Semiconductor Electronics quiz

The energy gap of an insulator is typically:

The energy gap of silicon is about:

Doping silicon with a pentavalent impurity produces:

The majority charge carriers in a p-type semiconductor are:

In forward bias, the width of the depletion region:

The small reverse current in a diode is due to:

The resistivity of a semiconductor with rise in temperature:

The output frequency of a full-wave rectifier for a 50 Hz input is:

The barrier potential of a silicon p-n junction is about:

Which of the following is a trivalent impurity?

What is a hole? How does it move in a semiconductor? (2 marks)

Why is a p-type semiconductor electrically neutral even though holes are majority carriers? (2 marks)

Distinguish between diffusion current and drift current in a p-n junction. (2 marks)

Why does the current in a forward-biased diode rise sharply after a certain voltage? (2 marks)

Write the relation between electron and hole concentrations in a doped semiconductor. (2 marks)

What is the knee voltage of a diode? (2 marks)

Why are silicon diodes preferred over germanium diodes? (2 marks)

Why is a filter used after a rectifier? (2 marks)

How does the energy band diagram of an n-type semiconductor differ from that of an intrinsic one? (2 marks)

What happens to the depletion region under reverse bias? (2 marks)

Germanium has an intrinsic carrier concentration of 2.4 x 10^19 m^-3. When doped with donors at 4 x 10^22 m^-3, find the hole concentration. (3 marks)

Pure silicon has 5 x 10^28 atoms per m^3. It is doped with 1 ppm of indium. Find the hole and electron concentrations (ni = 1.5 x 10^16 m^-3). (3 marks)

The energy gap of germanium is 0.66 eV. Find the minimum photon energy and maximum wavelength that can excite an electron across the gap (hc = 1240 eV nm). (3 marks)

A 220 V rms, 50 Hz supply is stepped down by a transformer with turns ratio 10:1 and fed to a rectifier. Find the rms and peak voltages of the secondary and the output frequency for half-wave and full-wave rectification. (3 marks)

A germanium diode (drop 0.3 V) is connected in forward bias with a 270 ohm resistor to a 3 V battery. Find the current in the circuit. (3 marks)

Read the passage and answer the questions. A mobile phone charger converts 230 V AC mains to about 5 V DC. Inside, a transformer reduces the voltage and four diodes in a bridge arrangement convert AC into DC, followed by a capacitor. (i) What is the function of the diodes? (ii) Is this half-wave or full-wave rectification? (iii) Why is a capacitor used? (5 marks)

Read the passage and answer the questions. In a chip factory, a silicon wafer is doped with phosphorus in one region and boron in another to form a junction. (i) Which region becomes n-type and which p-type? (ii) What forms at the junction? (iii) Why is only a tiny amount of dopant used? (5 marks)

Read the passage and answer the questions. A technician tests a diode with a multimeter. In one direction it shows low resistance; when the leads are reversed it shows very high resistance. (i) What does this show about the diode? (ii) Which reading corresponds to forward bias? (iii) What would two low readings indicate? (5 marks)

Read the passage and answer the questions. Diamond has a band gap of about 5.4 eV, silicon 1.1 eV and germanium 0.7 eV, while in copper the bands overlap. (i) Classify each material. (ii) Which semiconductor has more intrinsic carriers at room temperature? Why? (iii) Why does copper conduct well? (5 marks)

Read the passage and answer the questions. A student increases the reverse bias voltage across a diode slowly. The current remains very small and almost constant up to a certain voltage, after which it suddenly increases. (i) Why is the current small at first? (ii) What is the sudden rise called? (iii) Why may the diode be damaged? (5 marks)

Explain the classification of solids into metals, semiconductors and insulators using energy band diagrams. (6 marks)

Explain intrinsic and extrinsic semiconductors with diagrams of the silicon lattice for n-type and p-type doping. (6 marks)

Explain the formation of a p-n junction, the depletion region and the barrier potential with diagrams. (6 marks)

Draw circuit diagrams for studying the forward and reverse characteristics of a p-n junction diode. Draw the I-V curve and explain its features. (6 marks)

Explain the working of half-wave and full-wave rectifiers with circuit diagrams and input-output waveforms. (6 marks)