TELLURIUM ALKYLS
Several organotellurium compound, including alkyls, effective screened and characterized for their application as MOVPE precursors. In particular, accurate vapour pressure measurements of these compounds were performed.[i]
[i] J.E. Hails, S.J.C. Irvine, J. Crystal Growth, 1991, Vol. 107, Iss. 1–4, p. 319-324, « Screening of organotellurium compounds for use as MOVPE precursors », https://doi.org/10.1016/0022-0248(91)90477-M, https://www.sciencedirect.com/science/article/pii/002202489190477M
Dimethyltellurium (dimethyltelluride) TeMe2
Vapor pressure of dimethyltellurium TeMe2: logP (Torr) = 7.97 – 1865/ T(K)
Dimethyltellurium TeMe2 (M = 157.68) is pale yellow liquid (d = 1.96 g/ml), with melting point -10°C, boiling point 82°C. TeMe2 has vapor pressure (Torr): 40.6/ 20°C, 51.9/ 25°C (other data 51/ 25°C), 65.8/ 30°C, 82.8/ 35°C, 103.4/ 40°C, 128.3/ 45°C, 158.1/ 50°C,
Vapor pressure formula: logP (Torr) = 7.97 – 1865/ T(K) (Fig.)
TeMe2 for CdTe by MOCVD
Gas phase composition of the byproducts during CdTe films growth by MOVPE (mole fraction of CH4 and C2H6 byproducts versus H2 mole fraction)
Dimethyltellurium TeMe2 (with CdMe2 as Cd precursor), was used as Te source for the deposition of CdTe layers on GaAs substrates by MOCVD at 150-600°C temperature, using H2 or He carrier gas; the growth results were compared to the quantum chemical calculations.
The growth rate of CdTe using H2 carrier gas is bv a factor of ~3 higher than using He as carrier. It was suggested that atomic hydrogen is produced in the reaction between methyl radical adsorbed on the surface and H2 molecules; atomic H quickly reacts with precursor molecules (like TeMe2), producing TeMe species that adsorb on the surface and thus increase the growth rate.
The kinetic constants for the gas phase reaction TeMe2 + H -> TeMe + CH4 , calculated with quantum chemical method B3LYP/3-21G ( k=A*exp(-Ea/RT), were determined to be LogA = 13.8, Ea/R=3150 (units consistent with mol, cm3, s)
The proposed surface kinetic scheme for CdTe growth is presented in Table [i]:
Gas phase composition of the byproducts during CdTe films growth by MOVPE (mole fraction of CH4 and C2H6 byproducts versus H2 mole fraction) confirms the proposed CdTe growth mechanism (Fig):
[i] H. Hill, D.J. Hunt, S.J.C. Irvine, WO/1991/018129
Table . Surface kinetic scheme for CdTe CVD growth using TeMe2 (and CdMe2)
TeMe2 for CdZnTe by MOVPE
Dimethyltellurium (dimethyltelluride) TeMe2 was applied as Te-precursor for the growth of (100)-oriented CdZnTe layers by atmospheric-pressure MOVPE. The growth mechanism
of CdZnTe (abrupt increase of composition to ZnTe over Zn/Cd >0.8 in the gasphase) layers was explained by the differences in the growth characteristics of CdTe and ZnTe, namely higher growth rate of CdTe vs. ZnTe and higher desorption rate from the growth
surface for Zn vs Cd species. High crystal quality CdZnTe layers were grown in a wide range of Zn compositions, with double-crystal XRD ROC FWHM being the best (<320 arc-sec) for x<0.3 and x>0.75. [i]
[i] K. Yasuda, K. Mori, Y. Kubota, K. Kojima, F. Inukai, Y. Asai and T. Nimura, J. Electronic Materials, 1998, Vol.27, Number 8, 948-953, DOI: 10.1007/s11664-998-0126-z, "Growth characteristics of CdZnTe layers grown by metalorganic vapor phase epitaxy using dimethylzinc, dimethylcadmium, diethyltelluride, and dimethyltelluride as precursors "
TeMe2 for HgTe by MOVPE
Dimethyltellurium TeMe2 (combined with HgMe2 as mercury source), was applied for the epitaxial growth of HgTe layers on CdTe substartes by glow discharge PECVD at low deposition temperature Tdep = 85°C. []
Diethyltellurium (diethyltelluride) TeEt2
TeEt2 vapor pressure formula: logP (Torr) = 7.99 – 2093/ T(K))
Diethyltellurium (diethyltelluride) TeEt2 (M = 185.7), is amber liquid with melting point mp.<-78°C, boiling point bp.137°C, density d = 1.599 g/ml (20°C). Diethyltellurium is quite volatile with following vapor pressure (Torr) variation vs. temperature: 7.1/ 20°C, 9.3/ 25°C, 12.2/ 30°C, 15.8/ 30°C, 20.3/ 40°C, 25.8/ 45°C, 32.6/ 50°C. (vapor pressure formula written in Arrhenius coordinates form is logP (Torr) = 7.99 – 2093/ T(K)).
