Gas Phase Interactions between Triethylindium and Trimethylgallium
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GAS PHASE INTERACTIONS BETWEEN TRIETHYLINDIUM AND TRIMETHYLGALLIUM P. D. AGNELLO AND S. K. GHANDHI Electrical, Computer and Systems Engineering Department, Rensselaer Polytechnic Institute, Troy, NY. 12180 ABSTRACT A study of the room temperature gas-phase interactions between gallium and indium alkyls was undertaken using a mass spectrometer sampling system, mounted on a low pressure organometallic vapor phase epitaxial reactor. Mixtures of triethylindium with triethylgallium or trimethylgallium were investigated. Both combinations formed addition compounds; moreover, the triethylindium-trimethylgallium mixture underwent alkyl exchange. Both admixtures showed reduced reactivity towards arsine. A structure for the addition compound is proposed. INTRODUCTION Ga0. 4 71n 0 . 5 3 As films, lattice matched to InP, are important because of their suitability for the fabrication of optoelectronic devices. Device requirements for ultra- thin layers, abrupt changes in doping and composition, and uniform growth over large areas, make organometallic vapor phase epitaxy (OMVPE) ideally suited (1] for these applications. However, the growth of indium containing compounds by OMVPE is complicated by a room temperature, parasitic reaction between the indium bearing species and the group V hydride [2]. A lack of understanding of these reactions has prevented this growth technique from achieving its full potential. EXPERIMENTAL A description of the sampling system has been given (3]. In summary, the sample was taken by a 150 gm I.D. silica capillary which reached into the system from the gas inlet end by means of flexible stainless steel bellows. The gases exiting the capillary impinged on a 100 gm dia. orifice in a skimmer chamber. This orifice connected directly to a mass spectrometer in a bakeable UHV system. The transit time of the sample from the capillary to the ionizer of the mass spectrometer was less than 0.2 sec. The reactor was held at a pressure of 152 torr with a hydrogen carrier gas flow of 3 slm. Organometallic reactants were Et 3 In, Me3Ga and Et 3 Ga, which were studied separately and as mixtures. Experiments were carried out over flow conditions which include the range of pressure and flow conditions over which device quality Gao. 4 71n 0 . 5 3 As has been grown by us. The organometallic reactant flows were premixed and transported in hydrogen gas to the reaction chamber, at which point the arsine was introduced, when required. Data was taken at room temperature, which we have shown [3] to be essentially the same as the gas temperature right up to the susceptor during growth. RESULTS AND DISCUSSION
Mat. Res. Soc. Symp. Proc. Vol. 131. t1989 Materials Research Society
98
In one set of experiments, we have monitored the fragments Et3Ga, and the mixture of these due to 0.02 torr of Et 3 In, The sampling organometallic compounds, in the absence of AsH3. probe position was 2.5 cm from the reactor inlet for these Figure l(a) shows the mass spectrum for Et3Ga alone measurements. over the range from 65 to 130 AMU, where
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