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# KTU B.Tech S3 model Questions for Solid State Devices

## KTU B.Tech S3 model Questions for Solid State Devices

### EC 203: SOLID STATE DEVICES

Time: 3 Hrs                                                                                                                      Marks: 100

PART A

( Answer any One from 1 and 2. Q.No: 3 is Compulsory )

i) Draw the energy level diagram of an intrinsic semiconductor, n-type semiconductor and  p-type semiconductor. (3)

ii) What are different carrier scattering mechanisms? (2)

iii) Compute the number of holes in a heavily doped (n = 1×1018/cm3) n-type semiconductor material with intrinsic concentration ni =1.5×1010/cm3. (2)

iv) For a GaAs semiconductor (Eg = 1.43 eV), determine the minimum wavelength of an incident photon that can interact with a valence electron and elevate to the conduction band. (3)

OR

2.

i) Define quasi Fermi level. When do they exist? (2)

ii) What is diffusion capacitance? Is it a capacitance that is always present in junctions? (2)

iii) Derive Einstein Relation.                                                                                        (6)

3.

i) Determine the value of Hall electric field in the case of a Ge sample of length 0.1 cm, width of 0.01cm and          thickness of 0.001cm, doped with 1017 acceptor atoms/cm3. Assume that the current flowing through the                sample is 5mA and the magnetic field applied is 1 μT. (10)

ii) Derive the continuity equation. (10)

PART B

(Answer any One from 4 and 5. Q.No: 6 is Compulsory)

4   i) Discuss briefly the temperature dependence of diode V-I characteristics.(2 marks)

ii) Draw the energy band diagram of a metal semiconductor contact and explain its working.

(8 marks)

OR

5   i) Compute the number of holes in a heavily doped (n = 1×1018/cm3 ) n-type semiconductor material with                        intrinsic concentration ni =1.5×1010/cm3 (2 marks)

ii)The forward current of a Silicon Schottky barrier diode and a pn junction diode are 1mA    each. The reverse                saturation currents of both the diodes are 10×10-7 A. Compute the value of the reverse saturation current of                  the pn junction diode if the difference in the forward voltages of the two diodes is 0.25 V.  (8  marks)

6     i) Discuss the construction and V-I characteristics of a Schottky diode (10 marks)

ii) Discuss the switching transients in a pn diode. (10 marks)

PART C

(Answer any One from 7 and 8. Q.No: 9 is Compulsory)

7   i) Describe the switching characteristics of a BJT. (10 marks)

ii) Compute the base width required to achieve a base transport factor βT=0.95. Given that DB=10cm2 /s and             τB=10-7 s. (10 marks)

OR

8    i) Identify and explain the two modes of operation of the MOSFET. (10 marks)

ii) An n-type MOSFET has W = 25µm, L = 2.5µm, tOX = 400Å, µn = 800cm2 /Vs and VT=0.8V. Compute the                 value of ID for VGS=1 V. (10 marks)

9    i)Derive a relation for the threshold voltage of a MOS capacitor (10 marks)

ii) A 0.3 µm single crystal of silicon is subjected to incident light normal to the surface having power of 20mW.               Given the attenuation factor for silicon at the frequency of the light is 5×104 cm-1 and the index of refraction                 of  silicon is 3.5. Determine the power absorbed by the crystal. (10 marks)

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