Growth of AlxGa1−xAs parabolic quantum wells by real-time feedback control of composition

Epitaxial AlxGa1−xAs structures whose compositions x vary continuously with thickness according to a given input function have been grown by chemical-beam epitaxy under closed-loop ellipsometric control. 200- and 500-Å parabolic quantum wells analyzed by photoreflectance and secondary-ion mass spectrometry, respectively, show that actual compositions follow target values to within 0.02 in x. Growth of the 200-Å profile was controlled using compositions ellipsometrically determined for the outermost running 3.1 Å (∼1 monolayer) of depositing material.