Trimethylindium InMe3 is the most commonly used precursor for MOVPE deposition of indium-containing compound semiconductors. It is a solid with relatively low vapour pressure, but still sufficient for MOVPE applications.
Trimethylindium in combination with ammonia and with addition of HCl was used for InN film growth by MOVPE. The low decomposition temperature of InN and relatively high thermal stability of NH3 necessitate the use of a high NH3 /TMIn ratio to prevent In droplet formation on the surface. The addition of Cl in the form of HCl at Cl/ In molar ratio range of 0.3–1.4 to the growth chamber allowed the growth of high quality InN films without the formation of a second In phase at a very low value of the N/ In molar inlet ratio 2500. Photoluminescence spectra in the temperature range of 144 to 4.5 K showed a broad spectral band with a cutoff energy close to the reported minimum of the InN band gap energy 0.65 eV.[498] The explanation why addition of Cl to the deposition system can prevent deposition of In droplets during MOVPE of InN, is the following . At typical InN deposition temperatures, the dominant InClx species is InCl. The effect of adding HCl to the reactor can be seen by comparing the Gibbs energy of the etching reactions for liquid In and solid InN to produce InCl and H2 in addition to N2 in the InN case (Fig). It is clear that HCl attack of pure indium metal is preferred over reaction with InN and the large negative G° at typical growth temperature should yield a significant reaction extent. G° for etching InN is zero at 900 K, suggesting that at higher growth temperature, the addition of HCl will produce significant decrease in InN growth rate and possibly no growth.
The pyrolysis mechanisms of TMIn were first investigated in toluene carrier in 1964 [[i]]. The pyrolysis reaction was proposed to consist of three consecutive homolytic fission steps:
In(CH3)3 → (CH3)2In + CH3 (1)
In(CH3)2 → CH3In + CH3 (2)
In(CH3) → In + CH3 (3)
According to kinetic study, reactions (1) and (2) occur almost simultaneously yielding monomethylindium (InMe) as a reaction intermediate, relatively stable at temperatures lower than 480°C. At higher temperature, reaction
(3) proceeds to yield atomic indium as one of the final reaction products. InMe has been identified by in situ Raman spectroscopy in MOCVD conditions. [[ii]]
[i] M. G. Jacko, S. J. W. Price, Can. J. Chem., 1964, 42, 1198.
[ii] C. Park, W.S. Jung, Z.S. Huang, T.J. Anderson, J. Mater. Chem., 12(2), 356-360 (2002).
Trimethylindium is the most common precursor used for the deposition of InP layers by MOCVD/MOVPE
InMe3 was applied as precursor for the deposition of InGaO layers by MOCVD [[i]]
[i] C.E. Knapp, G.Hyett, I.P. Parkin, Claire J. Carmalt, Chem. Mater., 2011, 23 (7), pp 1719–1726, « Aerosol-Assisted Chemical Vapor Deposition of Transparent Conductive Gallium−Indium−Oxide Films »
Trimethyl-indium trimethyl-phosphine adduct InMe3·PMe3 is a low-melting solid (mp. 45°C) with vapor pressure from 5.5Torr at -20°C to 58.2 Torr at 30°C (vapor pressure vs. temperature equation logP(Torr) = 10.98 – 3204/T (K))
InMe3·PMe3 has been applied for the MOCVD as In-P single source precursor; the formation of unwanted polymer products during epitaxial growth could be avoided by this approach.
