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

**MODEL QUESTION PAPER Prepared by **__ktubtechquestions.com__

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**THIRD SEMESTER B.TECH DEGREE EXAMINATION JANUARY 2017**

**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 = 1×10^{18}/cm^{3}) n-type semiconductor material with intrinsic concentration n_{i} =1.5×10^{10}/cm^{3}. **(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 10^{17} acceptor atoms/cm^{3}. 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 = 1×10^{18}/cm^{3} ) n-type semiconductor material with intrinsic concentration n_{i} =1.5×10^{10}/cm^{3} **(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=10cm^{2} /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 = 800cm^{2} /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 5×10^{4} 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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