problem 1:
a) What do you mean by Fermi level? By indicating the position of Fermi level in intrinsic, n-type and p- type semiconductor, describe its significance in semiconductors?
b) Sketch V-I characteristics of a PN diode for the given conditions:
i) R_{f} = 0, V_{γ} = 0, R_{r }= ∞
ii) R_{f} = 0, V_{γ}= 0.6V, R_{r} = ∞
iii) R_{f }= Non-zero, fixed value, V_{γ} = 0, R_{r }= ∞
iv) R_{f }= Non-zero, fixed value, V_{γ} = 0. 6V, R_{r }= ∞
Where V_{γ }is the cut-in voltage, R_{f }is the forward dynamic resistance & R_{r }is the reverse dynamic resistance of the diode.
problem 2:
a) What do you understand about the depletion region at a PN junction, with the help of essential diagrams and derive expression for barrier potential.
b) Derive the expression for transition capacitance, C_{T} of a PN diode.
problem 3:
a) With the help of necessary sketches describe the potential distribution in an open circuited PN junction.
b) With the help of V-I Characteristics, describe the operation of a PN Diode under Forward bias and Reverse bias.
problem 4:
a) Describe Avalanche and Zener break down mechanisms in semiconductors and also compare them?
b) For Zener diode circuit shown in figure below, find out V_{L}, V_{R}, I_{Z} & R.
problem 5:
a) Describe the V-I characteristics of Zener diode and distinguish between Avalanche and Zener Break downs.
b) In a Zener diode regulator, the supply voltage = 300V, V_{z} = 220V, I_{z} = 15mA and load current = 25mA. Compute the value of resistor required to be connected in series with the Zener diode.
problem 6:
a) Describe the effect of temperature on V-I characteristics of a diode.
b) Differentiate between drift and diffusion current in a semiconductor. Illustrate continuity equation.