Following on earlier LBNL developments of high-purity germanium (HPGe), lithium-drifted silicon (Si(Li)) and single-polarity charge sensing in CdZnTe (CZT), the current 2000 ft² SDL cleanroom (shown in Fig. 1) facilitates thin film deposition and photolithography to transform semiconductor substrates into high resolution radiation detectors. Connected labs allow for advanced integration and characterization by students and researchers creating radiation detection and imaging systems that find their way deep underground for neutrino science, vehicle and airborne for nuclear security, or space-borne for gamma-ray astronomy. The diversity of projects and researchers at the SDL fosters truly state of the art solutions to challenges in radiation detection and imaging. A few of the more recent solutions are highlighted below.

Building on the fundamental CZT development work by former SDL director Paul Luke, researchers at the SDL were recognized last year with an R&D100 award for developing a sphere of CZT detector modules at the heart of a portable real-time handheld coded aperture and Compton imager, PRISM. This instrument utilizes the self-occlusion of its own 100 dense detectors to implement truly 4pi coded aperture imaging without the need for heavy masks.

Figure 2. The SDL-fabricated front-end electronics for LEGEND-200.

Despite advances in silicon purity, a demand still exists for Si(Li) detectors, a gap in commercial manufacturing that the SDL is uniquely capable of filling. Current projects include fabrication of upgrade detectors for the Internal conveRsion Electron Ball Array (fIREBAll) detector at U Washington.

This year, the SDL’s fabrication capabilities were expanded to include an ion implanter, allowing for highly customizable implants from gas and solid sources up to 200 keV at room or LN2 temperatures. Implantation is a key step in the production of neutron transmutation doped (NTD) Ge thermistors at the heart of the CUPID neutrinoless double-beta decay (0νββ) experiment.

Cleanroom fabrication methods for detectors have translated to innovations in low-radioactive background electronics for HPGe readout, as in the Low Mass Front End (LMFE) electronics (shown in Fig. 2) developed for both the Majorana Demonstrator and the LEGEND-200 0νββ experiment. The SDL is also key to the development of the new ASIC-based ultra-radiopure front ends for the anticipated LEGEND-1000 experiment.