Dimethylzinc trialkylamine adducts
The tralkylamine adducts ZnMe2(NR3) are less pyrophoric than ZnMe2, because amine inhibit prereaction with the oxygen source, and facilitate purification. ZnMe2(NR3) are volatile; the vapor pressures of some of them have been reported [4]
The 1:1 adduct of dimethyl zinc with triethylamine ZnMe2(Et3N) is an attractive precursor for the growth of zinc based II‐VI compounds (ZnO, ZnSe, ZnTe) by MOVPE due to its high purity and suppression of unwanted pre‐reactions. The saturated vapor pressure measured by Epison ultrasonic monitor under dynamic conditions are up to a factor of 10 smaller than the static measurements (log10p=9.80–2596/T); it agree closely with the growth rate measurements.
Dimethylzinc-triethylamine (DMZn-TEN) , in conbonation with tBuOH as oxygen source, has been applied as precursor for ZnO growth by MOCVD [[i]] (see tertiary butanol (tBuOH) as oxygen precursor.
[i] B Hahn, G Heindel, E Pschorr-Schoberer, W Gebhardt, Semicond. Sci. Technol. 1998, 13, 788 doi:10.1088/0268-1242/13/7/022)
Dimethylzinc triethylamine adduct ZnMe2-NEt3 has been applied as zinc MOCVD precursor for the growth of extremely high purity ZnSe layers. [[i][PS1] ] The advantage of this precursor is that it avoids one of the problems in MOVPE of Zn chalkogenides: for the successful achievement of p-type doping the preparation of material with very low electron background concentrations is neded to avoid compensation effects. The classical zinc precursors like ZnMe2 lead to prereactions and is invariably contaminated by trace amounts of iodine I [[ii]] .Use of dimethylzinc triethylamine adduct Zn Me2-NEt3 avoids this issues and the material purity can be increased [[iii]]
The optimum ZnSe growth parameters using ZnMe2-NEt3 are: growth temperature 280 °C, VI/II molar ratio 5, reactor pressure 40 Torr. The grown ZnSe samples were characterised by low temperature photoluminescence and reflectivity experiments. PL spectra at 2 K spectrum have show that the use of Me2Zn-NEt3 led to a dramatic decrease of the donor bound exciton intensity and a correlated increase of the free exciton intensity. For the first time, free excitons and excited states up to the second (3s) were observed in reflectivity spectra.
[i] T. Cloitre, N. Briot, O. Briot, B. Gil, R.L. Aulombard, A.C. Jones, Materials Science and Engineering: B, Vol 21, Iss 2–3, 20 November 1993, Pages 169–173, “Optical characterization of extremely high purity ZnSe grown by metal-organic vapour phase epitaxy using dimethylzinc-triethylamine adduct”
[ii] Jones, Wright and co-workers (Semicond. Sci. Technol., 6 (1991) A 36; J. Cryst. Growth, 94 (1989) 441; J. Cryst. Growth, 104 (1991) 297)
[iii] Wright et al. (J. Cryst. Growth, 94 (1989) 441; J. Cryst. Growth, 104 (1991) 297),
Dimethylzinc(triethylamine adduct ZnMe*NEt3, in combnation with tBu2Se, tBu2S and Mg(MeCp)2 precursors, has been applied as optimized Zn precursor for the preparation of ZnMgSSe heterostructures by MOVPE. ZnMgSSe single layers and heterostructures have been grown on GaAs substrates in a low-pressure MOVPE system at 400 hPa (40mbar) and 330°C. Reproducible adjustment of the S and Mg contents in a wide range was achieved by optimization of the growth process and allowed to control the band gap and the lattice constant simultaneously. Near-band edge emissions of up to 3.35 eV were demonstrated for the pseudomorphic ZnMgSSe layer structures (lattice-matched or strain-balanced). An inhomogeneous broadening of photoluminescence (PL) emissions and high-resolution X-ray diffraction (HRXRD) peaks due to phase separation was observed especially for lattice-matched samples. ZnMgSSe/ZnSe multi quantum well (MQW) structures have been grown and characterized in order to study the effects on the luminescence properties. [[i] ]
[i]H. Kalisch, M. Lünenbürger, H. Hamadeh, J. Xu, M. Heuken, Journal of Crystal Growth, Volumes 184–185, 2 February 1998, Pages 129–133 , “Optimized metalorganic vapour phase epitaxy of ZnMgSSe heterostructures”,
http://www.sciencedirect.com/science/article/pii/S0022024898803084
Dimethylzinc-triethylamine adduct ZnMe∙NEt3, in combination with TeiPr2, has been applied as the MOVPE source for the successfully growth of ZnTe layer on GaAs substrates by low pressure MOVPE at temperatures as low as 300°C. For growth temperatures ranging between 300 and 450°C, the growth rate is kinetically limited at the growing interface with activation energy 28 kcal/mol. A linear variation of the growth rate with either change of overall growth pressure, or with both ZnMe∙NEt3 and TeiPr2 molar flows was observed at 375°C growth temperature. The optimal growth conditions Tg = 350°C, VI/II = 2, p = 40 Torr.were deteremined on the basis of the low temperature reflectance and PL measurements. The relative intensity of the As-related bound exciton emission at 2.367 eV decreased with increase of growth temperature, while the unknown acceptor related bound exciton emission at 2.356 eV decreased linearly with the growth rate. [[i]][[ii] ] (see aslo TeiPr2)
