Learning outcomes of the course unit
The aim is to present and discuss an organic class of transport phoenomena in the condensed matter. The choice is oriented to electronic transport in semiconductors due to a rich available phoenomenology also in the field of low dimensional structures.
Recommended propaedeutics: Solid State Physics, Elements of Statistical Physics
Course contents summary
ELECTRONIC TRANSPORT IN SEMICONDUCTORS
General properties of semiconductors
Energy band structures:direct and indirect energy gaps. Effective masses of electrons and holes. Impurity levels. Shallow impurities in the effective mass approximation. Deep levels. Equilibrium statistics of electrons and holes. Temperature and doping dependence of the Fermi energy. Intrinsic and exaustion regimes. Low temperature freezing of carriers. Compensation mechanisms. The case of semi-insulating GaAs.
Introduction to transport phoenomena
Bloch oscillations and collision processes. Boltzmann equation. The collision integral in the relaxation time approximation. Electrical conductivity in the ohmic regime: spherical and ellipsoidal energy surfaces. Scattering processes. Ionized impurity scattering and phonon scattering. Transport phoenomena in the particle kinetic model.
Electron in a magnetic field. Landau quantization and level degeneracy. Ciclotron resonance of electrons and holes. Classical magneto-transport. Hall effect and magnetoresistance. Geometrical megnetoresistance. Quantum magneto-transport. Orbit and flux quantization. The Shubnikov-de Haas effect. The extreme quantum limit. The 2D electron gas and the quantum Hall effect. The balistic regime:quantization of the electrical conductance in 1D systems.
Transport of excess carriers
Space charge and dielectric relaxation. Generation and recombination of carriers. Lifetime of excess carriers. Space-time evolution of non equilibrium electrons and holes. Continuity equations of currents. The ambipolar equation. Stationary solutions of the ambipolar equation: iniection and exctration of minority carriers. Time dependent solutions: the Haynes-Shockley experiment. Application to the case of charge transport in the p/n junction.
---NOTES BY THE LECTURER
Teaching methods: oral lectures
Evaluation methods : oral examination