Improved thermal stability of antimony‐doped amorphous selenium film for X‐ray flat‐panel detectors

Abstract

Amorphous selenium (a-Se) film is a promising photoconductive material for X-ray flat-panel detectors (FPD) application. However, a-Se tends to be crystalline Se at near room temperature. This remarkable temperature sensitivity limits its practical application. To prevent the near-room-temperature crystallization of a-Se film, we fabricate antimony (Sb)-doped a-Se films using a vacuum evaporation technique equipped with an in situ cooling trap. We experimentally demonstrate that the Sb doping improves the thermal stability of a-Se film while possessing a similar X-ray photoelectric conversion efficiency as the pure a-Se film. After air annealing at 50 8C for 90 min, the X-ray diffraction (XRD) results of the 4.1 at.% Sb-doped a-Se film shows no detectable crystallization diffraction peak. Upon applying an electric field of 10 V mm À1 , such Sb-doped a-Se film exhibits dark current density below 1 nA cm À2, while under an X-ray dosage of about 4 mGy, the annealed Sb-doped a-Se film shows a photocurrent density of more than 100 nA cm À2 .

Investigations on Structural, Optical and X-Radiation Responsive Properties of a-Se Thin Films Fabricated by Thermal Evaporation Method at Low Vacuum Degree

“…The dark current density measured at different bias voltage remains a 10 −7 A/mm 2 order of magnitude (Figure 4b), although the dark current rises with increasing bias voltage. Further, X-radiation responsive characterization with the current gain (G) of 2.52× of sample appears at weak electrical field (0.25 V/mm–1.25 V/mm), and the strong electrical field is not required by a-Se thin films comparing with driving electrical filed (tens of volts per micron) of a-Se thick films [2,4,5,7,8]. It can be seen from Figure 4c that the photogeneration current of a-Se thin films has a rapid response without obvious tailing both X-ray on and X-ray off, suggesting the low trap effects and high deposition quality of thin films [19].…”

“…The thermal evaporation method is a good way to prepare a-Se films [4,5,6], and the background vacuum operating 10 −3 Pa to 10 −4 Pa is a current preparation condition [7,8,9]. However, it is well known that a high vacuum degree implies expensive equipment requirements and lots of vacuum preparation time, which apparently increase the production costs.…”

“…By comparison, the vacuum degree of 10 −2 Pa is very easy and quick to be achieved for any vacuum equipment. On the other hand, several reports have preferred to investigate the a-Se thick films with a thickness of tens of microns to hundreds of microns [4,5,6,7,10], since a-Se thick films can absorb more X-ray energy and thus produce a higher photocurrent; further, the systematic research on the a-Se thin films with the thickness of a few microns is rare [8]. Nevertheless, the low crystallization temperature, 40–50 °C, is a fatal disadvantage of a-Se thick films, as it seriously restricts its practical applications [11,12].…”

Sustainable Recycling of Selenium‐Based Optoelectronic Devices

“…[ 1 , 2 , 3 , 4 , 5 ] Amorphous Se (a‐Se) stands as the currently market‐dominant photoconductive material in X‐ray imaging industry, particularly in X‐ray flat‐panel detectors for digital mammography. [ 6 , 7 ] Crystalline Se (c‐Se) is regaining significant attention as a promising absorber for top cells in multi‐junction solar cells and indoor photovoltaics (IPVs) due to its suitable wide bandgap of ≈ 1.9 eV, [ 8 , 9 , 10 , 11 , 12 , 13 ] excellent intrinsic phase and environmental stability to ambient conditions such as humidity, light and oxygen, [ 14 , 15 , 16 ] and nontoxicity as an essential element for humans. [ 17 , 18 , 19 ] In addition, the high piezoelectricity, thermoelectricity, and nonlinear optical responses of Se have also propelled its widespread use in various applications including wearable piezoelectric devices, thermoelectric devices, optical limiters, and field‐effect transistors.…”

Flexible Broadband Photodiodes Based on Amorphous Te0.4Se0.6 Thin Films

“…Selenium (Se) is the sole elemental glass that remains in an amorphous state at room temperature, primarily composed of interlinked −Se–Se– chains. ,, Notably, amorphous Se (a-Se) exhibits exceptional optoelectronic characteristics that find extensive application in photoconductor devices. − For example, a-Se-based photoconductors have been widely used for X-ray detection and imaging. − However, it is worth mentioning that the fabrication of photodiode-type devices using a-Se has been relatively limited. In comparison, photodiodes possess superior low dark current and ultrafast response, which are more desired for advanced applications.…”