REACTION-MECHANISMS GOVERNING THE SELECTED-AREA GROWTH OF III-V SEMICONDUCTORS BY CHEMICAL BEAM EPITAXY

The molecular surface chemistry underlying the selected-area growth of III-V semiconductors by chemical beam epitaxy is reviewed. Homoepitax ial growth of III-V semiconductors occurs efficiently because of high reactive sticking probabilities of the group III precursor, and effici ent reaction pathways resulting in the conversion of the initial chemi sorbed species into elemental Ga on the semiconductor surface. In cont rast it is shown that the sticking probability of triethyl gallium on the dielectric masks employed in selected-area epitaxy is vanishingly low, and any free Ga species produced become trapped in an inert oxidi zed form within the surface layers. As a result the production of meta llic Ga species on the surface does not occur, hence growth of the III -V semiconductor is not observed The interaction between As and trieth yl gallium when adsorbed on the dielectric mask has also been examined . As increases the group III sticking probability and brings about a d irect reaction which results in the formation of GaAs. It is suggested that this group V-induced modification of the group III surface chemi stry underlies the loss of selectivity observed in selected-area epita xy experiments when low growth temperatures or high group V over-press ures are used.