Question

Which is the wrong statement in the following sentences?
A device in which P and N− type semiconductors are used is more useful than a vacuum type because
A) power is not necessary to heat the filament
B) it is more stable
C) very less heat is produced in it
D) its efficiency is high due to a high voltage drop across the junction.

Answer 1

The electrical conductivity of a semiconductor material is between that of a conductor, such as metallic copper, and that of an insulator, such as glass. Its resistivity decreases as the temperature rises, whereas metals have the reverse effect. By adding impurities ("doping") into the crystal structure, its conducting characteristics can be changed in beneficial ways.

Complete answer:
A semiconductor diode is a device made up of only one p–n junction. A depletion area occurs at the junction of a p-type and an n-type semiconductor, where the lack of mobile charge carriers prevents current flow. When the device is forward biassed (connected with the p-side at a greater electric potential than the n-side), the depletion zone shrinks, allowing for considerable conduction, but when the diode is reverse biassed and the depletion region expands, only a very tiny current can be generated.
The number of charge carriers in a crystal is substantially increased by doping. A doped semiconductor is called "p-type" when it includes free holes, and "n-type" when it contains free electrons. To regulate the concentration and locations of p- and n-type dopants, semiconductor materials used in electronic devices are doped under exact circumstances. Many p- and n-type areas can exist in a single semiconductor device crystal; the p–n junctions between these regions are responsible for the beneficial electrical behaviour. A hot-point probe may be used to quickly detect whether a semiconductor sample is p- or n-type.
A vacuum tube, also known as an electron tube, is a device that regulates electric current flow in a high vacuum between electrodes separated by an electric potential difference. The phenomenon of thermionic emission of electrons from a heated cathode is utilised for a variety of fundamental electronic tasks such as signal amplification and current rectification in the form known as a thermionic tube or thermionic valve.
A device that uses P and N type semiconductors is more helpful than a vacuum tube because it has a higher efficiency due to a lower voltage drop across the junction.
Hence option (D) is correct.

Note:
A diode's most frequent purpose is to allow an electric current to flow in one direction (the forward direction of the diode) while blocking it in the opposing direction (the reverse direction). As a result, the diode may be thought of as an electrical check valve. Rectification is the term for this unidirectional characteristic, which is used to convert alternating current (AC) to direct current (DC). Diodes and other rectifier types can be employed to extract modulation from radio signals in radio receivers.