Several erbium pyrazolate complexes were synthesized and characterized, namely tris(3,5-di-tert-butylpyrazolato)bis(4-tert-butylpyridine)erbium(III) (yield 63%), tris(3,5-di-tert-butylpyrazolato)bis(pyridine)erbium(III) (88%), tris(3,5-di-tert-butylpyrazolato)bis(n-butylimidazole)erbium(III) (48%), tris(3,5-dimethylpyrazolato)bis(4-tert-butylpyridine)erbium(III) (50%), and tris(3,5-di-tert-butylpyrazolato)(3,5-di-tert-butylpyrazole)erbium(III) (59%), as potential erbium MOCVD precursors. They were synthesized by the reaction of Er metal with 3,5-dialkylpyrazole (alkyl = tBu or Me), Hg(C6F5)2, and a neutral nitrogen donor (4-tert-butylpyridine, pyridine, n-butylimidazole, or 3,5-di-tert-butylpyrazole). Tris(3,5-di-tert-butylpyrazolato)bis(4-tert-butylpyridine)erbium(III) could be also obtained in 41% yield by the treatment of ErCp3 with 3,5-di-tert-butylpyrazole (3 equiv) and 4-tert-butylpyridine (2 equiv) in toluene at ambient temperature for 24 h.
The crystal structures of these complexes (determined by single crystal XRD) revealed 7- and 8-coordinate erbium atoms with all-nitrogen coordination spheres and η2-pyrazolato ligands (the preference η2-bonding of the pyrazolato ligand over the η1-bonding mode was explained by molecular orbital calculations).
Erbium complexes containing
3,5-di-tert-butylpyrazolato ligands were obtained in a high state of purity and could be sublimed without decomposition at 150 °C/ 0.1 Torr), and were therefore proposed as potential precursors for the MOCVD deposition of erbium-containing layers.[[i]]
[i] D. Pfeiffer, B.J. Ximba, L.M. Liable-Sands, A.L. Rheingold, M.J. Heeg, D.M. Coleman, H.B. Schlegel, Th.F. Kuech, Ch.H. Winter, Inorg. Chem., 1999, 38 (20), pp 4539–4548, DOI: 10.1021/ic990319o , « Synthesis, Structure, and Molecular Orbital Studies of Yttrium, Erbium, and Lutetium Complexes Bearing η2-Pyrazolato Ligands: Development of a New Class of Precursors for Doping Semiconductors »
Erbium tris(di-tertbutylpyrazolate) bis(4-tertbutylpyridine) adduct Er(tBu2pz)3(4-tBupy)2 was applied as precursor for the growth of erbium-doped GaAs films by MOCVD. Better defined erbium emitting centers were achieved with this precursor compared to those obtained with cyclopentadienyl-based precursors. Some of the incorporated Er atoms form optically active centers identified as Er-2O; the
optical line shape attributed to these optical centers is much sharper and intense than in GaAs:Er doped using cyclopentadienyl-based Er precursors. Co-doping of GaAs: Er with shallow donors results in a quenching of the Er-related luminescence, whereas co-doping
with shallow acceptors causes no significant change in the Er-based spectrum. Deep level transient spectroscopy (DLTS) performed on Si or Se co-doped GaAs:Er showed the presence of several electron traps in the upper half of the band gap. [[i]]
[i] J.G. Cederberg, T.D. Culp, B. Bieg, D. Pfeiffer, C.H. Winter, K.L. Bray, T.F. Kuech, J. Cryst. Growth, 1998, Vol. 195, Iss. 1–4, p.105–111, « Erbium-doped GaAs grown using the novel precursor tris(3,5-di-tert-butylpyrazolato)bis(4-tert-butylpyridine)erbium »