Why only p or n type semiconductor cannot be use as diode or any electronic device why only combination of p or n type semiconductor are used as device?

P-type and N-type semiconductors alone cannot function as diodes or electronic devices because they lack a junction that facilitates the control of current flow. A diode requires a p-n junction to create an electric field that allows current to flow in one direction while blocking it in the opposite direction. This junction is essential for the rectifying behavior of diodes, enabling them to manipulate electrical signals effectively. Therefore, the combination of p-type and n-type semiconductors is necessary to form the essential structures for various electronic devices.