIc = 10.3 mA
Digital noise characteristics
BER at 10-9: C/N = 24.3 dB
Laser 1.55 m
Photo-HBT
Opticalattenuator
EOM 5 dBm
LNA
MPG2 Generator
16 QAMmapping
I Qmodulator1.6 GHz
OL29.475 GHz
Filtre27.875 GHz
BERmeasurements
OL2.4 GHz
OL29.475 GHz
27.875
GHz
1.6 GHz800 MHz30 dB
Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 10
OEIC using photo-HBTs
-25
-15
-5
5
15
25
35
45
55
10 15 20 25 30 35 40
Frequency (GHz)
TZ
Gai
n (
dB
Oh
m)
GTZ @ 28 GHz = 50 dBOhm
4 GHz
Photodetection at 27.875 GHz
1,E-12
1,E-11
1,E-10
1,E-09
1,E-08
1,E-07
1,E-06
1,E-05
1,E-04
1,E-03
14 16 18 20 22 24 26 28C/N (dB)
BE
R PINPavg = 1 dBm
photo-HBT circuitPavg = -5 dBm
Data signal : 25 Mbit/s 16 QAM
PhotoHBT
/4 line
CB VC
E
OutIn
IB
h
RBp
ol
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
Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 11
B B B B
PLOPRF
Cascode cells28 GHz
Photo-HBT
B B
PLO PRF
Chip size : 1634 x 1300 µm2
42 GHz
Chip size : 2850 x 1600 µm2
Optoelectronic mixers using photo-HBTs
Upconversion mixer from 2 GHz to 28 GHz and to 42 GHz
HBTphotoPDmodeout
circuitoutconv
)(IFPIF)(LOP
G
Gconv
28 GHz 17.8 dB
42 GHz 9.2 dB
Mixer
Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 12
Top illuminated PIN photodiode
P
I
N
Trade-off between efficiencyand speed (bandwidth)The better performances with aPhotoabsorption layer of 400nm: Bandwidth = 30 GHz R = 0.30 A/W
Photoabsorption layer
The main attraction of this device is itscompatibility for integration with SHBTs.For example, this photoreceiver realized byD. 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
PINphotodiode
SHBT-based preamplifier
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.
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 photoreceiverNeed of photodiodes with broad bandwidth, high responsivity and high output power
Back illuminated UTC photodiode
p-Contact Subcollector
Barrier
Basep+p+
p+
Collectorn
n+
Opticalabsorption region
Space-chargeregion
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
Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 15
Back illuminated UTC photodiode
p+ : Base contact
p+ : Barrierp+ : Base
absorption layer
Composite collector
Sub-collector
InP-Substrate
Thickness (nm)
Responsivity (A/W)
Bandwidth (GHz)
Vpp (V)
Collector Base 208 140 140
0.16 A/W
0.16 A/W
152 GHz 114 GHz 125 GHz
0.65 V 1.9 V 0.6 V
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
Workshop PHOTOTRANSISTORS Septembre 9, 2003, Budapest / Hungary C. Gonzalez 16
Light
Thickness (nm)
Responsivity (A/W)
Bandwidth (GHz)
Collector Base 200 280
0.43 A/W
54 GHz
Output power dependance on input light
UTC photo-HBT 20 GHz 19 GHzPopt 2.5 dBm 2.5 dBmPRF -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
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