Semiconductors and Semiconductor Devices Physics - Semiconductors and Semiconductor Devices

Two identical p-ri 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:

1. Circuit 1 and circuit 2.
2. Circuit 2 and circuit 3.
3. Circuit 3 and circuit 1.
4. Circuit 1 only.

In a p-n junction with open ends:

1. There is no systematic motion of charge carriers.
2. Holes and conduction electrons systematically go from the p-side to the n-side and from the n side to the p-side respectively.
3. There is no net charge transfer between the two sides.
4. There is a constant electric field near the junction.

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

1. There will not be a steady current in the circuit.
2. There will be a steady current from the n-side to the p-side.
3. There 'will a steady current from the p-side. to the n-side.
4. There may or may not be a current depending upon the resistance of the connecting wire.

In a semiconductor:

1. There are no free electrons at 0K.
2. There are no free electrons at any temperature.
3. The number of free electrons increases with temperature.
4. The number of free electrons is less than that in a conductor.

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

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.

1. 'Collector' and 'base'.
2. 'Base' and 'emitter'.
3. 'Collector' and 'emitter'.
4. 'Base' and 'base'.

In a transistor:

1. The emitter has the least concentration of impurity.
2. The collector has the least concentration of impurity.
3. The base has the least concentration of impurity.
4. All the three regions have equal concentrations of impurity.

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 diffluse from the p-side to the n-side in a p-n junction, the n-side gets positively charged. Explain.

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

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

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

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

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

1. From the p-side.
2. From the n-side.

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?

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 620nm. What is the band gap?

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

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 conμnuously take place?

Find the current through the battery circuits shown in figure.