An In surface segregation effect during the growth of InGaAs on GaAs by molecular-beam epitaxy has been studied by reflection high-energy electron diffraction measurements supported by a segregation model. Indium atoms segregate at a ratio of more than 0.8 under the conventional growth conditions for InGaAs, which causes the formation of accumulated In atoms on the surface. The transition from two-dimensional to three-dimensional growth occurs when the amount of In reaches around 1.7 monolayer with a nominal alloy composition greater than 0.25. This transition determines the upper limit on the In composition of the InGaAs layer for application as an electron channel in modulation-doped field-effect transistors.

A model is proposed for describing the origin of the growth mode transition from two to three dimensions during the molecular-beam epitaxial growth of InGaAs on GaAs [H. Toyoshima, T. Niwa, J. Yamazaki, and A. Okamoto, Appl. Phys. Lett. 63, 821 (1993)]. In this model the amount of In atoms on the surface arising from surface segregation is crucial in determining the growth mode transition, which provides the upper limit of the In composition and/or the thickness of InGaAs for device applications. The increase of these limited values for a modulation-doped structure with an InGaAs channel has been implemented on the basis of this model. A lower substrate temperature and a higher As4 pressure during the InGaAs growth greatly suppress the In segregation ratio leading to the decrease of the amount of In on the surface. These growth conditions enable the upper limit of the In composition and/or the critical thickness of the InGaAs channel to be increased, which further verifies the validity of the proposed model. The surface of the InGaAs with the higher In composition is, however, metastable and can be stabilized by depositing AlGaAs or GaAs more than 3 monolayers thick on it. Modulation-doped structures with high electron transport properties have been successfully grown as high as the In composition of 0.45 by controlling the growth kinetics of InGaAs.

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