DETECTION AND REDUCTION OF INDIUM SEGREGATION DURING MOLECULAR-BEAM EPITAXIAL-GROWTH OF INGAAS/GAAS USING INSITU REFLECTION MASS-SPECTROMETRY

The use of reflection mass spectrometry (REMS) as an in situ diagnostic for surface segregation of indium during InGaAs layer growth is reported. InGaAs growth at substrate temperatures above 500-degrees-C yields a REMS signature which indicates a thickness-dependent surface In content. Adapting a simple segregation model [K. Muraki, S. Fukatsu, Y. Shiraki, and R. Ito, Appl. Phys. Lett. 61, 557 (1992)], the segregation ratio R was extracted under various deposition conditions in real time. The segregation ratio obtained during InGaAs/GaAs multiple quantum well growth at 500-530-degrees-C suggests the presence of InGaAs composition grading near interfaces, and agrees qualitatively with ex situ characterization by x-ray diffraction. The high values of R (0.7-0.8) observed under normal device-layer growth produces a surface layer with high In content (i.e., InAs). The segregation ratio was not sensitive to unrelaxed layer strain, but showed a large increase under conditions which probably produce island (three-dimensional) growth. Methods for preparation of high-quality InGaAs layers with more abrupt AlGaAs/InGaAs/GaAs heterointerfaces are discussed, such as use of a two-step growth procedure or the incorporation of thin ''cap layers'' prior to high temperature AlGaAs growth.