Introduction:
A Schottky diode is a type of diode that is constructed using a metal-semiconductor junction, where the metal acts as the anode. This diode allows for fast switching speeds and low voltage drops, making it suitable for various applications such as rectification, voltage clamping, and power protection.

Explanation:
In a Schottky diode, the aluminum metal acts as the anode. Let's understand why it is the anode and not the cathode or any other terminal.

Anode:
The anode is the positive terminal of a diode. It is the terminal through which the current enters the diode when it is forward biased. In a Schottky diode, the aluminum metal is in contact with the semiconductor material (usually n-type), forming a metal-semiconductor junction. The aluminum metal has a lower work function compared to the semiconductor material. This difference in work function creates a built-in electric field at the junction, which facilitates the flow of majority charge carriers (electrons in the case of n-type semiconductor).

Cathode:
The cathode is the negative terminal of a diode. It is the terminal through which the current exits the diode when it is forward biased. In a Schottky diode, the cathode is connected to the semiconductor material, forming a semiconductor-metal junction. The semiconductor material has a higher work function compared to the metal. This difference in work function creates a barrier for the flow of majority charge carriers, limiting the current flow.

Gate and common terminal:
The terms "gate" and "common terminal" are not applicable to a Schottky diode. These terms are commonly used in other electronic components such as transistors and integrated circuits.

Conclusion:
In a Schottky diode, the aluminum metal acts as the anode, which is the positive terminal of the diode. The aluminum forms a metal-semiconductor junction with the semiconductor material, allowing for fast switching speeds and low voltage drops. Understanding the terminal designations is essential for correctly using and analyzing the behavior of Schottky diodes in electronic circuits.