BARBIER, Remi (University of Lyon 1 - IPNL) - NDIP 11 - IN2P3
BARBIER, Remi (University of Lyon 1 - IPNL) - NDIP 11 - IN2P3
BARBIER, Remi (University of Lyon 1 - IPNL) - NDIP 11 - IN2P3
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Part I : PMT - photocathode and quantum efficiency<br />
Definitions:<br />
E 0<br />
EC EF EV γ<br />
PC band Model<br />
• EF Fermi level<br />
• EV valence band<br />
E g<br />
Alkali Photocathode<br />
• E0 vacuum level<br />
• EC conduction band<br />
• W th thermionic Work Function: W th = E 0 - E F<br />
• E A electron affinity: E A = E 0 – E C<br />
P e<br />
QE = ( 1 − R)<br />
× Pν µ ×<br />
1+ 1 µL<br />
• material<br />
• Cristal quality<br />
• Electron Affinity<br />
Rémi Barbier, <strong>NDIP</strong> 20<strong>11</strong>, <strong>Lyon</strong>, France, July 4-8 tutorial : photodetectors<br />
EC E0 E V<br />
γ<br />
R: reflection coefficient<br />
P ν : pe Prob. to be above E 0<br />
µ: full absorption coefficient<br />
L: pe mean escape length<br />
P e : Prob. to escape<br />
W Positive Electron Affinity<br />
phe<br />
• Wph photoemission threshold<br />
Wph = E0 – EV = Eg + EA Negative Electron Affinity<br />
CsO2 is applied -> NEA<br />
Alkali PC vacuum<br />
Wph = Eg III-V PC<br />
vacuum<br />
Wth ph<br />
Wph > Wth EA > 0<br />
NEA < 0<br />
phe<br />
Schottky effect:<br />
An external electric field at the PC<br />
surface has an effect on the<br />
photoemission efficiency: the potential<br />
barrier is reduced by an amount ΔW th<br />
€<br />
ΔW th =<br />
eΕ<br />
4πε 0<br />
E accelerating field<br />
W ph<br />
E g<br />
III-V Photocathode<br />
E F<br />
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