Epitaxial growth and the physics of quantum wells Flashcards

1
Q

What deposition technique is Molecular Beam Epitaxy?

A

An ultra-high vacuum technique.

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2
Q

Why are high temperatures used to prepare for MBE?

A

To remove the oxide layer formed prior to loading the chamber.

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3
Q

Why is the atomic beam switched on and off during growth?

A

To allow different semiconductors to be grown in layers.

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4
Q

Why is the sample rotated during growth?

A

To ensure the layers are deposited uniformly.

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5
Q

Why is it important to maintain a high vacuum in a MBE system?

A

So no residual gases get incorporated into the growing semiconductor layers, degrading their quality.

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6
Q

If opened to the atmosphere what must be completed before MBE can recommence?

A

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.

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7
Q

What is Reflection High-Energy Electron Diffraction (RHEED)?

A

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.

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8
Q

What processes can RHEED monitor?

A

The oxide removal, surface temperature and the growth rates of the semiconductor.

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9
Q

What does the temperature of the substrate determine?

A

The probability of atoms sticking to the surface and their mobility across the growth surface.

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10
Q

What does the temperature of the effusion cells determine?

A

The flux intensity of the atoms and the species of the atoms.

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11
Q

What deposition process is Metal-Organic Vapour Phase Epitaxy?

A

A gas flow deposition process.

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12
Q

How is a semiconductor grown in MOVPE?

A

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.

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13
Q

What effect does layering semiconductors with different lattice constants have?

A

If the structure becomes thick enough the elastic strain energy increases and eventually breaks the bonds in the lattice.

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14
Q

Why do broken bonds have a detrimental effect on the quality of the semiconductor?

A

They allow an electron and a hole to recombine without generating a photon (radiative recombination).

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15
Q

What is the critical thickness?

A

The thickness at which the elastic energy is sufficient to break the bonds in the lattice.

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16
Q

What is an exciton?

A

A system of an electron and a hole.

17
Q

How is the energy of an electron and a hole affected in an exciton?

A

The energy is reduced by an amount known as the exciton binding energy.

18
Q

Give two reasons energy calculations will be overestimates.

A

We assume potential wells are infinite and we do not include the exciton binding energy in our simple model.