New Materials for Photon Counting Avalanche Photodiodes

Josef Blazej

Czech Technical University Prague, Brehova 7, 115 19 Prague, Czech Republic

Keywords: Solid State Single Photon Detector, Gallium, Compound Semiconductors, Avalanche Photodiode (APD).

Abstract: The experimental results acquired on avalanche photodiodes based on III-V semiconductor materials and

operated as single photon counters with picosecond timing resolution are reported. The semiconductor

structures fabricated on the basis of GaAs, GaP and GaAsP have been operated in a Geiger mode and

employed in a photon counting experiment at the wavelengths from near ultraviolet to near infrared. The

dark count rates, photon counting sensitivity and timing resolution have been measured for the experimental

diode samples.

1 INTRODUCTION

The solid state photon counters with high timing

resolution are of interest of numerous electro-optical

techniques: laser range finding, optical time domain

reflectometry, time resolved spectroscopy, quantum

cryptography and others. At present, the most

promising technique to detect single photons by use

of a solid state detector is an Avalanche Photodiode

(APD) op-erated in the Geiger mode. In this

operating mode the diode is pulse biased above its

breakdown voltage; no current is flowing until an

avalanche is triggered by an incoming photon or a

thermally generated carrier. The current pulse rise

time marks the photon’s arrival time. An external

electrical circuit, either passive or active (Cova et

al., 1983), is used to quench the avalanche and to re-

apply the bias to the diode.

Our previous research and development in the

field of single photon avalanche diodes resulted in a

large aperture silicon APD based detector package

with and active quenching circuit well adopted for

applications listed above (Prochazka et al., 1996).

The quantum efficiency corresponds to silicon, it

drops for the wavelengths longer than 1.1 μm and

shorter than 0.35 μm. In an attempt to increase the

quantum efficiency in the near infrared, the

structures based on germanium doped silicon have

been tested. For individual photon detection in the

near infrared, the germanium APDs in a cryogenic

environment has been em-ployed. This package has

been used as an echo signal detector in the satellite

laser ranging system operating at so-called eye safe

wavelength 1.54 μm in the Communication

Research Labs., Tokyo, Japan (Prochazka et al.,

1996, Kunimori et al, 2000). For the

telecommunication applications at the 1.55 μm

wavelength the thermoelectrically cooled photon

counter based on an InGaAs/InP avalanche

photodiode has been developed (Prochazka, 2001).

For the applications in satellite laser ranging, the

increase of a timing resolution of the detector is

required. Recent developments resulted in a custom

designed APD on silicon having a diameter of

0.2 millimeters in diameter exhibiting a dark count

rate below 60 kHz. The APD chip is cooled by a

three stage thermoelectrical cooler and enclosed in a

miniature evacuated package. The detector is

equipped with the electronic compensation of the

detection delay dependence on optical signal

strength. This way, the detector may be employed

for signals of single up to several thousands of

photons (Kirchner et al., 1997). The timing

resolution of 60 picoseconds FWHM is achieved on

single photon signal level. It is the value three times

worse than necessary for one millimetre precision

required in this application. Additionally, the non-

standard data distribution when detecting individual

photons at the wavelength above 0.6 μm represents a

serious limitation. The timing resolution can be

compensated by data post-processing utilizing

famous detector delay stability. But the problems

with response distribution are inherent and for some

wavelength crucial. That is why, new materials for

the photon counting detection structures have been

investigated. The III-V materials have been selected

in an attempt to reach higher timing resolution and

238

Blazej, J.

New Materials for Photon Counting Avalanche Photodiodes.

DOI: 10.5220/0005656802360240

In Proceedings of the 4th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2016), pages 238-242

ISBN: 978-989-758-174-8

standard data distribution. The perspective

applications in the ultraviolet are another reason for

the III-V materials experiments.

2 III-V PHOTON COUNTING

AVALANCHE PHOTODIODES

The spectral sensitivity of the GaAs, GaP and

GaAsP are plotted on Figure 1. The diodes on GaP

are of special interest due to their sensitivity in the

ultraviolet. All the diodes have been manufactured

using a conventional planar technology. The active

area of the diode is octagonal with the “diameter” of

350 μm. The GaAs and GaAsP diodes are

constructed to be illuminated on an active area, due

to the technology reason, the GaP diode is of “reach

through” construction.

