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Electricity and Electronics > Introduction to Semiconductors and Diodes > Flashcards

Introduction to Semiconductors and Diodes Flashcards

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1
Q

How can materials be classified?

A

Conductors, semi = conductors or insulators

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2
Q

What happens to semi conductors, as temperature increases?

A

The resisitivity is reduced and ultimately to a point where they become effectively conductors

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3
Q

What happens is the valence shell of an atom doesnt have its full complement of electrons?

A

The electrons can be easily detached from their orbital bonds, and the material has properties associated with an electrical conductor

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4
Q

What is silicon considered in its pure state

A

Insulator

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5
Q

Examples of semiconductors

A

Silicon and Germanium

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6
Q

What does doping refer to?

A

The addition of small number of foreign atoms(impurities) to modulate its electrical properties

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7
Q

Negative (N-type) semiconductor

A

Doped with an impurity that has has 5 electrons in its vallence shell, resulting in an excess of free electrons

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8
Q

Positive type (p-type) semiconductor

A

Doped with an impurity that has 3 valence electrons, resulting in “hole” (absence of electrons) that can conduct current

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9
Q

Why can the holes conduct current?

A

Because they can accept electrons from adjacent atoms, effectively moving the “hole” over to the next atom. Thus a positive current of “moving holes” is produced

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10
Q

Effects of n-type or p-type conductor

A

Convert a good insulator into a viable conductor

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11
Q

What is a diode

A

A two-terminal device, having an anode and cathode terminal

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12
Q

Silicon diode

A

Allows current flow im one direction (forward bias) and blocks in the other (reverse bias).

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13
Q

What is a common use of a silicon diode?

A

Rectifier

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14
Q

What is the defining charcateristic of a diode?

A

-low resistance to current flow in one direction(the forward direction)
-high resistance in the other

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15
Q

What is the main process used to change the conductivity of semiconductors

A

Doping

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16
Q

What is a p-n junction?

A

Piece of semiconductor material in which part of the material is p-type and the other is n-type

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17
Q

When do we assume that a hole is a positive charge carrier and an electron is a negative charge carrier?

A

p-n junction of semiconductor material

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18
Q

How does the presence of p-type semiconductor contribute to current flow

A

Holes in a p-type semiconductor act as positive charge carriers. When electrons move to fill these holes, it creates the effect of current flow, as the movement of holes can be seen as a positive charge moving through the material.

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19
Q

Transfer characteristic

A

Describes how the output of an electronic component or circuit changes in response to its input

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20
Q

How to generate a steady DC output

A

Add a capacitor to the basic rectifier

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21
Q

Zener diodes

A

conduct in the forward direction and also conducts readily in reverse bias when the reverse voltage reaches a critical value called the breakdown voltage.Used as voltage regulator

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22
Q

Led

A

Light-emitting diode.Emit light os a specific colour when current flows through them.Used as indicator.

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23
Q

Application of Half-wave rectifier

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A

Converts AC into DC

24
Q

Breakdown voltage

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A

Voltage at which Zener diode conducts in reverse bias.

25
Application of zener diode
Voltage regulation
26
Forward bias
The positive terminal of a battery is connected to the p-type side, and the negative terminal is connected to the n-type side.This allows current flow
27
Reverse bias
The positive terminal of a battery is connected to the n-type side, and the negative terminal is connected to the p-type side.This blocks current flow.
28
Role of capacitor in half-wave rectifier
Smooths the output voltage.Charging during the positive half-cycle and discharging during the negative half-cycle, providing a more continuous DC output.
29
Colour of LEDs
Depends on the composition of the semiconductor material
30
Mechanical based switch
Two-state device, which offers huge electrical resistance in one state and zero in the other
31
Classes of transistor
bipolar and field effective
32
What role do diodes play in protecting components in DC circuits?
Diodes protect components in DC circuits by allowing current to flow in one direction while blocking it in the reverse direction. This prevents damage from reverse voltage spikes. Zener diodes can also regulate voltage, ensuring stable operation of sensitive components.
33
Transistor
Three terminal devices that can perform two functions and are fundamental to electronic systems- amplification and switching
34
Regions of transistors
collector, base, emitter
35
Base
A thin region of the transistor that controls the current flow between the collector and the emitter
36
Collector
The terminal where the majority of the current flows out of the transistor
37
Emitter
The terminal where the majority of the current flows into the transistor
38
Relation Ie
Ib+Ic
39
Current gain
Ic/Ib
40
How does the movement of holes in a p-type semiconductor differ from the movement of electrons in an n-type semiconductor?
In a p-type semiconductor, holes represent the absence of electrons and move through the lattice as electrons from neighboring atoms fill these vacancies, effectively creating a positive charge movement. Conversely, in an n-type semiconductor, free electrons move randomly and can drift towards a positive electrode when an electric field is applied, contributing to current flow.
41
Discuss the concept of a junction diode and its operational principles.
A junction diode is formed by joining p-type and n-type semiconductors, creating a depletion layer at the junction where charge carriers recombine. This structure allows current to flow easily in one direction (forward bias) while blocking it in the opposite direction (reverse bias), making it essential for rectification in electronic circuits.
42
What factors influence the conductivity of a semiconductor, and how does temperature play a role?
The conductivity of a semiconductor is influenced by the type and concentration of dopants, as well as temperature. As temperature increases, more electrons gain sufficient energy to break free from their covalent bonds, increasing the number of charge carriers and thus enhancing conductivity.
43
Depletion layer
The region at both sides of a p-n junction in which there are no holes or free electrons, i.e. theres is no charge carriers in this region. It thus behaves as an insulator
44
Applications of rectifiers
-Driving d.c. motor from a.c. mains -Production of direct-voltage supplies for electronic amplifiers
45
Rectification
The process of obtaining unidirectional current and voltages from alternating currents and voltages
46
Describe voltage in diodes when in forward bias
When the voltage is in forward direction, there is no voltage drop across the diode and current flows unimpeded
47
Describe voltage in diodes when in reverse bias
When the applied voltage acts in reverse direction, a voltage drop appears across the diode and no current flows
48
Base resistor
Protects the transistor from excessive currents
49
Off region
-Between 0 and 0.7V -No base current flows -No collector current flows -The load voltage aprox 0V -Vout aprox 12 V -The transistor is switched off
50
Linear region
-Base current starts to flow -Large collector current flows through the load -Voltage across theload increases so Vout decreases
51
On or saturation region
-Vin increases as vout decreases -The collector current reaches a maximum value,and further changes to Vin have no effect -The transistor is saturated -Load voltage is less than power supply voltage -Vout around 0.2V
52
Why should the linear region be avoided, when the transistor operates as a switch
-The load will not have the full supply voltage across it -Vce is not zero and neither is Ic, meaning that power is disspated in the collector-emitter junction, which can cause the transistor to overheat
53
Vin<0.7V
-Vbe=Vin -Vce=Vs(supply voltage
54
Vin>0.7V
-Vbe=0.7V -Vce=0V
55
How can the transistor produce gain?
By collecting a load effectively between the collector and the common terminal
56
How do half wave rectifiers work?
Each time the supply voltage goes through its positive cycle, it will charge the capacitor to almost its peak value. When the supply reverses, the capacitor will discharge, mantaining the flow of current through the load resistor

Electricity and Electronics (5 decks)

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