Fundamentals of semi-conductors

Question

Question 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.

Question 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.

Question 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.

Question 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.

Question 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.

Question 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.