Synthesis of TeEt2:
Laboratory scale: Sodium Na is reacting with Te metal in liquid NH3 followed by reaction of formed Na2Te with bromoethane EtBr. This reaction is satisfactory, although some amount of polyalykyltellurides. (Et2Ten n≥2) may be formed. Although polytellurides break down on heating producing Et2Te and tellurium metal, but yields of Et2Te are significantly lowered.
Industrial scale synthesis of Et2Te: the safe handling of large atmosphere of “white spot” nitrogen purified by amounts of liquid ammonia can be problematic technically. Another method was developed, which includes production of Na2Te in aqueous solution, followed by direct reaction with bromoethane. The Et2Te formed by this method is very pale yellow liquid, that can readily be extracted and purified, and is obtained in high yield and is practically polytelluride-free. [[i]]
Diethyltellurium was successfully applied as Te source for the deposition of thin layers of metal tellurides by MOCVD.
[i]D.V. Shenai-Khatkhate, E.D. Orrell, J.B. Mullin, D.C. Cupertino, D.J. Cole-Hamilton, J. Cryst. Growth, Vol. 77, Iss. 1–3, 1986, p.27-31, « Preparation and purification of metal alkyls for use in the MOCVD growth of II/VI compound semiconductors », https://doi.org/10.1016/0022-0248(86)90277-0
https://www.sciencedirect.com/science/article/pii/0022024886902770
TeEt2 for ZnTe by laser-assisted MOVPE
Diethyltelluride TeEt2, in combination with ZnMe2, was applied as precursor for the ZnTe growth on (100),
(110) and (111) Zn and Te substrates by Ar+-ion laser-assisted MOVPE at atmospheric pressure. Good-quality epitaxial layers were grown at low substrate temperatures by using the (100) substrates. For (100)-oriented substrates, the growth rate was strongly
enhanced under illumination, with quantum yield for forming ZnTe molecules by photons being as high as 3%. By comparison of the precursor transport rate and the growth rate, it was concluded that both the diethyltelluride and the dimethylzinc precursors become
decomposed by illumination. However, for other substrate orientations, the effect of illumination to the growth rate was nearly absent, meaning that source gas molecules were effectively decomposed on the (100) surfaces under illumination.[i]
[i] M. Nishio, H. Ogawa, A. Yoshida, J. Cryst. Growth, 1991, vol.115, iss.1–4, p.284–288, "Effect of Ar laser-illumination upon ZnTe growth in atmospheric-pressure MOVPE"
TeEt2 for ZnTe/HgTe superlattices by MOVPE
Diethyltellurium TeEt2 was applied as Te source for the deposition of ZnTe/HgTe superlattices on { }B CdTe, { }B GaAs and {100} GaAs substrates by MOVPE. It was found that the presence of the Zn precursor, dimethyl zinc (DMZn) seriously affected the growth of HgTe, requiring to ensure complete flushing of the reactor between ZnTe and HgTe phases of the growth cycle. SEM, EDX, RHEED, XTEM and IR transmission spectroscopy were used for ZnTe/HgTe superlattice characterisation.[i]
