1. Frontiers in Photocathode R&D
Matt Wetstein1,2, Bernhard Adams3, Matthieu Chollet3, Igor Veryovkin4, Alexander Zinovev4, Thomas Prolier4, Zikri Yusof1, Zeke Insepov5, Klaus Attenkofer3
1: High Energy Physics (ANL); 2: Enrico Fermi Institute (UofC); 3: Advanced Photon Source (ANL); 4: Material Sciences (ANL); 5: Mathematics and Computing Sciences (ANL)
Conventional Photocathodes Limitations and Challenges
The Photocathode: Key For In-Vacuum Photon Detection
Goals of the Advanced Photocathode Design
Two types of cathodes are used: MULTI-ALKALI and III-V SEMICONDUCTOR
LARGE REFLECTION LOSSES (for non-normal incidence)
IN VACUUM ASSEMBLY necessary
the SURFACE VARIATIONS over time result in EFFICIENCY LOSSES
Suffix
Photocathode
Input Window
-71
GaAs
Borosilicate Glass
-73
Enhanced Red GaAsP
-74
GaAsP
-76
InGaAs
Non
Multialkali
Synthetic Silica
-01
Enhanced Red Multialkali
-02
Bialkali
-03
Cs-Te
Photocathodes are converting photons into “free” electrons and therefore determine:
the QUANTUM EFFICIENCY
the SPECTRAL RESPONSE FUNCTION
the ANGULAR AND MOMENTUM DISTRIBUTION of the free electrons
principle TIME RESOLUTION of the detector unit
principle NOISE BEHAVIOR
Overall Goal is to provide photocathode material:
With high quantum efficiency (>25%)
With tunable spectral response
With long device lifetime
Compatible with large area project (8”x8”)
Which permits simple and high-yield detector assembly
First year goals :
Establishing characterization and calibration tools
Gaining growth expertise in III-V semiconductors
First 33-mm dia. N and P based transmission PC wit QE>15%
Evaluation of Field-Enhanced versus NEA-Enhanced PC
Hamamatsu:
Photocathode properties determine:
the MANUFACTURING PROCESS (vacuum assembly)
the LIFE TIME of the detection unit
largely the COST of large area detectors
the WORKING CONDITIONS of the detector
HEP Leading a Cross-Division,
Cross-Institutional Effort
Argonne National Laboratory
Berkeley SSL
U. Chicago
High Energy Physics
Advanced Photon
Source
Mathematics and Computing Sciences
Photocathode Fabrication
Nano-structured Photocathodes
Material Sciences
First Year: III-V Photocathode production
Phosphorus-based systems: Collaboration with Prof. Xiuling Li (UIUC)
Optimization of doping profile with reflection PC’s
Work on transfer process (GaAs substrate to glass)
Surface reconstruction and Negative Electron Affinity-layer
Nitrogen-based systems: Collaboration with Prof. Jim Buckley (WashU)
ALD coating of Al2O3 on glass versus transfer process
Surface reconstruction and negative electron-affinity layer
Nano-structured P- & N-based systems: Collaboration with Prof. Jonas Johansson (U. of Lund)
Dark current of GaAsP nano-rod structure
Growth on glass
Field-enhancement versus negative electron-affinity layer
New opportunities by nano-technology
Reduction of reflection losses (light trap)
Heterogeneous structure permits multi-functionality (electrically, optically, electron-emission, “ion-etching resistant”)
Increased band-gap engineering capabilities
Utilization of “glass” substrates
Expertise and know-how of multi-billion industry (IR-detectors)
U. Of Lund
U. of IL Urbana
Washington U
Testing and Characterization Fundamental Understanding Leads to New Design Rules
Unique and complementary facilities for testing and characterizing QUANTITATIVELY QUANTUM EFFICIENCY, PHOTO ABSORPTION & REFLECTION, SURFACE CHEMISTRY & MORPHOLOGY, WORK FUNCTION & BAND-GAP, TEMPORAL and NOISE BEHAVIOR of Photocathodes:
Surface sciences approaches: Materials Sciences Division
Electronic and optical characterization: Advances Photon Sources
Theoretical Modeling: Mathematics and Computer Sciences Division
Compatibility of setups allows rapid screening of many samples to determine all critical parameters, and investigate the correlation between surface properties and photocathode performance.
A U.S. Department of Energy laboratory managed by UChicago Argonne, LLC.