ELEX 4 Semiconductor Theory and Diodes

In a silicon crystal, covalent bonding is primarily formed through the sharing of how many valence electrons per atom?

4

The forbidden energy gap of a semiconductor refers to the energy required to move an electron from the:

Valence band to the conduction band

Which material exhibits a negative temperature coefficient of resistance?

Germanium

At absolute zero temperature, an intrinsic semiconductor behaves as a:

Perfect insulator

In an N-type semiconductor, the majority carriers are:

Electrons

Which impurity atom is commonly used to create a P-type silicon semiconductor?

Boron

The primary reason silicon is preferred over germanium in most electronic devices is because silicon:

Has better thermal stability

When a PN junction is formed, electrons diffuse from the N-side to the P-side mainly because of:

Carrier concentration gradient

The immobile ions left behind near a PN junction form the:

Depletion region

Under forward bias, the depletion region of a diode:

Narrows

A silicon diode typically begins conducting heavily at approximately:

0.7 V

A germanium diode has a barrier potential closest to:

0.3 V

In reverse bias, the diode current is primarily due to:

Minority carriers

Which current in a semiconductor is caused by charge carriers moving because of an electric field?

Drift current

Diffusion current is directly caused by:

Carrier concentration gradient

If the temperature of a silicon diode increases, its reverse saturation current will:

Increase rapidly

The reverse saturation current of a diode approximately:

Doubles for every 10°C rise

The thermal voltage VT at room temperature is approximately:

26 mV

In the Shockley diode equation, the ideality factor η for germanium is usually:

1

Determine the diode current of a silicon diode with IS=20 n, VD=0.65 V, η = 2 at room temperature.

5.37 mA

The conductivity of a semiconductor depends primarily on:

Charge carrier concentration

Which statement about intrinsic semiconductors is correct?

Electron concentration equals hole concentration

A diode operating in the reverse breakdown region may still function safely provided:

The current is externally limited

Zener breakdown usually occurs in:

Heavily doped PN junctions

Avalanche breakdown is primarily caused by:

Impact ionization

Which diode is specifically designed to operate in the reverse breakdown region?

Zener diode

A Schottky diode differs from an ordinary PN junction diode because it uses:

A metal-semiconductor junction

The main advantage of a Schottky diode is its:

Fast switching speed

Which diode is commonly used as a voltage-variable capacitor?

Varactor diode

The diode known for negative resistance characteristics is the:

Tunnel diode

Which device converts light energy directly into electrical current?

Photodiode

An LED emits light because of:

Electron-hole recombination

A half-wave rectifier ideally utilizes what percentage of the AC input cycle?

50%

The maximum theoretical efficiency of a half-wave rectifier is approximately:

40.6%

The primary advantage of a full-wave rectifier over a half-wave rectifier is:

Higher rectification efficiency

A bridge rectifier requires how many diodes?

4

In a bridge rectifier, the peak inverse voltage requirement per diode is approximately:

Half that of a center-tapped full-wave rectifier

The ripple frequency of a full-wave rectifier supplied by a 60 Hz source is:

120 Hz

A capacitor filter in a rectifier circuit primarily functions to:

Reduce ripple voltage

Increasing the filter capacitance in a rectifier generally causes the ripple voltage to:

Decrease

A clipper circuit is mainly used to:

Remove portions of a waveform

A clamper circuit changes the:

DC level of the waveform

In an ideal diode model, a forward-biased diode behaves as a:

Short circuit

In the piecewise linear diode model, the diode after cut-in voltage is approximated as:

Voltage source with small resistance

Determine the output DC voltage of an ideal half-wave rectifier supplied by a sinusoidal input with peak voltage of 20 V.

6.37 V

A silicon diode has a threshold voltage of 0.7 V at 25°C. If the temperature rises to 75°C, the approximate threshold voltage becomes:

0.60 V

Which statement best describes majority carriers in a P-type semiconductor?

Holes introduced by acceptor atoms

In reverse bias, the electric field across the depletion region:

Increases

A diode with an open-circuit failure will most likely cause a rectifier circuit to:

Produce little or no output voltage

A 12 V RMS transformer feeds an ideal bridge rectifier with capacitor filter. The approximate peak DC voltage across the filter capacitor is:

16.97 V