Halide lead perovskites have attracted increasing attention in recent years for ionizing radiation detection due to their strong stopping power, defect-tolerance, large mobility-lifetime (μτ) product, tunable bandgap and simple single crystal growth from low-cost solution processes. In this review, we start with the requirement of material properties for high performance ionizing radiation detection based on direct detection mechanisms for applications in X-ray imaging and γ-ray energy spectroscopy. By comparing the performances of halide perovskites radiation detectors with current state-of-the-art ionizing radiation detectors, we show the promising features and challenges of halide perovskites as promising radiation detectors.

/pdf/halide-lead-perovskites-for-ionizing-radiation-detection-4e2dp84ory.pdf

Halide lead perovskites for ionizing radiation detection

Halide perovskite semiconductors are poised to revitalize the field of ionizing radiation detection as they have done to solar photovoltaics. We show that all-inorganic perovskite CsPbBr3 devices resolve 137Cs 662-keV γ-rays with 1.4% energy resolution, as well as other X- and γ-rays with energies ranging from tens of keV to over 1 MeV in ambipolar sensing and unipolar hole-only sensing modes with crystal volumes of 6.65 mm3 and 297 mm3, respectively. We report the scale-up of CsPbBr3 ingots to up to 1.5 inches in diameter with an excellent hole mobility–lifetime product of 8 × 10−3 cm2 V−1 and a long hole lifetime of up to 296 μs. CsPbBr3 detectors demonstrate a wide temperature region from ~2 °C to ~70 °C for stable operation. Detectors protected with suitable encapsulants show a uniform response for over 18 months. Consequently, we identify perovskite CsPbBr3 semiconductor as an exceptional candidate for new-generation high-energy γ-ray detection. Energy resolution of high-energy photon detectors is desired for applications ranging from biomedical imaging to homeland security. In this work, perovskite-based γ-ray detection with 1.4% energy resolution is demonstrated.

CsPbBr3 perovskite detectors with 1.4% energy resolution for high-energy γ-rays

LBNL-44898 Preprint ORLANDO LAWRENCE BER&<.lELlEY NAT~DNAL LABORATORY ERNlES~lr Three-Dimensional Position Sensing and Field Shaping in Orthogonal-Strip Germanium Gamma-Ray Detectors M. Amman and P.N. Luke Engineering Division January 2000 Submitted to Nuclear Instruments and Methods in Physics Research - Section A .:::i no.. rn CD CD A OJ ()Ulrn s:: z CD 0 rn -SCD::o -I. -s -'zn IlJOrn r+.-I <OJ CD CD n r+ zO---- IlJlQ IlJ :::i1Sl otn -s'< IlJ o o 0-1lJ IlJ -S -S r+1 '< CD -s::O -II o n Z OJ OJ lO OJ

Three-dimensional position sensing and field shaping in orthogonal-strip germanium gamma-ray detectors.

Lead-halide perovskites have demonstrated astonishing increases in power conversion efficiency in photovoltaics over the last decade. The most efficient perovskite devices now outperform industry-standard multi-crystalline silicon solar cells, despite the fact that perovskites are typically grown at low temperature using simple solution-based methods. However, the toxicity of lead and its ready solubility in water are concerns for widespread implementation. These challenges, alongside the many successes of the perovskites, have motivated significant efforts across multiple disciplines to find lead-free and stable alternatives which could mimic the ability of the perovskites to achieve high performance with low temperature, facile fabrication methods. This Review discusses the computational and experimental approaches that have been taken to discover lead-free perovskite-inspired materials, and the recent successes and challenges in synthesizing these compounds. The atomistic origins of the extraordinary performance exhibited by lead-halide perovskites in photovoltaic devices is discussed, alongside the key challenges in engineering such high-performance in alternative, next-generation materials. Beyond photovoltaics, this Review discusses the impact perovskite-inspired materials have had in spurring efforts to apply new materials in other optoelectronic applications, namely light-emitting diodes, photocatalysts, radiation detectors, thin film transistors and memristors. Finally, the prospects and key challenges faced by the field in advancing the development of perovskite-inspired materials towards realization in commercial devices is discussed.

