Surface Science: Foundations of Catalysis and Nanoscience

Chapter 7. Growth & Epitaxy: Supplemental Material

The 2014 Nobel Prize in physics was awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura “for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources”. Paraphrasing from Nobelprize.org, the first LEDs were studied and constructed during the 1950s and 1960s. They emitted light at different wavelengths, from the infrared to the green. However, emitting blue light proved to be a difficult task, which took three more decades to achieve. It required the development of techniques such as MBE and MOVPE for the growth of high-quality crystals as well as the ability to control p-doping of semiconductors with high bandgap, which was achieved with GaN only at the end of the 1980s. The development of efficient blue LEDs also required the production of GaN-based alloys with different compositions (such as AlGaN and InGaN) and their integration into multilayer structures such as heterojunctions and quantum wells. The development of efficient blue LEDs is a fascinating story at the intersection of surface science, materials science and solid state physics. The history of development for gallium-nitride-based light-emitting diodes (LEDs) is reviewed by Nakamura and Krames in this article.

The 2014 Nobel Prize in physics built on the foundation laid by Zhores I. Alferov and Herbert Kroemer, who won the 2000 Nobel Prize in physics "for developing semiconductor heterostructures used in high-speed- and opto-electronics" and to Jack S. Kilby "for his part in the invention of the integrated circuit". Kroemer described his work in this paper. Alferov's address is found here. These papers contain short reviews of the physics, technology of preparation and applications of quantum wells and superlattices.

Etching can be performed with either a liquid phase or a gas phase in contact with the solid. I do a lot of work on etching silicon in aqueous solutions to form porous silicon. You can read more about ther here.

Laser induced processes with a reactive gas phase can also be used to modify the structure of solids and you can read more about that here.

You can learn more about surface structure modification and corrosion from the Surface Science and Corrosion Group in Erlangen.

Integrated circuits (as well as many micromachines and nanoscale devices) are fabricated in cleanrooms. The technology behind this fundamental application of surface science is complex and well developed. Here is an introduction to the machinery and science behind cleanrooms, lithography and device fabrication from BYU.

Questions and Exercises

  1. Calculate the relative impingement rates of Ga and As if Ga is dosed as TMG and As is dosed from AsH3 with both gases held at 300 K and 10-4 Pa.
  2. Why does the growth rate of Si during SiH4 CVD increase rapidly as the temperature is increased about 800 K, eventually reaching a rate limited only by the SiH4 flux?
  3. Calculate the relative rates of adsorption of Si from SiH4 and Si2H6 if both gases are dosed onto a surface at 10-4 Pa and 900 K. Note that SiH4 adsorption has an activation barrier of 14 kJ mol-1 and Si2H6 has and activation energy of -3 kJ mol-1. Assume that the preexponential factor for the sticking coefficient is unity in both cases.
  4. What is the difference between stress and strain?
  5. What is a sharp interface?
  6. What is the critical thickness of an epitaxial layer?
  7. The Stranski-Krastanov growth mode is the most common in semiconductor heteroepitaxy. Describe it.
  8. Describe Ostwald ripening and its driving force.
  9. What is the only growth mode that is observed at equilibrium for homoepitaxy?
  10. Why is step down diffusion more likely than step up diffusion?
  11. Why does kinetically controlled homoepitaxial growth on the (100) plane of fcc metals generally lead to flatter surfaces than growth on (111) planes?
  12. What types of structures are associated with catalytic growth?
  13. Explain the difference between float growth and root growth.
  14. What is the difference between a pit and a pore?
  15. What is the difference between anodic and electroless etching?
  16. What leads to porous solid formation during etching rather than simple surface roughening?

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