Quantum Well Structures and FabricationsA PRESENTATION OF THE DIFFERENT QUANTUM WELL STRUCTURES AND THEIR FABRICATION PROCESS BY TIM KOSANKE AND BLAKE CARLSON

MAY 1, 2013

Key Concepts• What is a quantum well and what does it do?

• What materials are used to fabricate the quantum well structures and methods of fabrication?

• What are the practical uses of quantum well structures and how do they apply to the real world?

What is a quantum well?• A quantum well is similar to a

potential well, the difference being that is only contains discrete energy values. [8]

• Generally, a quantum well is formed when a thin layer of a narrow-gap semiconductor material lies between a thicker layer of wider-gap material. [1]

• The size of the quantum wells are generally between 1 and 20 nm. [1]

Example of a GaAs rectangular well [4]

The Behavior of Quantum Well Structures• Band gaps act as a barriers between the ground state bands and

conduction bands, preventing electrons from reaching the conduction band unless they gain more energy.

• Once an electron reaches the conduction band, the excess energy is released and the electron falls back to its ground state.

• If the gaps are too wide for electrons to jump easily, thin semiconductors are placed in the gap area.

• This allows for easy manipulation of the electrons and their energy.

• The wells create narrow streams of energy making it more focused. [1]

More examples of quantum well structures

Example of a parabolic quantum well [4]

Second example of rectangular quantum well [7]

Commonly used materials and methods of quantum well fabrication• Some of the commonly used materials used to create

quantum wells include: Gallium Arsenide between Aluminum Arsenide and Indium Gallium Nitride between Gallium Nitride.

• There are two methods of fabrication which include: molecular beam epitaxy and chemical vapor deposition. [8]

Molecular Beam Epitaxy• Epitaxy means the growth of a film

with a crystallographic relationship between substrate and the film.

• Creating quantum wells like this is often expensive but highly accurate.

• The process is often carried out in a vacuum and uses multiple alloys to grow the alloy films. [3]

• Elements are heated until they are gaseous and then condense onto the wafer.

• The term beam refers to the evaporated atoms that do not interact with each other until they reach the wafer. [6]

Typical components and layout of the main chamber of MBE system

[6]

Chemical Vapor Deposition• Similar to BME, but instead

is a chemical process where the wafer is exposed to volatile precursors, which then react and decompose on the substrate to create the film.

• A precursor is a chemical compound that takes part in the chemical reactions producing another chemical compound. [2]

A chemical vapor deposition method using plasma [2]

Practical Uses of Quantum Well Structures • Quantum wells can be seen

mostly in the making of diode lasers. [1]

• These lasers include red lasers for DVDs and handheld laser pointers, infrared lasers for fiber optic transmitters, and blue lasers for Blu-ray players, etc… [7]

• The Navy has recently demonstrated that a laser can be used to destroy surveillance drones. Video of Navy using a laser to take down

a surveillance drone [5]

Summary and Conclusion• Quantum wells are potential wells with discrete energy

values.

• Quantum wells are formed using one of two methods: molecular beam epitaxy or chemical vapor deposition.

• Quantum wells are seen mostly in the fabrication of laser diodes.

• Quantum wells have lead to some very useful products in our society, i.e. Blu-ray lasers, DVD lasers, free electron lasers (medical purposes, military uses).

References• [1] Bates, Angie. "What Is a Quantum Well?" WiseGeek. Ed. Lauren Fritsky.

Conjecture, n.d. Web. 28 Apr. 2013. <http://www.wisegeek.com/what-is-a-quantum-well.htm>.• Used to describe what a quantum well is, the behavior of a quantum well, and what they are used

in.

• [2] "Chemical Vapor Deposition." Wikipedia. Wikimedia Foundation, 21 Apr. 2013. Web. 28 Apr. 2013. <http://en.wikipedia.org/wiki/Chemical_vapor_deposition>.• Used to describe the CVD process.

• [3] Christensen, Thomas M. "Physics of Thin Films." Molecular Beam Epitaxy. University of Colorado, Colorado Springs, 17 Mar. 2010. Web. 29 Apr. 2013. <http://www.uccs.edu/~tchriste/courses/PHYS549/549lectures/mbe.html>.• Used to explain the MBE process.

• [4] Frensley, William R. "Quantum Wells." Quantum Wells. University of Texas, Dallas, 21 May 1995. Web. 28 Apr. 2013. <http://www.utdallas.edu/~frensley/technical/hetphys/node11.html>.• Used as a resource for rectangular and parabolic quantum well structure pictures.

References Cont.• [5] Knightskross. "U.S. Navy Laser Test Takes Down Drone." YouTube. YouTube,

08 Apr. 2013. Web. 28 Apr. 2013. <http://www.youtube.com/watch?v=l5qKSKsfUPM>.• Used for video of Navy laser destroying surveillance drone.

• [6] "Molecular Beam Epitaxy." Wikipedia. Wikimedia Foundation, 21 Apr. 2013. Web. 28 Apr. 2013. <http://en.wikipedia.org/wiki/Molecular_beam_epitaxy>.• Used to describe the MBE process.

• [7] Schubert, E. F. "Quantum Wells (QWs)." Rensselaer Polytechnic Institute, 2003. Web. 28 Apr. 2013. <http://www.ecse.rpi.edu/~schubert/Course-ECSE-6290%20SDM-2/1%20QWs%20MQWs%20and%20SLs.pdf>.• Used as a resource for a quantum well structure picture.

• [8] "Quantum Well." Wikipedia. Wikimedia Foundation, 29 Mar. 2013. Web. 28 Apr. 2013. <http://en.wikipedia.org/wiki/Quantum_well>. • Used to describe some of the uses of quantum wells and what a quantum well is.

List of Five Key Concepts• Quantum wells are similar to potential wells but with

discrete energy values.

• Quantum wells are placed so electrons can jump from valence band to conduction band more easily.

• Quantum wells create a more focused, narrow stream of energy.

• Quantum wells are created using either molecular beam epitaxy or chemical vapor deposition.

• Quantum wells are seen mostly in the fabrication of laser diodes.