(SEM V) THEORY EXAMINATION 2022-23 ADVANCE SEMICONDUCTOR DEVICE

Course: B.Tech (Electronics / Electrical / Related Branches)

Semester: V                                                               Subject Code: KEC-056

Title: Advance Semiconductor Device                        Maximum Marks: 100

Duration: 3 Hours

Paper Type: Theory

Sections:

Section A: Short conceptual questions — 20 marks

Section B: Descriptive questions — 30 marks

Section C: Analytical / Device working — 50 marks

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

All questions are compulsory.

Define the term Crystal Structure:

The regular 3D arrangement of atoms or molecules in a solid, forming a repeating lattice pattern.

Describe the term Insulators:

Materials with a wide energy band gap (typically >3 eV) that prevent free movement of electrons, e.g., glass, rubber.

Explain the term Bipolar in BJTs:

Bipolar Junction Transistor (BJT) operation involves both electrons and holes as charge carriers, hence "bipolar".

What is a Non-Volatile Memory Device?

A memory that retains data even after power is removed, e.g., Flash, EEPROM, ROM.

What is Noise in Circuits?

Unwanted electrical signals that distort or interfere with the intended signal in a circuit.

Explain the term V-I Characteristics:

Relationship between voltage (V) across a device and the resulting current (I) through it — defines its electrical behavior.

Define Power Devices:

Semiconductor devices designed to handle large voltages and currents (e.g., SCRs, MOSFETs, IGBTs).

Elaborate the term Radioactive:

The spontaneous emission of energy or particles from unstable atomic nuclei (used in radiation-based sensors).

Describe the term Photoconductor:

A material whose conductivity increases when exposed to light (used in photoresistors).

Define the term Sensors:

Devices that detect physical quantities (temperature, pressure, light) and convert them into electrical signals.

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

Attempt any three questions.

(a) Energy Band Theory

Energy Band: Range of energy levels that electrons can occupy.

Comparison:

(b) Scaling and Short Channel Effects in FETs

As MOSFET dimensions shrink, electric field increases → short-channel effects:

Drain Induced Barrier Lowering (DIBL)

Velocity Saturation

Threshold voltage roll-off

Hot carrier effect

(c) Tunnel Diode

Working Principle: Quantum tunneling through a narrow depletion region in heavily doped p–n junction.

V–I Characteristics: Shows negative resistance region used in high-frequency oscillators.

(d) Light Emitting Diode (LED)

Working: Forward bias causes electron-hole recombination in a semiconductor, emitting photons.

V–I Characteristics: Nonlinear — current increases exponentially beyond threshold voltage.

Applications: Displays, indicators, optical communication.

(e) FPGA Architecture

Field Programmable Gate Array: Consists of configurable logic blocks (CLBs), interconnects, and I/O blocks.

Enables custom digital circuit design using hardware description languages (HDLs).

SECTION C — Analytical / Device Working (5 × 10 = 50 Marks)

Attempt one part from each question (Q3–Q7).

Q3. Metal–Semiconductor Devices or Varactor Diode

(a) Schottky Diode:

Formed between metal and n-type semiconductor.

V–I Curve: Shows fast switching and low forward voltage drop (~0.3 V).

Applications: High-speed rectifiers, RF detectors.

(b) Varactor Diode:

A diode with voltage-dependent junction capacitance.

V–I Curve: Reverse-biased operation.

Use: Voltage-controlled oscillator (VCO).

Q4. Heterojunction BJT or JFET

(a) Heterojunction BJT:

Combines two semiconductor materials with different band gaps (e.g., GaAs-AlGaAs).

Improves speed and gain for microwave applications.

(b) JFET (Junction Field Effect Transistor):

Current controlled by electric field across p–n junction.  V–I Curve: Linear region followed by saturation region.  Applications: Amplifiers, switches.

Q5. BARITT or TUNNETT Diode

(a) BARITT (Barrier Injection Transit-Time) Diode:

Generates microwave oscillations via injection and drift of minority carriers.

(b) TUNNETT Diode:

Uses avalanche breakdown and tunneling for negative resistance generation.

Used in microwave oscillators and amplifiers.

Q6. Thyristors or LASER Diode

(a) Thyristor (SCR):

Four-layer (PNPN) device with latching behavior.   Used in AC power control, rectifiers.

(b) LASER Diode:

Light Amplification by Stimulated Emission of Radiation.

V–I Curve: Sharp threshold current beyond which coherent light is emitted.

Used in optical communication and barcode scanners.

Q7. CCD or Mechanical Sensors

(a) Charge-Coupled Device (CCD):

Converts light into electrical charge and shifts it for processing.   Used in digital imaging and astronomy.

(b) Mechanical Sensors:

Measure parameters like pressure, strain, or displacement.

Based on piezoelectric, capacitive, or resistive principles.

Key Topics Covered

Semiconductor fundamentals & energy bands        Tunnel, Varactor, LED, LASER diodes

BJTs, FETs, and heterojunction devices                      Power devices and thyristors

FPGA architecture                                                      Sensors and optoelectronic devices