A Large Area Avalanche Photodiode (LAAPD) was studied, aiming to access its
performance as light detector at low temperatures, down to -80 C. The excess
noise factor, F, was measured and found to be approximately independent of the
temperature. A linear dependence of F on the APD gain with a slope of 0.00239
+/- 0.00008 was observed for gains above 100. The detection of low intensity
light pulses, producing only a few primary electron-hole pairs in the
photodiode, is reported.Comment: 16 pages, 7 figures; was presented at 3-rd conference "New
  Developments in Photodetection" Beaune, France, June 17-21, 2002; submitted
  to NI

A.J.P.L. Policarpo

F. Neves

Hauger

Lecomte

M.I. Lopes

McIntyre

Moszynsky

R.F. Marques

Solovov

V. Chepel

V.N. Solovov

English

arXiv

A Large Area Avalanche Photodiode was studied, aiming to access its performance as light detector at low temperatures, down to -80°C. The excess noise factor, F, was measured and found to be approximately independent of the temperature. A linear dependence of F on the APD gain with a slope of 0.00239±0.00008 was observed for gains >100. The detection of low intensity light pulses, producing only a few primary electron-hole pairs in the photodiode, is reported.http://www.sciencedirect.com/science/article/B6TJM-48343C5-6/1/cfbd9d61bf7dfaa42e9a9b41eb71e0b

Solovov, V. N.

Neves, F.

Chepel, V.

Lopes, M. I.

Marques, R. F.

Policarpo, A. J. P. L.

