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: http://jp.hamamatsu.com/products/sensor-etd/pd014/index_en.html 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. http://cqd.eecs.northwestern.edu/research/ebeam.php A U.S. Department of Energy laboratory managed by UChicago Argonne, LLC.