New Group III Precursors for the Movpe of GaAs and InP Based Material
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NEW GROUP III PRECURSORS FOR THE MOVPE OF GaAs AND InP BASED MATERIAL
M. HOSTALHE AND L. POHL E. Merck, Frankfurter Strape 250, D-6100 Darmstadt, Fed. Rep. of Germany A. BRAUERS, P. BALK, V. FRESE, H. HARDTDEGEN*, R. HOVEL AND G.K. REGEL Institute of Semiconductor Electronics Aachen Technical University D-5100 Aachen, Fed. Rep. of Germany *Permanent address: ISI, KFA Julich, D-5170 Julich, Fed. Rep. Of Germany A. MOLASSIOTI, M. MOSER AND F. SCHOLZ 4. Institute of Physics University Stuttgart, Pfaffenwaldring 57 D-7000 Stuttgart 80, Fed. Rep. of Germany H. SCHUMANN, K.U. HARTMANN AND W. WASSERMANN Department of Inorganic and Analytic Chemistry Technical University Berlin D-1000 Berlin, Fed. Rep. of Germany
ABSTRACT This paper presents proposals for the synthesis of several group III metal organics (In, Ga, Al compounds) and preliminary results on their use in the MOVPE (metal organic vapor phase epitaxy) of III-V semiconductors. The common feature of all these precursors is that they are saturated by inter- or intramolecular coordination. They are even non-pyrophoric and air resistant which is an interesting aspect with respect to safe handling. In addition, the compounds are liquid at room temperature with a low but sufficient vapor pressure for MOVPE without additional heating of the source. During the last few years MOVPE (metal organic chemical vapor epitaxy) has gained acceptance as a technique for the growth of III-V semiconductor films and layered structures for industrial application. Generally, the trimethylaluminium, trimethylgallium and trimethylindium (TmA, ThG and TMI) are used in combination with the group V hydrides, AsH, and PH3 [1-2]. The conventional trialkyls possess an unsaturated orbital at the metal atom. Therefore they are highly reactive towards atoms or molecules with a free electron pair. This characteristic implies undesirable behavior of the source materials in several respects. One undesirable feature of the group III sources is that they all are extremely sensitive to oxygen so that it is difficult to avoid alkoxy contamination of the material. Moreover, the compounds are highly pyrophoric. Another aspect is the unwanted formation of adducts upon mixing of the trialkyls with the group V compounds, which has been observed for In sources. Whilst the high reactivity towards oxygen (and the resulting alkoxy contamination) will affect the properties of AlGaAs grown from standard source materials, the formation of adducts makes the control of the growth of ternary and quaternary compounds very difficult. These undesired reactions of the metal organics can be suppressed by occupying the free orbital through formation of an intermolecular adduct e. g.
Me.Ga + Pie3
(-) (+) P Me3Ga - Pie3
(1)
An advantage of adducts is the protection of the organometallic precursors possible a against attack by nucleophilic impurities which makes transportation to the deposition zone and a release without side-reactions by a simple thermal dissociation process. Mat. Res. Soc. Symp. Proc. Vol. 145. 01989 Mat
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