Show that the capacitance across a graded junction is inversely proportional to the one third power of effective voltage applied across it.

How does the concentration gradient of the impurity affect the value of junction capacitance of graded junction diode?

Show that the depletion layer capacitance of an abrupt n⁺ − p junction (C_T) can be approximated as

Draw the band diagram for a forward biased p-n homojunction showing clearly the quasi Fermi-levels F_n(x) and F_p(x) throughout the homojunction and for several diffusion lengths on either side of the homojunction. Explain qualitatively the variations in F_n and F_p.

Explain why the charge storage capacitance is not important for a reverse biased homojunction.

Sketch energy band diagrams to distinguish between a metal, an insulator and a semiconductor.

Which types of charges are present on the two opposite faces of the homojunction (electrons, holes, immobile negative charge, immobile positive charge)?

What types of carriers are present in the space charge region? Do carrier generation or recombinations take place in the space charge region?

Why is the space charge region also called the depletion region?

What is the size of the depletion width (micron, milli metre, and centimetre)?

What is the size of inherent potential barrier across the homojunctions of Ge and Si diodes? What does their polarity look like?

What is the effect of the external voltage applied across the homojunction? Explain forward and reverse bias.

What do you understand by reverse saturation current? What gives rise to it? What is the ratio of forward and reverse current in a homojunction diode?

When does the homojunction diodes offer very high resistance?

What proportion of impurity should be mixed in an intrinsic Ge or Si for manufacturing a homojunction diode?

Show that the diffusion capacitance across a forward biased abrupt junction is given as where g is the diode incremental conductance.

What happens to the diffusion capacitance in the reverse bias case? (C_D neglected w.r.t. C_T)

How do the C_T and C_D compare in forward bias case? (C_T <<< C_D).

Calculate the value of diffusion capacitance across the abrupt junction of a forward biased Ge diode (η = 1) if 26 mA current passes through it. (26 mA/26 mV = g = 1/Ω, C_D = τ).

What is the value of diffusion capacitance if the lifetime of the minority carrier is 20 μs? (20 μF).

What would be the time constant of the diode in Problem-7? (time constant = C_D/g = very small due to very small dynamic conductance of the diode).

Obtain donor concentration in an abrupt Si p-n junction with electrostatic potential of

How is a varactor diode used for tuning a TV?

How is a Schottky diode callled hot carrier diode?

How is a Schottky diode different from a singal diode?

How do you distinguish between two leads of an LED?

The potential barrier across a p-n homojunction is due to

(a) negative and positive charge carriers on the same side

(b) immobile donor and acceptor ions

(c) negative and positive charge carriers on opposite sides

Depletion voltage is

(a) more for Ge

(b) more for Si

(c) equal in Si and Ge

Depletion voltage increases with

(a) forward bias

(b) reverse bias

(c) without forward and reverse biases

Depletion width has

(a) negative charge carriers

(b) positive charge carriers

(c) no charge carriers

Depletion width with forward bias

(a) increases

(b) decreases

(c) remains constant

Homojunction capacitance with increasing reverse bias

(a) increases

(b) decreases

(c) remains constant

Forward bias across p-n homojunction means

(a) only positive terminal connected to p-type

(b) positive terminal connected to p and negative to n

(c) positive terminal connected to n and negative to p

In an unbiased p-n homojunction current does not flow because

(a) carriers do not cross the homojunction

(b) equal and opposite charge carriers cross the homojunction

(c) same type of charge carriers cross the homojunction in opposite direction

Diffusion current is due to

(a) different concentrations of the two types of charge carriers in the same region

(b) different concentrations of same type of charge carriers in different regions

