Sumários

T5 - 1d conductivity

18 Outubro 2022, 14:00 • Maria Margarida Cruz

Confinement in a gas d=2 ("Quantum point contact"). Ballistic transport.
Landauer formula for non-reflecting contacts. Contact resistance. Contribution of one or more sub-bands. Coherent transport through a one-dimensional conductor with a scattering center . Associated resistance. Coherent transport through a one-dimensional conductor with two centers of dispersion. Landauer formula extended to non-reflecting contacts and presence of scattering centers.
Important lengths in the mesoscopic system. Conclusions for the behavior of the system based on the relationship between the characteristic lengths.

Problems 3

11 Outubro 2022, 16:30 • Maria Margarida Cruz

Continuation of the discussion of selected problems of series 2.
Evaluation problem 1.

T4 - Surface and interface electronic states

11 Outubro 2022, 14:00 • Maria Margarida Cruz

Surfaces and interfaces. p-n junction as the example of an interface between semiconductors. surface states.
Modification of surface electronic states: band adjustment and "band-bending"."Pinning" of the Fermi energy. Semiconductor metal junctions. Schottky barrier. Rectifier contacts and ohmic contacts.
MOS interface and two-dimensional electron gas formation (2DEG). Production of 2DEG using junctions of two different semiconductors. Triangular potential well

Problems 2

4 Outubro 2022, 16:30 • Maria Margarida Cruz

Resolution and discussion of selected problems of series 2.

T3 - Diffusive transport

4 Outubro 2022, 14:00 • Maria Margarida Cruz

Classification of materials into conductors, insulators and semiconductors and relationship with their electronic structure. Hole definition and its characteristics. Pure semiconductors and doped semiconductors. The tight binding approach for electronic states in semiconductors.
Transport by electronic states. Contribution to the transport of a filled band. Electrical transport in macroscopic  materials using semi-classical model. Boltzmann equation. Approximation of relaxation time. Diffusive transport. Transport on a two-dimensional conductor. Relaxation of confinement in a two-dimensional gas and transition to a three-dimensional gas. Einstein relations between mobility and diffusion constant.