Thus, InMe3·PMe3 was used for MOCVD growth of InP epitaxial layers at 500°C, with a growth rate of ~1 µm/h. Background doping with net carrier concentration of n≏5-1015 cm-3 was achieved.[500]
Semi-insulating Fe-doped InP was grown by MOCVD using the adduct Me3In·PMe3 as the In source, and ferrocene as the dopant, at optimum temperatures of 600–650°C with 6 μm/h growth rate. Background doping level of n = (1−2)x1015 cm−3 and resistivity 2×108 Ωcm were achieved. Surface morphology change with growth temperature and V/III ratio was studied. [501]
Trimethylindium-triethylphosphorus adduct InMe3·PEt3 was applied as MOCVD precursor for the growth of InP epitaxial layers having good crystallographic quality and background carrier concentrations 2 x 1015 cm-3. [502]
The pyrolysis of InMe3·PEt3 on glass, InP (100) was studied by flow-tube method as part of an investigation of the MOCVD epitaxial deposition of InP. The adduct pyrolyses via gas-phase dissociation to the two constituents followed by InMe3 decomposition. [503]
Liquid adduct of trimethylindium with diisopropylamine InMe3·iPr2NH has been investigated as indium precursor for MOVPE growth of InP. Layers with low temperature mobilities in excess of 100,000 cm2/V•s could be grown. When growing InGaAs, some side reactions between InMe3-HNiPr2 and AsH3 were observed, which did not significantly affect the layer quality. [499]
The purity of ethyldimethylindium is an important factor that can affecting the layer quality. F.e., in 1990 measurements by Fourier transform ion cyclotron resonance mass spectrometry (FTICR) revealed the purity of ethyldimethylindium 73%, with some admixture of trimethylindium (10%) and methyldiethylindium (18%).[573]
Ethyldimethylindium InEtMe2 (EDMIn) in combination with tertiarybutylphosphine (TBP) was used for low-pressure metalorganic MOVPE of InP thin films. The growth rate dependence on the V/III ratios indicated that a EDMIn:TBP parasitic reaction exists. However, InP layers grown using EDMIn and TBP showed good electrical and optical properties, comparable to those using a conventional source material combination of trimethylindium (InMe3) and phosphine (PH3). The highest electron mobility at 77 K is 56000 cm2/V • s with a free carrier concentration of 1.0 × 1015 cm-3. Sharp and well resolved exciton peaks were observed in 4.0 K PL spectra. [504]
Ethyldimethylindium InEtMe2 was applied for the growth of high purity InP and InGaAs by low-pressure MOVPE on 2 inch InP substrates. InP layers had carrier concentrations ~ 1014 cm−3 and electron mobilities 109,000 cm2/V·s at 77 K. InGaAs films background doping was in the low 1015 cm−3 range and electron mobilities ~9500 cm2/V·s at 300 K and 45,000 cm2/V·s at 77 K; X-ray rocking curves had a FWHM <30 arcsec (10−4 lattice constants). InEtMe2 was directly compared with InMe3: at identical partial pressures of both precursors, the growth rate of InP was ~100% higher by using InEtMe2, the growth efficiency was increased due to a lower thermal stability of the ethyldimethylindium. [505]
Triethylindium InEt3 is very unstable and therefore was considered as less suitable as precursor for MOCVD applications. However, it was reported to be used for the growth of epitaxial InGaP layers by ALD and In2O3 by CVD.
Triethylindium InEt3 and oxygen were applied for the In2O3 growth by thermal CVD on sapphire at 350°C substrate temperature. The vertically aligned rod-like structure with triangular cross section having cubic structure were grown, exhibiting preferred crystallographic orientation in the [111] direction. Visible emission was observed in the photoluminescence spectra of In2O3 structures under excitation at 325 nm. [506]
InGaP layers were grown by ALD using InEt3 as indium source. The films were closely matching GaAs substrates irrespective of the growth conditions. The growth was performed by alternate exposures to InEt3, PH3, GaMe3, and PH3 fluxes. Band gap of 1.78 eV, the lowest value reported for ordered alloys, was found by room-temperature photoreflectance. Photoluminescence shows an anomalous temperature dependence; TEM indicate that ordering takes place preferentially on (111) alternating planes. [507]
InMe(iPr)2 has ben proposed as potential for In-contaning layers MOCVD [[i]]
[i] DV Shenai-Khatkhate… - US Patent 7,166,734, 2007 - Google Patents
http://www.freepatentsonline.com/y2006/0047132.html