UGC NET Electronic Science December 2021 Question Paper with Answer Key & Detailed Solutions

• UGC NET Electronic Science December 2021 Question Paper with Answer Key and Detailed Solutions

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1. (D)

2. A

3.C

4.A

5.B

6) In a silicon oxidation model,

B/A

is the linear rate constant and τ accounts for the shift in the time coordinate to account for the presence of the initial oxide layer, then the linear law is represented as:

1.

B/A*

(t - τ) 

2.

A/B*

(t - τ) 

3.

B/A*

(t + τ) 

4.

Bt/Aτ

Answer: C

Solution

Logical Breakdown of Silicon Oxidation

To understand the formula, we look at the Deal-Grove Model. This model describes how an oxide layer (SiO₂) grows on a silicon wafer over time.

Step 1: Understanding the Variables

• t (Time): The actual duration the silicon stays in the oxidation furnace.
• τ (Tau): This accounts for the Initial Oxide Layer. Wafers usually have a tiny bit of oxide (native oxide) before we start. τ represents the "equivalent time" it would have taken to grow that pre-existing layer.
• B/A (Linear Rate Constant): This constant tells us how fast the silicon is reacting when the oxide is very thin.

Step 2: The General Equation

The full Deal-Grove equation for oxide thickness (x_o) is:

x_o² + Ax_o = B(t ± τ)

7) In a silicon oxidation model, if C_G and C_S are the oxidant concentration in the bulk of the gas and oxidant concentration adjacent to the oxide surface, respectively, then the gas phase flux are:
(h_G is the gas phase mass transfer coefficient)

1.

h_G/C_G - C_S

2.

h_G/C_G + C_S

3.

h_G(C_G - C_S) 

4.

h_G(C_G + C_S) 

Answer: C

Solution

Fundamental Logic of Question 7

This question is about Mass Transport. It asks how fast oxygen gas moves from the furnace atmosphere to the surface of the silicon.

Step 1: Identify the "Push" (Driving Force)

Nature moves substances from high concentration to low concentration. The oxidant starts at C_G (high) and moves toward C_S (low). The "pushing force" is the difference: (C_G - C_S).

Step 2: Identify the "Ease of Movement"

The variable h_G is the mass transfer coefficient. Think of it like "Conductivity." It tells us how easily the gas molecules can slip through the air to reach the surface.

Step 3: Combine into the Flux Law

In all transport physics, Flux = (Coefficient) × (Driving Force).

Flux = h_G × (C_G - C_S)

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