Novel Manufacturing Process for Low-Cost, High-QE Photocathodes

Large area high-performance photodetectors are sought for future High-Energy Physics experiments in order to enhance the detection probability of extremely rare events. The photocathode is a key element that determines the performance of the detector. Cathodes with high quantum efficiency, large and uniform photosensitive area, UV-visible sensitivity, cryogenic compatibility, and low radioactivity are of particular interest for neutrino and dark matter detection. Currently there is a scalability issue that is hampering the production of such detectors owing to challenges with the cathode growth. The scalability problem with photodetector manufacturing is attributed to the cathode growth process. This problem is being address with a disruptive new method to grow alkali antimonide photocathodes via thermal evaporation of pre-synthesized compounds instead of the traditional growth methods. The proposed process is rapid, simple and has numerous other advantages over the traditional method for growing cathodes towards a high efficiency and a uniform large area response. The innovation here is the bulk preparation of compounds using impurity-free and radio-pure raw elements and the subsequent thermal vapor deposition of the stoichiometric photocathode thin film across large areas. The Phase I research and development demonstrates the feasibility of growing high performance photocathodes using thermal evaporation technique. During Phase I, the following was accomplished (1) synthesis of stoichiometric bulk photocathode compounds, (2) process development to evaporate the compounds into high-performance, large-area crystalline photocathodes, and (3) integrate the photocathodes with MCP detectors to carry out QE mapping and UV response. Photocathodes with peak quantum efficiency up to 23% were grown in large and small formats. The Phase II research and development will focus on transitioning the novel cathode growth process into a commercial photodetector manufacturing process. In Phase II, focus will be laid on process development for Na2KSb, K2CsSb and Cs3Sb photocathodes on large area photodetectors measuring 8”×8”. The technology will enable cost-effective photocathode deposition over large areas, and will be the enabling technology for the realization of highly efficient, cost-competitive new detectors for key science drivers in particle physics such as the search for dark matter and the studies of the nature of neutrinos. Availability of such detectors with VUV sensitivity and improved timing and position performance will not only have a profound impact on particle physics but will also have a transformational impact on critical fields including medical imaging through advances in positron emission tomography detectors, and nuclear detection for homeland security applications.