Mechanisms for Si dopant migration in molecular beam epitaxy AlxGa1-xAs

Because of well-known surface segregation effects in molecular beam epitaxy growth, Si dopant atoms deposited as thin layers in AlxGa1-xAs typically become distributed over many atomic layers. We have measured the Si depth distributions in (100) and (311)A samples grown at temperatures between 420 and 655 degrees C, with Al fraction x = 0, 0.1, and 0.32. The surface migration decay length Lambda for a Si atom on a growing (100) surface is strongly temperature dependent but nearly independent of x, with Lambda approximate to 8 nm at 655 degrees C. The x = 0(100) measurements show evidence for a minimum value Lambda approximate to 0.6 nm at low temperatures and a maximum value Lambda approximate to 8.5 nm at high temperatures. The data are in accord with a thermally activated surface segregation process with activation energy (1.8 +/- 0.4) eV acting in parallel with a temperature independent surface segregation mechanism. The (311)A surface shows Lambda = (3.3 +/- 0.1) nm virtually independent of temperature for x = 0. The Si decay length for the (311)A surface strongly increases with x, and for x = 0.32 there is no significant difference in Lambda for the (100) and (311)A surfaces. (C) 2000 American Institute of Physics. {[}S0021-8979(00)05920-X].