[i] P.A. Clifton, J.T. Mullins, P.D. Brown, N. Lovergine, A.W. Brinkman, J. Woods, Journal of Crystal Growth, Vol. 99, Iss. 1–4, January 1990, Pages 468–472, "Growth of HgTe-ZnTe strained layer superlattices by MOVPE "
TeEt2 for CdZnTe MOVPE
Diethyltellurium (diethyltelluride) TeEt2 has been applied used as Te-precursor for the atmospheric-pressure MOVPE deposition of (100)-oriented Cd1-xZnxTe
films (and compared with TeMe2 as Te-source). Cd1-xZnxTe layers having high crystal quality were obtained with double-crystal XRD rocking curve FWHM <320 arc-sec for x<0.3 and x>0.75. [i]
[i] K. Yasuda, K. Mori, Y. Kubota, K. Kojima, F. Inukai, Y. Asai, T. Nimura, J. Electronic Materials, 1998, Vol.27, No. 8, 948-953, DOI: 10.1007/s11664-998-0126-z, « Growth characteristics of CdZnTe layers grown by metalorganic vapor phase epitaxy using dimethylzinc, dimethylcadmium, diethyltelluride, and dimethyltelluride as precursors »
Diisopropyltelluride (diisopropyltellurium) TeiPr2
Fig. Vapor pressure formula for TeiPr2 : logP (Torr) = 8.288 – 2309/ T(K)
Diisopropyltelluride TeiPr2 (M = 213.77) is light yellow-orange liquid (d = 1.365 g/ml) with melting point -55°C, boiling point 49°C/ 14 Torr,
Vapor pressure (Torr): 2.6/20°C, 3.5/25°C, 4.65 (other data 5)/30°C, 6.2/35°C, 8.1/40°C, 10.6/45°C, 13.8/50°C, 55/ 80°C;
Vapor pressure formula in Arrhenius form (Fig.) : logP (Torr) = 8.288 – 2309/ T(K)
TeiPr2 (+ZnMe2(Et3N), ZnEt2) for ZnTe by AP MOVPE
Fig. TeiPr2 vapor pressure vs temp in Arrhenius coordinates
Diisopropyltelluride TeiPr2 (combined with ZnMe2(Et3N) and ZnEt2) was applied as Te source for the atmospheric pressure MOVPE growth of zinc telluride ZnTe layers
on GaAs (100), GaSb (100) and ZnTe (100) substrates at 350°C. The deposited ZnTe films were characterized by Hall effect measurements and PL at 2 K. Light hole, heavy hole and bound exciton transitions were well resolved in the PL spectra; most of the
transitions were assigned. The dependence of purity of the ZnTe on the composition and stoichiometry of the substrates was studied. The partial pressure ratios of the alkyls metalorganic precursors (TeiPr2 vs ZnMe2(Et3N) or ZnEt2) were optimized; the applicability
of various As, Bi, Ga, In and I alkyls as p- or n-type dopants for ZnTe was investigated, it was determined that tetraethylbiarsine As2Et4 and ethyliodide EtI are promising alkyls for p- and n-type doping of ZnTe. [[i]]
[i] W Kuhn, H P Wagner, H Stanzl, K Wolf, K Worle, S Lankes, J Betz, M Worz, D Lichtenberger, H Leiderer, W Gebhardt, R Triboulet, Semicond. Sci. Technol. 1991, 6 A105 doi:10.1088/0268-1242/6/9A/019, « The MOVPE growth and doping of ZnTe »
TeiPr2 (+Ge[NMe2]4] for C-doped GeTe MOCVD
Fig. Optical reflectivity vs. temperature for GeTe, GeTeC4% and GeTeC10% blanket layers (at constant temperature rate 10 °C/min). The sudden transition is the signature of the crystallization process.
