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Development of Multi-Pixel Photon Counters (1)

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Development ofMulti-Pixel Photon Counters (1)

S.Gomi, T.Nakaya,

M.Yokoyama, M.Taguchi, (Kyoto University)

T.Nakadaira, K.Yoshimura, (KEK)

for KEK-DTP photon sensor group

Oct.31.2006 Hawaii

- Introduction
- Measure the fundamental performance
- Check the MPPC raw signal
- GAIN
- noise rate
- Cross-talk rate
- Photon Detection Efficiency ( PDE )
- Linearity

- LASER test( KEK-DTP LASER system)

Introduction

- Multi-Pixel Photon Counter ( = MPPC ) is a new type of photo detector developed by Hamamatsu Photonics (HPK).
- MPPC consists of 100~1600 small avalanche photo diodes( APD ) in 1mm×1mm sensitive region.

1pixel

6mm

MPPC

Sensitive region of MPPC

400pixel type

- Each APD pixel operate in Geiger mode. Gain is proportional to the applied voltage above the breakdown voltage( Vbd ).

- In Geiger mode, the output charge Q from a single pixel is independent of the number of injected photons within the pixel.

Extrapolated to GAIN=0

Vbd

V

Combining the output from all the pixels, the total charge from one MPPC is quantized to multiples of Q .

MPPC advantages

Compact

Insensitive to magnetic field

High gain( ~106 ), low bias voltage( ~70V )

Low-cost

5mm

6mm

the MPPC is an excellent photon counting device

- We measured the basic performance of two kinds of MPPC, 100 pixel type, and 400 pixel type.

Measure the fundamental performance

check the MPPC raw signal

gain

noise rate

cross-talk rate

Photon Detection Efficiency ( PDE )

Linearity

- MPPC has good photon counting capability. We can observe 1p.e signal peak, 2p.e signal peak, …

* ADC distribution *

1p.e signal

2p.e

1p.e

2p.e

…

3p.e

pedestal

4p.e …

set up

blue LED

- Measuring the little light from the blue LED by MPPC.
- Gain is measured by ADC distribution.

MPPC

ADC distribution

* STATUS DATA *

400 pixel MPPC

BIAS : 70.0V / VBD =68.8V

- Gain of MPPC is defined as this equation.
- Gain is measured by analyzing ADC distributions of MPPC signals.

1p.e signal

2p.e

3p.e

pedestal

4p.e …

The gain can be estimated at intervals between 1p.e and the pedestal.

Gain 100pixel

Gain 400pixel

- From gain-voltage relation, the break down voltage can be measured.

69.6 70 70.6

69 69.5 69.8

Bias voltage [V]

Bias voltage [V]

MPPC is a high gain device.

Blue: 15degree

Green: 20degree

Red: 25degree

The break down voltage depends on the temperature.

Gain 100pixel

Gain 400pixel

0.2 1 1.6 0.8 1 2 2.4

DV

DV

- Gain is a function of DV.

Blue: 15degree

Green: 20degree

Red: 25degree

- MPPC is a noisy photo detector. The origin of these noises is the thermo electron. So, the signals of noise are 1p.e signal typically.
- The noise rate is measured by counting the rate of signal with their height over the threshold, imposed on 0.5p.e and 1.5p.e .

“ 1p.e noise ”

0.5 p.e = threshold

“ 2p.e noise ”

1 p.e

Noise signal of 100pixel MPPC at 25 degree.

( integrated )

1.5 p.e = threshold

Blue: 15degree

Green: 20degree

Red: 25degree

Noise rate [ MHz ] 100pixel

Noise rate [ kHz ] 400pixel

- 1p.e noise rate is about 100~400 kHz.
- 2p.e noise rate is about 0~200 kHz.

400kHz

500kHz

1p.e

2p.e

1p.e noise

2p.e noise

100kHz

100kHz

69.5

69.1

70

69.2 70 70.4

Bias voltage [V]

Bias voltage [V]

Noise rate [ MHz ] 100pixel

Noise rate [ kHz ] 400pixel

- 1p.e noise rate is a function of both temperature and DV.

400kHz

500kHz

1p.e

2p.e

1p.e

2p.e

100kHz

100kHz

1

0.4

1.6

0.5 1 1.5 2 2.3

DV

DV

Blue: 15degree

Green: 20degree

Red: 25degree

2p.e noise rate seem to be a function of DV. This is due to “Cross-talk”.

- The origin of the cross-talk is presumed to be optical photons emitted during avalanche which enter neighboring pixels and trigger another Geiger discharge.

APD that should not detect any photons from outside also operate signals.

Neighborhood pixel

Avalanche

g

“ Cross-talk “

g

- The probability of cross-talk is estimated by the number of 1p.e .

