Properties of Semiconductors - NEET Physics Questions

Question 1: moderate

Intrinsic germanium and silicon at absolute zero temperature behave like :

1. Superconductor

2. Good semiconductor

3. Ideal insulator

4. Conductor

View Answer

At absolute zero temperature (0 K), intrinsic germanium and silicon behave like insulators due to the following reasons:

No Free Charge Carriers: At absolute zero, all the electrons in the material occupy the lowest energy states, and there are no thermally excited electrons available to conduct electricity. This means there are no free charge carriers (electrons or holes).
Wide Band Gap: Both germanium and silicon have a band gap (about 0.66 eV for germanium and 1.1 eV for silicon). At absolute zero, the thermal energy is insufficient to excite electrons across this band gap from the valence band to the conduction band.

As a result, intrinsic germanium and silicon cannot conduct electricity at absolute zero, behaving as insulators.

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Question 2: moderate

If the ratio of the concentration of electrons to that of holes in a semiconductor is 7/5 and the ratio of currents is 7/4 then what is the ratio of their drift velocities :

1. 5/8

2. 4/5

3. 5/4

4. 4/7

View Answer

The ratio of electron to hole currents is given by:

$\frac{I_n}{I_p} = \frac{7}{4}$

The ratio of electron to hole concentrations is:

$\frac{n}{p} = \frac{7}{5}$

Using the current formula

$I = q n v A$

$I = q n v A$ , the ratio of drift velocities (

$\frac{v_n}{v_p}$

$v ^{p} v ^{n}$ ) can be found as:

$\frac{I_{n}}{I_{p}} = \frac{n v_{n}}{p v_{p}}$

Substitute the given ratios:

$\frac{7}{4} = \frac{\frac{7}{5} \cdot v_n}{v_p}$

Simplifying:

$\frac{v_{n}}{v_{p}} = \frac{5}{4}$

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Question 3: moderate

GaAs (with a band gap = 1.5 eV) as an LED can emit :

1. Blue light

2. Green light

3. Infrared rays

4. Ultraviolet rays

View Answer

GaAs (Gallium Arsenide) with a band gap of 1.5 eV can emit light in the infrared region of the electromagnetic spectrum.

The energy of a photon emitted by an LED is related to its wavelength by the equation:

$E = \frac{hc}{\lambda}$

Solving we get

$λ= 826 nm which lies in infrared region.💬 Discuss this QuestionQuestion 4: moderate The resistivity of a pure semiconductor is 0.5 Ωm. If the electron and hole mobility be 0.39 m²/V-s and 0.19 m²/V-s respectively then calculate the intrinsic carrier concentration. 1. \[2.16\times 10^{19}/m^{3}\] 2. \[4.32\times 10^{19}/m^{3}\] 3. \[10^{20}/m^{3}\] 4. None of these View Answer 💬 Discuss this QuestionQuestion 5: moderate A Ge specimen is doped with Al. The concentration of acceptor atoms is \[\sim 10^{21} atom/m^{3}\]. Given that the intrinsic concentration of electron hole pairs is \[\sim 10^{19}/m^{3}\], the concentration of electrons in the specimen is : 1. \[10^{17} /m^{3}\] 2. \[10^{15} /m^{3}\] 3. \[10^{4} /m^{3}\] 4. \[10^{2} /m^{3}\] View Answer According to mass action law \[ n_{e}\times n_{h}= n_{i}^{2} \] \[ n_{h}=10^{21} ; n_{i}= 10^{19}; n_{e}=n_{i}^{2}/n_{h} = n_{e}= 10^{38}/10^{21}= 10^{17} \] 💬 Discuss this QuestionQuestion 6: moderate The contribution in the total current flowing through a semiconductor due to electrons and holes are 3/4 and 1/4 respectively. If the drift velocity of electrons is 5/2 times that of holes at this temperature, then the ratio of concentration of electrons and holes is : 1. 6 : 5 2. 5 : 6 3. 3 : 2 4. 2 : 3 View Answer Current i = neAv \[ \frac{I_{1}}{I_{2}}= \frac{n_{1}}{n_{2}} * \frac{v_{d1}}{v_{d2}} \] \[ \frac{3}{1}= \frac{n_{1}}{n_{2}} * \frac{5}{2} \] \[ \frac{n_{1}}{n_{2}} = \frac{6}{5} \] 💬 Discuss this Questiondocument.addEventListener('DOMContentLoaded', function () {
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