148 + Interview Questions in Electronic Devices and Circuits in Electronics and Communication Engineering Page 1 InterviewSolution

1.	An extrinsic semiconductor sample has 6 billion silicon atoms and 3 million pentavalent impurity atoms. The number of electrons and holes is
Answer» When pentavalent impurity is added, the number of fresh electrons is very large as compared to number of holes.

Discussion

2.	What is the effect of cut in voltage on the wave form of output as compared to input in a semiconductor diode?
Answer» Since the duration of output waveform is less than 180°, output voltage is less than input voltage.

Discussion

3.	As temperature increases the number of free electrons and holes in an intrinsic semiconductor
Answer» Increase of temperature increases conductivity of semiconductors.

Discussion

4.	As comparated to an ordinary - diode, the extent of impurity atoms in a tunnel diode
Answer» Tunnel diode has heavily doped p and n regions.

Discussion

5.	As temperature increases the forbidden gap in silicon increases.
Answer» With increase in temperature, the forbidden gap decreases.

Discussion

6.	The channel of JFET consists of
Answer» The channel in JFET may be n type or p type. If channel is n type, gate is p type and if channel is p type gate is n type.

Discussion

7.	In a bipolar junction transistor = 0.98, I= 2 μA and 1 = 15 μA. The collector current I is
Answer»

Discussion

8.	For a photoengraving the mask used is
Answer» The mask that is prepared first is called the master mask made from glass substrates covered by thin chromium film. From the master masks are prepared working masks by contact pointing and used for Photolithography which means Photo engraving.

Discussion

9.	When a - junction is reverse biased
Answer» Holes and electrons move away from junction and therefore resistance increases to a high value.

Discussion

10.	If a sample of germanium and a sample of Si have the impurity density and are kept at room temperature then
Answer» Since the majority of charge carrier is better in Ge than in Si, for the same concentration of charge carriers, the conductivity of Ge is higher than that of Si.

Discussion

11.	When a large number of atoms are brought together to form a crystal
Answer» Inner shell electrons are tightly bound to the nucleus. Their energy levels cannot be affected by presence of other atoms.

Discussion

12.	Determine the transistor capacitance of a diffused junction varicap diode of a reverse potential of 4.2 V if C(0) = 80 pf and V = 0.7 V
Answer» , Here n = for diffused junction .

Discussion

13.	At room temperature the barrier potential in a silicon diode is
Answer» This 0.7 V is also called cut in voltage. When forward voltage is 0.7 V or less there is no current.

Discussion

14.	In a varactor diode the increase in width of depletion layer results in
Answer» Capacitance is inversely proportional to distance between plates.

Discussion

15.	In given figure a silicon diode is carrying a constant current of 1 mA. When the temperature of the diode is 20°C, V is found to be 700 mV. If the temperature rises to 40°C, V becomes approximately equal to
Answer» Id = Io(eVD/ηVT - 1) By considering , then = eVD/ηVT Id is constant according to question, VD a T .

Discussion

16.	A reverse voltage of 18 V is applied to a semiconductor diode. The voltage across the depletion layer is
Answer» Almost whole of reverse voltage is across depletion layer.

Discussion

17.	In degenerate type semiconductor material, the Fermi level,
Answer» This is due to heavy doping.

Discussion

18.	In active filter circuits, inductances are avoided mainly because they
Answer» In active circuit, Inductors are used by Op-Amp resistors and capacitor instead of simple inductor.

Discussion

19.	When a -- transistor is operating in active region, the current in the region is due to
Answer» Since emitter is p-type, emitter current is mainly due to holes. This current diffuses through the base.

Discussion

20.	In a JFET
Answer» Since gate current is very small. ID and Is are almost equal.

Discussion

21.	If the drift velocity of holes under a field gradient of 100 V/m is 5m/sec. Their mobility is
Answer» E = μ . Vd μ =.

Discussion

22.	In a P type silicon sample, the hole concentration is 2.25 x 10 / cm. If the intrinsic carrier concentration is 1.5 x 10/ cm the electron concentration is
Answer» Electron concentration .

Discussion

23.	The behaviour of a JFET is similar to that of
Answer» Both JFET and vacuum triode are voltage controlled devices.

Discussion

24.	An increase in junction temperature of a semiconductor diode
Answer» Reverse saturation current doubles for every 10°C rise in junction temperature.

