How many 1s energy states are present in one mole of sodium vapor? Are they all filled in normal condition? How many 3s energy states are present in one mole of sodium vapor? Are they all filled in normal conditions?

There are energy bands in a solid. Do we have really continuous energy variation in a band or do we have very closely spaced but still discrete energy levels?

The conduction band of a solid is partially filled at 0 K. Will it be a conductor, a semiconductor or an insulator?

In semiconductors, thermal collisions are responsible for taking a valence electron to the conduction band. Why does the number of conduction electrons not go on increasing with time as thermal collisions continuously take place?

When an electron goes from the valence band to the conduction band in silicon, its energy is increased by 1.1 eV. The average energy exchanged in a thermal collision is of the order of kT which is only 0.026 eV at room temperature. How is a thermal collision able to take some of the electrons from the valence band to the conduction band?

What is the resistance of an intrinsic semiconductor at 0K?

We have valence electrons and conduction electrons in a semiconductor. Do we also have ‘valence holes’ and ‘conduction holes’?

When a p-type impurity is doped in a semiconductor, a large number of holes are created. This does not make the semiconductor charged. But when holes diffuse from the p-side to the n-side in a p-n junction, the n-side gets positively charged. Explain.

The drift current in a reverse based p-n junction increases in magnitude if the temperature of the junction is increased. Explain this on the basis of creation of hole-electron pairs.

An ideal diode should pass a current freely in one direction and should stop it completely I the opposite direction. Which is closer to ideal—vacuum diode or a p-n junction diode?

Consider an amplifier circuit using a transistor. The output power is several times greater than the input power. Where does the extra power come from?

Electric conduction in a semiconductor takes place due to

An electric field is applied to a semiconductor. Let the number of charge carriers be n and the average drift speed b v. If the temperature is increased.

Let n_p and n_e be the numbers of holes and conduction electrons in an intrinsic semiconductor.

Let n_p and n_e be the numbers of holes and conduction electrons in an extrinsic semiconductor.

A p-type semiconductor is

When an impurity is doped into an intrinsic semiconductor, the conductivity of the semiconductor.

If the two ends of a p-n junction are joined by a wire,

The drift current in a p-n junction is

The diffusion current in a p-n junction is

Diffusion current in a p-n junction is greater than the drift current in magnitude.

Two identical p-n junctions may be connected in series with a battery in three ways figure. The potential difference across the two p-n junctions are equal in

Two identical capacitors A and B are charged to the same potential V and are connected in two circuits at t = 0 as shown in figure. The charges on the capacitors at a time t = CR are, respectively,

A hole diffuses from the p-side to the n-side in a p-n junction. This means that

In a transistor,

An incomplete sentence about transistors is given below:

The emitter- ………. Junction is ……………… and the collector ……………… junction is ………………. The appropriate words for the dotted empty positions are, respectively.

In a semiconductor.

In a p-n junction with open ends,

In a p-n junction,

The impurity atoms with which pure silicon may be doped to make it a p-type semiconductor are those of

The electrical conductively of pure germanium can be increased by

A semiconducting device is connected in a series circuit with a battery and a resistance. A current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops to almost zero. The device may be

A semiconductor is doped with a donor impurity.

Let i_E, i_C and i_B represent the emitter current, the collector current and the base current respectively in a transistor. Then

In a normal operation of a transistor,

An AND gate can be prepared by repetitive use of

Calculate the number of states per cubic metre of sodium is 3s band. The density of sodium is 1013 kg m^–3. How many of them are empty?

In a pure semiconductor, the number of conduction electrons is 6 × 10¹⁹ per cubic metre. How many holes are there in a sample of size 1 cm × 1cm × 1 mm?

Indium antimonide has a band gap of 0.23 eV between the valence and the conduction band. Find the temperature at which kT equals the band gap.

The band gap for silicon is 1.1 eV.

(a) Find the ratio of the band gap to kT for silicon at room temperature 300 K.

(b) At what temperature does this ratio become one tenth of the value of 300 K? (Silicon will not retain its structure at these high temperatures)

When a semiconducting material is doped with an impurity, new acceptor levels are created. In a particular thermal collision, a valence electron revives an energy equal to 2kT and just reaches one of the acceptor levels. Assuming that the energy of the electron was at the topo edge of the valence band and that the temperature T is equal to 300 K, find the energy of the acceptor levels above the valence band.

The band gap between the valence and the conduction bands in zinc oxide (ZnO) is 3.2 eV. Suppose an electron in the conduction band combines with a hole in the valence band and the excess energy is released in the form of electromagnetic radiation. Find the maximum wavelength that can be emitted in this process.

Suppose the energy liberated in the recombination of a hole-electron pair is converted into electromagnetic radiation. If the maximum wavelength emitted is 820 nm, what is the band gap?

Find the maximum wavelength of electromagnetic radiation which can create a hole-electron pair in germanium. The band gap in germanium is 0.65 eV.

In a photodiode, the conductivity increases when the material is exposed to light. It is found that the conductivity changes only if the wavelength is less than 620 nm. What is the band gap?

Let ΔE denote the energy gap between the valence band and the conduction band. The population of conduction electrons (and of the holes) is roughly proportional to e^–ΔE/2kT. Find the ratio of the concentration of conduction electrons in diamond to that in silicon at room temperature 300 K. ΔE for silicon is 1.1 eV and for diamond is 6.0 eV. How many conduction electrons are likely to be in one cubic meter of diamond?

