3.4 SEMICONDUCTOR AND P-N JUNCTION

Question 1

electrical property(властивості) of material

Conductors

Answer 1

materials with many free electrons. These electrons can easily be made to flow through the material

examples: all metals, semi-metals like carbon-graphite, antimony, arsenic

Question 2

electrical property of material

Insulator

Answer 2

materials that have a very few free electrons

examples: plastic, glass, wood

Question 3

electrical property of material

Semiconductors

Answer 3

materials that behave like** insulators when pure**, but will conduct when an impurity(домішки) is added and/or in response to light, heat, voltage
examples: elements:silicon, germanium
compounds: gallium arsenide

Question 4

In an isolated atom

Answer 4

the electron occupy discrete energy levels

Question 5

band theory

Answer 5

https://i.pinimg.com/originals/4b/ea/3f/4bea3f03e999d4b4d20c8206b52a8c56.jpg

Question 6

band gap is

Answer 6

is the range in a solid where no electron state can exist.

Question 7

fermi level is

Answer 7

the maximum permitted energy an electron in a specific structure can possibly have at temperature 0

Question 8

Conductor’s structure

Answer 8

the highest occupied energy band is only partially fillled (conduction (top) band). There are many empty levels available close to the occupied levels for the electrons to move into.
Electrons can flow easily from one atom to another

Question 9

Insulator’s structure

Answer 9

the highest occupied band is completely full of electrons (valence band(bottom)). There is NO electrons in the conduction band. And there is a band gap which so large and electons almost never cross it

Question 10

Semiconductor’s structure

Answer 10

Valence band is completely** full**, but the band gap is small. Due to temerature the electrons can jump the gap
Increasing temperature increasing the number of electrons in conduction band

Question 11

Bonding in Semiconductor

Answer 11

the most common materials are silicon and germanium, which have 4 valency
Therefore there are a few free electrons aviable to conduct
these semiconductors have a large resistance

Question 12

A positive hole is

Answer 12

a lack of electron/ free space, which is positively charged, when electron leaves its position in the crystal lattice
BUT
In an intrinsic (внутрішній) semiconductor, the number of holes is equal to the number of electrons which causes the small currentof drifting electrons

Question 13

Doping is

Answer 13

the conductivity of pure (intrinsic) semiconductors which can be improved by the addition of imparities during manufacture

Question 14

n-type has

Answer 14

As arsenic nucleus with extra free electon (‘negative’)

Question 15

p-type has

Answer 15

In indium nucleus with additional hole (‘positive’)

Question 16

how doping affects band structure

Answer 16

students’ notes p27

https://th.bing.com/th/id/OIP.g5qXs7uBPwQX43w4ePIBaAHaDC?pid=ImgDet&rs=1

Question 17

p-n junction (it functions as diode)

Answer 17

https://www.mksinst.com/mam/celum/celum_assets/Figure_8-Semiconductor_Handbook_800w.jpg

https://4.bp.blogspot.com/-KW29JLAHhxQ/W-lO79Hxm1I/AAAAAAAABvQ/99nkXracKds-YqjtIIxgUEj3pOT7Rq5GACLcBGAs/w1200-h630-p-k-no-nu/PN-Junction%2BDiode%2BSymbol.png

Question 18

the DONOR LEVEL is

Answer 18

an isolated energy level in the band gap with free electrons in n-type
where fermi level is raised

Question 19

the ACCEPTOR LEVEL is

Answer 19

an isolated energy level in the band gap in p-type with free holes
whrere fermi level is lowered to just below this energy

Question 20

biasing the diode

Answer 20

1. Forward-biased (cell connected: positive to p-type, negative to n-type) comforable to use, big current
2. Reverse-biased (opposite) very small current, very big, ‘high’ deplation layer where it is difficult to electrons to move ‘uphills’

Question 21

dapletion layer has

Answer 21

no free charged carries

Question 22

the PHOTODIODE

Answer 22

a p-n junction in a transparent coating will react to light
Can be used in two modes:
1. Photovoltaic mode
2. Photoconductive mode
https://learningaboutelectronics.com/images/photodiodesymbol.png

Question 23

Photovoltaic mode

Answer 23

has NO bias voltage
using more incident light (more photons incident per second)
The **voltage **generated is propotional to the light intensity
many photodiodes connected together form the basis of solar cells

Question 24

PHOTOCONDUCTIVE MODE

Answer 24

has reverse bias
in the dark DIODE DOESN’T conduct
A greater intensity of light will lead to more free charge carries and **less resistance **
Acts as a light dependant resistor (LDR)