Semiconductor Avalanche Diode Detectors for Quantum Cryptography

20leos05.qxd 10/5/06 2:15 PM Page 23
FWHM, ps
1000
800
600
400
200
40μm
20μm
10μm
Excess Bias, %
SPAD 3Q
T = 175K
4 5 6 7 8 9 10 11 12 13
After Pulsing Probability
1
0.1
200K
190K
0.01
180K
170K
0.001
160K
0.0001
1μ 10μ 100μ 1m 10m 100m 1
Delay, s
Figure 4. Device jitter (full-width-at-half-maximum) of SPAD-3Q
with device diameters of 10, 20 and 40 μm.
Figure 6. Afterpulsing probability versus time after avalanche for
SPAD-3Q at operating temperatures of 160K, 170K, 180K, 190K
and 200K.
Noise Equivalent Power, WHz −1/2
10 −12
10 −13
10 −14
10 −15
10 −16
S1 PMT
Si SPAD (300K)
Hamamatsu R5509a-73
PMT (193K)
Ge SPAD
(77K)
SPAD 3Q (150K, 200K)
10 −17
250 500 750 1000 1250 1500 1750 2000
Wavelength, nm
After Pulsing Probability
1
0.1
Full SPAD
No InGaAs
0.01
0.001
InP Only
T = 200K
0.0001
1μ 10μ 100μ 1m 10m 100m 1
Delay (s)
Figure 5. Noise equivalent power spectra of several selected singlephoton
detectors
with the InGaAs layer removed and the second was with
both the InGaAs and InGaAsP layers removed. Whilst these
measurements are ongoing at the time of writing, it appears
that similar lifetimes and activation energies are observed –
leading to the likelihood of the afterpulsing behaviour
being dominated by the InP layer.
Of particular relevance to the application of quantum
key distribution is the count rate limitation imposed by the
deleterious effects of afterpulsing in these SPADs – effects
which have reduced QKD clock rates to, typically, MHz
rates, far less than the potential rates afforded by consideration
alone of the subnanosecond jitter in these devices,
which, in the absence of afterpulsing, should permit GHz
clock rates as previously demonstrated with Si-based
SPADs [4][5].
Figure 7. Afterpulsing probability versus time after avalanche at
operating temperature of 200K for (1) SPAD-3Q; (2) similar structure
without InGaAs layer; (3) similar design without InGaAs
and InGaAsP
IV. Infrared Single-
Photon Detectors in
Quantum Key Distribution
The application of quantum key distribution places particular
requirements on the performance of infrared photoncounting
detectors. In quantum key distribution systems, a
figure of merit used is the quantum bit error rate (QBER),
which can be simply described [12] as:
QBER =
N WRONG
N WRONG + N RIGHT
where N WRONG is the rate of spurious counts and
N RIGHT is the rate of correct counts in the time slot of
expected photon arrival. The spurious counts can result
from a number of factors external to the detector, for exam-
October 2006 IEEE LEOS NEWSLETTER 23