Carrier generation in semiconductors: Minority carriers in a semiconductor are most frequently activated (generated) by which mechanism under normal conditions?

Introduction / Context:
In semiconductors, ”majority carriers” dominate conduction (electrons in n-type, holes in p-type), while ”minority carriers” exist in much smaller numbers but are crucial for diode and transistor action. Recognizing how minority carriers are generated helps explain leakage current, temperature effects, and PN-junction behavior.

Given Data / Assumptions:

• We consider intrinsic and doped semiconductors at or near equilibrium.
• Thermal energy (lattice temperature) is present.
• External fields or mechanical stress are not dominant unless specified.

Concept / Approach:
Thermal energy excites valence electrons across the bandgap into the conduction band, creating electron–hole pairs. In doped material, doping sets the majority carrier concentration, but minority carriers are still primarily produced by thermal generation and recombination processes. Forward bias of a PN junction injects minority carriers across the junction in operation, but the fundamental ”activation” mechanism that maintains their equilibrium population is thermal generation (heat).

Step-by-Step Solution:

Verification / Alternative check:
Leakage current in reverse-biased diodes grows with temperature, reflecting enhanced thermal generation of carriers. Shockley diode equation and temperature dependence of intrinsic carrier concentration n_i (which increases rapidly with T) support this picture.

Why Other Options Are Wrong:

• Dopants: Establish majority carriers and alter the Fermi level; they do not ”activate” minorities directly.
• Forward bias: Causes injection during conduction, not the fundamental source of equilibrium minority carriers.
• Pressure: Mechanical effects can alter band structure but are not the typical cause cited for minority carrier generation.

Common Pitfalls:
Confusing the operating mechanism of a forward-biased diode (injection) with the equilibrium existence of minority carriers (thermal generation).

Final Answer:
heat