RCAAP - Repositório Científico de Acesso Aberto de Portugal

Low-temperature performance of a large area avalanche photodiode

Estudo Geral

Crossref

Nuclear Instruments and Methods in Physics Research A 504 (2003) 53–57
Low-temperature performance of a large area avalanche
photodiode
V.N. Solovov*, F. Neves, V. Chepel, M.I. Lopes, R.F. Marques,
A.J.P.L. Policarpo
LIP-Coimbra and CFRM, Physics Department, University of Coimbra, Coimbra 3004-516, Portugal
Abstract
A Large Area Avalanche Photodiode was studied, aiming to access its performance as light detector at low
temperatures, down to 80C. The excess noise factor, F ; was measured and found to be approximately independent of
the temperature. A linear dependence of F on the APD gain with a slope of 0.0023970.00008 was observed for gains
>100. The detection of low intensity light pulses, producing only a few primary electron–hole pairs in the photodiode,
is reported.
r 2003 Elsevier Science B.V. All rights reserved.
PACS: 85.60.Gz; 85.60.Dw; 70.70.+m
Keywords: Photodetectors; Excess noise factor; Avalanche photodiode; LAAPD
1. Introduction
Large Area Avalanche Photodiodes (LAAPD)
are of great interest for high efﬁciency detection of
low intensity light pulses from scintillators. In spite
of some drawbacks, they can compete successfully
with photomultiplier tubes (PMT) in many appli-
cations that require very compact detector packa-
ging (in Positron Emission Tomography, for
instance), low sensitivity to magnetic ﬁelds (as in
some space applications and accelerator experi-
ments) or low intrinsic radioactivity as required
for the low background experiments (e.g., dark
matter search). Very good time and energy
resolutions have been achieved with LAAPDs
with various scintillators, namely inorganic crys-
tals [1,2] and liquid xenon [3].
Operation at low temperature can be not only a
necessity, as in the case of liquid xenon [3], but also
a favorable option. In fact, to operate the LAAPD
at low temperature has two advantageous effects:
(1) the dark current noise decreases dramatically,
(2) the voltage required to achieve a certain gain
becomes lower. In our previous work [4], both
effects were investigated as a function of the
temperature between 25C and 100C.
In a detector with a LAAPD readout, the noise
and the ﬂuctuations of the avalanche gain contribute
to the energy resolution of the system. The later is
usually expressed in terms of the excess noise factor,
F [5]. Previous measurements of the energy resolu-
tion in liquid xenon excited with alpha-particles [3],
*Corresponding author. Tel.: +351-239-410666; fax: +351-
239-829158.
E-mail address: solovov@lipc.ﬁs.uc.pt (V.N. Solovov).
0168-9002/03/$ - see front matter r 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0168-9002(03)00751-4
indicated a value of F signiﬁcantly larger than that
usually reported for room temperature.
In this paper, we report on measurements of the
excess noise factor as a function of the gain at low
temperatures (down to 80C). The results of
observation of very low intensity light pulses that
produce only a few primary electron–hole pairs in
the photodiode are also presented.
2. Experimental set-up
In our measurements we used a windowless
LAAPD, 5mm in diameter, from Advanced
Photonix, Inc. [6]. This photodiode, manufactured
using beveled-edge technology, has low dark
current and relatively small capacitance (typically,
about 30 nA and 25 pF, respectively, at room
temperature and a gain of 200).
The set-up used for the measurements is
schematically depicted in Fig. 1. The APD con-
nected to a low-noise charge sensitive preampliﬁer
(Cremat CR-101D) was mounted inside a metallic
cage and placed into a liquid nitrogen cryostat.
Light pulses of 0.5ms in duration were produced
by a green LED driven by a pulse generator. The
LED was mounted in a black box outside the
cryostat and optically connected to the APD
through an optic ﬁber. The intensity of light pulses
generated by the LED was monitored by a PMT
(Hamamatsu R1668). The output signal of the
APD was ampliﬁed by a charge sensitive preampli-
ﬁer followed by a spectroscopy ampliﬁer (Canberra
2021). Semigaussian shaping with shaping time of
1ms was used. The ampliﬁed and shaped signals
from both the APD and the PMT were digitized by
a peak ADC (LeCroy 2259B) and stored in a PC-
based multichannel analyzer. The PC also con-
trolled the LED and calibration pulsers and,
synchronously, provided a gate for the ADC. The
linearity, ampliﬁcation, pedestal (offset) and the
electronic noise of the whole spectrometric channel
were measured using calibration pulses from a high
precision pulser fed to the input of the preampliﬁer
through a capacitance of 2.4 pF. The calibration
was veriﬁed by observing the pulse height spectrum
due to direct conversion of 60keV g-rays (from an
241Am source) in the photodiode at unitary gain.
For precise measurement of the excess noise
factor it is very important to maintain the stability
of the APD gain during the acquisition. This
requires stable bias voltage and temperature as the
gain strongly depends on both of them, especially
at high gain values.
In our measurements, the stability of the bias
voltage was better than 0.1V. To reduce the ripples
from the HV power supply (CAEN N471), an RC-
ﬁlter with a time constant of 1 s was used. The
variations of the temperature were measured with a
precision of 0.02C using a platinum thermoresistor
ﬁxed directly on the photodiode. During the
acquisition of a single data point, the temperature
variation did not exceed 0.2C.
3. Experimental methods and results
3.1. Measurement of gain
For each value of the bias voltage, the amplitude
distribution of the APD charge signals was
recorded. The gain was then found as the ratio
Pulser
GG
PA A
A
Calib. 
Pulser
P
ADC
F
LED
PA
M
T
GATE
A0
A1
CAMAC
+HV
Fiber
PC
Fig. 1. The experimental set-up for studying the low-tempera-
ture performance of APDs: PA—charge sensitive preampliﬁer;
A—spectroscopy ampliﬁer; GG—gate generator; F—RC ﬁlter.
V.N. Solovov et al. / Nuclear Instruments and Methods in Physics Research A 504 (2003) 53–5754
of the mean amplitude found from the distribution
to that measured at low voltage (Vbias ¼ 400V),
where the gain is unitary [7]. Some results are
plotted in Fig. 2.
3.2. Measurement of excess noise factor
In an avalanche photodiode, the random
character of the multiplication process of the
electron–hole pairs under an electric ﬁeld intro-
duces the so-called multiplication noise, which is
characterized by the excess noise factor, F ; deﬁned
as
F ¼
/m2S
/mS2
¼
/m2S
M2
ð1Þ
where m is the gain of an avalanche in the
photodiode and M ¼ /mS [8].
By considering the statistical nature of the
avalanche formation, it was shown that F can be
approximated to
FEkeffM þ 2
1
M
 
