Syllabus Part 66 Module 4.1 (B1.1 Excluded) (B2 – Level 2) Materials, electron configuration, electrical properties; P and N type materials: effects of impurities on conduction, majority and minority characters; PN junction in a semiconductor, development of a potential across a PN junction in unbiased, forward biased & reverse biased conditions;
Comments on Syllabus Although it is not included, however, without knowledge of the semiconductor, a student will not be able to understand how a diode or transistor works. Due to this requirement, the subject is included in the program.
Introduction Modern Electronics ◦ 19th Century – Thomas Edison discovered heated metal emitted charged particles. Led to discovery of thermionic valve. ◦ 1940 – transistor was invented by Bell Laboratories ◦ 1950s’ – development of integrated circuit ◦ 1960s – prediction that the number of transistors in IC would be doubled every 18 months. ◦ 2007 – an advanced IC contained 55 mil transistors
Atomic Structure ◦ 1913 – Bohr – Beginning of the basic theory of atomic structure.
Valence Shell The tendency of atoms to gain or loss electrons depends on the number of electrons in the outmost shell. The outmost shell is known as valence shell and the electrons is known as valence electrons.
Energy Bands x-axis- the allowed energy levels numbered from 1 to 5. The y-axis shows each levels energy in electron volts (eV) One electron volt is the energy that an electron gains when it travels through a potential difference of one volt (1 eV = 1.6 x 10-19 Joules).
Energy in Atoms As in previous slide, the energy level is discreet. Electrons are in either conduction bands or valence band. Materials with large amount of electrons in the conduction bands are good conductor.
Electron Flow Hole FlowDoped with Arsenic Conduction Intrinsic flow – there is no impurities added
Doping Process … A pure silicon or germanium are insulator. It has valence electrons of 4. Adding impurities will change the characteristic of the semiconductor. If elements with 5 valent electrons is added, it will have one electron balance, thus become N-type, negative type with electrons as the current carrier.
… Doping Process If an element with 3 electrons is added, then it will be P-type with holes. P type or positive type will conduct current via holes, similar to the conventional flow of current. Example of impurities for N-types are arsenic and phosphorous. Example of impurities with 3 valent electron and used to manufacture P type semiconductor is boron, gallium and indium.
N-type semiconductor The doping is done by 5 valence electrons – pentavalent impurity. ◦ Example arsenic, antimony, bismuth and phosphorous.
P-Type Semiconductor Doping with impurities with 3 valence electrons or trivalent will produce a P- type semi-conductor. ◦ Example of trivalent materials are – alluminium, indium, gallium, boron ◦ Concept of minor and major carriers.
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