Te(iPr)2, combined with Ge[NMe2]4, was applied as Te precursor for MOCVD deposition of carbon-doped GeTe (GeTeC) layers as novel material for Phase-Change Memories
(PCM). Initially, GeTeC blanket layers were investigated, with focus on GeTeC amorphous phase stability (analysed by optical reflectivity and electrical resistivity measurements),
and on GeTeC structure and composition (determined by XRD and Raman spectroscopy). GeTeC-based PCM devices electrical properties (resistance drift, data retention performances, RESET power and current, SET time) were measured. GeTeC-based devices demonstrated
very good data retention properties and reduction of RESET current, making them suitable for both embedded and stand-alone PCM applications.[[i]]
[i] G. Betti Beneventi, L. Perniola, V. Sousa, E. Gourvest, S. Maitrejean, J.C. Bastien, A. Bastard, B. Hyot, A. Fargeix, C. Jahan, J.F. Nodin, A. Persico, A. Fantini, D. Blachier, A. Toffoli, S. Loubriat, A. Roule, S. Lhostis, H. Feldis, G. Reimbold, T. Billon, B. De Salvo, L. Larcher, P. Pavan, D. Bensahel, P. Mazoyer, R. Annunziata, P. Zuliani, F. Boulanger, Solid-State Electronics, 2011, Vol. 65–66, p. 197–204, Selected Papers from the ESSDERC 2010 Conference, Carbon-doped GeTe: A promising material for Phase-Change Memories
http://www.sciencedirect.com/science/article/pii/S0038110111002383
TeiPr2 (+ZnMe2, ZnEt2) for ZnTe by MOVPE
Diisopropyltelluride TeiPr2 (DIPTe), combined with ZnMe2 or ZnEt2, was applied for the deposition of zinc telluride (ZnTe) thin films by MOVPE. The reaction chemistry of the ZnTe growth
process was studied by on-line gas chromatography and IR spectroscopy. Two growth regimes depending on the II/VI ratio were revealed: in the first regime (using low II/VI ratio), the group VI compound (TeiPr2) was consumed in excess, whereas in the
second regime (using higher II/VI ratio values) the group II compound (ZnMe2 or ZnEt2) was consumed in excess. The crossover point was at II/VI = 5.0 for DMZn and at II/VI = 0.3 for DEZn, however under all growth conditions stoichiometric ZnTe layers were
obtained. The excess consumed TeiPr2 was converted into volatile diisopropylditelluride Te2IPr2 and isopropyltellurol iPrTeH; whereas the excess consumed DEZn or DMZn produced zinc metal; these byproducts accumulated in the outlet of the reactor. The hydrocarbon
products generated from the iPr and Et ligands indicated radical disproportionation, recombination, and hydrogenation reactions; however, Me ligands underwent mainly surface hydrogenation producing CH4. [[i]]
[i] K.J. Wilkerson, M.J. Kappers, R.F. Hicks, J. Phys. Chem. A, 1997, 101 (13), p.2451–2458, DOI: 10.1021/jp963990c, « Reaction Chemistry of ZnTe Metalorganic Vapor-Phase Epitaxy »
J. Phys. Chem. A, 1997, 101 (13), pp 2451–2458, DOI: 10.1021/jp963990c
Di-n-propyltelluride (di-n-propyltellurium) TenPr2
Fig. Te(nPr)2 vapor pressure plot (Arrhenius coordinates)
Te(nPr)2 is much less volatile than Te(Pri)2; the pressure measurements were very consistent, giving linear dependence in the Arrhenius coordinates: lgP(Torr)=8.857-2620/T. The Arrhenius plot is shown in Fig. : the extrapolation of vapour pressure equation gave 1.62 Torr at 30°C (vs. previously published vapour pressure 2.0 Torr at 30°C) [4]. At 20°C the vapour pressure is 0.82 Torr (below the usual criteria of 1 Torr/ 20°C for suitability as an MOVPE precursor for (Hg,Cd)Te), meaning that sufficiently high growth rate of (Hg,Cd)Te is unlikely to be achieved using Te(nPr)2 as Te source.
