Question

Select the CORRECT statement(s) regarding semiconductor devices.

• A. Electrons and holes are of equal density in an intrinsic semiconductor at equilibrium.
• B. Collector region is generally more heavily doped than Base region in a BJT.
• C. Total current is spatially constant in a two terminal electronic device in dark under steady state condition.
• D. Mobility of electrons always increases with temperature in Silicon beyond 300 K.

Hint:

In steady-state semiconductor operation, total current is always position-independent. Also, intrinsic semiconductors always satisfy $n=p$ at equilibrium.

Answer 1

The Correct Option is A, C

Statement (A): True
In an intrinsic semiconductor at equilibrium, the electron concentration $n$ equals the hole concentration $p$, i.e., \[ n = p = n_i. \] Thus electrons and holes have equal density. Statement (B): False
In a BJT:
- The Emitter is the most heavily doped.
- The Base is lightly doped.
- The Collector is moderately doped (lighter than emitter).
Hence the collector is not more heavily doped than the base.
Statement (C): True
In steady state and in the dark (no photogeneration), for any two-terminal semiconductor device, the total current \[ J_{\text{total}} = J_n + J_p \] is spatially constant because charge cannot accumulate anywhere inside in steady state. This follows from \[ \frac{\partial \rho}{\partial t} = 0 \quad \Rightarrow \quad \nabla \cdot J = 0. \] Statement (D): False
In silicon, electron mobility decreases with temperature above 300 K due to increased phonon scattering. It does not increase. Final Answer: (A) and (C)