Epitaxial growth and the physics of quantum wells Flashcards
What deposition technique is Molecular Beam Epitaxy?
An ultra-high vacuum technique.
Why are high temperatures used to prepare for MBE?
To remove the oxide layer formed prior to loading the chamber.
Why is the atomic beam switched on and off during growth?
To allow different semiconductors to be grown in layers.
Why is the sample rotated during growth?
To ensure the layers are deposited uniformly.
Why is it important to maintain a high vacuum in a MBE system?
So no residual gases get incorporated into the growing semiconductor layers, degrading their quality.
If opened to the atmosphere what must be completed before MBE can recommence?
The ultra-high vacuum must be re-established and the chamber must be heated to high temperatures to remove gas atoms stuck to any surfaces.
What is Reflection High-Energy Electron Diffraction (RHEED)?
A method of monitoring the growth using electron beams aimed at a glancing angle to the surface so the diffraction pattern can be detected and an image formed.
What processes can RHEED monitor?
The oxide removal, surface temperature and the growth rates of the semiconductor.
What does the temperature of the substrate determine?
The probability of atoms sticking to the surface and their mobility across the growth surface.
What does the temperature of the effusion cells determine?
The flux intensity of the atoms and the species of the atoms.
What deposition process is Metal-Organic Vapour Phase Epitaxy?
A gas flow deposition process.
How is a semiconductor grown in MOVPE?
The substrate is heated to high temperatures and gases are flowed across the surface. The high temperatures cause the gases to react and deposit the relevant semiconductor.
What effect does layering semiconductors with different lattice constants have?
If the structure becomes thick enough the elastic strain energy increases and eventually breaks the bonds in the lattice.
Why do broken bonds have a detrimental effect on the quality of the semiconductor?
They allow an electron and a hole to recombine without generating a photon (radiative recombination).
What is the critical thickness?
The thickness at which the elastic energy is sufficient to break the bonds in the lattice.
