(SEM V) THEORY EXAMINATION 2023-24 ADVANCE SEMICONDUCTOR DEVICE

Subject Overview: Advance Semiconductor Device (KEC056)
 

The subject Advance Semiconductor Device (ASD) is one of the most essential courses in the 5th semester of B.Tech (ECE, EEE, and related branches). It focuses on the physics, construction, and characteristics of advanced semiconductor components — such as MOSFETs, JFETs, IMPATT diodes, laser diodes, photodiodes, and thyristors.
 

It builds upon the basic concepts of semiconductor physics studied earlier and moves toward special-purpose electronic devices used in high-frequency communication, optoelectronics, and power control systems.
 

The main goal of this subject is to make students understand how modern semiconductor devices work, their fabrication principles, and their practical applications in modern electronics and communication systems.
 

Exam Details (Based on Uploaded Paper – Page 1)
 

Course: B.Tech (Semester V)

Subject Code: KEC056

Subject Title: Advance Semiconductor Device

Duration: 3 Hours

Maximum Marks: 100

Paper ID: 310408

Exam Year: 2023–24

Note: Attempt all sections. If any data is missing, make suitable assumptions.

Paper Pattern Overview
 

The paper is divided into three major sections – A, B, and C, similar to other AKTU-style technical exams.

Section A – 10 short answer questions × 2 marks each = 20 Marks

Tests fundamental concepts and definitions.

Section B – Any 3 descriptive questions × 10 marks = 30 Marks

Focuses on device operation, characteristics, and theory.

Section C – Any 1 part from each question × 10 marks = 50 Marks

Tests derivations, explanations, and in-depth understanding of semiconductor devices.

SECTION A — Short Answer Questions (10 × 2 = 20 Marks)

This section tests your concept clarity and recall ability. Each question carries 2 marks.

Here’s a breakdown with explanations 

Non-uniform Doping:
Refers to the variation of impurity concentration across a semiconductor material. It’s used to control the electric field, mobility, and junction properties in devices like BJTs and MOSFETs.

Depletion Region:
A region in a p–n junction where mobile charge carriers are absent. It contains only fixed ions and forms the junction’s barrier potential.

Special Features of MESFETs:
Metal–Semiconductor Field Effect Transistors (MESFETs) are used for high-frequency amplification and microwave applications. They use a Schottky junction instead of a p–n junction.

Pinch-off Voltage in JFET:
The voltage at which the drain current stops increasing with drain-to-source voltage, as the conducting channel gets “pinched off.”

Resonant Tunneling:
Occurs when electrons pass through multiple barriers at specific energy levels, seen in resonant tunneling diodes (RTDs).

Tunneling:
A quantum mechanical phenomenon where electrons penetrate through an energy barrier they classically shouldn’t cross, used in tunnel diodes.

Transistor vs. Thyristor:
A transistor is a three-layer device with continuous current control, while a thyristor (SCR) is a four-layer device acting as a switch once triggered.

Advantages of Laser Devices:
Laser diodes emit coherent, monochromatic, and highly directional light — ideal for communication, medical, and industrial use.

Chemical Sensors:
Semiconductor-based devices that detect gases or chemicals by measuring changes in conductivity or voltage.

Photodiode:
A light-sensitive diode that converts light energy into current, used in optical communication and sensing applications.

SECTION B — Descriptive Questions (Any 3 × 10 = 30 Marks)
 

These are analytical and explanatory questions that check your ability to explain circuit operation and derive relationships.
 

Let’s understand each question:
 

SCR (Silicon Controlled Rectifier):
Explain the structure, operation, and characteristics, emphasizing latching and holding current.
Discuss Tunnel and Zener diodes — their symbols, operation, and application differences.

SCRs are power-control devices, while Zener diodes are used for voltage regulation.

N-Channel JFET Operation:
Describe how a JFET works under pinch-off conditions. Derive the transconductance relation showing how output current changes with gate voltage.

TRAPATT Diode:
Draw its structure and explain how avalanche breakdown and transit-time effects produce microwave oscillations. Used in radar and high-power transmitters.

Radiative Transitions:
Explain spontaneous and stimulated emissions in semiconductors. Discuss differences between power devices (high current handling) and conventional devices (signal-level operation).

Photo Detector and Solar Cell:
Explain working principles, energy band diagrams, and I–V characteristics. Discuss how solar cells convert light into electric energy using photovoltaic effect.

SECTION C — Long Answer / Derivation Questions (Any 1 Part from Each)
 

This section is the most detailed and scoring. It requires you to explain or derive key formulas, device structures, or operation mechanisms.
 

Question 3 — Semiconductor Fundamentals
 

(a) Explain n-type and p-type semiconductors with diagrams. Derive the formula for minority carrier lifetime, showing recombination process.

(b) Derive expressions for conductivity, mobility, and diffusion of carriers, relating charge movement to current density.

Question 4 — MOSFET Device Analysis

(a) Describe the structure, operation, and I–V characteristics of a MOSFET. Explain the three regions: cutoff, linear, and saturation.

(b) Derive the threshold voltage expression, and explain factors that affect it — oxide thickness, substrate doping, and temperature.

Question 5 — Microwave Semiconductor Devices

(a) Explain IMPATT diode working and the transferred electron mechanism, where negative resistance is generated for high-frequency oscillations.

(b) Discuss tunneling phenomenon and V–I characteristics of tunnel diode. Mention semiconductor materials like GaAs and Ge used in fabrication.

Question 6 — Power and Light Devices

(a) Explain Thyristors, draw their V–I characteristics, and describe their turn-on and turn-off behavior.

(b) Explain LED working principle, including recombination of charge carriers and light emission. Discuss materials like GaAsP and InGaN and applications in displays, indicators, and lighting.

Question 7 — Optoelectronic and CCD Devices

(a) Explain photoconductivity, its working mechanism, and applications in light sensors and automatic systems.

(b) Discuss the principle, storage, and transfer of charge in CCDs (Charge-Coupled Devices) used in cameras and imaging sensors.

Key Concepts to Revise

Semiconductor physics — carrier drift, diffusion, and recombination

PN junction theory and depletion region

MOSFET and JFET working principles

Tunnel diode and quantum tunneling

Thyristor and SCR operation

IMPATT, TRAPATT, and Gunn diodes

Photodiodes, solar cells, LEDs, and LASERs

Carrier lifetime, mobility, and diffusion equations

Exam Strategy

Start with short definitions and formulas (Section A) to secure quick marks.

Include neat labeled diagrams for devices in Section B & C — every diagram adds clarity and marks.

For derivations, clearly state assumptions, formulas, and units.

Mention applications for every device (e.g., “Used in microwave amplifiers,” “Used in power control,” etc.).

Focus on device comparison questions — transistor vs thyristor, diode types, or MOSFET vs JFET.

Conclusion

The Advance Semiconductor Device (KEC056) exam paper is designed to test both conceptual understanding and analytical ability. It moves beyond basic semiconductor theory to explore advanced devices used in modern electronics, communication systems, and photonics.

Mastering this subject helps build a strong base for VLSI design, optoelectronics, microelectronics, and power electronics — essential domains in today’s electronics industry.