P-N Diode - Free MCQ Practice Test with solutions, NEET Physics Class 12

Photo diode is used to detect light. 
In a reverse biased condition, the width of the depletion region increases as the applied reverse bias voltage increases across the diode. So, by applying a larger voltage, more of the incident photons are converted to electric current thereby increasing the efficiency.
In forward biased conditions, the width of the depletion region decreases so only a small portion of the incident photons get converted to electric current and hence the efficiency is less.
Hence photo diode in reverse biased condition detects light.

Correct option: C

Forward bias reduces the electric field across the depletion region, which lowers the potential barrier at the p-n junction.

When the potential barrier is lowered, majority carriers can cross the junction more easily and the junction current increases.

Hence the correct statement is that the potential barrier is lowered under forward bias; options A and B are incorrect and option D is not applicable.

There are two types of ions -anions are the - ve ones & cations are the +ve ones.As we know current flow from +ve to - ve, so During electrolysis or forward biasing anions move to anodes that are +ve in nature whereas cations move to cathodes which are -ve in nature.

The diode will reach its trigger point at lower voltage with rise in ambient temp, and at higher voltage for lower temp. As increased in temp, it accounts larger diode current than its previous current. When we talk about REVERSE SATURATION CURRENT, yes the diode current is dependable on it, because the (IS) i.e., reverse saturation current mainly depends on temp.

The varactor diode is used in a place where the variable capacitance is required, and that capacitance is controlled with the help of the voltage. The Varactor diode is also known as the Varicap, Voltcap, Voltage variable capacitance or Tunning diode.

Option D is correct.

In a p-type semiconductor, doping is done with trivalent atoms (called acceptors); each acceptor atom accepts an electron from the valence band and thereby creates a hole in the valence band.

Consequently, holes are the majority carriers while free electrons are the minority carriers in p-type material.

Pentavalent atoms act as donors and produce n-type semiconductors where electrons are majority carriers; therefore pentavalent dopants are not used to make p-type semiconductors.

Thus the statement that holes are majority carriers and trivalent atoms are the dopants correctly describes a p-type semiconductor; the other options are incorrect.

The diffusion of charge carriers across a junction takes place from the region of higher concentration to the region of lower concentration. In this case, the p-region has greater concentration of holes than the n-region. Hence, in an unbiased p-n junction, holes diffuse from the p-region to the n-region.

The p-n junction has the very useful property that electrons are only able to flow in one direction. As current consists of a flow of electrons, this means that current is allowed to flow only in one direction across the structure, but it is stopped from flowing in the other direction across the junction.

In an n-type silicon, the electrons are the majority carriers, while the holes are the minority carriers. An n-type semiconductor is obtained when pentavalent atoms, such as phosphorus, are doped in silicon atoms.

Atoms with one less valence electron result in "p-type" material. These p-type materials are group III elements in the periodic table. Therefore, p-type material has only 3 valence electrons with which to interact with silicon atoms.