The drain current density including both drift and diffusion component is given by:

91. The drain current density including both drift and diffusion component is given by:

[Question ID = 799][Question Description = S2_qSNz_PG_ETS_Q91]

1. qμ_n·nE_y − qD_n∇n [Option ID = 3193]

2. qnE_y + qD_n∇n [Option ID = 3194]

3. qnμ_n + qD_n∇n [Option ID = 3195]

4. qμ_n·nE_y + qD_n∇n [Option ID = 3196]

Answer :- 4

Solution

Drift Current: Drift current is caused by electric fields. The direction of the drift current is always in the direction of the electric field. The drift current density is given by

J_drift = σE, where σ = Conductivity = qnμ_n

Hence, J_drift = qnμ_nE

Diffusion Current: Diffusion current is caused by variation in the carrier concentration and it's direction is from a higher concentration region to a lower concentration region.

For electrons, J_diffusion = +qD_n

dn(x) /dx

= +qD_nΔ_n

For holes, J_diffusion = −qD_p

dp(x)/ dx

= −qD_pΔ_p

Solution:

The drain current density including both drift and diffusion component is given by

J = J_drift + J_diffusion

J = qnμ_nE_y + qD_nΔ_n

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