Physics

Semiconductors and Diodes

461 Questions

Semiconductors and diodes form the foundation of modern electronics, covering topics like intrinsic carrier concentration and Zener breakdown. Questions often explore the characteristics of bipolar junction transistors (BJT) and the properties of doped silicon materials. This topic is crucial for physics and electronics engineering competitive exams.

Zener diode breakdownBJT circuit analysisIntrinsic carrier concentrationDoping in semiconductorsEmitter follower circuit

Semiconductors and Diodes Questions

Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

A transistor is used as a common emitter amplifier with a load resistance $2 K ohm $. The input resistance is $150 Ohm $. Base current is charged by $20 \mu A$ which results in a change in collector current by $1.5 mA$. The voltage gain of the amplifier is

  1. $900$
  2. $1000$
  3. $1100$
  4. $1200$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

We know that voltage gain, $\dfrac{V _o}{V _i}=\beta\dfrac{R _L}{R _I}$


Where, $\beta=\dfrac{I _C}{I _B}=\dfrac{1.5mA}{20\mu A}=75$

Hence, voltage gain=$75\times\dfrac{2000}{150}=1000$

Hence, answer is option-(B).

Multiple choice physics electrical conductivity of liquids does liquid conduct electricity? liquids conduct electricity do liquids conduct electricity?

Which of the following is not true about LED?

  1. There are two wires (called leads) attached to an LED.

  2. While connecting to a circuit, the longer lead of LED is always connected to the positive terminal of the battery.

  3. While connecting to a circuit, the shorter lead of LED is always connected to the positive terminal of the battery.

  4. LED can be used to detect weak current.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

While connecting to a circuit, the longer lead is always connected to the positive terminal of the battery and the shorter lead is connected to the negative terminal of the battery.

Multiple choice physics electrical conductivity of liquids does liquid conduct electricity? liquids conduct electricity do liquids conduct electricity?

In LEDs, the longer lead is connected to ................ and the shorter lead is connected to .................. .

  1. negative terminal; positive terminal

  2. positive terminal; negative terminal

  3. negative terminal; neutral terminal

  4. positive terminal; neutral terminal
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In LEDs, the longer lead is connected to the positive terminal and the shorter lead is connected to the negative terminal.

Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

What will be the conductivity of pure silicon crystal at 300 K temperature if  electron cottoer pair at this temperature is $ 1.072 \times 10^{10} /cm^3 $ and $ \mu _n = 1350 cn^2 /V-s and \mu _p = 480 cm^2/ V-s $ ?

  1. $ 3.14 \times 10^{-4} mho /cm $
  2. $ 3.14 \times 10^{-5} mho /cm $
  3. $ 3.14 \times 10^{-6} mho /cm $
  4. $ 3.14 \times 10^{3} mho /cm $
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

Doping of $As$ with $Si$ is called :

  1. n-type semi-condutor

  2. p-type semi-conductor

  3. intrinsic semi-conductor

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$As$ is a member of group $V$ and has 5 electrons in its outermost shell. 


When $Si$ is doped with group $V$ elements such as $As$ then, $Si$ forms four bonds with $As$ and one extra electron is left free for conduction. 

Since the conduction is due to the presence of free electrons, therefore, it is known as n-type semiconductor.

Therefore, the option is A.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

An n-type semi-conductor is formed when a trace amount of impurity is added to silicon. The number of valence electrons in the impurity atom must be: 

  1. $3$
  2. $5$
  3. $1$
  4. $2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

An n-type semiconductor is due to the presence of a free electron in the semiconductor. Since silicon is an element having $4$ valence electrons, in order to have a free electron, it must be doped with an element having one more valence electron than silicon. 


Hence the number of valence electron in the impurity must be $4+1=5.$

Therefore, option B is correct.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

p type semi conductor is formed when trace amount of impurity is added to silicon. The number of valence electrons in the impurity atom must be:

  1. $3$
  2. $5$
  3. $1$
  4. $2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

To form a p-type semiconductor, one must add elements from boron family to the silicon atom.

Boron family has 3 valance electrons so, number of valance electrons in the impurity atom must be 3.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids
Assertion (A): Group-$13$ doped crystals of silicon are called a p-type semiconductors.
Reason (R): Holes (positive in charge) appear to be responsible for the semiconducting properties.

  1. Both Assertion and Reason are true and Reason is the correct explanation of Assertion

  2. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion

  3. Assertion is true but Reason is false.

  4. Assertion is false but Reason is true
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Doping silicon with Group 13 elements creates holes because there are fewer valence electrons than in silicon. These holes act as positive charge carriers, making it a p-type semiconductor.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

Assertion: Group-$15$ doped crystals of silicon are called an n-type semiconductor.


Reason: Neutrons are responsible for the semiconducting properties.

  1. Both Assertion and Reason are true and Reason is the correct explanation of Assertion

  2. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion

  3. The Assertion is true but Reason is false

  4. The Assertion is false but Reason is true
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Group-15 doped crystals of silicon are called a n-type semiconductors because of the presence of a valence electron and electrons are responsible for the semiconducting properties.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

Which of the following, when doped into ultrapure germanium, will convert it into a p-type semiconductor?

  1. $C$
  2. $As$
  3. $In$
  4. $Na$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When a pure semiconductor is doped with trivalent elemental impurity $p$ type semiconductors are formed

(A) $C\longrightarrow Tetravalent$
(B) $As\longrightarrow Pentavalent$
(C) $Indium$ $(In)\longrightarrow$ $Trivalent$
(D) $Na\longrightarrow$ $Monovalent$
Thus Indium ($In$) will convert ultrapure germanium into p-type semiconductor.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

In a n-type semiconductor, which of the following statements is true?

  1. Electrons are majority carriers and trivalent atoms are dopants.

  2. Electrons are minority carriers and pentavalent atoms are dopants.

  3. Holes are minority carriers and pentavalent atoms are dopants.

  4. Holes are majority carriers and trivalent atoms are dopants.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The n-type semiconductor can be produced  by doping impurity atoms of valence 5 i.e, pentavalent atoms like phosphorous and so electrons are majority charge carriers and Holes are minority charge carriers.

So correct answer is option C.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

With which one of the following elements silicon should be doped so as to give p-type of semiconductor?

  1. Selenium

  2. Boron

  3. Germanium

  4. Arsenic
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The n-type semiconductors are obtained when $Si$ or $Ge$ are doped with elements of group 15, eg, Arsenic $(As)$, while p-type semiconductors are obtained when $Si$ or $Ge$ are doped with traces of group 13 , ie Indium $(In)$ , Boron $(B)$.

So the correct option is $B$.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

Which of the following is true about the charge acquired by $p-$type semiconductors?

  1. Positive

  2. Neutral

  3. Negative
  4. Depends on concentration of $p$ impurity
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$p-$type semiconductors have a larger hole concentration than electron concentration. In p-type semiconductors, holes are the majority carriers and electrons are the minority carriers. $p-$type semiconductors are created by doping an intrinsic semiconductor with acceptor impurities. A common $p-$type dopant for silicon is boron or gallium. There will be no charge on the semiconductor.

So, correct answer is option $B$.