Discussion

25.	Which of these has 3 layers?
Answer» p layer, i layer and n layer.

Discussion

26.	As per Einstein's equation, the velocity of emitted electron in photoelectric emission is given by the equation
Answer» Some electrons have less energy than Fermi level E and, therefore, more energy than Uw to escape. Therefore, this equation has inequality sign.

Discussion

27.	For an P-channel enhancement type MOSFET determine the drain current if K = 0.278 x 10A/V, V = -4V, V = -2V, Voltage equivalent at 27°C = 26 mV.
Answer» Drain current Id = k (\|Vgs\| - \|VT\|)2 = 0.278 x 10-3(4 - 2)2 = 1.11 mA.

Discussion

28.	The skin depth of copper is found to be 66 mm at 1 MHz at a certain temperature. At the same temperature and at 2 MHz, the skin depth would be approximately
Answer» Skin depth =

Discussion

29.	When - junction is reverse biased the holes in material move towards the junction and electrons in material move away from the junction.
Answer» Both holes and electrons move away from junction.

Discussion

30.	An incremental model of a solid state device is one which represents the
Answer» Incremental model is used for ac response at one operating point.

Discussion

31.	For an n-channel enhancement type MOSFET, if the source is connected at a higher potential than that of the bulk (V > 0), the threshold voltage V of the MOSFET will
Answer» VT depends upon MOSFET construction, hence it will Independent from MOSFET parameters.

Discussion

32.	Which of these has a layer of intrinsic semiconductor?
Answer» The intrinsic layer is in between p and n layers.

Discussion

33.	In a bipolar transistor
Answer» Base is very thin and therefore recombination is minimum in both p-n-p and n-p-n transistors.

Discussion

34.	If for a silicon -- transistor, the base to emitter voltage (V) is 0.7 V and the collector to base voltage V is 0.2 Volt, then the transistor is operating in the
Answer» Transistor will operate in active mode because VBE = 0.7 volt, (Base emitter junction is forward biased) VCB = - VBC = - 0.2 V (Base to collector junction is reverse biased).

Discussion

35.	The number of doped regions in a bipolar junction transistor is
Answer» p, n, p or n, p, n.

Discussion

36.	Donor energy level is type semiconductor is very near valence band.
Answer» It is near conduction band.

Discussion

37.	GaAs has an energy gap 1.43 eV the optical cut off wavelength of GaAs would lie in the
Answer» GaAs has very large band gap and high carrier mobility.

Discussion

38.	The drain characteristics of JFET in operating region, are
Answer» The drain current is almost constant. Therefore, characteristics is flat.

Discussion

39.	As temperature increases
Answer» Therefore, conductivity increases.

Discussion

40.	When a reverse bias is applied to a - junction, the width of depletion layer.
Answer» Therefore, the resistance is very high.

Discussion

41.	The Hall constant in Si bar is given by 5 x 10 cm/ coulomb, the hole concentration in the bar is given by
Answer» .

Discussion

42.	Which statement is false as regards holes
Answer» Holes do not exist in conductors.

Discussion

43.	Photo electric emission can occur only if
Answer» The frequency of incident radiation has to be more than threshold value. Wavelength is inversely proportional to frequency. Therefore wavelength of incident radiation must be less than threshold value.

Discussion

44.	When the - curve of a photodiode passes through origin the illumination is
Answer» i is plotted on y-axis and v on x-axis. When passing through origin current can be zero only.

Discussion

45.	An type silicon bar 0.1 cm long and 100 μm in cross-sectional area has a majority carrier concentration of 5 x 10/m and the carrier mobility is 0.13 m/V- at 300k. If the charge of an electron is 1.6 x 10 coulomb, then the resistance of the bar is
Answer» Resistance of bar(R) = l = 0.1 cm, A = 100 x 10-6 m2 σ = neμn + Peμp But bar is of n type then it can be approximated to σ = neμn.

Discussion

46.	The threshold voltage of a MOSFET can be lowered by Of the above statement
Answer» Increasing the substrate concentration lowers threshold voltage. Gate oxide layer has no effect an threshold voltage.

Discussion

47.	In which device does the extent of light controls the conduction
Answer» The resistance of photosensitive device depends on the light.

