Structural characterization of AlGaAs/GaAs multiquantum-well structures grown on silicon

Abstract

Abstract AlGaAs/GaAs multiquantum-well (MQW) structures deposited on Si(001) substrates misoriented by 4° toward 〈110〉 have been fabricated by molecular beam epitaxy (MBE) and a combination of organo-metallic chemical vapour deposition (OMCVD) and MBE. Such structures are of great interest for a better understanding of the growth of III–V compounds on misoriented silicon substrates. We have grown structures with 100 or 150 periods of GaAs wells 80 A thick and Al 0.25 Ga 0.75 As barriers 150 A thick. These structures have been studied by X-ray double crystal diffraction (DCD) and compared with those grown on GaAs substrates. We observe: (a) a tilt of the (001) planes of MQW and GaAs with respect to (001) silicon planes in the range of 0.04–0.2°. This is attributed to the initial misorientation of the silicon substrate and the 4% lattice mismatch between GaAs and silicon; (b) a perpendicular strain (ϵ⊥) of about −10 −3 corresponding to a stress parallel to the (σ∥) of about 2 × 10 8 Pa. This observation is related to the difference of thermal expansion coefficients of GaAs/AlGaAs and silicon, acting when the sample is cooled to room temperature; (c) a defect density in the range of 10 6 −10 7 cm −2 ; (d) in the best case; a full width at half maximum of the satellite peaks three times wider than those measured on GaAs substrates; (e) a misorientation of the MQW with respect to the (001) GaAs planes of about 3° toward 〈110〉 direction. The crystalline and stacking quality of the MQW structures are checked with scanning transmission electron microscopy (STEM) studies.