(c) same concentration in two regions

Total current through any p-n homojunction is only due to

(a) drift of charge carriers

(b) diffusion of charge carriers

(c) both types of charge carriers

The forward current in p-n homojunction increases rapidly

(a) from zero onwards

(b) only after the value of potential barrier

(c) when the depletion area becomes equal to space charge area

Zener breakdown refers to

(a) forward bias region

(b) reverse bias region

(c) no bias region

Avalanche breakdown voltage is

(a) lower than Zener

(b) higher than Zener

(c) equal to Zener breakdown voltage

Zener breakdown depends on

(a) electric field created across the depletion region

(b) velocity of the carries

(c) no. of donor ions

(d) no. of acceptor ions

Both avalanche and Zener breakdowns are commonly known as

(a) Zener breakdown

(b) avalanche breakdown

(c) current breakdown

Zener diodes are

(a) specially doped p-n homojunction

(b) normally doped p-n homojunction

(c) lightly doped p-n homojunction

Zener diodes are used as

(a) reference voltage elements

(b) reference current elements

(c) reference resistance

The reverse saturation current with increasing reverse bias

(a) increases

(b) decreases

(c) remains constant

The magnitude of reverse saturation current is

(a) less than forward current

(b) larger than forward current

(c) equal to forward current

With rise in temperature reverse saturation current

(a) increases linearly

(b) increases exponentially

(c) decreases linearly

With increasing temperature, the homojunction voltage

(a) increases

(b) decreases

(c) remains constant

The current of a semiconductor diode is expressed as

(a)

(b) I_o, KT

(c)

(d)

The dynamic resistance of a diode is expressed as

(a)

(b)

(c)

Potential barrier for Ge p-n homojunction is

(a) 0.2 V

(b) 0.02 V

(c) 0.7 V

Potential barrier across Si diode is

(a) 0.2 V

(b) 0.7 V

(c) 1 V

The voltage drop across an ideal diode is

(a) 0.2 V

(b) 0.7 V

(c) 0 V

Resistance of an ideal diode is

(a) very large

(b) zero

(c) small.

The current flow in a diode is

(a) unidirectional

(b) bi-directional

(c) none of these

Diode is a

(a) polar sensitive device

(b) non-polar sensitive device

(c) bipolar sensitive device

Diodes can be used as

(a) amplifier

(b) rectifier

(c) filter

V-I characteristics of diode can result in

(a) static resistance only

(b) dynamic resistance only

(c) none of these

Diffusion current in a p-n homojunction is influenced

(a) by concentration gradient of carriers

(b) applied voltage

(c) concentration of carriers

Drift current is influenced by

(a) magnitude of voltage

(b) concentration of carriers

(c) concentration gradient of carriers

Increasing reverse bias

(a) decreases the homojunction capacitor

(b) increases the homojunction capacitor

(c) has no effect on its capacitor

Homojunction capacitance is related with barrier potential as

(a) C = KV^−1/2

(b) C = KV^1/2

(c) C = KV

(d)

Reverse break down in p-n homojunction at high temperature occurs

(a) at higher reverse bias

(b) at lower reverse bias

(c) at forward bias

The reverse saturation current I_co of Si diode varies as

(a) T²

(b) T³

(c) T^1/2

(d) T^3/2

Schottky diode is

(a) a p-n homojunction device formed by using two-different semiconductors

(b) a metal semiconductor device formed by using materials of opposite work functions

(c) a device consisting of a semiconductor and a noble metal

(d) an ordinary point contact diode

If the reverse bias applied across a step p-n homojunction diode is increased four-times, then the depletion layer capacitance of the diode becomes

(a) half

(b) double

(c) one-third

(d) one-fourth

A Schottky diode has

(a) a larger voltage drop than that of an ordinary diode

(b) good ohmic resistance

(c) a negligible storage time

(d) mainly minority carrier current

The ECL gates are basically meant for

(a) low power

(b) high power

(c) high speed

(d) high voltage

In a p-n homojunction diode

(a) the depletion capacitance increases with increase in the reverse bias

(b) the depletion capacitance decreases with dicrease in the reverse bias

(c) the diffusion capacitance increases with increase in the forward bias

(d) the diffusion capacitance is much higher than depletion capacitance when forward biased