Semiconductors

Question 1

Semiconductor

Answer 1

A material thats resistivity as between that of a good conductor and a good insulator (silicone , germanium)

Question 2

When temperature increases in a semiconductor

Answer 2

Resistance decreases current increases

Question 3

Holes

Answer 3

An electron breaks free from covalent bond and leaves a gap in the atom

Question 4

Intrinsic conduction

Answer 4

Is the movement of charges through a pure semiconductor with equal number of electrons and holes

Question 5

Movement of electrons and holes in a semiconductor material in series

Answer 5

Negative electrons flow towards positive battery
positive flow twords negative battery

Question 6

Thermistor

Answer 6

An electrical component whose resistance decreases rapidly with increasing temperature

Question 7

LDR ( light dependant resistor)

Answer 7

Electrical component whose resistance decreases rapidly when light shines on it

Question 8

Doping

Answer 8

The addition of a small amount of atoms of another element into a semiconductor to increase its conductivity

Question 9

Extrinsic conduction

Answer 9

The movement of charges through a doped semiconductor with an unequal amount of electrons and holes

Question 10

N-type semiconductor

Answer 10

A semiconductor in which electrons are the majority charge carriers ( in this case a phosphorus atom has been doped into the semiconductor and with each extra atom introduces an extra atom for conduction)

Question 11

P-type semiconductor

Answer 11

A semiconductor in which holes are the majority charge carriers ( in this case the boron atom has been doped into the semiconductor and now there is an electron missing creating an extra hole)

Question 12

P-N junction

Answer 12

The junction ( when p-type and n-type attach )between the p-type and the n-type layers is referred to as the p-n junction

Question 13

Depletion layer

Answer 13

The region between the p-n junction that contains no free majority charge carriers ( they cancel out and they behave as insulators )

Question 14

The depletion region ( diffusion)

Answer 14

1.Due to thermal agitation free electrons in n-type diffuse over to p-type and combine with nearby positive holes and result in the region being depleted of two charge carriers
2.some p-type holes diffuse over to ntype materials and combine electrons resulting in two less charge carriers

Question 15

Depletion region result

Answer 15

After p-type and n-type exchange holes and electrons the depletion region is formed this causes there to be no free charge carriers resulting in the material insulating (work now needs to be done to bring charge from one side of the depletion region to another ) therefore a p.d exists

Question 16

Forward biased P-N junction (in series)

Answer 16

Positve terminal connected to p-type
Negative terminal connected to n-type
( width of depletion region reduces )
(Electrons are repelled from negative terminal and drive into depletion region)
(Positive holes are repelled into depletion region )
(If the voltage across terminals is greater than the junction voltage the depletion layer is broken down and the region becomes a conductor)

Question 17

Reversed - biased p-n junction

Answer 17

Positive terminal connected to n-type
Negative terminal connected to p-type
(Electrons now attract to positive terminals )
(Positive holes are attracted to negative terminals)
(Depletion region grows bigger )
(Depletion layer is increased )
(No charges actually move through the depletion region , remains an insulator )

Question 18

Current flow in a forward biased p-n junction

Answer 18

Comducts current

Question 19

Current flow in reverse biased p-n junction

Answer 19

Does not conduct current

Question 20

Applications of p-n junction

Answer 20

Electronic systems , leds, computers converts ac to dc

Question 21

A semiconductor diode

Answer 21

Only allows current to flow in one direction

Question 22

Diodes

Answer 22

When placed in series with a semiconductor and light bulb when switch is closed the it is forward biased when it is put in the other way round then it is reversed bias

Question 23

LED

Answer 23

Consists of junction diode made from semiconducting material

Light is emitted when it is forward biased and brightness is aproximately proportional to the forward current