Higher Physics - Unit 3 - Semiconductors Introduction

I created my own revision notes for all units of the Higher Physics course.

These are revision notes for part of the 3rd unit (Radiation and Matter), section 3 (Optoelectronics and Semi-conductors). I've uploaded all the subsections of this section in different files as they are otherwise too large.

Semiconductors Introduction covers:
• Examples of conductors, semiconductors and insulators
• Semiconductors and resistance
• Doping meaning
• Semiconductor and electrons
• n-type semiconductor
• p-type semiconductor

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  • Created by: Visser
  • Created on: 08-05-10 16:38
Preview of Higher Physics - Unit 3 - Semiconductors Introduction

First 314 words of the document:

SEMICONDUCTORS
Materials can be placed into three groups according to their electrical resistance:
CONDUCTORS: silver, copper, iron, graphite
SEMICONDUCTORS: silicon, germanium, gallium arsenide, indium antimonide
INSULATORS: wood, paper, plastic
Insulators and pure semiconductors have a very high resistance, while conductors have a very low resistance. The addition of
heat, light or a voltage to pure semiconductors causes a few electrons to escape from their atoms, leaving behind `holes'. This
decreases the resistance and a small current can exist.
DOPING: the deliberate addition of impurities into a semiconductor decreases its resistance.
SEMICONDUCTOR
Semiconductor materials have four electrons in their outer shells.
Each atom forms four covalent bonds to four other atoms.
N- TYPE SEMICONDUCTOR
The pure semiconductor with four electrons in its outer shell is doped with an
impurity with five electrons in its outer shell. Four of the electrons in the outer
shell of the impurity are `used up' in bonding with the surrounding atoms, but
the FIFTH ELECTRON IS A FREE CHARGE CARRIER.
N-TYPE MATERIAL: the majority of the free charge carriers are negative
The pure semiconductor and impurity are both electrically neutral; the n-type material is also ELECTRICALLY NEUTRAL.
P- TYPE SEMICONDUCTOR
The pure semiconductor with four electrons in its outer shell is doped with an
impurity with three electrons in its outer shell. The three electrons of the
impurity are `used up' in bonding with the surrounding atoms and there is A `HOLE'
WHERE THE `MISSING' ELECTRON SHOULD BE.
P-TYPE MATERIAL: the majority of the free charge carriers are positive
The resistance of the semiconductor is reduced because there are free charge carriers.
The pure semiconductor and impurities are both electrically neutral so the n-type and p-type materials are also
ELECTRICALLY NEUTRAL.

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