Radiation Tolerant Diamond Gain Structures for Photon Detection

Current state-of-the-art Silicon Photomultiplier (SiPM) technology suffers several drawbacks, including weak radiation resistance, high dark current rate, weak photon detection efficiency in UV wavelengths, high gain sensitivity to the temperature variation, and the necessity to operate at -40 °C in a harsh radioactive environment with the increased operating cost. The photodetectors for collider and intensity frontier experiments require a novel low-cost wide-bandgap technology with internal gain that has fast response, good radiation hardness, low dark current, and reduced gain sensitivity to temperature. We will develop an advanced diamond-based technology with a controllable internal gain for UV photon detection that utilizes the inherent advantages of diamond material and allows us to overcome the current SiPMs limitations naturally. The internal gain in diamond will utilize a focusing effect that consists of a substantial increase of electric field near a small size electrode on a top diamond plate surface (readout dot) opposite a second electrode (back pad) that is substantially larger. Adding the small-bias ring around the dot on the surface or fabricated underneath and optimizing substrate thickness and electrode sizes will allow controlling gain conditions under the readout dot. The novel controllable gain photomultiplier technology will have a very low leakage current (~ pA), inherent diamond high radiation tolerance and longevity, the absence of thermal runaway issues, and the ability to operate at room temperature without cooling due to extremely high intrinsic diamond thermal conductivity. All these features make the novel technology very compact and cost-effective. Under Phase 1 of the project, we will focus on the diamond controllable internal gain structure's optimized design with surface or subsurface embedded control ring. We will also fabricate test structures with surface electrodes and compare gain radiation tolerance between fabricated diamond structures and COTS SiPMs. The novel diamond controllable internal gain approach will overcome conventional limitations of current state-of-the-art SiPMs technology on radiation tolerant, gain temperature insensitive, operation reliable, with low dark current rate compact photomultipliers. It will allow HEP, military, and industrial applications, where harsh radiation condition is a key requirement. The advanced diamond-photomultiplier technology with controllable internal gain may become an established device of choice for a variety of applications beyond HEP needs, e.g., for monitoring and surveillance of radioactive waste in nuclear power plants, in time of flight positron emission tomography (TOF-PET), nuclear medicine, lifetime fluorescence spectroscopy (including improved sensitivity for COVID-19 testing), distance measurements in LIDAR applications, astrophysics, quantum-cryptography, and related applications as well as in military deployment.