Effect of electron transport properties on unipolar CdZnTe radiation detectors: LUND, spectrumplus and coplanar grid

Abstract

Device simulations of(1) the laterally-contacted-fipo~aI-nuc~em detector (LUND), (2) the SpectrumPlus, (3) and the coplanar grid made of CdO.gZM.ITe (CZT)were performed for 'S7CSirradiation by 662.15 keV gamma-rays. Realistic and controlled simulations of the gamma-ray interactions with the CZT material were done using the MCNP4B2 Monte Carlo program, and the detector responses were simulated using the Sandia three-dimensional multielectrode simulation program (SandTMSP).The simulations were done for the best and the worst expected carrier nobilities and lifetimes of currently commercially available CZT materiaIs for radiation detector applications-For the simulated unipolar devices, the active device volumes were relatively large and the ener~q resolutions were fairly good, but these performance characteristics were found to be very sensitive to the materials properties. The internal electric fields, the weighting potentials, and the charge induced efficiency maps were calculated to give insights into the operation of these devicesTbe snbmittd mannaoript h k authored by a contractor of i&e un~ed States Government under contiad. Accordingly the Lkited States Gov. emment retains a non. excl~i~, royalty-free license to publish or re. produce the published form of this contribution, or aIlow others to do SO, for United Statea Gov~~t ppeeea.,- L IntroductionTheunipol= mdiation detectors madeofsemi-insulating C&.gZm.lTe (CZT),2] have recently received much attention, due to their potential for improved gma-ray detection sensitivi~andenergy resolution [3][4][5][6]. Because theeIectron rnobilities are -20 times larger than the hole nobilities and because the electron lifetimes are at least -10 times longer than the hole lifetimes in these materials [7,8], these unipolar devices are designed to depend only on the electron's transport properties.However, because of the unknown variation in the starting detector materials, the high cost of materials and fabrication, and the relatively complex geometries and operating conditions that are characteristic of these unipolar detector designs, quantitative experimental determination of their active volume and energy resolution are typically extremely difilcult. And it is just as difficult to determine how robust these perfommnce to these difficult tasks is to use validated computer programs for the characteristics are with respect to the inevitable variation of the of the carrier transpofi properties.A solution simulation of these devices. A device simulation can give the total control of the device and materials parameters and, in addition, it can allow the examination of all device finctions. We have performed device simulations of three recendy deveIoped unipolar detectors made of Cc&.gZnO.lTe:(1) the laterally-contacted-unipolar-nuclear detector (LUND) [Ref. 3,41,(2) DISCLAIMERPortions of this document may be illegible in electronic image products.Images are produced from the best available original document.was used for realistic and controlled interaction of gamma...