The conductivity of a pure semiconductor is roughly proportional to T^3/2 e^–ΔE/2kT where ΔE is the band gap. The band gap for germanium is 0.74 eV at 4 K and 0.67 eV at 300 K. By what factor does the conductivity of pure germanium increase as the temperature is raised from 4 K to 300 K.

Estimate the proportion of boron impurity which will increase the conductivity of a pure silicon sample by a factor of 100. Assume that each boron atom creates a hole and the concentration of holes in pure silicon at the same temperature is 7 × 10¹⁵ holes per cubic meter. Density of silicon is 5 × 10²⁸ atoms per cubic meter.

The product of the hole concentration and the conduction electron concentration turns out to be independent of the amount of any impurity doped. The concentration of conduction electrons in germanium is 6 × 10¹⁹ per cubic meter. When some phosphorus impurity is doped into a germanium sample, the concentration of conduction electrons increases to 2 × 10²³ per cubic meter. Find the concentration of the holes in the doped germanium.

The conductivity of an intrinsic semiconductor depends on temperature as σ = σ₀ e^–ΔE/2kT, where σ₀ is a constant. Find the temperature at which the conductivity of an intrinsic germanium semiconductor will be double of its value at T = 300 K. Assume that the gap for germanium is 0.650 eV and remains constant as the temperature is increased.

A semiconducting material has a band gap of 1 eV. Acceptor impurities are doped into it which create acceptor levels 1 meV above the valence band. Assumed that the transition from one energy level to the other is almost forbidden if kT is less than 1/50 of the energy gap. Also, if kT is more than twice the gap, the upper levels have maximum population. The temperature of the semiconductor is increased from 0K. The concentration of the holes increase with temperature and after a certain temperature it becomes approximately constant. As the temperature is further increased, the hole concentration again starts increasing at a certain temperature. Find the order of the temperature range in which the hole concentration remains approximately constant.

In a p-n junction, the depletion region is 400 nm wide and an electric field of 5 × 10⁵ V m^–1 exists in it.

(a) Find the height of the potential barrier.

(b) What should be the minimum kinetic energy of a conduction electron which can diffuse from the n-side to the p-side.

The potential barrier existing across an unbiased p-n junction is 0.2 volt. What minimum kinetic energy a hole should have to diffuse from the p-side to the n-side if

(a) the junction is unbiased,

(b) the junction is forward biased at 0.1 volt and

(c) the junction is reverse biased at 0.1 volt?

In a p-n junction, a potential barrier of 250 meV exists across the junction. A hole with a kinetic energy of 300 meV approaches the junction. Find the kinetic energy of the hole when it crosses the junction if the hole approached the junction

(a) from the p-side and

(b) from the n-side

When a p-n junction is reverse biased, the current becomes almost constant at 25 μA. When it is forward biased at 200 mV, a current of 75 μA is obtained. Find the magnitude of diffusion current when the diode is

A. unbiased

B. reverse biased at 200 mV and

C. forward biased at 200 mV.

The drift current in a p-n junction is 20.0 μA. Estimate the number of electrons crossing a cross section per second in the depletion region.

The current voltage characteristic of an ideal p-n junction diode is given by

i = i₀ (e^eV/kT – 1)

Where the drift current i₀ equals 10 μA. Take the temperature T to be 300 K.

(a) Find the voltage V₀ for which e^eV/kT = 100. One can neglect the term 1 for voltages greater than this value.

(b) Find an expression for the dynamic resistance of the diode as a function of V for V > V₀.

(c) Find the voltage for which the dynamic resistance is 0.2 Ω

Consider a p-n junction diode having the characteristic i= i₀(e^eV/kT – 1) where i₀ = 20 μA. The diode is operated at T = 300 K.

(a) Find the current through the diode when a voltage of 300 mV is applied across it in forward bias.

(b) At what voltage does the current double?

Calculate the current through the circuit and the potential difference across the diode shown in figure. The drift current for the diode is 20 μA.

Each of the resistances shown in figure has a value of 20 Ω. Find the equivalent resistance between A and B. Does it depend on whether the point A or B is at higher potential?

Find the currents through the resistances in the circuits shown in figure.

What are the readings of the ammeters A₁ and A₂ shown in figure? Neglect the resistances of the meters.

Find the current through the battery in each of the circuits shown in figure.

Find the current through the resistance R in figure if (a) R = 12 Ω (b) R = 48 Ω

Draw the current voltage characteristics for the device shown in figure between the terminals A and B.

Find the equivalent resistance of the network shown in figure between the points A and B.

When the base current in a transistor is changed from 30 μA to 80 μA, the collector current is changed from 1.0 mA to 3.5 mA. Find the current gain β.

A load resistor of 2 kΩ is connected in the collector branch of an amplifier circuit using a transistor in common-emitter mode. The current gain β = 50. The input resistance of the transistor is 0.50 kΩ. If the input current is changed by 50 μA,

(a) by what amount does the output voltage change,

(b) by what amount does the input voltage change and

(c) what is the power gain?

Design a logical circuit using AND, OR and NOT gates to evaluate .

Show that is always 1.