Question

Which current does not contribute to a uniformly doped semiconductor:

• A. Single-Phase Current
• B. Drift Current
• C. Diffusion Current
• D. Direct Current

Hint:

Associate the two main currents with their driving forces:

\textbf{Drift} \(\rightarrow\) Electric Field (\(E\))
\textbf{Diffusion} \(\rightarrow\) Concentration Gradient (\(dn/dx\))
A "uniformly doped" semiconductor in equilibrium has no E-field and no concentration gradient, so both currents are zero. The question is asking which one doesn't contribute \textit{due to uniformity}, which directly points to diffusion.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question asks which type of current is absent in a uniformly doped semiconductor under thermal equilibrium conditions (i.e., no external fields or gradients).
Step 2: Detailed Explanation:
There are two primary mechanisms for current flow in a semiconductor:


Drift Current: This current is caused by the motion of charge carriers (electrons and holes) under the influence of an applied electric field. In the absence of an electric field, there is no net drift, so the drift current is zero.
Diffusion Current: This current arises from the net motion of charge carriers from a region of high concentration to a region of low concentration. It is driven by a concentration gradient (\(dn/dx\) or \(dp/dx\)).

The problem states the semiconductor is uniformly doped. This means that the concentration of dopant atoms (and therefore the concentration of majority carriers) is the same everywhere throughout the material. In a state of thermal equilibrium, this results in a constant carrier concentration throughout the crystal.
Since there is no concentration gradient (\(dn/dx = 0\) and \(dp/dx = 0\)), there is no driving force for diffusion. Therefore, in a uniformly doped semiconductor at equilibrium, the diffusion current is zero.
Options A and D are types of electrical current in a general sense but not fundamental transport mechanisms within the semiconductor material itself.
Step 3: Final Answer:
Diffusion current requires a carrier concentration gradient, which is absent in a uniformly doped semiconductor at equilibrium.