Bis-trifluoromethyl-telluride Te(CF3)2
Fig. Auger spectrum of ZnTe layer grown using Te(CF3)2
Bis-trifluoromethyl-telluride Te(CF3)2 was reported to be very volatile (vapor pressure as high as 531 Torr /20°C.
Te(CF3)2 (+ZnMe2) for ZnTe growth by MOCVD
Te(CF3)2 was tested for the growth of ZnTe films, but the growth rate was low even at 500°C. Auger spectra (after sputtering) of the layer grown using Te(CF3)2 showed that the film contained mainly Zn and Te, but also some O impurity (and very slight C contamination), but no indication of any F impurity.
The XRD spectra of layer grow using Te(CF3)2 revealed (111) peak and broadened (400) reflection peak.
Tert-butyl-trifluoromethyl-telluride TetBu(CF3)
Fig. ZnTe growth rate using Te(tBu(CF3) vs temperture in Arrhenius coordinates
Tert-butyl-trifluoromethyl-telluride TetBu(CF3) was synthesized, characterized and its high volatility was determined (it has vapor pressure 17.8 Torr/20°C).
Pyrolysis of TetBu(CF3) in H2 and He was investigated using molecular beam mass spectroscopy at reduced pressure. It was determined that the decomposition starts at 230°C and occurs by 2 competing pathways: a) homolysis of tert-buty-Te bond, and b) β-hydrogen
elimination. The latter pathways prevails at 250-450°C temperature, as was concluded from the high isobutene / isobutene ratio observed. The primary product of β-hydrogen elimination is trifluoromethyltellurol, which is unstable and decomposes to
difluorocarbene, tellurium and HF; difluorocarbene undergoes dimerization to tetrafluoroethene, or reacts with isobutene yielding 1,1-difluoro-2,2-dimethycyclopropane. HF reacts with ZnMe2 (during ZnTe growth) and leads to ZnF2 contamination of the layers.[i]
[i] M. Danek, S. Patnaik, K.F. Jensen, D.C. Gordon, D.W. Brown, R.U. Kirss, Chem. Mater., 1993, 5 (9), pp 1321–1326, DOI: 10.1021/cm00033a023, « tert-Butyl(trifluoromethyl)tellurium: a novel organometallic chemical vapor deposition source for zinc telluride »,
Te(tBu)(CF3) (+ZnMe2) for ZnTe by MOCVD
![Fig. ZnTe growth rate (using TetBuCF3) vs. [Te/Zn Ratio]](/____impro/1/onewebmedia/i284852689472036090.jpg?etag=%221b68c-5db44839af051%22&sourceContentType= "Fig. ZnTe growth rate (using TetBuCF3) vs. [Te/Zn Ratio]")
Fig. ZnTe growth rate (using TetBuCF3) vs. [Te/Zn Ratio]
TetBu(CF3) was tested as Te precursor for the growth of ZnTe thin films by MOCVD at 280-550°C. ZnTe layers grown at temperatures <400°C were contaminated by ZnF2 crystallites ranging in size from 1 to 20µm, depending on growth temperature and Te/Zn ratio. At temperature higher than 400°C, relatively pure ZnTe layers were grown.
