Direct Thermal Growth of Large Scale Cl-doped CdTe Film for Low Voltage High Resolution X-ray Image Sensor

Abstract

Polycrystalline cadmium telluride (CdTe) X-ray photodetector with advanced performance was fabricated in a Schottky diode form by direct thermal deposition (evaporation) on pixelized complementary metal oxide semiconductor (CMOS) readout panel. Our CdTe X-ray detector shows such a variety of benefits as relatively low process temperature, low cost, low operation voltage less than 40 V, and higher sensitivity and spatial resolution than those of commercial a-Se detectors. CdTe has cubic Zinc Blende structure and maintains p-type conduction after growth in general. For low voltage operation, we succeeded in Cl doping at all stage of CdTe film deposition, and as a result, hole concentration of p-type CdTe was reduced to ~1012 cm−3 from ~1015 cm−3, and such concentration reduction could enable our Schottky diode with Ti electrode to operate at a reverse bias of less than 40 V. Our CdTe Schottky diode/CMOS pixel array as a direct conversion type imager demonstrates much higher resolution X-ray imaging in 7 × 9 cm2 large scale than that of CsI/CMOS array, an indirect conversion imager. To our limited knowledge, our results on polycrystalline CdTe Schottky diode/CMOS array would be very novel as a first demonstration of active pixel sensor system equipped with directly deposited large scale X-ray detector.

Characterization of Flexible Amorphous Silicon Thin-Film Transistor-Based Detectors with Positive-Intrinsic-Negative Diode in Radiography

“…However, as mentioned above, the light spreading phenomenon increases with the thickness of the scintillator. Thus, this imaging system has a poorer spatial resolution [ 37 , 38 ]. As one of the methods to overcome this problem, a deconvolution method that removes blurring using software is often suggested as a supplement [ 39 ].…”

Neutron Irradiation Effects on Boron Nitride-Based Ceramics for Use in X-ray Detection

“…Currently, the direct conversion of X-ray to electrical signal of commercial detectors is mainly based on amorphous selenium (α-Se) and cadmium zinc telluride (CZT). Other materials with high atomic numbers have also shown great potential for X-ray detection and imaging, such as CdTe, − lead oxide, polycrystalline HgI 2 , − and metal halide perovskites. − However, most of the current X-ray detection materials are still suffering from the poor stability, particularly under intense ionizing irradiation. It could be mainly due to the high attenuation coefficient of these dense materials with “heavy” atoms, and the incident high energy photons could be easily intercepted and have a great potential to generate large density of defects .…”

The X-ray Sensitivity of an Amorphous Lead Oxide Photoconductor

“…The requirement for a relatively low deposition temperature makes single-crystalline photoconductors unsuitable for use in direct conversion imaging detectors. As for the disordered (polycrystalline and amorphous), high-Z semiconductors that can produce large-area detectors, polycrystalline layers of PbI 2 [8][9][10], HgI 2 [10][11][12], CdTe [13], Cd 1-x Zn x Te [14], BiI 3 [15], ZnO [16], PbO [17,18], perovskites [19], and amorphous PbO (a-PbO) [20,21] are considered promising. However, at the current stage of their technology, the majority of the materials in this list exhibit signal lag-a residual current that continues to flow after X-ray exposure [17,18,22].…”