Fig. 1. Comparison of conceptual design of X-ray detectors and corresponding X-ray response mechanism. (a) Conventional X-ray detectors with TFT readout. (b) Proposed X-ray detectors with vacuum FEA readout.

Fig. 2. Implementation and characterizations of the X-ray detectors. (a) Schematic layout of the vacuum cold cathode X-ray detector. (b) Actual picture of the fabricated X-ray detector. (c) Arrays of patterned ZnO NWs (top image) and cross-sectional view of ZnO NWs (bottom image). (d) Field emission J-E curve of the ZnO NWs with inset showing the corresponding F-N curve. (e) Typical XRD pattern of β-Ga2O3 bulk photoconductor. (f) Total mass attenuation of X-rays in β-Ga2O3 bulk photoconductor showing the contribution from Compton scattering, photoelectric effect, and pair production and that of a-Se and CsPbBr3 photoconductors.

Fig. 3. Detection performance and operation principle of the proposed X-ray detector. (a), (b) Dark current and photocurrent of the X-ray detector at low and high electric fields. (c) F-N curves of the dark current and photocurrent. (d)–(f) Schematic of the operation principle of X-ray detector at different applied electric fields. (g) The detection sensitivity versus applied electric field curves of the X-ray detector. (h) Internal gain versus electric field curve of the detector under X-ray illumination with the X-ray tube voltage of 6 kV and the X-ray tube current of 0.6 mA. (i) The detection sensitivity versus X-ray tube voltage curves of the X-ray detector with inset showing the theoretical determination of detector sensitivity as a function of X-ray energy. (The experimental value was measured using a DC X-ray tube without beam filters.)

Fig. 4. Temporal response of the X-ray detector. (a)–(c) Time-dependent photocurrent of the X-ray detector with pulsed X-ray source on and off at 5  V μm-1 electric field. (d) The SNRs under different X-ray dose rates with inset showing the temporal responses under different X-ray dose rates.

Table 1. Comparison of Performance Metrics of Direct-Conversion X-ray Detectors Based on Different Photoconductors and Photoelectron Multiplication Mechanisms