Semiconductors

Step 1: Understanding the forward bias of a p-n junction.
In a forward biased p-n junction diode, the p-type side is connected to the positive terminal and the n-type side is connected to the negative terminal. This reduces the potential barrier, allowing current to flow. The Fermi level ( ) moves closer to the conduction band in the n-type material and closer to the valence band in the p-type material.
Step 2: Identifying the correct diagram.
Option (A) shows the energy bands with the correct behavior for a forward biased p-n junction. The Fermi energy levels are shifted as expected in forward bias, and the conduction and valence bands are aligned correctly.
Step 3: Conclusion.
Thus, the correct energy-band diagram for a forward biased p-n junction diode is shown in option (A).

Step 1: Recall the relation between charge density and electric field.
From Poisson’s equation, where is the charge density and is the permittivity of the semiconductor.
Step 2: Analyze the given profile.
The charge density varies linearly with , being negative on the p-side and positive on the n-side. Therefore, the derivative of with respect to is linear, implying that must vary quadratically if were constant, but since is linear, will vary linearly.
Step 3: Determine the behavior of .
- The slope of on the p-side is positive (since is negative). - The slope of on the n-side is negative (since is positive). At , the electric field passes through zero because the net electric field in equilibrium must balance across the junction.
Step 4: Graphical interpretation.
Thus, increases linearly from to 0, and decreases linearly from 0 to , forming an inverted V-shape centered at the origin.
Step 5: Final Answer.
Hence, the correct graph is the one shown in Option (B).

Step 1: Understanding the energy band diagram.
In a semiconductor energy band diagram, the Y-axis represents the energy level (showing conduction and valence bands), while the X-axis typically represents spatial distance across the material.
Step 2: Explanation.
Flat band means that there is no band bending, indicating zero electric field inside the semiconductor. Therefore, the diagram shows how the energy levels remain constant along the distance.
Step 3: Final Answer.
Hence, Y represents energy and X represents distance.