Low Cost, Radiation Tolerant Semiconductor Detectors for Charged Particle Spectroscopy

Single-crystalline chemical vapor deposition diamond meets a majority of the radiation tolerance and performance parameters needed to survive in extreme environments, such as measuring isotopes from heavy ion beams near zero degrees. All semiconductor materials degrade under these conditions, yet the excellent resolution of semiconductor detectors is required to enable the separation of isotopes. The major limiting factor for diamond is the cost, since it requires periodic replacement under extreme conditions. The cost for diamond is a reflection on the market for the semiconductor and the fabrication costs. By using a material such as GaN, SiC, or AlN, which have established markets for transistors and diodes, the production of sensors can be made at scale. Recent advances in the production of GaN substrate wafers and epitaxial growth provides a means to produce a solid-state charged particle detector at a low cost, while including additional features, such as an avalanche multiplication region to enhance signal to noise. Silicon avalanche photodiodes have been shown to provide both better spectroscopic and timing resolution compared to silicon drift (unity gain, surface barrier) detectors without internal avalanche multiplication. The growth of diamond is not mature enough to enable doped structures at low costs, such as what is achievable with a GaN epitaxy grown using chemical vapor deposition. Dual-sided growth on a GaN substrate with GaN avalanche and high conductive layers will provide a high performance solid- state detector. Though GaN is a leading candidate, other materials that may provide a lower cost alternative, and a material will be selected for the research effort. Within the Phase-I effort, we will design, simulate, and fabricate a prototype detector. Advancing the technology to demonstrate feasibility, we plan to demonstrate an energy resolution of less than 2% using alpha particles and a time resolution of less than 500 ps. Along with physics instrumentation, the solid-state detectors are used for nuclear instruments in a myriad of industries. The technology to be developed in the project will support applications where the detectors will be exposed to high radiation fields or accumulated doses, such as those found in the nuclear industry, sciences, medicine, and space applications.