What photo detector is generally used with a TFT array in indirect digital imaging?

• A. Cadmium telluride (CdTe)
• B. Amorphous selenium (a-Se)
• C. Amorphous silicon (a-Si)
• D. Gallium arsenide (GaAs)

Answer: (C)

In indirect digital imaging systems, the photodetector typically employed with a thin-film transistor (TFT) array is amorphous silicon (a-Si). This material plays a critical role in converting light into an electrical signal, which then gets processed to create an image.

Amorphous silicon is favored because it provides several advantages in terms of performance and manufacturing. It has a high degree of uniformity, which is essential for digital imaging, ensuring that the captured images are consistent across the entire detector surface. Additionally, amorphous silicon can be produced using relatively simple and cost-effective deposition techniques, making it a practical choice for constructing large-area detectors used in radiography.

Furthermore, a-Si works effectively in conjunction with scintillators (such as cesium iodide or gadolinium oxysulphide), which convert the X-ray photons into visible light. The amorphous silicon layer then captures the emitted light and converts it into an electrical charge that the TFT array can read to form digital images.

In contrast, the other options listed, while also used in various imaging applications, do not typically pair with TFT arrays in the context of indirect digital imaging. For instance, cadmium telluride (CdTe) and gall