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V.V. Bakin, D.V. Gorshkov, H.E. Scheibler,
S.N. Kosolobov and A.S.Terekhov
Rzhanov Institute of Semiconductor Physics SB RAS, Novosibirsk, Russia
E-mail: [email protected]
Outlook
1. Motivation.
Studies of NEA-photocathodes
1
2. Actual models of (Cs,O)-activation layer.
3. Photoelectron escape model.
4. Parallel plate electron spectrometers.
5. Summary.
2. Actual models of (Cs,O)-activation layer.
2
Semiconductor
cb
F
vb
z
Vacuum
O2
Cs
vac
Photocathode activation
3. Photoelectron escape model.
vac
Semiconductor
cb
F
vb
z
Vacuum
vac
Semiconductor
cb
F
vb
z
Vacuum
cb
F
vb
Semiconductor
z
Vacuum
vac
CsxOy
2. Actual models of (Cs,O)-activation layer.
3
Heterojunction model Dipole layer model
3. Photoelectron escape model.
2. Actual models of (Cs,O)-activation layer.
Heterojunction model Dipole layer model
Prolonged activation
4 3. Photoelectron escape model.
Ne( lon)-distributions
2. Actual models of (Cs,O)-activation layer.
Heterojunction model Dipole layer model
Prolonged activation
5 3. Photoelectron escape model.
Ne( lon)-distributions
HJ-model
DL-model
3. Photoelectron escape model.
4. Parallel plate electron spectrometers.
vac
z
in
phJex
phJin
ph
ex
ph
escJ
JP
NEA-photocathode band diagram
cb
vb
(Cs,O)-layer
6
3. Photoelectron escape model.
vb
vac Vs ≈ 0.6 eV
BBR ≈ 10 nm
NEA-photocathode band diagram
and surface scattering processes
cb
z
(Cs,O)-layer
4. Parallel plate electron spectrometers.
1. Surface optical
phonons.
1 2
2. Surface
plasmons.
3. BBR- induced
random
electric field.
4. (Cs,O)-induced
random
electric field.
hole plasma
7
3. Photoelectron escape model.
vac ħ ≥ g
cb
vb
thermalized hot
ballistic
z
(Cs,O)-layer
4. Parallel plate electron spectrometers. 8
3. Photoelectron escape model.
ħ ≥ g
cb
vb
thermalized hot
ballistic
z
(Cs,O)-layer
4. Parallel plate electron spectrometers.
surface phonon losses
surface plasmon losses
9
spectrometers
3. Photoelectron escape model.
4. Parallel plate electron spectrometers.
A.S. Terekhov, D.A. Orlov, SPIE Proc. v.2550, p.157 (1995)
Experiment
10
3. Photoelectron escape model.
4. Parallel plate electron spectrometers.
Experiment
D.A. Orlov et.al., JETP Letters v.71, p.220 (2000)
11
3. Photoelectron escape model.
4. Parallel plate electron spectrometers.
Experiment
12
V.V. Bakin et. al., JETP Letters v.77, p.167 (2003)
V.E. Andreev et.al., Journal of Inversed and Ill-
Posed problems, v.7, No.5, p.427 (1999)
Ne( , ) -spectrometer Theory
5. Summary.
4. Parallel plate electron spectrometers.
photocathode collector
13
dd)],(N,d,H,E[G)H,U(J eretph
V.E. Andreev et.al., Journal of Inversed and Ill-
Posed problems, v.7, No.5, p.427 (1999)
Experiment
Ne( , ) -spectrometer Theory
5. Summary.
4. Parallel plate electron spectrometers.
V.V. Bakin et. al., JETP Letters v.77, p.167 (2003)
14
dd)],(N,d,H,E[G)H,U(J eretph
V.E. Andreev et.al., Journal of Inversed and Ill-
Posed problems, v.7, No.5, p.427 (1999)
dd)],(N,d,H,E[G)H,U(J eretph
Experiment
Ne( , ) -spectrometer Theory
5. Summary.
4. Parallel plate electron spectrometers.
15
V.E. Andreev et.al., Journal of Inversed and Ill-
Posed problems, v.7, No.5, p.427 (1999)
Experiment
Ne( , ) -spectrometer Theory
5. Summary.
4. Parallel plate electron spectrometers.
16
dd)],(N,d,H,E[G)H,U(J eretph
4. Parallel plate electron spectrometers.
U1 U2
CCD
camera
lens
p-GaN (Cs,O)-
photocathode luminescence
screen
monochromator
1
mm
MCP
Ø ~20 m
lens
E
Ne( tr) -spectrometer
eUd2r tr
loneU
)(N)r(I tree
rd]U,d),(N[I)rr()r(I treeifph
5. Summary. 17
4. Parallel plate electron spectrometers.
Ne( tr) -spectrometer
5. Summary. 18
Experiment
I ph, a.
u.
4. Parallel plate electron spectrometers.
Ne( tr) -spectrometer
5. Summary. 19
Experiment
4. Parallel plate electron spectrometers.
Ne( tr) -spectrometer
5. Summary. 20
Experiment
I ph, a.
u.
Summary
• p-GaAs (Cs,O) – photocathodes with practically useful values of QEs (> 10%) can
be activated with considerably different properties of (Cs,O) – layers, which lead to
different escape models and to different energy distributions of emitted electrons.
• Low temperature studies of photoemission of from p-GaAs (Cs,O) – photocathodes
enable us to develop photoelectron escape model, which is based on size
quantization of electron spectra within band bending region, includes inelastic
scattering of photoelectrons by surface optical phonons and by surface plasmons.
Ballistic photoemission and diffusive scattering of emitted electrons are revealed
also.
• Transverse energy distribution of photoelectrons from p-GaN (Cs,O) – photocathode
was measured within broad range, which enable one to calculate MTE and to
evaluate the halo of electron beam.
21