Metalorganic vapour phase epitaxy

Metalorganic vapour phase epitaxy (MOVPE) is a chemical vapour deposition method of epitaxial growth of materials, especially compound semiconductors from the surface reaction of organic compounds or metalorganics and metal hydrides containing the required chemical elements. For example, indium phosphide could be grown in a reactor on a substrate by introducing Trimethylindium ((CH₃)₃In) and phosphine (PH₃). Alternative names for this process include organometallic vapour phase epitaxy (OMVPE), metalorganic chemical vapour deposition (MOCVD) and organometallic chemical vapour deposition (OMCVD). Formation of the epitaxial layer occurs by final pyrolisis of the constituent chemicals at the substrate surface. In contrast to molecular beam epitaxy (MBE) the growth of crystals is by chemical reaction and not physical deposition. This takes place not in a vacuum, but from the gas phase at moderate pressures (2 to 100 kPa). As such this technique is preferred for the formation of devices incorporating thermodynamically metastable alloys. It has become the dominant process for the manufacture of laser diodes, solar cells, and LEDs.

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Reactor components

• A reactor is a chamber made of a material that does not react with the chemicals being used. It must also withstand high temperatures. This chamber is composed by reactor walls, liner, a susceptor, gas injection units, and temperature control units. Usually, the reactor walls are made from stainless steel or quartz. To prevent over heating, cooling water must be flowing through the channels within the reactor walls. Special glasses, such as quartz or ceramic, are often used as the liner in the reactor chamber between the reactor wall and the susceptor. A substrate sits on a susceptor which is at a controlled temperature. The susceptor is made from a material resistant to the metalorganic compounds used; graphite is sometimes used. For growing nitrides and related materials, a special coating on the graphite susceptor is necessary to prevent corrosion by ammonia (NH₃) gas.

• Gas inlet and switching system. Gas is introduced via devices known as 'bubblers'. In a bubbler a carrier gas (usually nitrogen or hydrogen) is bubbled through the metalorganic liquid, which picks up some metalorganic vapour and transports it to the reactor. The amount of metalorganic vapour transported depends on the rate of carrier gas flow and the bubbler temperature. Allowance must be made for saturated vapours.

• Pressure maintenance system

• Gas Exhaust and cleaning System. Toxic waste products must be converted to liquid or solid wastes for recycling (preferably) or disposal. Ideally processes will be designed to minimize the production of waste products.

Metalorganic gases

A non-exhaustive list of metalorganic chemicals used to grow semiconductors by MOVPE.

• Aluminium
  • Trimethylaluminium CAS 75-24-1
  • Triethylaluminium CAS 97-93-8

• Gallium
  • Trimethylgallium (TMG or TMGa)
  • Triethylgallium (TEG or TEGa)
  • Triisopropylgallium (TIPG or TIPGa) Ga(C₃H₇)₃

• Indium
  • Trimethylindium (TMI or TMIn)
  • Triethylindium (TEI or TEIn)
  • Di-isopropylmethylindium (DIPMeIn)

• Germanium
  • Isobutylgermane (IBGe)
  • Dimethylamino germanium trichloride (DMAGeC)

• Nitrogen
  • Phenyl hydrazine
  • Dimethylhydrazine
  • Ammonia

• Phosphorus
  • Phosphine
  • Tertiarybutyl phosphine (TBP)

• Arsenic
  • Arsine AsH₃
  • Phenylarsine
  • Tertiarybutyl arsine (TBAs)

• Antimony
  • Trimethyl antimony (TMSb)
  • Triethyl antimony (TESb)
  • Stibine SbH₃

• Cadmium
  • Dimethyl cadmium (DMCd)

• Tellurium
  • Dimethyl telluride (DMTe)
  • Diethyl telluride (DETe)
  • Diisopropyl telluride (DIPTe)

Semiconductors grown by MOVPE

III-V semiconductors

• AlGaAs
• AlGaInP
• AlGaN
• AlGaP
• GaAsP
• GaAs
• GaN
• GaP
• InAlAs
• InAlP
• InSb
• InGaAlAs
• InGaAlN
• InGaAsN
• InGaAsP
• InGaAs
• InGaN
• InGaP
• InN
• InP

II-VI semiconductors

• Zinc selenide (ZnSe)
• HgCdTe
• ZnO
• Zinc sulfide (ZnS)

IV Semiconductors

• Si
• Ge
• Strained silicon

See also

• Thin-film deposition

Environment, Health and Safety

• Environment, Health and Safety Aspects of Metalorganic Sources used in MOVPE Growth of Compound Semiconductors: From Journal of Crystal Growth (2004).

Further reading

Gerald B. Stringfellow (1999). Organometallic Vapor-Phase Epitaxy: Theory and Practice (2nd ed.). Academic Press (ISBN 0-12-673842-4).