Selective-area metalorganic molecular beam epitaxy of GaAs using metalorganic chloride gallium precursors

Selective-area metalorganic molecular beam epitaxy at low growth temperatures using diethylgallium chloride (DEGaCl) and dimethylgallium chloride (DMGaCl) was investigated and significantly different results from those with metalorganic vapor-phase epitaxy were obtained. In the DEGaCl/As-4 and DMGaCl/As-4 systems, growth rates were extremely low or zero because DEGaCl and DMGaCl on the substrate surface decomposed to GaCl, which then desorbed very quickly. Therefore, these precursors and triethylgallium (TEGa) were used simultaneously to obtain a high growth rate and improve the selectivity in the TEGa/As-4 system. In both the TEGa/DEGaCl/As-4 and TEGa/DMGaCl/As-4 systems, high growth rates over 1 mu m/h and perfect selectivity were obtained at 500 degrees C. Even at a low temperature of about 400 degrees C, selectivity was perfect when DMGaCl was added: DMGaCl was more effective than DEGaCl. DMGaCl irradiation only prior to growth improves the selectivity in the TEGa/As-4 system; therefore, cleaning the mask surface with chlorine-containing species was found to be important in both systems. In the TEGa/DMGaCl/As-4, system, moreover, enhanced desorption of TEGa by interaction with methyl radicals supplied by DMGaCl was also found to improve selectivity. This was indicated by the experimental results in which selectivity was improved by adding trimethylgallium or trimethylindium to the TEGa/As-4 system.