[i] T. Cloitre, N. Briot, O. Briot, B. Gil, R.L. Aulombard, Journal of Crystal Growth, Volume 133, Issues 1–2, 1 October 1993, Pages 101–107, “Low pressure metalorganic vapour-phase epitaxy growth of ZnTe using triethylamine dimethyl zinc adduct”
[ii] 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 )
Dimethylzinc triethylamine adduct ZnMe2·NEt3 has been applied as a p-dopant source in the growth of GaAs and Al0.3Ga0.7As alloys by MOVPE. The dopling efficiency using this adduct in these alloys and in InP is lower than the doping efficiency with ZnMe2. [288]
Dimethylzinc tetramethylmethylenediamineadduct ZnMe2(TMMDA) has been applied as precursor for the growth of ZnSe, ZnCdSe layers and ZnCdSe based heterostructures by MOVPE; the growth conditions and the solid composition versus gas phase composition were compared with those grown using triethylamine-dimethylzinc adduct (TEA:DMZ). has been studied for both adducts. The structural properties of ZnSe layers below the critical thickness have been studied versus the initial growth conditions; spectroscopic properties of the heterostuctures versus abruptness of the heterointerfaces was investigated. [289]
ZnMe2(TMMDA) has been applied for the growth of ZnSe-ZnS strained layer superlattices by low pressure MOVPE at 300'C. Improved layer purity and lower homogeneous gas phase premature reactions were achieved compared to ZnMe2. [290]
Dimethylzinc tetramethylethylenediamine adduct ZnMe2(TMEDA) was applied for the growth of Zn-doped GaAs layers by MOCVD; reproducible p-type doping in the range 1015 - 1017 cm-3 was achieved. No measurable memory effect was observed despite the precursor is solid [291, 292]
ZnMe2(triazine) (as compared to ZnMe2(NMe3), has been successfully applied as Zn precursor for the growth of high quality single crystal ZnSe layers by MOCVD, without any significant pre-reaction of the constituent reactants. One of the reasons for the improved purity of layers grown using adducts (compared to unadducted ZnMe2) is the removal of iodine I (an n-type donor in ZnSe) by the adducting process. Free exciton dominated photoluminescence proved high ZnSe layer quality. [[i]]
[i] P.J. Wright, B. Cockayne, P.J. Parbrook, A.C. Jones, P. O'Brien, J.R. Walsh
Journal of Crystal Growth, Volume 104, Issue 3, August 1990, Pages 601–609, “MOCVD Layer growth of ZnSe and ZnS / ZnSe multiple layers using nitrogen containing adducts of dimethylzinc”
Vapor pressure of the series of dimethyl zinc adducts including triethylamine, 1,3,5-trimethyltriazine and 1,3,5-triethylhexahydro-1,3,5-triazine has been studied using static measurement at various mole ratios of ligand to ZnMe2 at 0°C, in order to assess the suitability of these compounds as zinc MOCVD precursors. [[i] ]
The x-ray crystal structure of dimethylzinc ,3,5-trimethyltriazine adduct Me2Zn [(CH2NMe)3]2 has been determined. This adduct been successfully tested for the growth of high-quality ZnSe by MOCVD. [[ii]]
[i] Paul O'Brien, M. Azad Malik, John R. Walsh, Anthony C. Jones, Advanced Materials for Optics and Electronics, Vol.7, Issue 3, pages 117–121, May 1997, “Vapour Pressure Studies of Some Nitrogen Donor Adducts of Dimethylzinc Used in the Deposition of Materials by MOCVD”
[ii] Michael B. Hursthouse, Majid. Motevalli, Paul. O'Brien, John R. Walsh, Anthony C. Jones
Organometallics, 1991, 10 (9), pp 3196–3200, DOI: 10.1021/om00055a041
The liquid dimethylzinc triethyltriazine adduct ZnMe2·C3N3Et3 , in compared with other liquid adducts with trimethylamine and tetramethylmethylene diamine has been applied as p-dopant of InP and InGaAs by MOVPE. Doping range was found to be dependent on the adduct vapour pressure, with achievement of reproducible doping over the range 5 × 1015 to 1018 cm−3. Excellent surface morphology of grown p-doped InP and InGaAs layers was obtained; no detrimental gas phase reactions were observed. [[i]]
[i] A.C. Jones, S.A. Rushworth, P. O'Brien, J.R. Walsh, C. Meaton, , Journal of Crystal Growth, Volume 130, Issues 1–2, May 1993, Pages 295–299, “The use of dimethylzinc-amine adducts for the p-doping of InP and related alloys”
Diethylzinc N,N,N’,N’-tetraethylethylenediamne adduct ZnEt2(TEEDA) has been applied as precursor for the growth of ZnO by CVD; it is advantageous versus unadducted zinc alkyls, as it is non-pyrophoric. ZnEt2(TEEDA) is liquid at room temperature, its vapor reacts wit EtOH depositing ZnO at substrate temperature 400-500°C; fluorine doped films were obtained using benzoyl fluoride as fluorine source. [[i],[ii]]
[i]R.G. Gordon, H.Liang, Book of Abstracs, 216th ACS National Meeting, Boston, aug 23-27, 1998.
[ii] R.G. Gordon, K. Kramer, H. Liang, US Patent, 6,071,561 (2000)