100 200 300 400 500 600 700 800 900 1000

0.1

100

GaAs

GaAsP

GaP

Absolute sensitivity [mA/W]

Wavelength [nm]

Figure 1: The spectral sensitivity of GaAs, GaP and

GaAsP according to (Van Stryland et al., 1996).

The diodes have been tested in a passive

quenching circuit consisting of a serial resistor

1 MegaOhm blocked by a 20 picoFarad capacitor.

The example of the output pulse of the GaAsP diode

is on Figure 2. The break voltage at a room

temperature is 24 Volts with a drift of 15 mV/K. The

break voltage of the successful GaAs and GaP

diodes was 40 Volts and 24 Volts, respectively. The

amplitude of the pulse is one half of the value of bias

above the break voltage. It indicates relatively low

serial differential resistance of the structure above its

break, 50 Ohms typically. It makes the diodes

attractive for application as photon counters

operated in an active quenching and gating mode.

The output pulses parameters were similar for all

three diode materials.

3 EXPERIMENTAL SETUP

In all the following experiments, the diodes have

been operated in an active quenching and gating

mode, using a circuit developed for silicon photon

counting detectors (Prochazka et al., 1992). The

block scheme of the test setup is on Figure 3.

Figure 2: GaAsP diode output pulse in a passive

quenching scheme, diode biased 2 V above break voltage,

bandwidth 400 MHz, fall time 1.5 ns, width 5.2 ns.

The time-correlated photon counting scheme has

been used. The laser diode (LD) provided optical

pulses 32 picoseconds long at 0.757 μm. The signal

has been attenuated using the neutral density filters

(ND). The Active Quenching and Gating Circuit

generated the NIM timing pulses. The Time to

Amplitude Converter (TAC) provided the timing

resolution of 20 picoseconds per channel. The data

from the TAC have been processed in the

Multichannel Analyzer Card in a personal computer.

The gate signal has been generated and the repetition

rate of the experiment has been controlled by the

Pulse Generator. The useful signal detection rate on

the single photon level has been used for a rough

estimate of the relative detection efficiency in

comparison to the silicon based diode.

PULSE GENERATOR

LASER PULSER

HAMAMATSU PLP01

757 nm, 5 mW

ACTIVE

QUENCHING

AND GATING

APD

in THERMOSTAT

0.3 m

TIME TO

AMPLITUDE

CONVERTER

MULTICHANNEL

ANALYZER

Figure 3: Block scheme of the detector test setup, time

correlated photon counting experiment.

4 EXPERIMENT RESULTS

AND DISCUSSION

Characteristics of photon counters have been

New Materials for Photon Counting Avalanche Photodiodes

239

measured for selected materials in visible range due

to available picosecond laser source. The

experiments with high energy photons have been

completed, its review is in paper (Blazej et al.,

2007). Some specific characteristics of detectors

under study like mutual interaction in visible

wavelength range of closely running detector have

been published in other paper (Blazej et al, 2006).

The luminescence of these type structures are also

disscused in reference (Gontaruk et al., 2014).

Figure 4: GaAsP structure photo.

4.1 GaAsP

The dark count rate of the GaAsP avalanche

photodiodes as a function of the bias above the break

is plotted on Figure 5, the measurement has been

carried out with the repetition rate 100 Hz.

012345

0.1

100

Dark count [MHz]

Bias voltage [V]

Figure 5: Dark count rate of the GaAsP diode as a function

of bias above break, diode operated in an active quenching

and gating circuit.

Considering the diode active area, the dark count

rate is in principle comparable to the silicon based

SPADs, which is of the order of 1 MHz, 5 V above

the break, at the same temperature and active area

100 μm in diameter. The dark count rate can be

reduced by diode cooling. On the Figure 6 see the

plot of the dark count rate versus temperature. The

decrease of the dark count rate with temperature is

rather low in comparison to silicon or germanium

diodes, one order of magnitude per 60 K.

The timing resolution has been measured in an

arrangement described on Figure 3. For comparison

purposes, the reference APD on silicon (SPAD)

(Prochazka et al., 1992) has been employed. The

results are summarized on Figure 7, the photon

counting time response of the GaAsP diode (upper

curve) and silicon SPAD (lower curve). Note equal

width of both the distributions and a highly non-

symmetrical data distribution (tail) of the silicon

SPAD in contrast to a nearly ideal normal

distribution of the GaAsP diode.

