American Society of Radiologic Technologist (ASRT) Practice Exam

When do charges separate in amorphous silicon?

1. When light interacts with the array

2. When the CCD activates the array

3. When an electric field is applied

4. When the capacitor is activated

The correct answer is: When an electric field is applied

Amorphous silicon exhibits unique electronic properties, particularly in how it responds to external stimuli. Charges within amorphous silicon separate when an electric field is applied because the electric field provides the necessary force to separate the electron-hole pairs generated by incident light. In the context of photodetectors or imaging arrays, when photons hit the amorphous silicon material, they can excite electrons, creating electron-hole pairs. However, without an electric field, these pairs might recombine rather than being utilized for signal processing. The electric field enables the movement of the electrons toward the anode and the holes toward the cathode, which contributes to the generation of a usable electrical signal. This is a crucial mechanism for the function of many imaging technologies, including those found in digital cameras and other imaging devices that utilize amorphous silicon as a photoconductive layer.