Direct synthesis of II3-V-2 compound semiconductors by the heterovalent exchange reaction

It is shown that it is possible to synthesize thin films of the II3-V-2 com pound Zn3As2 by the heterovalent exchange reaction (HER) of dimethylzinc in H-2 with GaAs substrates at 350 degrees C. These films are of a very high structural quality, being both epitaxial and highly ordered in nature as sh own by an extensive transmission electron microscopy study. Using compariso ns with simulated images and diffraction patterns, it is shown that the Zn3 As2 formed is of the low-temperature cu phase, which is stable below about 190 degrees C. The lack of free gallium present on the surface suggests tha t methyl radicals are responsible for transport of exchanged gallium into t he vapour phase. The high structural quality of the layers grown by this te chnique suggests that the HER is a promising method of circumventing the us ual problems of mismatched epitaxial growth and that a wide range of thin-f ilm materials may possibly be grown.