ð1 keff Þ for Mb1 ð2Þ
where keff is the effective ionization rate ratio [9].
The ﬂuctuations of the amplitude of the charge
signal of an APD illuminated with light pulses can
be expressed as [5]:
s2
A2
¼
sn
MN0
 2
þ
F  1
N0
þ d2 ð3Þ
where A  MN0 is the average amplitude of the
pulses at the photodiode output expressed in
number of electrons, N0 the average number of
primary electron–hole pairs created by a single
light pulse, s2 the variance of the signal amplitude
distribution (in number of electrons), sn the
electronic noise at the input of the preampliﬁer
(r.m.s. in number of electrons), and d2 is the
relative variance in N0 and can be written as
d2 ¼
1
N0
þ e2 ð4Þ
where e2 includes all the non-Poisson contributions
to the ﬂuctuations in N0: In the present measure-
ments, the contribution to e2 is only due to the
ﬂuctuations of the intensity of the light source and
the gain non-uniformity in the photodiode. Repla-
cing Eq. (4) in Eq. (3), one gets
s2 ¼ s2n þ M
2N0F þ e2M2N20 : ð5Þ
If the light source is stable and the ﬂuctuations due
to the gain non-uniformity are not relevant such
that e5
ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
F=N0
p
; the last term in Eq. (5) can be
neglected (in our measurements, the lowest value
of
ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
F=N0
p
is obtained at FE2 and N0E5000;
which gives e50:02) and the excess noise factor
determined from the expression:
F ¼
s2  s2n
M2N0
ð6Þ
or, more conveniently,
F ¼
s2  s2n
M2N20
N0 ¼
s2  s2n
A2
N0: ð7Þ
For measuring the excess noise factor, the
amplitude distribution of the APD output signals,
as well as the distribution of the calibration pulses,
were acquired for different values of the gain. A
typical pulse height spectrum is shown in Fig. 3.
From these distributions, the following values
were determined: s2 and A as the variance and
the mean of the APD signal distribution and s2n as
the variance of the distribution of the calibration
pulses. The value of N0 was measured at M ¼ 1 as
the mean charge signal amplitude expressed in
number of electrons. In the beginning of each run,
N0 was set approximately to 4000 e and was kept
constant as long as the output signal did not
saturate the preampliﬁer. Then, the amplitude of
1450 1500 1550 1600 1650 1700
100
1000
 T = -20°C
 T = -40°C
 T = -60°C
 T = -80°C
AP
D
 G
ai
n,
 M
Bias voltage (V)
Fig. 2. Dependence of the APD gain on the bias voltage at
different temperatures.
V.N. Solovov et al. / Nuclear Instruments and Methods in Physics Research A 504 (2003) 53–57 55
the light pulse was decreased and a new value for
N0 was calculated from the ratio of PMT signals.
These measurements were carried out for gains
up to 2000 in the temperature range from 0C
down to 80C. The results for 40C and
80C for M > 100 are represented in Fig. 4, as
examples. In all the cases, the excess noise factor
increases linearly with gain, i.e.,
F ¼ F0 þ kM: ð8Þ
No temperature dependence of F0 and k was
observed within the experimental errors (Fig. 5).
Averaging the values of F0 and k obtained by
ﬁtting the data for different temperatures with
Eq. (8), one gets F0 ¼ 1:8770:02 and k ¼
0:0023970:00008: These results are consistent
with those presented in Ref. [10].
Fig. 6 shows the electronic noise, sn; as a
function of the APD gain for different tempera-
tures. For Tp 40C and MX5; the noise is
approximately constant and E250 electrons
(r.m.s.). At higher temperatures (T ¼ 20C),
the noise increases dramatically for large gains
due to the increase of the dark current.
3.3. Low-intensity signal detection
The reduction of the dark current at low
temperature allows the detection of light signals
of very low intensity, which produce just a few
primary electron–hole pairs in the photodiode. In
