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⚛️ Physics  ·  Semiconductor Electronics  ·  NEET & JEE

The diffusion length of minority carriers L = sqrt(D × tau). In short devices (L<sub>device</sub> << L):

Answer: Most carriers reach the junction (low recombination loss).

  • A Most carriers recombine before reaching junction according to conventional understanding
  • B Most carriers reach the junction (low recombination loss)
  • C Diffusion is negligible in routine practice overall
  • D Drift dominates usually in most cases under typical conditions

Correct answer: B. Most carriers reach the junction (low recombination loss)

Explanation: If device length much shorter than diffusion length, minority carriers traverse the base/region with minimal recombination. High efficiency (solar cells, BJT base).

Conductorconduction bandvalence bandbands overlapSemiconductorconduction bandvalence bandsmall gap (~1 eV)Insulatorconduction bandvalence bandlarge gap(> 3 eV)

Conductors have overlapping bands, semiconductors have a small energy gap that can be bridged by heat or doping, and insulators have a large gap that blocks conduction.

Concept context

Band theory, p-n junction, diodes, transistors, logic gates, and integrated circuits.

Read the full Semiconductor Electronics notes →