## Podcast Beta

## Questions and Answers

If the number density of atoms in the silicon specimen is known, how many acceptor atoms will there be per cubic centimetre?

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What happens to the probability of electrons being found in the conduction band of an intrinsic semiconductor at finite temperature?

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What is the typical ionization energy of a donor in silicon?

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The reverse saturation current in a PN-junction diode is non-zero.

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What will be the effect of applying a potential difference across an insulator, semiconductor, and metal?

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What is the forward voltage drop for a diode in a circuit?

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Calculate the maximum wavelength of light required to create a hole in a P-type semiconductor with acceptor levels 57 meV above the valence band.

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What is the current flowing through a plate of Ge crystal given the conditions?

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If Ge and Si diodes conduct at 0.3 V and 0.7 V respectively, what should happen if the Ge diode connections are reversed?

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For a transistor amplifier in common-emitter configuration, what is required to determine the current gain?

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## Study Notes

### Semiconductor and Electronics - JEE HOTS

#### Doping and Semiconductor Properties

- A silicon specimen can be made into a P-type semiconductor by doping, on average, one Indium atom per silicon atom.
- The number density of atoms in the silicon specimen determines the number of acceptor atoms in silicon per cubic centimeter.

#### Probability of Electrons in Conduction Band

- The probability of electrons to be found in the conduction band of an intrinsic semiconductor at a finite temperature:
- Decreases exponentially with increasing band gap
- Is not independent of the temperature and the band gap

#### Ionisation Energy of Donor in Silicon

- The typical ionisation energy of a donor in silicon is 0.05 eV.

#### PN-Junction Diode

- Reverse saturation current in a PN-junction diode is 10^-12 A at T = 300 K.
- Forward current for a voltage of 0.5 V is 10^-3 A.

#### Insulator, Semiconductor, and Metal

- Current passing through:
- An insulator at T = 0 K is zero
- A semiconductor at T = 0 K is zero
- A metal at T = 0 K is finite
- A P-N diode at T = 0 K is finite, if it is reverse biased

#### Diode Circuits

- Current supplied by the battery when its positive terminal is connected to A is 5 mA.
- If the forward voltage drop for the diode is 0.5 V, the current will be 10 mA.

#### Acceptor Levels and Hole Creation

- A P-type semiconductor has acceptor levels 57 meV above the valence band.
- The maximum wavelength of light required to create a hole is 2175 nm.

#### Transistor Amplifier

- Current gain in a transistor amplifier in common emitter configuration is 50.
- Output voltage of the amplifier will be 10 V.

#### Semiconductor Concentrations and Mobility

- Concentrations of electrons and holes in a semiconductor are 8 Ã— 10^18/m^3 and 5 Ã— 10^18/m^3 respectively.
- Mobilities of electrons and holes are 2.3 m^2/volt-sec and 0.01 m^2/volt-sec respectively.

#### Half-Wave Rectification

- RMS voltage across R in a half-wave rectification circuit is approximately 141.4 V.

#### Diode Characteristics

- Voltage across the diode is independent of current above the knee point (0.7 V).
- The minimum current required to be above the knee point is 1 mA.

#### Transistor Applications

- Voltage gain and power gain in a transistor amplifier in CB mode are 69.7 and 68.25 respectively.

#### Bohr Radius

- Bohr radius of the fifth electron of phosphorus acting as a dopant in silicon is 1.35 nm.

#### PN-Junction Diodes in Series

- The correct increasing order of resistance between A and B will be D1, D2, and D3.

#### Diode Circuits with Capacitors

- The voltage across the capacitor in a diode circuit with a capacitor is 220 V (rms) AC.

#### Semiconductor Current Flow

- Current flowing through a Ge plate with an applied voltage of 2 V is 2 mA.

#### Semiconductor Current Components

- Contribution to the total current flowing through a semiconductor due to electrons and holes are 2 mA and 1 mA respectively.

#### Diode Voltage Drops

- Ge and Si diodes conduct at 0.3 V and 0.7 V respectively.
- Reversing the Ge diode connection changes the value of V0 by 0.4 V.

#### Logic Gates

- The combination of gates shown produces a NOR gate.
- The system is equivalent to the following logic gate: NAND.
- The output F of the circuit is represented by F = A + BC.
- The diagram of a logic circuit produces an output F = AB + C.

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## Description

Practice questions on doping, semiconductor properties, and electron probability in conduction band for JEE HOTS exam.