Movpe of Rare Earth Doped III-V Semiconductors
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F. SCHOLZ, J. WEBER 1 , K. PRESSEL2 , A. DORNEN 4. Physikalisches Institut, UniversitAt Stuttgart, Pfaffenwaldring 57, D-W-7000 Stuttgart 80, Germany
ABSTRACT
Different III-V compound semiconductors have been doped with the rare earth (RE) elements Yb, Er, and Tm using atmospheric pressure metalorganic vapor phase epitaxy. Best results have been obtained using the novel metalorganic compounds tris-isopropyl-cyclopentadienyl-RE as precursors which have an acceptable vapor pressure and can be used as liquids at bubbler temperatures of 600-900C. Only Yb has been found to occupy a regular lattice site in InP, whereas the other RE show complex optical spectra because of their incorporation in form of different centers and clusters. Introduction In the recent years, Rare Earth elements (RE) incorporated into semiconductor host material have attracted high interest because of their inneratomic optical transitions whose spectral positions are well defined and insensitive to temperature and influences of the host material, because they are screened by outer electronic shells. Nevertheless they can be excited via the
semiconductor
host
material,
and
therefore,
simple
spectrally
well
defined light emitting devices should be feasible. Besides, the study of the excitation and decay processes is an interesting research topic for the interaction of the solid state band structure and single atomic states.
In first attempts, doping by liquid phase epitaxy has been studied [1,2], but the success of these experiments was limited due to the high reactivity of the RE which had to be used in elemental form, and only rather low doping concentrations could be realized. With ion implantation techniques [3-6], high concentrations have been attained, but only in locally well defined small regions. Only the today well developed modern methods like Molecular Beam Epitaxy (MBE) and Metalorganic Vapor Phase Epitaxy (MOVPE) allowed the incorporation of high RE concentrations in a wide range of semiconductor host materials and specially designed epitaxial structures. MBE is mainly limited to phosphorus free material, and so the incorporation of Yb and Er into GaAs and AIGaAs by the latter method has been reported [7-9]. In this contribution, we like to focus on the RE doping of Ill-V semiconductors by MOVPE. In contrast to MBE, most Ill-V materials can be grown by this method, and therefore, the doping of various III-Vs with many RE by MOVPE has been published [10-17]. The main aspect will be drawn on the MOVPE technique itself. We will describe the studies about suitable RE precursors as a stringent prerequisite and their application in conventional atmospheric pressure MOVPE. Furthermore, characteristic results will be 1Now with: Alcatel-SEL Research Center, D-W-7000 Stuttgart, Germany Now with: Institut fOr Halbleiterphysik, D-0-1200 Frankfurt (Oder), Germany
2
Mat. Res. Soc. Symp. Proc. Vol. 301. ©1993 Materials Research Society
given, mainly for the elements ytterbium (Yb) and erbium into InP, and thulium (Tm) in GaAs and Galn
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