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 b ecome distributed over many atomic layers. We have measured the Si depth di stributions in (100) and (311)A samples grown at temperatures between 420 a nd 655 degrees C, with Al fraction x = 0, 0.1, and 0.32. The surface migrat ion decay length Lambda for a Si atom on a growing (100) surface is strongl y temperature dependent but nearly independent of x, with Lambda approximat e 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 maxim um value Lambda approximate to 8.5 nm at high temperatures. The data are in accord with a thermally activated surface segregation process with activat ion energy (1.8 +/- 0.4) eV acting in parallel with a temperature independe nt surface segregation mechanism. The (311)A surface shows Lambda = (3.3 +/ - 0.1) nm virtually independent of temperature for x = 0. The Si decay leng th 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].