PHYS208 Lecture Thursday 15 th April 2010 P-N-Junction part 1 THE FIRST 18 pages background from previous lectures 4 pages of new lecture calculations with comments PHYS208 - spring 2010 - page 1
For work with P-N junction Exam presentation http://web.ift.uib.no/amos/phys208/text2010/exam_2008_latex/pn_junction_ex_2008.pdf thursday's and following week's text (handwritten notes) http://web.ift.uib.no/amos/phys208/2008/2008_p-n-junction.pdf ( to be used together with the above pn_junction_ex_2008.pdf ) Some of the formalism is nicely discussed also in http://web.ift.uib.no/amos/phys208/text2008/phys208_trygve_slides.pdf THE FIRST 18 pages or so background from previous lectures PHYS208 - spring 2010 - page 2
Electrons and holes When we reverse energy, the holes take the same role as electrons note the sign on µ 2008 SLIDE NOTE PHYS208 - spring 2010 - page 3
Once more about electrons and holes; Ferromagnetic fluid story once more Concept of holes We have discussed one more illustration of holes: BUBBLES PHYS208 - spring 2010 - page 4
COPY OF OLDER NOTE Starting Impurities OLDER NOTE Semiconductors might contain various impurities. However, only the type of impurities discussed below DOPING by controlled impurities of one or other type P or N and the abrupt JUNCTION ( two types of doping in the same crystal structure with a sharp border ) appears to be useful for devices and instruments PHYS208 - spring 2010 - page 5
P N Impurity atoms have 3 valence electrons Acceptor P-type (hole, positive charge carriers) Impurity atoms have 5 valence electrons Donor N-type (electron, negative charge carriers) COPY OF OLDER NOTE PHYS208 - spring 2010 - page 6
The atom-like states of impurities explained; Bohr-like 'atom' relations More details on the following slide from 2008... COPY OF OLDER NOTE PHYS208 - spring 2010 - page 7
Impurity States Donors from 2008 slide PHYS208 - spring 2010 - page 8
Starting P-N junction PHYS208 - spring 2010 - page 9
The following three slides show how the 'acceptor levels' Can be created ABOVE the valence band edge We start by showing how the 'donor levels'are created BELOW the conduction band edge PHYS208 - spring 2010 - page 10
Impurity States - Donors PHYS208 - spring 2010 - page 11
Impurity States - Acceptors PHYS208 - spring 2010 - page 12
Impurity States - Acceptors Acceptor Bound State PHYS208 - spring 2010 - page 13
Do these 'inclined bands' Look strange to you? We have used such picture before! And with a nice explanation - see the following 2 slides Picture from 1954 article on p-n-junction for solar cell Physical Review PHYS208 - spring 2010 - page 14
Do the 'inclined bands'of previous slide look strange to you? We have used such picture before! The forces on electrons Copy is here and a copy of nice explanation on the following slide PHYS208 - spring 2010 - page 15
'inclined bands' The forces on electrons PHYS208 - spring 2010 - page 16
We have discussed one more illustration of holes: BUBBLES Bubbles travel uppwads Stones are falling downwards We have discussed one more illustration of holes: BUBBLES And Helium-filled balloon And thus the whole story of Archimedes law and buoyancy OPPDRIFT (norwegian) Any floating object displaces its own weight of fluid. Archimedes of Syracuse PHYS208 - spring 2010 - page 17
Riddle: Train accellerates. A lamp or rubber ball will hang as shown in the upper picture Helium-filled balloon in the same train: How will it place itself? PHYS208 - spring 2010 - page 18
(A) (B) A related riddle: how fast did you give the answer: A stone is placed on a toy boat. The stone is now moved to the water. What will happen? Result (A) or result (B)? Will the level of water in the container rise or sink? And thus the whole story of Archimedes law and buoyancy OPPDRIFT (norwegian) Any floating object displaces its own weight of fluid. Archimedes of Syracuse PHYS208 - spring 2010 - page 19
Diffusion, Fick's first law of diffusion, conductivity, Ohm's Law, drift velocity, mobility, Equillibrium as cancellation of currents PHYS208 - spring 2010 - page 20
Equillibrium as cancellation of currents; Diffusion caused by gradient of density; what is 'Diffusion constant' D? ELECTRIC FIELD IS GRADIENT OF ELECTROSTATIC POTENTIAL. Evaluate potential difference PHYS208 - spring 2010 - page 21
Einstein Nernst: Diffusion against force related to Boltzmann Use the same equation as before with different aim: Now the Field is known and constant PHYS208 - spring 2010 - page 22
Einstein Nernst: gives us the diffusion constant / mobility relation JUST IN THE FORM needed for the potential difference. PHYS208 - spring 2010 - page 23