Fig. 7, it is shown the spectrum corresponding to
N0 ¼ 4:3; N0 being the mean number of electron–
hole pairs per light pulse (we observed similar
spectra for N0 varying from 3 to 7 electron–hole
pairs). For these measurements, the light pulse
amplitude was set initially rather high and N0 was
measured with the APD at M ¼ 1: Then, the light
intensity was reduced and N0 re-calculated using
the PMT signals as reference.
0 20 40 60 80 100 120 140 160
0
1000
2000
3000
4000
5000
6000
Co
un
ts
Charge, 103e
Fig. 3. A typical pulse height spectrum due to the LED (at the
right) and calibration pulses (at the left). The horizontal axis
shows the charge at the preampliﬁer input. Temperature is
60C, APD gain is 33, N0=4000 electrons.
2
4
6 T = -40°C
F0 = 1.74±0.06
k = 0.00249±0.00010
0 500 1000 1500 2000 2500
2
4
6
8
Ex
ce
ss
 n
oi
se
 fa
ct
or
, F
F0 = 1.94±0.06
k = 0.00241±0.00007
T = -80°C
Gain, M
Fig. 4. Dependence of the excess noise factor on the APD gain
at 40C and 80C. The straight line F ¼ F0 þ kM is ﬁtted
to the experimental results with F0 and k as adjusted
parameters.
-80 -60 -40 -20 0
1.7
1.8
1.9
2.0
2.1
2.2
2.4
2.6
2.8
3.0
F 0
k*
10
3
Temperature, °C
Fig. 5. F0 and k obtained at different temperatures.
V.N. Solovov et al. / Nuclear Instruments and Methods in Physics Research A 504 (2003) 53–5756
To avoid possible non-linearity in the ﬁrst
channels of the ADC, an offset was added by
sending a test pulse of ﬁxed amplitude and
duration to the preampliﬁer input simultaneously
with the light pulse. The value of the offset was
equivalent to 1500 electrons at the photodiode
output. Hence, the broad pulse distribution in
Fig. 7 corresponds to the offset light pulses while
the sharp peak at the left is due to the test pulses
only and is acquired with the LED turned off. The
upper axis in Fig. 7 was scaled to the number of
primary electron–hole pairs by dividing the
charge measured at the photodiode output by the
APD gain, M : Similar spectra were observed in
Ref. [10].
4. Conclusions
The excess noise factor of a LAAPD was
measured as a function of gain and temperature.
For the APD gains >100, it was found to be linear
with gain and practically independent on tempera-
ture in the range from 0C down to 80C. The
amplitude distributions of the signals with the
average number of primary electron–hole pairs as
small as 3 to 7 were measured, thus showing the
possibility of detection of very low intensity light
pulses.
Acknowledgements
This work was ﬁnanced by the project CERN/
FNU/43729/2001 from the Funda,c*ao para a
Ci#encia e Tecnologia, Portugal.
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[6] Model 197-70-73-520, Advanced Photonix, Inc.
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[8] J.A. Hauger, et al., Nucl. Instr. andMeth. A 337 (1994) 362.
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1 10 100 1000
200
300
400
500
600
700
800
900
1000
2000
El
ec
tro
ni
c 
no
is
e,
 σ
n 
(el
ec
tro
ns
 r.m
.s.
)
APD Gain, M
 T = -20 C
 T = -40 C
 T = -60 C
 T = -80 C
°
°
°
°
Fig. 6. Dependence of the electronic noise at the preampliﬁer
input on the APD gain and temperature (the preampliﬁer was
connected to the APD).
0 5000 10000 15000
0
20
40
60
80
100
4.3e, M=600
Co
un
ts
Charge, e
0 5 10 15 20 25
primary electron-hole pairs
Fig. 7. A spectrum of the APD output signals corresponding to
a mean number of primary electron–hole pairs equal to 4.3.
Temperature is 40C, APD gain is 600.
V.N. Solovov et al. / Nuclear Instruments and Methods in Physics Research A 504 (2003) 53–57 57


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Low Temperature Performance of a Large Area Avalanche Photodiode

Low Temperature Performance of a Large Area Avalanche Photodiode

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