Discussion

48.	A semiconductor diode is biased in forward direction and carrying current I. The current due to holes in material is
Answer» Small current due to minority carriers also. Therefore hole current is less than.

Discussion

49.	Between which regions does BJT act like switch?
Answer» In cut off mode a BJT is an open switch and in saturation mode it is a closed switch.

Discussion

50.	The reverse saturation current of a diode does not depend on temperature.
Answer» It increases with increase of temperature.

Discussion

Explore topic-wise InterviewSolutions in .

An extrinsic semiconductor sample has 6 billion silicon atoms and 3 million pentavalent impurity atoms. The number of electrons and holes is

What is the effect of cut in voltage on the wave form of output as compared to input in a semiconductor diode?

As temperature increases the number of free electrons and holes in an intrinsic semiconductor

As comparated to an ordinary - diode, the extent of impurity atoms in a tunnel diode

As temperature increases the forbidden gap in silicon increases.

The channel of JFET consists of

In a bipolar junction transistor = 0.98, I= 2 μA and 1 = 15 μA. The collector current I is

For a photoengraving the mask used is

When a - junction is reverse biased

If a sample of germanium and a sample of Si have the impurity density and are kept at room temperature then

When a large number of atoms are brought together to form a crystal

Determine the transistor capacitance of a diffused junction varicap diode of a reverse potential of 4.2 V if C(0) = 80 pf and V = 0.7 V

At room temperature the barrier potential in a silicon diode is

In a varactor diode the increase in width of depletion layer results in

In given figure a silicon diode is carrying a constant current of 1 mA. When the temperature of the diode is 20°C, V is found to be 700 mV. If the temperature rises to 40°C, V becomes approximately equal to

A reverse voltage of 18 V is applied to a semiconductor diode. The voltage across the depletion layer is

In degenerate type semiconductor material, the Fermi level,

In active filter circuits, inductances are avoided mainly because they

When a -- transistor is operating in active region, the current in the region is due to

In a JFET

If the drift velocity of holes under a field gradient of 100 V/m is 5m/sec. Their mobility is

In a P type silicon sample, the hole concentration is 2.25 x 10 / cm. If the intrinsic carrier concentration is 1.5 x 10/ cm the electron concentration is

The behaviour of a JFET is similar to that of

An increase in junction temperature of a semiconductor diode

Which of these has 3 layers?

As per Einstein's equation, the velocity of emitted electron in photoelectric emission is given by the equation

For an P-channel enhancement type MOSFET determine the drain current if K = 0.278 x 10A/V, V = -4V, V = -2V, Voltage equivalent at 27°C = 26 mV.

The skin depth of copper is found to be 66 mm at 1 MHz at a certain temperature. At the same temperature and at 2 MHz, the skin depth would be approximately

When - junction is reverse biased the holes in material move towards the junction and electrons in material move away from the junction.

An incremental model of a solid state device is one which represents the

For an n-channel enhancement type MOSFET, if the source is connected at a higher potential than that of the bulk (V > 0), the threshold voltage V of the MOSFET will

Which of these has a layer of intrinsic semiconductor?

In a bipolar transistor

If for a silicon -- transistor, the base to emitter voltage (V) is 0.7 V and the collector to base voltage V is 0.2 Volt, then the transistor is operating in the

The number of doped regions in a bipolar junction transistor is

Donor energy level is type semiconductor is very near valence band.

GaAs has an energy gap 1.43 eV the optical cut off wavelength of GaAs would lie in the

The drain characteristics of JFET in operating region, are

As temperature increases

When a reverse bias is applied to a - junction, the width of depletion layer.

The Hall constant in Si bar is given by 5 x 10 cm/ coulomb, the hole concentration in the bar is given by

Which statement is false as regards holes

Photo electric emission can occur only if

When the - curve of a photodiode passes through origin the illumination is

An type silicon bar 0.1 cm long and 100 μm in cross-sectional area has a majority carrier concentration of 5 x 10/m and the carrier mobility is 0.13 m/V- at 300k. If the charge of an electron is 1.6 x 10 coulomb, then the resistance of the bar is

The threshold voltage of a MOSFET can be lowered by Of the above statement

In which device does the extent of light controls the conduction

A semiconductor diode is biased in forward direction and carrying current I. The current due to holes in material is

Between which regions does BJT act like switch?

The reverse saturation current of a diode does not depend on temperature.