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Because MBE takes place in UHV and has relatively low pressure of residual gas at the surface, analysis techniques such as reflection high energy diffraction and ellipsometry can be used during growth, both to study and control the growth process. The UHV environment also allows pre or post growth analysis techniques such as Auger spectroscopy.

Elemental and molecular sources

The effusion cell is used for the majority of MBE growth. All materials used in the cell are carefully chosen to be noninteracting with the element being evaporated. For example, the crucible is pyrolitic boron nitride. However, it has disadvantages, such as:

  • The evaporated species may be molecular, rather than monomeric, which will require further dissocation at the surface.
  • When the shutter is opened, the heat loss from the cell results in a transient in the beam flux which last for several minutes and cause variations of up to 50%.
  • The growth chamber must be opened up to replace the solid sources.

Cracker cells are used to improve the ratio of monomeric to molecular (or at least dimeric to tetrameric) particles from the source. The cracker cell, placed so that the beam passes through it after the effusion cell, is maintained at a high temperature (and sometimes high pressure) to encourage dissociation. The dissociation process generally requires a catalyst and the best catalysts for a given species have been studied.

Some elements, such as silicon, have low enough vapor pressure that more direct heating techniques such as electron bombardment or laser radiation heating are used. The electron beam is bent using electromagnetic focusing to prevent any impurities in the electron source from contaminating the silicon to be used in MBE. Because the heat is concentrated on the surface to be evaporated, interactions with and contamination from the crucible walls is reduced. In addition, this design does not require a shutter, so there is no problem with transients. Modulation of the beam can produce very sharp interfaces on the substrate. In laser radiation heating, the electron beam is replaced by a laser beam. The advantages of localized heating and rapid modulation are also maintained without having to worry about contamination from the electron source or stray electrons.

Some of the II-VI (12-16) compounds have such high vapor pressure that a Knudson cell cannot be used. For example, the mercury source must be kept cooler than the substrate to keep the vapor pressure low enough to be feasible. The Hg source must also be sealed off from the growth chamber to allow the chamber to be pumped down.

Two other methods of obtaining the elements for use in epitaxy are gas-source epitaxy and chemical beam epitaxy (CBE). Both of these methods use gas sources, but they are distinguished by the use of elemental beams in gas source epitaxy, while organometallic beams are used in CBE. For the example of III-V (13-15) semiconductors, in gas epitaxy, the group III material may come from an effusion cell while the group V material is the hydride, such as AsH 3 or PH 3 , which is cracked before entering the growth chamber. In CBE, the group V material is an organometallic, such as triethylgallium [Ga(C 2 H 5 ) 3 ] or trimethylaluminum [Al(CH 3 ) 3 ], which adsorbs on the surface, where it dissociates.

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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Source:  OpenStax, Chemistry of electronic materials. OpenStax CNX. Aug 09, 2011 Download for free at http://cnx.org/content/col10719/1.9
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