The ZnTe growth rate vs deposition temperature for varying TetBu(CF3) fluxes was plotted (Fig.2.8) [i]
In the low temperature region (where the films were contaminated with ZnF2 crystallites), the apparent activation energy of 23 kcal/mol was determined. The growth rate increased with the increase of the [Te/Zn] ratio. The
low temperature region ends with a sharp drop of the growth rate in the temperature range 375-420°C, depending on [Te/Zn] ratio. Above this transition temperature, the growth rate varied only slightly with substrate temperature and the ZnTe layers were
not contaminated with ZnF2 crystallites. The mechanism of the transition is not clear, but the character of the contamination indicated that the nucleation of ZnF2 on a growing ZnTe film plays an important role. At a high ZnTe growth rate, the nucleation of
ZnF2 may be too slow for the formation of the crystallites. Also, the absence of a ZnF2 phase at high temperatures was probably suppressed by the excess of Te. The growth rate in the high temperature region also
depended upon the [Te/Zn] ratio (see. f.e. Fig. 2.9 for ZnTe growth at 440°C). The tellurium source was rate limiting for [Te/Zn] ratios below -0.5. At [Te/Zn] of 0.6 the growth rate reached a maximum, and higher [Te/Zn] ratios region demonstrated growth
rate decrease. This phenomenon was explained by the presence of a parasitic reaction depleting DMZn. Estimates of the mass transfer rate based on the reactor and sample geometry indicated that the observed growth rate was well below the diffusion limit.[ii]
[i] M Danek . PhD Thesis, 1995, Massachusetts Institute of Technology, - dspace.mit.edu , « Chemical approaches to organometallic chemical vapor deposition of wide band-gap II-VI layers and nanocrystal composites »
Tert-butyl-methyltelluride TetBuMe
Methyl-tertiary-butyl telluride TeMetBu was assessed as a potential precursor for the growth of CdTe, HgTe and (Hg,Cd)Te by MOVPE. TeMetBu has low decomposition temperature and was successfully applied for the growth of HgTe.
Nevertheless, authors’ general conclusion was that TeMetBu is a very poor tellurium precursor;
the assumption was given that possibly all unsymmetrical tellurium alkyls containing a methyl group would also be poor tellurium precursors. [[i]]
[i] J.E. Hails, D.J. Cole-Hamilton, A. Ewan, D. McQueen, J. Cryst. Growth, 1998, Vol.183, Iss.4, p.594-603, « Gas-phase decomposition of MeTeBut and its relevance to the MOVPE of mercury cadmium telluride », doi.org/10.1016/S0022-0248(97)00505-8, www.sciencedirect.com/science/article/pii/S0022024897005058
Di-tert-butyl-telluride TetBu2
Fig. Te(tBu)2 vapor pressure plot:
logP (Torr) = 4.727-1323/T (K)
Synthesis of TetBu2 (and of related di-tert-butyl-ditelluride Te2(tBu)2 and di-neopentyltelluride Te(Nep)2 ) as well as their characterisation by high resolution 125Te NMR data and Mössbauer spectroscopy was described in [i]. The characterisation of TetBu2 by Fourier transform Raman and IR spectroscopies was reported in [ii].
Di-tert-butyl-telluride TetBu2 (M = 241.83) is liquid with vapor pressure (Torr):
2.3/ 30°C, 2.7/ 35°C, 3.2/ 40°C, 3.7/ 45°C, 4.3/ 50°C, 5.0/ 55°C, 5.7/ 60°C, 6.5/ 65°C, 7.4/ 70°C, 8.5/ 75°C, 9.6/ 80°C, 10.8/ 85ºC, in Arrhenius form vapor pressure equation was found to be following: logP
(Torr) = 4.727-1323/T (K) (Fig.). However, as can be seen from the plot, the measurements points were not very reproducible, supposedly due to partial decomposition (however no any black non-volatile residue (like Te) was found in the measurement cell).
[i] C.H.W. Jones, R.D. Sharma, J. Organomet. Chem., 1983, Vol. 255, Iss. 1, p. 61-70, « The preparation of di-t-butyl ditelluride and di-t-butyl telluride and the 125te NMR and Mössbauer spectra of some dialkyl tellurides and ditellurides », doi.org/10.1016/0022-328X(83)80173-9, https://www.sciencedirect.com/science/article/pii/0022328X83801739
[ii] M.J. Almond, C.A. Yates, D.A. Rice, P.J. Hendra, P.T. Brain, J. Molecular Struct., 1990, Vol. 239, p.69-82, « Vibrational spectroscopy of dimethyl telluride, diethyl telluride and di-tert-butyl telluride in the liquid phase », doi.org/10.1016/0022-2860(90)80203-V, www.sciencedirect.com/science/article/abs/pii/002228609080203V
TetBu2 (+Ge(NMe2)4, +Sb(NMe2)3) for GST films by CVD
Di-tert-butyl-telluride Te(tBu)2 (combined with Ge(NMe2)4 and Sb(NMe2)3 as Ge and Sb sources) was applied as Te source for the growth of precursors of crystalline Ge-Sb-Te alloys by selective Chemical Vapor Deposition. Te(tBu)2 (as well as Sb(NMe2)3) are chemisorbing but not decomposing on dielectric surfaces in the utilized temperature range, and the chemisorbed
species prevent the decomposition of the Ge precursor. This leads to the the deposition of Ge-Sb-Te material inside the vias, filling them upwards from the metal bottom electrode.
