In this class you are allowed, even encouraged, to bring a calculator. (Phones, however, are not allowed as per general department standards and practice.)
You will be asked to share your understanding of np junctions, fermi energy, carrier density and the origin of bands in crystals. Also drift current and diffusion current, mobility, effective mass and its relationship to bandwidth...
Some things that will help you:
Understand some basic definitions: n, p, bandwidth, bandgap, density of states...
A natural intuitive feel for and understanding how n and p are influenced by the relationship between the fermi energy and the band edge.
An understanding of the approximations we use (sometimes) to evaluate n and p. Good judgement regarding when some approximations are appropriate and when they are not. Confidence to decide what approximations to use. (Failure to make approximations can hurt you. It is often not okay to use the exact expression for something when an approximation can be made.)
A sense of energy scales and their importance and relationships. e.g. kT, bandwidth, E_gap, etc
An understanding of diffusion current.
An understanding of drift current.
Understand what a band represents. How many states are in a band?... the relationship between bandwidth, density of states and effective mass.
Added notes: The ability to actually calculate numbers, for current as well as n and p, will be tested.
Also, a deep understanding of the nature of an unbiased and biased np junction (negative on the n side) and the assumptions of the ideal junction approximations. Understand the concepts behind the assumptions, they are ideal, so not perfect, but in what way are they sort of reasonable? what thinking lies behind them? What are their consequences??
How do these equations look?
Are you going to give us the electric field equations as well? Including E(0) and the piecewise part?
ReplyDeleteMaybe it is better if you understand that going in?
ReplyDelete