ECE 874: Physical Electronics
This lecture by Prof. Virginia Ayres at Michigan State University explores the principles of recombination and generation processes, particularly in reverse-biased pn junctions. It addresses the effects of light on depletion regions and the mechanisms influencing electron and hole concentrations. The lecture also covers the fundamentals of drift and diffusion currents, equating drift and diffusion with changing charge carrier concentrations. Key equations and problem-solving strategies are presented for enhanced understanding of charge transport phenomena in semiconductor materials.
ECE 874: Physical Electronics
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Presentation Transcript
ECE 874:Physical Electronics Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University ayresv@msu.edu
Lecture 26, 27 Nov 12Chp. 05: Recombination-Generation Processes VM Ayres, ECE874, F12
baseline situation W VM Ayres, ECE874, F12
Reverse biassed pn junction: • Ideally in depletion region W: p = n = 0 • (always do have thermally generated ni/pi but internal field E in W continuously sweeps them out) VM Ayres, ECE874, F12
New stuff in the picture: the effect of light VM Ayres, ECE874, F12
Effect of shining light on reverse biassed pn junction: • In depletion region W: p = n ≠ 0 • In depletion region W: p = n = large • In depletion region W: VM Ayres, ECE874, F12
xpp VM Ayres, ECE874, F12
Lecture 26, 27 Nov 12Chp. 06: Currents VM Ayres, ECE874, F12
General assuming capture/emission coefficients don’t change much from equilibrium values: Steady state: (5.24) Equilibrium: 0 VM Ayres, ECE874, F12
Now include the ordinary mechanisms that can change n and p:drift currents and diffusion currents And anything else! drift diffusion VM Ayres, ECE874, F12
Now include the ordinary mechanisms that can change n and p:drift currents and diffusion currents And anything else! VM Ayres, ECE874, F12
Now include the ordinary mechanisms that can change n and p:drift currents and diffusion currents And anything else! 6.1: review of drift 6.2: review of diffusion 6.3: list of equations for dn/dt, dp/dt and J’s – no new material VM Ayres, ECE874, F12
Hw06 Prs. 6.3 and 6.4: Diffusion: diff diff A diffusion current happens anytime you have a spatial variation in the concentrations of n or p VM Ayres, ECE874, F12
Example problem: from Pr. 6.4: Put a red box around any region where n-type ness changes: dn/dx Put a blue box around any region where p-type ness changes: dp/dx -L -L/2 0 L/2 L VM Ayres, ECE874, F12
Example problem: from Pr. 6.4: Put a red box around any region where n-type ness changes: dn/dx Put a blue box around any region where p-type ness changes: dp/dx -L -L/2 0 L/2 L VM Ayres, ECE874, F12
Example problem: from Pr. 6.4: hole VM Ayres, ECE874, F12 -L -L/2 0 L/2 L
