What Is Cadmium Zinc Telluride?

Cadmium zinc telluride (Cd₁₋ₓZnₓTe, commonly abbreviated CZT) is a ternary II-VI semiconductor alloy formed by substituting a fraction of cadmium atoms in cadmium telluride (CdTe) with zinc, yielding a compound whose bandgap, lattice parameter, and charge transport properties can be tuned by varying the zinc mole fraction x. For x values between 0.1 and 0.2, CZT has a bandgap of approximately 1.6 to 1.7 eV and resistivity exceeding 10¹⁰ ohm-centimeters at room temperature, which are the conditions needed for it to function as a direct-conversion radiation detector without cryogenic cooling. This combination of properties distinguishes CZT from most competing semiconductor detector materials: germanium (Ge) provides superior energy resolution but requires cooling to liquid-nitrogen temperatures, while silicon lacks the density and atomic number needed to efficiently stop gamma rays. CZT is grown primarily by the traveling heater method (THM) and the modified Bridgman technique, both of which are slow, expensive processes that limit crystal yield and availability.

Material Properties and Crystal Growth

CZT adopts the zinc-blende crystal structure, and its quality as a radiation detector depends critically on the perfection of the grown crystal. Sub-grain boundaries, tellurium inclusions, and dislocations act as trapping centers that capture the charge carriers (electrons and holes) generated when a gamma-ray photon is absorbed, reducing the signal collected at the electrodes and degrading energy resolution. The most important material parameter for detector performance is the mobility-lifetime product (μτ) for electrons, which in good CZT crystals reaches 10⁻³ cm² V⁻¹. Hole transport is substantially inferior to electron transport in CZT, which has driven the development of unipolar charge collection electrode geometries that collect primarily the electron signal. The Washington State University CZT Crystal Growth Laboratory describes the growth and characterization challenges involved in producing large single-crystal CZT boules suitable for detector-grade substrates. Crystal sizes have grown from a few cubic centimeters in the 1990s to planar detector elements several centimeters on a side in current production.

Radiation Detection Performance

A 1 cm³ CZT detector can cover an energy range from approximately 30 keV to 3 MeV with an energy resolution of about 2.5 percent full-width at half-maximum (FWHM) at the 662 keV gamma line of Cs-137. Pixelated CZT detector arrays with volumes around 6 cm³ achieve energy resolutions below 1 percent FWHM at 662 keV and can perform Compton imaging to reconstruct gamma-ray source directions. These capabilities, combined with room-temperature operation and compact form factor, make CZT the material of choice for portable nuclear security instruments and handheld isotope identifiers. The PMC review of CZT array detector technology surveys advances in pixelation, application-specific integrated circuit (ASIC) readout electronics, and 3D position-sensing architectures that have substantially improved spectroscopic performance over the past two decades. CZT also serves as a substrate for epitaxial growth of mercury cadmium telluride (HgCdTe) detector arrays used in astronomical infrared instrumentation.

Device Architectures and Signal Processing

CZT detectors are fabricated by cutting and polishing crystals into planar or pixelated geometries, then applying metal contacts (commonly platinum or gold) by electroless deposition or sputtering. Unipolar collection geometries include the coplanar grid (CPG) configuration, in which two interdigitated grid electrodes are held at slightly different potentials to extract primarily electron charge, and 3D virtual Frisch collar (VFC) geometries that shape the electric field to improve charge collection uniformity. Single-sided strip detectors and fully pixelated arrays are used in medical imaging systems, particularly cardiac SPECT cameras, where the ability to record both energy and 3D position simultaneously enables new imaging algorithms. The ScienceDirect article on CZT as a nuclear radiation detector material traces the relationship between material quality, electrode geometry, and detector spectroscopic performance across the development of CZT from early planar detectors to modern pixelated arrays.

Applications

Cadmium zinc telluride has applications in a wide range of radiation measurement and imaging technologies, including:

• Nuclear security and nonproliferation, where handheld CZT spectrometers identify gamma-emitting isotopes at border crossings and ports
• Medical nuclear imaging, where CZT-based cardiac SPECT cameras achieve higher sensitivity and energy resolution than conventional scintillator systems
• Astrophysics, where CZT detector arrays on instruments such as the NuSTAR satellite perform hard X-ray and gamma-ray observations
• Industrial radiation monitoring, where CZT detectors replace scintillator-photomultiplier assemblies in compact, high-temperature environments
• HgCdTe substrate growth, where CZT provides a lattice-matched foundation for epitaxial infrared detector arrays