The number of pedestal are free to cross-talk

measurement

- the number of each p.e is assumed to be follow the Poisson distribution

The number of 1p.e : P(1)

( estimated by pedestal )

||

without cross-talk

The number of 1p.e : P(1)

( measured )

||

with cross-talk

This difference corresponds to the decrease by cross-talk.

The cross talk rate is determined.

Blue: 15degree

Green: 20degree

Red: 25degree

Cross-talk rate 100pixel

Cross-talk rate 400pixel

- Cross-talk rate at operation voltage defined by HPK is about 20% at 20degree. ( We measured within the wider range about bias voltage. )

50%

50%

10%

10%

69.6 70 70.6

69 69.5 69.8

Bias voltage [V]

Bias voltage [V]

Cross-talk rate 100pixel

Cross-talk rate 400pixel

- Cross-talk rate is a function of DV.

50%

50%

10%

10%

1

2

0.2 1 1.6 0.8 1 2 2.4

Delta V

DV

DV

Blue: 15degree

Green: 20degree

Red: 25degree

- Photon Detection Efficiency ( = PDE ) is defined as this equation. PDE consists of three elements.

Geometrical Efficiency. A ratio of active area to total area (50%~70%)

Quantum Efficiency of active area (60~80%)

Probability of Geiger discharge (60~90%)

Depending on MPPC type

Depending on wavelength of injected light

Depending on bias V

MPPC have the highest QE in Green light.

・only the light going through 1mmφslit is detected.

set up

Moving stage

1mmφslit

・The ratio of p.e of MPPC to that of PMT is taken as relative PDE of MPPC.

PMT

Blue LED

MPPC

( total area 1mm2)

PMT made by HPK, type H8643

Relative PDE 100pixel

Relative PDE 400pixel

- PDE is about 2~3 times higher than that of PMT.

3

2

2

1

1

69.6 70 70.6

69 69.5 69.8

Bias voltage [V]

Bias voltage [V]

Blue: 15degree

Green: 20degree

Red: 25degree

Relative PDE 100pixel

Relative PDE 400pixel

- PDE is a function of Delta V.

3

2

2

1

1

0.2 1 1.6 0.8 1 2 2.4

DV

DV

Blue: 15degree

Green: 20degree

Red: 25degree

MPPC have the fixed number of pixel

( 100pixel, 400pixel,… )

- The linearity become those equation.

MPPC is non-linear device when the number of injected photons is not small compared to pixel number.

Linearity 100pixel

Linearity 400pixel

linear

linear

- The green line shows the expectation value calculated from number of pixels.

Fired pixel [ % ]

Fired pixel [ % ]

25%

25%

Blue: DATA plot

Green: expectation

Blue: DATA plot

Green: expectation

Injected photoelectron per pixel

Injected photoelectron per pixel

MPPC can operate as linear device.

~25p.e about 100pixel type

~100p.e about 400pixel type.

LASER test(using KEK-DTP LASER system)

Picture of microscope

100μm

microscope

- Motivation
- ・study the response of each pixel of MPPC
- Uniformity within 1pixel
- Uniformity in each pixel

Laser source

λ=825nm

width 50ps

Laser spot size

≒10μm

MPPC

Uniformity…

- gain

Moving stage

1μm pitch (x , y)

- cross-talk rate

- efficiency

Feed back this information to HPK

efficiency

Sensitive region

Efficiency, Gain

(in sensitive region)

Cross-talk rate

(in sensitive region)

RMS/mean=2%

100pixel

Response within 1 pixels is uniform

High at edge of sensitive region

When the avalanche occur at edge of pixel, it is easy to emit to the next pixel(this is cross-talk).

Cross talk rate

GAIN

0.25

RMS/mean=2%

Response of each pixel is uniform

100pixel

efficiency

GAIN

RMS/mean=3%

RMS/mean=3%

- MPPC has good performance !

Supplements

- This ceramic package make their alignment by the out side frame.

- APD (Avalanche Photo Diode) is a photo-diode that amplify the signal by operating the electron avalanche, that occur on the regions of pn-connection with high electric field. This high electric field is formed by applying bias voltage oppositely.

Amplifying by electron avalanche

γ

V+

p+

absorption region

p

n

When the bias voltage exceed the threshold voltage ( that is named “Break Down Voltage” ), very little light can make APD to occur the electrical discharge. This amplify is become about 106, and the height of signal doesn’t relate to the number of injected photon.

hole

e-

GND

E

We can know only “the photon has come” or “not”.

- The results become linear.

Paper

set up

( to shade off LED light )

MPPC

The number of photons emitted to MPPC are monitored by PMT.

PMT

efficiency

400pixel

RMS/mean=1.7%

Cross talk rate

GAIN

0.25

RMS/mean=1.6%

efficiency

RMS/mean=3.4%

400pixel

Cross talk rate

GAIN

0.18

RMS/mean=2.9%