Semiconductors

Question 1

Semiconductor

Answer 1

A semiconductor is a substance whose resistivity is between that of a good conductor and a good insulator. The resistivity of a semiconductor decreases as its temperature increases

Question 2

Holes

Answer 2

When an electron breaks free from a covalent bond, it leaves behind a gap in the atom from which it came. This gap is called a positive hole or simple a hole

Question 3

Intrinsic Conduction

Answer 3

Conduction in a pure semiconductor due to electrons moving from negative to positive and an equal number of holes moving in the opposite direction is called intrinsic conduction. The semiconductor is called an intrinsic conductor

Question 4

The Thermistor

Answer 4

A thermistor is a semiconductor device whose resistance decreases rapidly with increasing temperature

Question 5

A Light Dependent Resistor

Answer 5

A light dependent resistor (LDR) is a semiconductor whose conductivity is increased when light shines on it

Question 6

Doping

Answer 6

The adding of small controlled amounts of certain impurities to a pure semiconductor to increase its conductivity is called doping

Question 7

N-Type Semiconductor

Answer 7

An n-type semiconductor is one in which the impurity added produces more free electrons available for conduction, e.g. phosphorus in silicon

Question 8

P-Type Semiconductor

Answer 8

A p-type semiconductor is a semiconductor in which the impurity added produces extra holes which are available for conduction, e.g. boron in silicon

Question 9

Extrinsic Conduction

Answer 9

Increased conduction in a semiconductor due to the addition of impurities is called extrinsic conduction. The semiconductor formed is called an extrinsic semiconductor

Question 10

P-N Junction

Answer 10

A p-n junction is a piece of semiconductor with part of it doped p-type and the rest doped n-type

Question 11

Depletion Layer

Answer 11

The depletion layer is the region at both sides of a p-n junction that contains no free majority charge carriers. It thus behaves as an insulator

Question 12

Junction Voltage

Answer 12

The p.d. that exists across a p-n junction caused by holes and electrons moving across the junction when it was formed is called the junction voltage

Question 13

P-N Junction Bias

Answer 13

A forward biased p-n junction conducts current

A reverse biased p-n junction does not conduct current