Feasibility study of direct-conversion x-ray detection using cadmium zinc telluride films

Abstract

Polycrystalline Cd(Zn)Te films deposited by vacuum thermal evaporation are investigated as a direct-conversion medium for x-ray detection. The use of evaporation techniques allows for the preparation of large-area films with the potential for large-area x-ray imaging with high spatial resolution. Films with compositions of Cd 1−x Zn x Te (x = 0.15, 0.25, 0.3) were prepared to a thickness of 20 µm on slide glass substrates with an aluminum or indium tin oxide (ITO) bottom electrode and a silver top electrode, with and without additional charge-blocking layers (CeO 2 and parylene dielectric) between the electrode and CdZnTe film to reduce leakage current. Composition and structural analyses of the as-deposited films confirm the development of polycrystalline CdZnTe. Leakage current in the CdZnTe film is approximately ten times lower than for a comparable CdTe film, and the lowest leakage is obtained for a film with composition of Cd 0.7 Zn 0.3 Te The use of ITO rather than aluminum as the bottom electrode provides a further improvement in leakage current and improved stability. The Cd 0.7 Zn 0.3 Te-based device with ITO electrode and chargeblocking layers achieves the highest total output charge (180.44 pC/cm 2 or 1.1 × 10 9 e − /cm 2 ) and signal-to-noise ratio (6.19 at applied bias of 30 V). The present experiments show that Cd 1−x Zn x Te in a multilayer structure with charge-blocking layers is feasible as a good radiation conversion layer for flatpanel radiation imaging systems.

Photoluminescence of CdZnTe thick films obtained by close-spaced vacuum sublimation

“…In order to obtain low cost and large-area uniform Cd 1 À x Zn x Te for X-ray imaging detectors [7] it is necessary to use films with the thickness of 30 mm [8,9] and higher instead of bulk crystals. Furthermore, since Cd 1 À x Zn x Te have p-type conductivity, they may be used as alternative top adsorber layers in solar cells with the optimal band gap about of (1.7-1.8) eV at x E0.30 for effective conversion of light absorption into electrical power.…”

Charge transport in pure and stabilized amorphous selenium: re-examination of the density of states distribution in the mobility gap and the role of defects

“…This imaging modality needs photoconductors that have a higher atomic number (Z). Higher Z semiconductors such as CdTe, CdZnTe, HgI 2 , PbI 2 , PbO have shown good potential for applications in direct conversion imaging with favorable electrical properties; see, for example, references [16][17][18][19][20][21][22][23][24] for a selection of potential high-Z semiconductors, some of which were reported in this journal.…”

Sigmoid-growth curve of lattice-constant against annealing-temperature of Cd1−xZnxTe thin films and its structural, optical and morphological characteristics

“…Kang et al deposited polycrystalline Cd 1 À x Zn x Te films by vacuum evaporation to investigate its property as a transducer for x-ray detection. Experiments revealed that multilayered Cd 1 À x Zn x Te structures, along with charge-blocking layers, are suitable transduction elements in flat-panel radiation imaging systems [10]. Kim et al investigated leakage currents and X-ray sensitivity of polycrystalline Cd 1 À x Zn x Te thin films as detectors for digital radiography.…”