4.2 Designer Band Gaps Flashcards
What is meant by a designer band gap?
Where band gaps are tailored for certain applications
Describe modulation doping
When electrons from the donors fall into the well
- They move around freely inside the well without bumping into donors which gives a very long mean free path and low dissipation
- No. electrons is limited by the charge that builds up
Describe the motion of an electron in the quantum well in a 2DEG
Free to move in x,y
Confinement in z
What wave do we expect in x,yz for the 2DEG?
Travelling wave in x, y
Standing wave in z
In which coordinates is the wavefunction periodic for the 2DEG
x and y (x+a, y+a) = (x,y)
Define the Quantum Hall Effect
When a large magnetic field is applied to a 2D semiconducting layer at low temperature and a transverse voltage can be measured
What is unique about the density of states for the 2DEG
It is constant and steps are observed
How can a p-n junction be created?
Stick a p doped material onto an n doped material
What is the region called at the p-n junction boundary and why?
Depletion region as the electrons in the n doped material annihilate the holes
Describe the location of the chemical potential for a p and n doped material
N doped - just under conduction band
P doped- just above valence band
Explain the shape of the longitudinal and transverse resistivity of a material when a B field is applied
The transverese shape is an increasing gradient with plateaus
The longitudinal falls down to 0 from an initial value, and then has sharp peaks in it aligning with the plateaus of the transverse resistivity
Why do we get plateaus and peaks in the transverse and longitidinal resistivity?
Because the application of the B field causes the electrons to move in circles, giving further quantisation of the orbits
