Silicon Detectors and DAQ principles for a physics experiment
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Transcript of Silicon Detectors and DAQ principles for a physics experiment
Silicon Detectors and DAQ Silicon Detectors and DAQ principles for a physics principles for a physics
experimentexperiment
Electronic properties of materials
Atoms are made of proton, neutrons (nucleus) and electrons
Valence and conduction electrons are responsible for the principal characteristics of different atoms
If some electron is promoted in the conduction band, what may occur?
1) Drift: an external field can move these electrons
2) Multiplication; if the field is strong enough
3) Recombination: if nothing happens, electrons fall back to valence band
What happens then?
How can we describe the situation?
p-n Junctions
Fermi level definition
Electrons and holes diffusion
Non equilibrium situation
Donors and acceptors ions field plays against diffusion and equilibrium is reached
Equilibrium !!! … ?
p-n Junctions
Equilibrium is reached when the two Fermi levels are at the same energy
A sort of slope is then created, hard to climb up and easy to roll down!
Equilibrium does not mean immobility!!!
p-n Junctions
Breakdown voltageVbr
Junctions are the basic devices for all semiconductor detectors!
V=RxI
Particles’ measurements
A particle passes through a silicon thickness, generating e-h pairs
e- and h+ are collected by anode and cathode (be aware of recombination…)
An electric field causes electron flow through the device and created charge can be collected (by capacitor for ex.)
SDD, a clever anti-recombination device
An electric field leads electrons, generated by particle flow (x-Rays or ionizing) to a small collector anode. At the same time holes are immediately removed from electron’s path by cathode strips.
Analog – Digital conversion
Digital signal; signal is a function of discrete numbers, F(N)
Analog signal; signal is a function of continuous numbers, usually time, F(t)
The world is analogic but Pc and analysis software can only work with digital informations…..
Analog signal have to be converted to digital signals!
Analog – Digital conversion
Converting analog signals into digital signals, some information may be lost … but are they really necessary?
MPPC (Multi Pixel Photon Counters) detectors
Each pixel acts like a p-n junction
Breakdown current is used
Output signals are summed
MPPCSignal coming out from the detecor is then:
QDC spectrum is then composed by several pixes with fixed distance
C
sV
R
tVQ
nst
mVV
tot12
92
1051052
1025102
2
)525(
)520(
CAA
AAQQ
preamp
tote
preampetot
195
12
det
det
103,1105105,7
105
Is the result ok?errors…..
st
VV
tR
VV
R
tQ
9
3
22
22
105
105
22
CQ
CQ
e
19
12
103,1
106,1
Huge errors due to the big error estimation on measured values of t and V