For an intrinsic (pure) semiconductor at room temperature, which processes are simultaneously present at any given time?

Introduction / Context:
Intrinsic semiconductors (e.g., pure silicon) contain equal concentrations of electrons and holes generated thermally. Even without doping, carriers are constantly being created and annihilated, and they move under the influence of thermal energy and fields. Recognizing this dynamic equilibrium is essential for understanding diode and transistor behavior.

Given Data / Assumptions:

• Intrinsic semiconductor at room temperature (approximately 300 K).
• No external doping; n = p (electron and hole concentrations are equal).
• Thermal generation and recombination are continuous processes.

Concept / Approach:
Carrier generation produces electron–hole pairs; recombination annihilates them. In equilibrium, the rates of generation and recombination balance, but both processes are ongoing. In the absence of an external field, random thermal motion dominates; with an applied field, carriers also experience drift superimposed on random motion.

Step-by-Step Explanation:
Thermal energy → creation of electron–hole pairs (holes are created).Existing electrons and holes recombine (recombination occurs).Even without bias, carriers undergo random motion; with electric fields, drift currents appear.Therefore, all listed phenomena occur simultaneously in intrinsic material.

Verification / Alternative check:
Textbook intrinsic carrier concentration ni for silicon at 300 K (≈ 10^10 cm^-3) implies significant ongoing generation–recombination. Thermal agitation ensures random carrier movement even in equilibrium.

Why Other Options Are Wrong:

• Choosing only one process ignores the steady-state balance where all processes coexist.

Common Pitfalls:

• Believing that “equilibrium” means no motion; in fact, it means no net change over time while microscopic motion continues.
• Assuming holes exist only in doped semiconductors; intrinsic materials also have holes.

Final Answer:
All of the above