The groth experiments were performed on patterned 200 mm wafers in a modified Applied Materials CVD chamber, attached to Endura HP 5500 platform, the growth conditions were following: chamber pressure 4 torr, Ar carrier gas flow 20-60 sccm (depending on the
precursor), at ca. 300°C deposition temperature. The precursor-containing ampoules and lines were heated to minimize adsorption during precursors transport. The varying shape and aspect ratio vias in which Ge-Sb-Te material was deposited, were formed either
in SiO2 or Si3N4 by a RIE exposing either TiN or W as the bottom contact; the bottom contact diameter was ~ 200 nm to 30 nm, and depth from ~250 nm to 150 nm. [[i]]
[i] A.G. Schrott, Ch.-F. Chen, E.A. Joseph, M. Breitwisch , R.K. Dasaka, R. Cheek, Y. Zhu, Ch. Lam, « Selective CVD deposition of phase change material alloys », www.epcos.org/library/papers/pdf_2010/Posters/PA17-AG_Schrott.pdf
Methylallyltellurium TeMe(allyl)
![Fig. Vapor pressure plot for TeMe(allyl): vapor pressure equation Lg P (Torr) = 8.146 - [2196/T]](/____impro/1/onewebmedia/i284852689471929101.jpg?etag=%221b68c-5db44839af051%22&sourceContentType= "Fig. Vapor pressure plot for TeMe(allyl): vapor pressure equation Lg P (Torr) = 8.146 - [2196/T]")
Fig. Vapor pressure plot for TeMe(allyl): vapor pressure equation Lg P (Torr) = 8.146 - [2196/T]
Methylallyltellurium TeMe(allyl), or Te(Me)(CH2CH=CH2), gives reproducible pressure measurements, resulting in the vapor pressure equation Lg P (Torr) = 8.146 - [2196/T] (Fig.5). For example, TeMe(allyl) vapour pressure is 4.48 Torr/ 20°C and 7.92 Torr/30°C, making it one of the most volatile of tellurium precursors. On returning to 0°C, the points obtained were close to, but not exactly the same, as those obtained at the start of the series of measurements, probably indicating slight decomposition of the sample during measurement. For comparison, the previous (less precise) data given in the Cyanamid literature reported vapour pressure equation Lg P = 7.718 - [2028/T] (corresponding to 6.3 Torr at 20°C and 10.6 Torr at 30°C).[[i]]
Methyl-allyl telluride has recently been used as an MOVPE precursor [[ii],[iii]]. Thus, Ghandhi et al. reported that HgTe could be grown using liquid Hg and TeMe(allyl) at 250-320°C
growth temperatures, proving that TeMe(allyl) volatility makes very promising as MOVPE precursor of Te-containing thin films.
[i] J.E. Hails, S.J.C. Irvine, J.B. Mullin, MRS Symp. Proc., 1989, Vol. 161 (Symp.E), p.343-349, « Vapour Pressure Measurements on Organotellurium Precursors for Movpe », doi.org/10.1557/PROC-161-343,
https://www.researchgate.net/profile/A_Franciosi/publication/232013349_In-Situ_Studies_of_Semimagnetic_Heterojunction_Parameters/links/00b495170f8b7e9c38000000.pdf#page=342
[ii] K. Ghandhi, I.B. Bhat and H. Ehsani, AppI. Phys. Lett, (1989), 55(2), 137
[iii] J.D. Parsons, L.S. Lichtmann, J. Crystal Growth, 86, 222 (1988).
