Semiconductor

Overview of Semiconductor Devices

  • Identify and Describe Semiconductor Devices

    • Understand operations, characteristics, and applications of various semiconductor devices such as:

    • Diodes

    • Zener diodes

    • LEDs (Light Emitting Diodes)

    • Solar cells

  • Analyze and Design Transistor-Based Circuits

    • Analyze and design circuits using Bipolar Junction Transistors (BJTs) in various configurations:

    • Common base

    • Common emitter

    • Common collector

    • Evaluate performance characteristics of BJTs

  • Understand and Utilize Field Effect Transistors

    • Comprehend fundamental operations of:

    • Junction Field Effect Transistors (JFETs)

    • Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs)

    • Apply JFETs and MOSFETs in designing amplifiers and circuits

  • Implement Operational Amplifier Configurations

    • Gain proficiency in operational amplifiers (Op-Amps)

    • Understand characteristics, configurations, and applications

    • Design inverting and non-inverting amplifiers

  • Apply Basic Concepts of Digital Electronics

    • Apply foundational knowledge of digital electronics:

    • Number systems

    • Boolean algebra

    • Logic gates

    • Implement basic combinational circuits:

    • Adders

    • Subtractors

Atomic Structure and Basic Concepts

  • Atomic Structure Components

    • Neutron

    • Proton

    • Electron

Energy Band Theory

  • Energy Bands: Conduction, Valence and Band Gap

    • Conductor: Material supporting a generous flow of charge under limited voltage

    • Insulator: Offers low conductivity under voltage pressure

    • Semiconductor: Intermediate conductivity between insulators and conductors

Semiconductors

  • Silicon Characteristics

    • Silicon (Si): A Group 4 element with 4 valence electrons

    • Configuration: Each Si atom shares electrons with 4 adjacent Si atoms

    • Preference for 8 electrons in the outer shell, similar to noble gases

  • Comparison between Silicon and Germanium

    • Silicon is favored due to:

    • Abundance

    • Ease of processing

    • Stable electrical properties

    • Advantages of germanium: Higher electron mobility

    • Dominance of silicon due to the ability to create stable insulating layers (SiO₂) and lower cost

Types of Semiconductors

  • Intrinsic Semiconductors

    • Pure form of semiconductor materials like germanium and silicon

    • Negative temperature coefficient: resistance decreases as temperature increases

    • Electrons from valence band can jump to conduction band with increased temperature, allowing current flow

  • Extrinsic Semiconductors

    • Formed by adding impurity atoms via the doping process

    • Common dopants: Antimony (5 electrons), Boron (3 electrons)

    • N-type and P-type semiconductors based on doping

    • N-type: Pentavalent impurity (e.g., phosphorus) provides excess free electrons

    • P-type: Trivalent impurity (e.g., boron) creates holes (absence of electrons)

Energy Bands in Solids

  • Energy Bands and Gaps

    • Valence Band: Contains electrons that are normally orbiting nuclei

    • Conduction Band: Contains free electrons capable of conduction

    • Forbidden Band: Energy gap with no electron presence

    • Movement of electrons requires energy to jump from valence to conduction band

Fermi Level

  • Definition

    • Fermi Level: Energy of the least tightly held electrons; critical for determining electronic properties

    • Fermi Energy: Value at absolute zero temperature, specific to each solid

Carrier Concentrations

  • Majority and Minority Carriers

    • N-Type: Electrons are the majority carriers, holes are minority carriers

    • P-Type: Holes are majority carriers, electrons are minority carriers

  • Dopants

    • Donor Impurities: Elements with 5 electrons that provide extra electrons (e.g., Group V elements)

    • Acceptor Impurities: Elements with 3 electrons that create holes (e.g., Group III elements like boron)

Charge Densities

  • Charge Density Relations

    • Semiconductor is electrically neutral: Positive charge density = Negative charge density

    • Charge density equations:

    • Positive charge density: $ND + p = NA + n$

    • N-Type: $ND = n$, $NA = 0$, with $n >> p$

    • P-Type: $p = NA$

Drift and Diffusion Currents

  • Drift Current

    • Motion of charged particles in an electric field:

    • Holes drift towards the negative terminal, electrons towards the positive terminal

  • Diffusion Current

    • Movement of particles from high to low concentration

Mass Action Law

  • Description

    • Relates concentrations of free electrons and holes under thermal equilibrium

Sample Calculations

  1. Minority Carrier Density Calculation

    • Given intrinsic carrier concentration: ni=1.5imes1016/m3n_i = 1.5 imes 10^{16}/m^3

    • After doping majority carriers: n=5imes1020/m3n = 5 imes 10^{20}/m^3

    • Calculate minority carrier density using: n2=ni∗pn^2 = n_i * p resulting in p=4.5imes1011/m3p = 4.5 imes 10^{11}/m^3

  2. Electron Concentration Calculation in P-Type

    • Given hole concentration: p=2.25imes1015/cm3p = 2.25 imes 10^{15}/cm^3 and intrinsic carrier concentration: ni=1.5imes1010/cm3n_i = 1.5 imes 10^{10}/cm^3

    • Use mass action law to find electron concentration: n=racni2pn = rac{n_i^2}{p} resulting in n=105/cm3n = 10^5/cm^3

  3. Resistivity Calculation of Intrinsic Semiconductor

    • Given intrinsic concentration: n=2.5imes109/m3n = 2.5 imes 10^9/m^3, electron mobility:  = 0.40 m^2/V-s, hole mobility:  = 0.20 m^2/V-s

    • Calculate conductivity: C = n e ( + )

    • Result: Resistivity <br>ho=0.4166 extΩ−m<br>ho = 0.4166 \, ext{Ω-m}

End of Notes