Large area avalanche photodiodes (LAAPDs) are uniquely sensitive semiconductor detectors that have a host of applications in high energy physics (HEP) experiments. These high voltage devices need to survive for several years in harsh radiation environments to be effective alternatives to the photomultiplier tubes that are presently used. The present LAAPD lifetime in a benign environment is limited to less than 1000 hr, and the lifetime in heavy particle environments has been found to be on the order of hours. The limited data collected to date indicate that the same mechanism is responsible for catastrophic device failure in both environments. These data also indicate that specific biasing circuitry, device design, and semiconductor processing improvements can be utilized to fabricate radiation-hardened LAAPDs. In Phase I, the ultraviolet (W) response of LAAPDs was increased by a factor of six at 300 nm, making these devices an attractive option for many HEP calorimetry applications where scintillator materials emit in the W and blue regions of the optical spectrum. In Phase II, the reliability of W-enhanced LAAPDs in a calorimeter environment will be addressed. Several innovative approaches based on recent advances in silicon materials growth and fabrication technologies will be explored. Throughout the project a statistical process control system will be utilized to assess the progress towards fabrication of LAAPDs with mean-time-to-failure of 100,000 hr.Anticipated Results/Potential Commercial Applications as described by the awardee: The project will increase the reliability of LAAPDs in both benign and radiation environments. Reliable LAAPDs can be used at installations such as the Stanford Linear Accelerator Center, the Fermi National Accelerator Laboratory, and the Centre European pour Recherche Nuclear. Commercial applications include positron emission tomography scanners, spectroscopy instruments, color processing equipment, and inspection systems.
