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Diffusion Presentation Transcript
1.DIFFUSION
2.What is Diffusion? It is the process by which atoms move in a crystal lattice. Goal – study diffusion of impurity atoms.
3.The nature of diffusion The wandering of an impurity atom in a lattice takes place in a series of random jumps. in all the three dimensions, a flux of diffusing species results if there is a conc. Gradient. additionally temperature, crystal structure and defect conc. ? important for the process.
4.What do we want to do and what should we know? We want to produce a p-n junction at the desired depth Desired dopant profile in the diffused region For this we should know Type of diffusion Temperature of diffusion Time for diffusion
5.Diffusion Systems Tube Open tube Sealed tube Diffusion source Solid Liquid Gaseous
6.Mechanism of diffusion Interstitial Diffusion Substitutional Diffusion Laws of Diffusion
7.Fick’s First Law Fick’s First Law states that particles diffuse from a higher conc. to a lower conc. The flux density is proportional to the conc. Gradient. Proof of Fick’s First Law
8.The net flux of atoms F* is leaving layer 1 for layer 2 is then
9.Need for second expression
10.The Continuity Equation and Fick’s Second Law
11.Solution of Fick’s Law
12.Assumptions in Fick’s Law
13.Corrections to the Simple Theory
14.Corrections to the Simple Theory
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