Abstract
Surface segregation of indium during molecular beam epitaxy of Ga 0.85In 0.15As/GaAs ( 1 ̄ 1 ̄ 1 ̄ ) quantum wells is studied by means of in situ X-ray photoelectron spectroscopy measurements. The intensity ratio of In-4d/Ga-3d core-level spectra is used to precisely determine the amount of segregated Indium at the surface during the growth of GaInAs on GaAs substrates. GaAs ( 1 ̄ 1 ̄ 1 ̄ ) substrates exactly oriented and tilted 2° toward [ 2 1 ̄ 1 ̄ ] or [ 2 ̄ 1 1 ] have been investigated. The results are compared to those obtained on (1 0 0) GaAs substrates. We show that the amplitude of the In segregation phenomenon is larger for the GaAs ( 1 ̄ 1 ̄ 1 ̄ ) substrate tilted 2° toward [ 2 1 ̄ 1 ̄ ] than for the other substrates investigated for growth temperatures ranging from 380°C to 540°C. Having determined by atomic force microscopy the dependence of the terrace step structure of the GaAs ( 1 ̄ 1 ̄ 1 ̄ ) surface with the direction of the substrate tilt, we propose a kinetic explanation of our results. We show that an increase of the In segregation phenomenon is related to an increase of the adatom diffusion length obtained by an increase of the growth temperature and/or a modification of the terrace step structure.
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