In order to carry out fundamental research on novel electronic, optical, and magnetic materials and devices, you have to understand the behavior of electrons in solids. This class aims at learning wave-like aspect of electrons in crystals, excitation of solids with low- (electrical) to high- (optical) frequency electromagnetic waves, and resultant optical properties of solids. Energy bands in the most advanced materials, in particular low dimension systems, will also be reviewed.
Get familiar with the meaning of the energy band in solids and understand physical bases about how light interact with solids.
Welcome to the Light and matters IIb (year 2015)
[Schedule]
June 11 general process (process, real band structure, Kronig-Penney model)
18 band structure 1 (zone folding, sp hybridization)
25 band structure 3 (Kronig-Penney model, exercise)
July 02 band structure 2 (discussion about Kronig-Penney model, quantum confinement 1)
09 quantum confienement 2
16 excitons, selection rules
23 Ultrafast phenomenon
[Subject to be discussed during the class]
1. Which is the better material for light emission, GaAs or diamond ?
2. Why a pure silicon crystal can not emit light easily?
(ans., level 1)
Because, the lifetime of carriers is long in a silicon crystal.
3. Why the lifetime of carriers is long in a silicon crystal?
(ans. level 2)
Perhaps, there is some fundamental problem in the radiative recombination process, isn't it?
(ans. level 3)
Because, it has the indirect gap structure. Silicon is a indirect-gap semiconductor.
4. What is the indirect-gap semiconductor?
5. Band structures are classified into how many patterns?
6. Why, in a crystal, electrons with k 0 can or can not occupy the lowest energy level ?
7. Why quantum wells and quantum dots are expected to be good candidate materials for light emitting devices?
[Results and Credits]
Will be evaluated by the report whose deadline will be Aug.6th, 2015.
Materials cited from a few standard textbooks will be used together with milestones papers.
Group discussions are planned.
None
Through discussions and a report whose deadline is Aug.6th, 2015.
hiro@isl.titech.ac.jp
Every Thursday from 13:00-15:00pm