# 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)