Abstract
The large mismatch of the coefficients of thermal expansion (CTE) between the metal contact and CdZnTe exerts thermal stress at the metal/CZT interface, which causes mechanical degradation of the contact in addition to the poor adhesion of the metallic thin film to CZT. To form a reliable and stable interface, the contact material should have better adhesion and a close match of the coefficients of thermal expansion with CZT/CdTe. Here, we report on our investigations of a novel non-metallic contact layer for use in radiation detector applications. The proposed ZnO:Al contact layer offers better adhesion due to the oxide interface, higher hardness and better matching of the CTE with CZT. It has high prospects for a reliable and stable device structure that can serve as a replacement to the common metallic electrodes used today. We evaluated AZO contacts to CZT and extracted the electronic characteristics, such as resistivity and mobility-lifetime product of electrons, and compared the results of the same characterization measurements for CZT with gold contacts. The present observations showed that the characteristics of CZT detectors with AZO contacts are nearly identical to the same detectors with gold contacts.
Highlights
The flat band energy diagrams of gold, cadmium zinc telluride (CZT) and aluminum-doped ZnO (AZO) are shown in Figure 2 before they are brought into contact
If the gold contact shows Schottky-type behavior, the AZO/CZT contact is expected to be ohmic in nature and vice versa
This portrays the fact that the band bending for the AZO/CZT contact is predominantly dominated by the interface density of states at the interface rather than by the differences in the work functions
Summary
X-ray and gamma-ray detectors are widely used today for various field applications in nonproliferation, national security, medical imaging and astronomical telescopes.[1,2,3,4,5] For more than two decades, cadmium zinc telluride (CZT) with 10% Zn has been the prime candidate for nucleardetector applications operable at room temperature.[6,7,8,9,10,11,12] Its high atomic number, high density, excellent optoelectronic properties and high mobility-lifetime product has made CZT the material of choice for high-resolution X-ray and gamma-ray detectors. In spite of drastic improvements in the yield of highquality CZT over the last few years, the stability of metal contacts to CZT still remains a challenge due to the poor match of the thermo-physical properties of the materials at the interfacial region. In order to arrest the degradation and increase the detector stability with time, the contact material should have good adhesion and a close match of the CTEs for the contact and CZT/CdTe. In order to arrest the degradation and increase the detector stability with time, the contact material should have good adhesion and a close match of the CTEs for the contact and CZT/CdTe To address this issue and enhance the reliability of the detector, we examined aluminum-doped ZnO (AZO) as an electrode material, substituting it for conventional metal electrodes used today for radiation detector applications. The principal advantage is the close match of the CTE of AZO with CZT. We report the materials and device characteristics of planar detector with AZO contacts and compared the results with gold contacts for the same CZT crystal
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