Correct option is C
A voltage-controlled capacitance semiconductor device, commonly known as a varactor diode (or varicap diode), operates based on the principle of varying capacitance with applied voltage.
Varactor Diode:
This device is designed to exploit the property that the capacitance of a p-n junction varies with the applied reverse bias voltage. When the varactor diode is reverse biased, the depletion region width changes with the applied voltage. As the reverse bias voltage increases, the depletion region widens, reducing the junction capacitance. Conversely, as the reverse bias voltage decreases, the depletion region narrows, increasing the junction capacitance.
Operation in Reverse Biased Mode: The varactor diode is specifically designed to operate in reverse bias because this mode allows control over the width of the depletion region and, consequently, the capacitance of the diode. In forward bias, the depletion region is minimal, and the capacitance control effect is lost. In breakdown region, the diode would conduct heavily and not exhibit its capacitance control properties effectively, likely leading to damage.
Thus, the correct mode of operation for a voltage-controlled capacitance semiconductor device is in reverse biased mode. Therefore, the correct answer is reverse biased mode.
