Introduction to Thermodynamics

• Physics encompasses the fundamental laws and principles governing the universe, covering a wide range of phenomena from subatomic particles to the cosmos.
• Classical mechanics, electromagnetism, thermodynamics, and quantum mechanics are the major branches of physics.
• Thermodynamics deals with the relationships between heat, work, and energy, and the laws that govern the efficiency of energy conversion.
• Semiconductors are materials with electrical conductivity between conductors and insulators, and their behavior is central to modern electronics.

Thermodynamics

• Thermodynamics is the study of energy, its transformations, and its relation to matter.
• It is governed by a set of fundamental laws that dictate the behavior of energy and matter in equilibrium.
• These laws are universal and apply to all physical systems, from microscopic particles to macroscopic objects.
• The first law of thermodynamics states that energy is conserved.
• The change in internal energy of a system is equal to the heat added to the system minus the work done by the system: ΔU = Q - W.
• The second law of thermodynamics introduces the concept of entropy.
• Entropy is a measure of the disorder or randomness of a system.
• The second law states that the total entropy of an isolated system always increases or remains constant in a reversible process.
• Spontaneous processes increase the entropy of the universe.
• The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero temperature is zero.
• Absolute zero is 0 Kelvin (-273.15 °C).
• Thermodynamic processes include isothermal (constant temperature), adiabatic (no heat exchange), isobaric (constant pressure), and isochoric (constant volume) processes.
• Thermodynamic cycles, such as the Carnot cycle and the Rankine cycle, describe the operation of heat engines and refrigerators.
• Heat engines convert thermal energy into mechanical work.
• Refrigerators transfer thermal energy from a cold reservoir to a hot reservoir, requiring work input.
• Enthalpy (H) is a thermodynamic property defined as H = U + PV, where U is internal energy, P is pressure, and V is volume.
• Gibbs free energy (G) is defined as G = H - TS, where T is temperature and S is entropy, and is used to predict the spontaneity of processes at constant temperature and pressure.
• Phase transitions, such as melting, boiling, and sublimation, involve changes in the physical state of a substance and are governed by thermodynamic principles.
• Chemical thermodynamics applies thermodynamic principles to chemical reactions, allowing the prediction of reaction equilibrium and spontaneity.

Semiconductor Physics

• Semiconductors are materials with electrical conductivity between that of conductors and insulators.
• Their conductivity can be controlled by temperature, impurities, and electric fields.
• Silicon (Si) and Germanium (Ge) are common semiconductor materials.
• Compound semiconductors like Gallium Arsenide (GaAs) and Indium Phosphide (InP) are also used.
• The electronic structure of semiconductors features a filled valence band and an empty conduction band separated by a band gap.
• The band gap energy (Eg) determines the energy required to excite an electron from the valence band to the conduction band.
• Semiconductors can be intrinsic (pure) or extrinsic (doped).
• Intrinsic semiconductors have an equal concentration of electrons and holes (electron vacancies).
• Extrinsic semiconductors are doped with impurities to increase either the electron (n-type) or hole (p-type) concentration.
• N-type semiconductors are doped with donor impurities that have extra valence electrons, such as phosphorus (P) in silicon (Si).
• P-type semiconductors are doped with acceptor impurities that have fewer valence electrons, such as boron (B) in silicon (Si).
• The Fermi level represents the energy at which the probability of finding an electron is 50%.
• In intrinsic semiconductors, the Fermi level is located near the middle of the band gap.
• In n-type semiconductors, the Fermi level is closer to the conduction band.
• In p-type semiconductors, the Fermi level is closer to the valence band.
• When a p-type and an n-type semiconductor are joined, a p-n junction is formed.
• At the p-n junction, electrons diffuse from the n-side to the p-side, and holes diffuse from the p-side to the n-side, creating a depletion region.
• The depletion region is devoid of free charge carriers and has a built-in electric field.
• Applying a forward bias to the p-n junction reduces the depletion region width and allows current to flow.
• Applying a reverse bias increases the depletion region width and blocks current flow.
• Semiconductor devices include diodes, transistors, and integrated circuits.
• Diodes allow current to flow in one direction only.
• Transistors, such as bipolar junction transistors (BJTs) and field-effect transistors (FETs), amplify or switch electronic signals.
• Integrated circuits (ICs) consist of numerous transistors and other components interconnected on a single chip.
• The performance of semiconductor devices is affected by temperature, with higher temperatures generally reducing carrier mobility and increasing leakage current.
• Semiconductor devices are used in a wide range of applications, including computers, smartphones, solar cells, and LED lighting.