Perovskite-inspired materials for photovoltaics - from design to devices

We present a new mechanism for thermally produced dark matter, based on a semi-annihilation-like process, $\ensuremath{\chi}+\ensuremath{\chi}+\mathrm{SM}\ensuremath{\rightarrow}\ensuremath{\chi}+\mathrm{SM}$, with intriguing consequences for the properties of dark matter. First, its mass is low, $\ensuremath{\lesssim}1\text{ }\text{ }\mathrm{GeV}$ (but $\ensuremath{\gtrsim}5\text{ }\text{ }\mathrm{keV}$ to avoid structure-formation constraints). Second, it is strongly interacting, leading to kinetic equilibrium between the dark and visible sectors, avoiding the structure-formation problems of $\ensuremath{\chi}+\ensuremath{\chi}+\ensuremath{\chi}\ensuremath{\rightarrow}\ensuremath{\chi}+\ensuremath{\chi}$ models. Third, in the $3\ensuremath{\rightarrow}2$ process, one dark matter particle is consumed, giving the standard-model particle a monoenergetic recoil. We show that this new scenario is presently allowed, which is surprising (perhaps a ``minor miracle''). However, it can be systematically tested by novel analyses in present and near-term experiments. In particular, the Co-SIMP model for thermal-relic dark matter can explain the XENON1T excess.

New Freezeout Mechanism for Strongly Interacting Dark Matter

Development of large size high-purity germanium crystal growth

Light, MeV-scale dark matter (DM) is an exciting DM candidate that is undetectable by current experiments. A germanium (Ge) detector utilizing internal charge amplification for the charge carriers created by the ionization of impurities is a promising new technology with experimental sensitivity for detecting MeV-scale DM. We analyze the physics mechanisms of the signal formation, charge creation, charge internal amplification, and the projected sensitivity for directly detecting MeV-scale DM particles. We present a design for a novel Ge detector at helium temperature (
 $$\sim $$
  4 K) enabling ionization of impurities from DM impacts. With large localized E-fields, the ionized excitations can be accelerated to kinetic energies larger than the Ge bandgap at which point they can create additional electron–hole pairs, producing intrinsic amplification to achieve an ultra-low energy threshold of $$\sim $$
  0.1 eV for detecting low-mass DM particles in the MeV scale. Correspondingly, such a Ge detector with 1 kg-year exposure will have high sensitivity to a DM-nucleon cross section of $$\sim $$
  5 
 $$\times $$
  10
 $$^{-45}$$
  cm
 $$^{2}$$
 at a DM mass of $$\sim $$
  10 MeV/c
 $$^{2}$$
 and a DM-electron cross section of $$\sim $$
  5 
 $$\times $$
  10
 $$^{-46}$$
  cm
 $$^{2}$$
 at a DM mass of $$\sim $$
  1 MeV/c
 $$^2$$
 .

/pdf/direct-detection-of-mev-scale-dark-matter-utilizing-3pc5wyz57m.pdf

Direct detection of MeV-scale dark matter utilizing germanium internal amplification for the charge created by the ionization of impurities

Zone refining is one of the most important procedures to purify germanium crystals for the fabrication of detectors in our laboratory. In order to properly zone refine high-purity germanium crystals, it is important to develop perfect cleaning procedures for raw materials, quartz tubes, and the containers holding raw materials. Additionally, vacuum levels, container types, the correct combination of ambient gases, the speed of zone travel, and the ratio of ingot length to molten zone length, all need to be carefully studied in order to obtain the best results possible. In this work, we investigate a number of influential factors in perfecting high-purity germanium crystal growth, specifically: cleaning procedures, boat composition, vacuum levels in the chamber, zone travel speed, and the ratio of ingot length to molten zone length. Using the van der Pauw Hall technique, we were able to measure the electrical properties of zone-refined ingots and analyze the origin and distribution of three main impurity elements (boron, aluminum and phosphorus) thereby allowing us to study potential contamination sources. After detailed analysis on the various influential factors, we were able to optimize the zone-refining procedures.

Investigation of influential factors on the purification of zone‐refined germanium ingot

Dislocation density control in high-purity germanium crystal growth

http://absimage.aps.org/image/MAR15/MWS_MAR15-2014-003662.pdf

Gang Yang

Papers

Development of large size high-purity germanium crystal growth

Direct detection of MeV-scale dark matter utilizing germanium internal amplification for the charge created by the ionization of impurities

Investigation of influential factors on the purification of zone‐refined germanium ingot

Dislocation density control in high-purity germanium crystal growth

Crystal growth and detector performance of large size High-purity Ge crystals