Papers by Author: Sang Sik Kang

Abstract: Amorphous selenium (a-Se) film has the potential to fulfill the requirements of a novel x-ray image detector because of its good photo-to-dark impedance ratio, large area coverage, and low temperature deposition. In this work were studied the structural, optical and electrical properties of thermally- evaporated a-Se film for the phosphor-light modulator (PLM). From the x-ray diffraction and electron microscopy experimental results, the deposited film had an amorphous phase without any re-crystallization or defects. Also, the light absorption in widely visible range of 400 ~ 630 nm was over 95 %. From the electrical measurements, the low dark current density of 2.8 nA/cm2 was obtained at 10 V/㎛. The x-ray sensitivity of the 270㎛-Gd2O3:Eu phosphor coupled 20㎛-Se film was 7.31 nC/cm2-mR. From such experimental results, the novel x-ray detector which incorporates phosphor coupled x-ray light modulator, makes an operation at low x-ray exposure possible, therefore, the applications as a medical imaging detector are shown below.

Abstract: In this paper, we present the imaging parameters and compare both mercuric iodide (HgI2) and amorphous selenium (a-Se) films. Using MCNPX code, we designed the film structure and its thickness for the optimized detector in the diagnostic x-ray range. The mercuric iodide film was formed by a wet binder process, while the amorphous selenium film was deposited by physical vapor deposition (PVD). These deposition methods are capable of being scaled up to sizes required in diagnostic imaging applications. The electronic properties are investigated using dark current, x-ray sensitivity and signal to noise ratio (SNR). From our results, the developed HgI2 film as an alternative to a-Se photoconductor, which is in practical use in flat panel x-ray imaging detector, will prove its usefulness in the future design and the optimization for various diagnostic modalities.

Abstract: We have developed a large area, flat panel detector for general applications to digital radiology. This paper presents the x-ray detection characteristics with various semiconductor radiation detectors (HgI2, PbI2, PbO, CdTe) derived by a novel wet coating process for large area deposition. The wet coating process could easily be made from large area films with printing paste mixed with semiconductor and binder material at room temperature. X-ray performance data such as dark current, sensitivity and signal to noise ratio (SNR) were evaluated. The HgI2 semiconductor was shown in much lower dark current than the others, and also has the best sensitivity. In this paper, reactivity and combination characters of semiconductor and binder material that affect electrical and x-ray detection properties would be verified through our experimental results.