Accession Number : ADA585611


Title :   Spatial Mapping of the Mobility-Lifetime (microtau) Production in Cadmium Zinc Telluride Nuclear Radiation Detectors Using Transport Imaging


Descriptive Note : Master's thesis


Corporate Author : NAVAL POSTGRADUATE SCHOOL MONTEREY CA


Personal Author(s) : Young, Jr, Peter J


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a585611.pdf


Report Date : Jun 2013


Pagination or Media Count : 95


Abstract : Cadmium zinc telluride (Cd1-xZnxTe) is an important material for room temperature nuclear radiation detectors due to its high stopping power for gamma rays combined with its good electron transport. However, CdZnTe crystals are susceptible to growth defects such as grain boundaries, twin boundaries, and tellurium (Te) inclusions which can compromise desirable energy resolution and electron/hole charge collection properties. The presence of these defects ultimately degrades the effectiveness of the nuclear radiation detector material. The ability to map electron and hole transport properties at high spatial resolution can provide new insight into the roles of individual defects. Experimentally, this study employs high-resolution ( 5 m) transport imaging to explore the effect of localized crystal defects on the spatial variation of carrier transport properties. The ambipolar diffusion length (Ld) and associated free carrier mobility-lifetime ( ) product are determined by imaging the recombination luminescence from carriers generated by an electron beam. Localized defects often are marked by regions of low intensity luminescence. At the same time, we observe increasing ambipolar diffusion length in the region immediately surrounding the defects. One explanation is that the gettering of point defects, such as interstitials and vacancies, associated with the formation of microscopic precipitates results in localized increases in the product. Initial results indicate that these variations occur over a region extending 10 m from the edge of the inclusion. Mathematically, this study employs the minority carrier diffusion equation to model the 3D diffusion of free charge carriers away from a point source. A non-linear least squares program using exact methods and asymptotic expansion methods is then used to fit this model to transport data imagery.


Descriptors :   *CADMIUM ZINC TELLURIDES , *DETECTORS , *RADIOACTIVE MATERIALS , ASYMPTOTIC SERIES , BOUNDARIES , CHARGE CARRIERS , CRYSTAL DEFECTS , CRYSTALS , DEFECTS(MATERIALS) , DIFFUSION , ELECTRON BEAMS , ELECTRON TRANSPORT , ELECTRONS , ENERGY , EQUATIONS , GAMMA RAYS , GETTERING , GRAIN BOUNDARIES , HIGH POWER , HIGH RESOLUTION , HOLES(ELECTRON DEFICIENCIES) , IMAGES , INCLUSIONS , INTENSITY , INTERSTITIAL , LEAST SQUARES METHOD , LUMINESCENCE , MAPPING , MATERIALS , METHODOLOGY , MODELS , NONLINEAR SYSTEMS , NUCLEAR RADIATION , NUCLEAR WEAPONS , PRECIPITATES , RECOMBINATION REACTIONS , REGIONS , RESOLUTION , SKILLS , SOURCES , SPATIAL DISTRIBUTION , STOPPING , TELLURIDES , TELLURIUM , THESES , TRANSPORT , TRANSPORT PROPERTIES , VARIATIONS , ZINC


Subject Categories : Inorganic Chemistry
      Miscellaneous Detection and Detectors
      Nuclear Physics & Elementary Particle Physics


Distribution Statement : APPROVED FOR PUBLIC RELEASE