Electronic Devices - May 2015

Electronics Engineering (Semester 3)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1 (a) What are non-ideal effects in BJT? Explain any one non-ideal effect in BJT.(5 marks) 1 (b) Determine the ideal reverse saturation current density in silicon p_N diode at 300°k Given Na=Nd=10¹⁶ cm^-3, ni=1.5×10¹⁰cm^-3(5 marks) 1 (c) With neat diagram explain the operation of UJT relaxation oscillator.(5 marks) 1 (d) Compare photo diode with phototransistor.(5 marks) 2 (a) Draw energy band diagram of P-N Junction for zero, forward, reverse bias clearly showing junction diagram, depletion width, fermi energy level and barrier potential.(10 marks) 2 (b) calculate the theoretical barrier height, built in potential barrier and maximum electric field in a metal semiconductor diode for zero applied bias consider a contact between tungsten and a type silicon doped to Nd=10¹⁶cm^-3 at T=300k.
The metal work function for tungsten is ϕm=4.55V and electron a affinity for silicon is x=4.01V.
Nc=2.8×10¹⁹ cm^-3, K=1.38×10^-23J/K, εs=11.7×8.85×10^-14, e=1.6×10¹⁹c.(10 marks) 3 (a) Calculate the threshold voltage V_TO at V_SB for a polysilicon gate n channel MOS transistor with the following parameters-
substrate doping density NA=10¹⁶ cm^-3 polysilicon gate doping density ND=2×10²⁰ cm^-3 gate oxide thickness tox=500A° oxide Interface fixed charge density NOX= 4×10¹⁰ cm^-2.(10 marks) 3 (b) Derive the drain current equation ID for MOSFET in ohmic and saturation regions.(10 marks) 4 (a) Draw and explain construction, working characteristics of JFET. Explain frequency limitation factors.(10 marks) 4 (b) Explain schottky effect. Derive the position of maximum barrier Xm.(10 marks)

Draw and explain, Construction and working of:

5 (a) (i) HEMT (MODFET)(5 marks) 5 (a) (ii) MESFET(5 marks)

Explain basic structure and characteristics of:

5 (b) (i) SCR(5 marks) 5 (b) (ii) DIAC(5 marks)

Solve any four of the following:

6 (a) Draw and explain Ebers-moll model of transistor.(5 marks) 6 (b) With the help of circuit diagram and characteristics explain application of zener diode as a voltage regulator.(5 marks) 6 (c) What are optocouplers? Explain any one application of optocoupler.(5 marks) 6 (d) Sketch and explain V-I and C-V characteristics of MOSFET.(5 marks) 6 (e) Explain channel length modulation with cross section of MOSFET. Write equation associated with this effect.(5 marks)