Lecture8-P-N+Junction+1 - ECE 3040: Microelectronic...

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ECE 3040 - Dr. Ying Zhang Georgia Tech ECE 3040: Microelectronic Circuits Lecture 8 Reading: Pierret 5.1-5.2
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ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture Photogeneration Each Photon with energy greater than Eg can result in one electron hole pair. () Sec cm e G x G where x G t p t n x LO L L Light Light = = = 3 # ) , ( ) , ( α λ G L is the photogeneration rate. In working problems, we often use one of two simplifying assumptions: ¾ The illumination is assumed to be uniform everywhere inside the sample. The light is being uniformly absorbed, and the generation profile can be approximately constant. ¾ The light is assumed to be absorbed in an infinitesimally thin layer near the semiconductor surface (surface absorption).
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ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture Indirect Recombination-Generation under Low-Level Injection ¾ Net rate of change in minority carrier concentration when material relaxes back to its equilibrium state: ¾ Introduce time constants, then Where, τ p and τ n are minority carrier lifetime; c p and c n are the hole and electron capture coefficients; N T is the concentration of R-G centers. p G R thermal p t p τ Δ = n G R thermal n t n Δ =
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ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture Continuity Equations ... , Re ... , Re etc light as such processes other All Generation n combinatio thermal Diffusion Drift etc light as such processes other All Generation n combinatio thermal Diffusion Drift t p t p t p t p t p t n t n t n t n t n + + + = + + + = There must be spatial and time continuity in the carrier concentrations ... , Re ... , Re 1 1 etc light as such processes other All Generation n combinatio thermal P etc light as such processes other All Generation n combinatio thermal N t p t p J q t p t n t n J q t n + + = + + =
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ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture Minority Carrier Diffusion Equation Simplifying Assumptions: 1) One dimensional case. We will use “x”. 2) We will only consider minority carriers 3) Electric field is approximately zero in regions subject to analysis (E 0). 4) The minority carrier concentrations IN EQUILIBRIUM are not a function of position. 5)
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This note was uploaded on 09/05/2009 for the course ECE 3040 taught by Professor Hamblen during the Spring '07 term at Georgia Institute of Technology.

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Lecture8-P-N+Junction+1 - ECE 3040: Microelectronic...

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