Gallium Nitride

Halide/Hydride vapor phase epitaxy

Gallium Monochloride precursor

In typical HVPE process for GaN deposition gallium monochloride GaCl and ammonia NH3 are used as precursors of gallium and nitrogen:

GaCl+NH3=GaN+HCl+H2

The reaction is exothermic, and the reaction driving force decreases with increasing temperature:

Typical deposition temperature for epitaxial growth is 800-1100°C. At lower temperatures the deposition rate decreases due to reaction kinetic limitation, at higher temperatures the deposition rate decreases as a result of a decrease in supersaturation:

GaN HVPE deposition rate temperature dependence
GaN HVPE deposition rate temperature dependence

Gallium trichloride precursor

GaN deposition by  reaction of gallium trichloride GaCl3 and ammonia

GaCl3 + NH3 = GaN + 3HCl

is endothermic and the reaction driving force increases with increasing temperature, that makes possible to deposit GaN at temperatures 1300-1400°C:

 

Maruska, H. P. and Tietjen, J. J., “The preparation and properties of vapor-deposited single-crystalline GaN”, Applied Physics Letters 15, 10 (1969), pp. 327-329.

Ban, Vladimir S., “Mass Spectrometric Studies of Vapor-Phase Crystal Growth II.”, Journal of the Electrochemical Society 119, 6 (1972), pp. 761–765.

Seifert, W. and Fitzl, G and Butter, E., “Study on the growth rate in VPE of GaN”, Journal of Crystal Growth 52 (1981), pp. 257–262.

Fornari, R. and Bosi, M. and Armani, N. and Attolini, G. and Ferrari, C. and Pelosi, C. and Salviati, G., “Hydride vapour phase epitaxy growth and characterisation of GaN layers”, Materials Science and Engineering: B 79, 2 (2001), pp. 159–164.

Usui, A., “Bulk GaN crystal with low defect density grown by hydride vapor phase epitaxy”, дюйм MRS Proceedings vol. 482, no. 1 (, 1997).

Malinovsky, V. V. and Marasina, L. A. and Pichugin, I. G. and Tlaczala, M., “The Growth Kinetics and Surface Morphology of GaN Epitaxial Layers on Sapphire”, Crystal Research and Technology 17, 7 (1982), pp. 835–840.

Koukitu, Akinori and Mayumi, Miho and Kumagai, Yoshinao, “Surface polarity dependence of decomposition and growth of GaN studied using in situ gravimetric monitoring”, Journal of Crystal Growth 246, 3 (2002), pp. 230–236.

Murakami, H., Takekawa, N., Shiono, A., Thieu, Q. T., Togashi, R., Kumagai, Y., … & Koukitu, A. (2016). Tri-halide vapor phase epitaxy of thick GaN using gaseous GaCl3 precursor. Journal of Crystal Growth, 456, 140-144.

Gallium CVD precursors

Halide precursors (HVPE)

Gallium Trichloride GaCl3

  • Melting point 78°C
  • Boiling point 201°C
  • Condensed phase density 2.47g/cm3 (at 25°C)
  • Molar mass  176.08 g/mol
GaCl3 saturated vapor pressure
Saturated vapor pressure of Gallium Trichloride (GaCl3)

Gallium Tribromide GaBr3

  • Melting point 122°C
  • Boiling point 279°C
  • Condensed phase density  3.69g/cm3 (at 25°C)
  • Molar mass  309.4g/mol

Gallium Triiodide GaI3

  • Melting point  210°C
  • Boiling point  346°C
  • Condensed phase density  4.15g/cm3 (at 25°C)
  • Molar mass   450.4g/mol

Metallic gallium chlorination

Gallium chlorides can be produced inside a reactor, by passing dry hydrogen chloride (HCl) or Chlorine (Cl2) gas over a boat with liquid gallium. The composition of produced chlorides mainly depends on chlorination temperature – at temperatures below ~350°C Gallium trichloride GaCl3 and it’s dimer Ga2Cl6 are main reaction products. At higher temperatures gallium monochloride GaCl becomes dominant.

Ga chlorination vapor composition
Main products of gallium chlorination with Hydrogen Chloride (HCl)