Intrinsic semiconductors at room temperature: The electrical current in an intrinsic semiconductor is primarily due to which carriers?

Introduction / Context:
Intrinsic semiconductors such as pure silicon or germanium have no intentional dopants. Thermal energy at room temperature excites electrons across the band gap, generating free electrons in the conduction band and holes in the valence band in equal numbers. Device physics and conductivity calculations rely on understanding these carriers.

Given Data / Assumptions:

• Material is undoped (intrinsic) at room temperature.
• Steady-state thermal equilibrium with intrinsic carrier concentration n_i.
• No ionic conduction in the solid lattice.

Concept / Approach:

Thermal generation produces electron–hole pairs (EHPs). In intrinsic material, n = p = n_i. Electrical conduction occurs because electrons and holes drift under electric fields and diffuse down concentration gradients; both contribute to total current density J = q(n μ_n + p μ_p)E + diffusion terms. Ions in the crystal lattice are fixed and do not partake in conduction.

Step-by-Step Solution:

Verification / Alternative check:

Hall effect measurements in intrinsic samples reflect the combined contribution of both carriers and often show temperature dependence consistent with n_i(T).

Why Other Options Are Wrong:

• “Holes” or “electrons” alone describes doped (extrinsic) conditions where one type dominates.
• “Ions” do not move in a rigid semiconductor lattice at room temperature.
• “Excitons only” are bound states; conduction requires free carriers.

Common Pitfalls:

• Assuming one carrier dominates in intrinsic material; that occurs after doping.

Final Answer:

holes and electrons