CARRY-OVER - A FUNDAMENTAL PROBLEM IN THE MOVPE GROWTH OF HETEROSTRUCTURES

We have investigated the MOVPE growth of GaAs, GaP. and InP using TMGa-TMN (trimethylgallium-trimethylamine), TMIn-TMN (trimethylindium-trimethylamine) and the hydrides arsine and phosphine in reactor cells covered with products of preceding deposition processes. By measurements of the misfit DELTA-a/a we find that besides arsenic also gallium and at higher growth temperatures even indium can be transferred from the predepositions into the epilayer. The mobilization of gallium is possible due to alkyl exchange reactions with indium-methyl-species. Indium is most probably mobilized due to its high vapour pressure at high growth temperatures. The extent of carry-over is limited within a range of a few percent impurity concentration.