Concerning drift and diffusion as the driving forces for carrier motion, ,which of the following statement is correct

Question

BlackTom AI · Accepted Answer

Starting from the physical picture of drift and diffusion in semiconductors, we consider how electric fields and concentration gradients drive carrier motion.
Option 1: 'Drift is the dominant mechanism for both majority and minority carrier currents.' This ignores the role of concentration gradients that cause diffusion, especially for minority carriers where gradients are typically strong, so this statement is overly simplistic and incorrect.
Option 2: 'Diffusion is the dominant mechanism for both majority and minority carrier currents.' In a biased semiconductor, majority carriers are strongly pushed by the electric field (drift) and contribute most to current through drift, so diffusion cannot be the sole dominant process for both types. This option misstates the balance between drift and diffusion.
Option 3: 'Drift is the dominant mechanism for the majority carrier current and diffusion is the dominant mechanism for the minority carrier current.' This captures the standard understanding: majority carriers respond primarily to the electric field via drift, while minority carriers, often present in lower concentration, diffuse down their concentration gradients, making diffusion the main transport mechanism for them in many contexts. It aligns with the typical drift-diffusion framework in semiconductors.
Option 4: 'Diffusion is the dominant mechanism for the majority carrier current and drift is the dominant mechanism for the minority carrier current.' This reverses the conventional roles of drift and diffusion for majority and minority carriers and contradicts the common physical intuition and established models, making it incorrect.
In summary, the core concept is that drift dominates for majority carriers due to the applied electric field, whereas diffusion plays the key role for minority carriers because their transport is largely governed by concentration gradients. The remaining options either ignore the field-driven drift effect or misattribute the dominant mechanism to both carrier types.

EESM5200 (L2) Part I: Topic 6 - Carrier Actions in a PN Junction

Concerning drift and diffusion as the driving forces for carrier motion, ,which of the following statement is correct

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