Radiation Detector Quality CdTe Deposited on X-Ray Sensor Chips

CdTe is considered to be an ideal semiconductor for X-ray and gamma-ray detectors. It is a wide bandgap semiconductor with high absorption coefficient and low electron-hole creation energy. Still, the use of this material is limited by the lack of availability and cost of large area crystals and challenges of coupling CdTe crystals with the read-out electronics. To overcome this problem, we investigated low-temperature growth of CdTe directly on the application-specific integrated circuit (ASIC). CdTe was deposited using modified close-space sublimation; water cooling was utilized to reduce substrate heating. Films, with thickness up to 500 µm, were grown at temperatures as low as 100 °C with the growth rates as high as 80 µm/hour. CdTe films were polycrystalline and highly resistive (9.0 × 10
⁷
- 2.0 × 10
⁸
Ohm*cm). The grain size increased with the substrate temperature while resistivity remained nearly constant. X-ray-generated current was recorded with excitation energies of interest (16.5 KeV - 50 KeV). We are exploring the low-temperature grown CdTe as a potential alternative to expensive single crystals and associated bonding costs which will enable development inexpensive high quality radiation imagers.