-100 -80 -60 -40 -20 0 20

0.1

Dark count [MHz]

Chip temperature [°C]

Figure 6: Dark count rate of the GaAsP diode as a function

of temperature, diode operated in an active quenching and

gating circuit, 5 V above the break.

The timing resolution 112 ps FWHM for both

samples has been limited by the experimental chain.

The single photon detection efficiency has been

found to be in the range 0.1 to 1 % at the testing

wavelength. The detection probability is a product of

two probabilities: probability of generating a carrier

and probability of the avalanche triggering.

According to Figure 1, the first probability should

exceed 10 %, thus the limiting factor in our detector

photon counting sensitivity was the low probability

14 16 18 20 22 24

100

1000

GaAsP

Number of counts

Time [ns]

Figure 7: Timing resolution of the GaAsP and silicon

photon counters operated 5 V above their break voltage,

FWHM = 112 ps for both diodes. Note high non-

symmetry of the silicon diode data distribution.

PHOTOPTICS 2016 - 4th International Conference on Photonics, Optics and Laser Technology

240

of avalanche triggering. This parameter may be

improved by the diode structure design and

optimization specifically for photon counting

purposes.

4.2 GaAs

The example of the timing resolution data of the

GaAs photon counter is on Figure 8. The diode has

been biased 5 Volts above the break. The dark count

rate of 20 MHz has been observed at +25 °C.

25 30 35 40

200

400

600

800

1000

Number of counts

Time [ns]

Figure 8: Timing resolution of the GaAs diode operated as

a photon counter operated 5 V above the break voltage,

FWHM = 230 picoseconds.

Comparing to the GaAsP diode, the timing

resolution is more than twice worse and the data

distribution exhibits a significant non-symmetric, the

percentage of the data points in the tail of the

distribution exceeds 70 %. This fact inhibits the

application of GaAs diodes for laser ranging

purposes. The dependence of the timing resolution

on the diode biasing is plotted on Figure 9.

0123456

200

400

600

800

1000

FWHM [ps]

Bias voltage [V]

Figure 9: Timing resolution of GaAs diode operated as a

photon counter versus bias above break voltage.

4.3 GaP

The GaP diode timing properties are demonstrated

on Figure 10, where the time correlated photon

counting results are plotted.

16 17 18

100

200

300

400

500

600

Number of counts

Time [ns]

Figure 10: Timing resolution of the GaP diode operated

5 V above the break voltage as a photon counter,

FWHM = 110 ps. Note good symmetry of the data

distribution.

Although the test wavelength has been outside the

main sensitivity of the material, see Figure 1, the

residual sensitivity permitted to carry out the

measurements. The photon counting probability was

of the order of 0.01 % in this case. The timing

resolution FWHM of 110 picoseconds has been

obtained, the data distribution is quite well

symmetric and close to normal one. The diode has

been biased 5 Volts above the break, the dark count

rate of 6 MHz has been measured. The relative

sensitivity and Signal to Noise Ratio (SNR) versus

voltage above the break is plotted on Figure 11.

0123456

1.0

1.5

2.0

2.5

3.0

3.5

SNR

SNR [a.u.]

Bias voltage [V]

Sensitivity

Sensitivity [a.u]

Figure 11: Sensitivity and SNR of the GaP diode based

photon counter versus bias above the break.

5 CONCLUSIONS

The avalanche diode structures operational as single

photon detectors with picosecond resolution on the

basis of the GaAs, GaP and GaAsP materials have

been designed, developed and tested. This is to our

knowledge the first published attempt to develop a

photon counting avalanche photodiode on the basis

of these materials. The timing resolution FHWM of

112, 275 and 110 picoseconds for the diodes on

GaAsP, GaAs and GaP, respectively, has been

obtained. The dark count rate comparable to existing

New Materials for Photon Counting Avalanche Photodiodes

241

silicon avalanche photodiodes has been measured.

The GaAsP and GaP photon counters exhibit time

correlated photon counting data distribution very

close to ideal normal distribution in the near infrared

wavelength. It is expected, that further tuning of the

diode structure and its optimization for photon

counting will result in a detector with timing

resolution better than silicon detectors and will

provide a nearly ideal data distribution in the near

infrared with the detection efficiency reaching 10 %.

ACKNOWLEDGEMENTS

This work has been carried out at the Czech

Technical University in Prague. Numerous grants

were provided by the Czech Grant Agency, Czech

Ministry of Education and by international agencies.

The recent publication has been supported by

MSMT CR grant RVO68407700.

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