Erbium Tris (Amide) Compounds as Source Molecules for Rare Earth Doping of Semiconducting Materials
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ABSTRACT
The homoleptic compound erbium{tris[bis(trimethylsilyl)]amide} displays high doping ability for incorporation of the rare earth element into epitaxially grown semiconducting host materials for fabrication of temperature-independent, monochromatic solid state optoelectronic devices. Electronic characteristics derived from erbium doped semiconducting films have been obtained. Several more volatile and lower melting representatives of this class of compounds have been synthesized, characterized by various analytical techniques and examined for their suitability to incorporate optically-active erbium centers into a semiconducting environment.
INTRODUCTION The discovery of the k. = 1.54 gtelectroluminescence signal in erbium implanted GaAs at 77 K soon was recognized to have technological importance. 1 -7 The wavelength of this transmission coincides with the minimum absorption wavelength of silica-based optical fibers. It arises from an internal 4f-4f electron transition of the rare earth ion Er 3 + (4f11), which occurs specifically between the 4113/2 and 4115/2 spin orbits. Because the partially filled 4f-subshell is screened effectively by larger, lower residing s- and p- orbitals, the energy of this emission relatively is independent of the host material, as well as ambient operation temperature. In addition, the narrow linewidth at room temperature offers high bandwidth capacity for optical communication systems. Some success has been obtained in employing metal amide compounds as designed dopants for semiconducting materials. 8 -12 Earlier extensions of this work to encompass lanthanide doping have been discussed. From previous investigations 13 -17 of various source compounds for erbium incorporation into semiconducting materials, Er{ N[Si(CH 3 )3] 2 }3 emerged as having significant advantage for use in OMVPE, compared with erbium cyclopentadienyl or 1318 19 diketonate counterparts. ,
111 Mat. Res. Soc. Symp. Proc. Vol. 415 ©1 99 6 Materials Research Society
EXPERIMENTAL
The synthesis of Er{N[Si(CH 3 )3] 2} 3 was accomplished by a salt elimination reaction between one equivalent of anhydrous erbium chloride and three equivalents of lithium{ [bis(trimethylsilyl)]amide} in diethyl ether at 0'C (eq. 1). ErCI 3 + 3 LiN[Si(CH 3 )3] 2
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------> Er{N[Si(CH 3 )3] 2} 3 + 3 LiCI(,-)
(1)
The purification process consisted of removing all volatiles at reduced pressure, extraction of the desired product in hexane, and subsequent filtration to separate insoluble lithium chloride. Ensuing repeated sublimation removed small amounts of unreacted lithium amide, and gave the desired compound as an air- and moisture-sensitive bright pink powder melting at 162'C and subliming at 140°C and 10-4 Torr. To satisfy the need for more volatile and lower melting examples, an analogous synthetic effort was instigated to encompass modified erbium amides with one trimethylsilyl unit replaced by a dimethylsilyl group and/or an alkyl group, respectively. The preparation of the alkali metal alkylsilylamide salts was accomplished
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