Te(Me)(allyl) for Cd(Hg, Zn)Te by MOCVD
Methylallyltellurium Te(Me)(CH2CH=CH2) (MATe), and for comparison diethyltellurium TeEt2 and diisopropyltellurium
Te(iPr)2, was tested as Te source for the MOCVD growth of CdTe, ZnTe, HgTe and solid solutions CdxZn1−xTe and HgxCd1−xTe (by using combining them with other volatile
organometallic compounds like CdMe2, ZnEt2, Zn(iPr)2 as corresponding metal sources). In order to reduce the trial-and-error experimental efforts of finding the optimal MOCVD process conditions (deposition temperature T, pressure P, initial composition of
the vapors X) and to limit them only to the P–T–X field of existence of the solid (CdTe, ZnTe, HgTe and solid solutions CdxZn1−xTe and HgxCd1−xTe), and obtaining an acceptable yield of the product, thermodynamic calculations and computer
simulation of the equilibrium composition were applied. The vapor pressure of the precursors (f.e. Te(Me)(allyl) ) is instrumental for changing the composition of the vapor in the reaction zone and thus it determines the composition x of the solid solution (therefore a choice of the particular combination of the precursors depended on the desired
composition of the film, especially in case of CdxZn1−xTe and HgxCd1−xTe solid solutions). The investigation of the equilibrium composition for II–VI telluride MOCVD systems was performed at temperatures up to 873 K (600°C) in H2 and
pressures up to 1 atm (inert gas atmosphere). [[i]]
[i] L Ben-Dor, J.H Greenberg, J. Cryst. Growth, 1999, vol. 198–199, Part 2, p. 1151–1156, « Equilibrium composition in II–VI telluride MOCVD systems »
Bis(allyl)tellurium Te(allyl)2
Fig. Te(allyl)2 vapor pressure Arrhenius plot (lgP(Torr) = 7.308 – 2125/T)
Bis(allyl)tellurium Te(allyl)2 was found to be thermally unstable even at ~0-30°C, making it not promising as Te precursor for MOCVD applications.
Thus, attempts at establishing the vapour pressure equation of Te(allyl)2 at 19°C resulted in irreproducible pressure versus time plots ( Fig. 6): successive plots always gave a lower pressure than those obtained previously, and in addition, the plots were not flat (the pressure was always slowly rising). At the end of the series of measurements the Te(allyl)2 completely disappeared, leaving black coating (presumably Te) inside the silica measurement cell. Not surprisingly, vapor pressure Arrhenius plot (lgP(Torr) = 7.308 – 2125/T) did not align in a good straight line (Fig. 7). (by other report, vapor pressure of Te(allyl)2 is 1.1Torr/ 20°C) The conclusion was that bis(allyl)tellurium is thermally unstable in the range 0-30°C (wad was slowly decomposing during the measurements according to following scheme:
(allyl) 2Te -> involatile product + volatile product
The involatile product ( Te or possibly diallylditelluride) could not be removed from the cell during the measurements and its concentration was steadily increasing. The volatile product, responsible for the slow rise in the pressure versus time plots, was removed within first 5 seconds of pumping cycle. According to initial Gas Chromatograph Mass Spectrometry work, it appeared that this volatile product is 1,5-hexadiene with boiling point 59°C.
Benzyl-trifluoromethyl-tellurideTe(CH2Ph)(CF3)
Benzyl-trifluoromethyl-telluride Te(CH2Ph)(CF3) was synthesized, characterized and was found to be very volatile.
Te(CH2Ph)(CF3) was proposed as potential Te CVD precursor for the growth of HgCdTe thin films. [i]
[i] D.C. Gordon, R.U. Kirss, D.W. Brown, Organometallics, 1992, 11 (8), pp 2947–2949, « Synthesis and characterization of volatile trifluoromethyl alkyl tellurides », DOI: 10.1021/om00044a043, https://pubs.acs.org/doi/abs/10.1021/om00044a043?journalCode=orgnd7
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