B026285 - SEMICONDUCTOR PHYSICS

The course objective is to provide basic knowledge of solid-state physics, with emphasis on the semiconductor materials and devices.

Luciano Colombo Fisica dei Semiconduttori
Casa editrice Zanichelli
ISBN 978-88-08-52054-8


slides of lectures:
http://www2.de.unifi.it/Fisica/Bruzzi/fss.html

Learning Objectives: The course intends to deepen a number of basic issues on the structure of matter. Then, it provides specific knowledges on semiconductor materials and of junction-based devices. Finally, an experimental application is considered, focussed on semiconductor solar cells.

- Quantum physics concepts such as: wave - particle dualism, distinguishable / indistinguishable particles, classical and quantum statistics (Maxwell Boltzmann, Fermi-Dirac and Bose-Einstein); simple applications of the Schoredinger equation; hydrogen atom orbitals and periodic table of elements.
- Solid State Physics Concepts: Cohesion energies for ionic, molecular and covalent crystals; crystalline lattices, amorphous materials, Miller indices and reciprocal lattice; Calculation of the energy-band diagram for metals, semiconductors and insulants in the approximation of weak periodic potential.
- Knowledge of electrical conduction models in semiconductors; Free carrier statistics in intrinsic and extrinsic semiconductors, electric and thermal transport models in semiconductors, Hall resistivity and coefficient.
- metal-semiconductor junctions and pn as building blocks of semiconductor devices. Heterojunctions. Nanotechnologies and quantum confinement devices.
- ability to properly address the problems related to the evaluation of the electrical and thermal parameters of a semiconductor material.
- Ability to undertake an experimental evaluation of the functional parameters of semiconductor solar cells.

Knowledge of geometry, mathematical analysis, classical physics according to programs of compulsory courses of a three-year degree in engineering.

Lectures and assignments, laboratory activity in groups

The final examination consists of an oral test, in which the candidate presents some of the main topics of the course. In particular, the discussion is aimed at verifying:
- The correct knowledge of concepts of quantum physics and solid state physics as wave - particle dualism, distinguishable / indistinguishable particles, classical and quantum statistics, Schoredinger equation, crystalline lattices, reciprocal lattice, energy band diagrams.
- the candidate's ability to correctly evaluating the electrical parameters of a semiconductor material and a junction device, her/his knowledge of electrical conductivity models in semiconductors, also with reference to the laboratory activity on semiconductor solar cells.

-OUTLINE OF QUANTUM MECHANICS: black body, photoelectric effect, matter-wave duality, uncertainty principle of Heisenberg, Schroedinger equation. Applications: electron in potential well, tunneling, atomic orbitals.
2-CLASSIFICATION OF SOLID AND PERIODIC STRUCTURES. Cohesion in solids: noble gases, Lennard-Jones potential, total energy and equilibrium properties. Ionic solids, Madelung constant, equilibrium properties. Crystal structure. Space lattice and base unit. Wigner-Seitz cell. Outlines of polycrystalline and amorphous materials. Reciprocal lattice and its properties. Brillouin zones. Diffraction of X-rays, neutrons and electrons.
3-ELECTRONS IN METALS: Classical (Drude) and quantum (Sommerfeld) Free Electron Theory. Calculation of the Fermi energy, speed and total energy for free electrons. Fermi-Dirac statistics. Calculation of the electronic contribution to the specific heat.
4-ELECTRONS IN PERIODIC POTENTIAL OF CRYSTAL: Bloch theorem, electrons in periodic potential weak, formation of bands of energy, band-gap. Number of states in an energy band, crystal momentum of the electron, effective mass. Defining holes. Construction of the Fermi surface: extended and reduced scheme zone. Band structure for various types of materials: insulators, semiconductors, metals.
5-LATTICE VIBRATIONS. Elastic waves in continuous media. Vibrations of linear chains with and without a base. Vibrations of a three-dimensional networks. The concept of phonon. Bose-Einstein statistics. Dispersion curves. Lattice contribution to the specific heat.
6-SEMICONDUCTOR MATERIALS: impurities states in semiconductors, doping. Carrier statistics in intrinsic and doped semiconductors. Equilibrium carrier concentrations as a function of temperature. Conductivity, Hall coefficient. Transport in semiconductors: continuity equation, diffusion, recombination and generation of carrier pairs, quasi-fermi levels, drift-diffusion model.
7-NON-HOMOGENEOUS SEMICONDUCTORS: omojunctions; metal / semiconductor junction, heterostructure: alignment of potential. Applications.
8- LAB ACTIVITY: Electrical properties of materials, IV and CV characteristics of semiconductor devices, solar cells.