SELECTIVE EPITAXY OF GAAS, ALXGA1-XAS, AND INXGA1-XAS

Many device structures benefit from the ability to selectively deposit epitaxial materials. Through the use of a masking material, such as Si3N4 or SiO2, on the substrate surface, patterns generated through standard lithographic procedures can be used to define regions for selective deposition. Highly selective growth can be achieved through the use of growth precursors which contain halogens, such as (C2H5)2GaCl and (C2H5)2 AlCl. These compounds decompose, most probably, to the volatile mono-halogen species, e.g. GaCl, and also generate HCl in the gas phase as a reaction by-product. We present experimental results on the morphology and growth behavior of GaAs, Al(x)Ga1-xAs using this selective epitaxy technique. Electrical and optical characterization has been carried out on these materials and selectively grown structures produced by this technique. The interface between the selectively grown material and the underlying substrate was investigated and the conditions for achieving high quality electrical interfaces were determined. A thermodynamic model of this growth chemistry predicts the trends in composition and growth rate. The thermodynamic model, based on the quasi-equilibrium of the halogen-based compounds with the substrate surface, indicates that the growth behavior is very similar to the inorganic-based growth of these compounds. Experimental applications of this technique to high speed digital device structures and sub-micron dimensioned optical structures are presented.