Quantum dots (QDs) have been investigated to realize high-performance opto-electronic devices. A use of a high lattice-mismatch is generally reported to fabricate self-assembling QDs, such as growth of InAs QDs on GaAs with its 7.2% lattice-mismatch. However, an emission wavelength from these InAs QDs appears around 1000nm, because an energy-band in these dots is strongly affected by a compressive strain from GaAs layer. This stress also causes a difficulty of stacked-QDs structure fabrications. In this paper, we report a growth technique of InAs QDs on AlGaSb buffer layer in the low lattice-mismatched (1.3%) InAs/AlGaSb system. We also discuss about a long wavelength emission from these QDs.
A GaAs buffer layer was formed on a GaAs (001) substrate at 580 deg.C by using molecular beam epitaxy (MBE). An AlGaSb layer on a 200 nm-thick AlSb buffer layer was formed on the GaAs sub. at 500 deg.C. InAs QDs of 1.7 or 4 ML (growth rate: 0.1 ML/s) were grown on the AlGaSb/GaAs with an As-flux (5.5x10^-7 Torr) irradiation. A size and density of QDs were estimated by using atomic force microscopy (AFM). Photoluminescence (PL) of Ar ion laser (514 nm) excitation was also measured from InAs QDs covered with AlGaSb layer and multi-stacked QDs embedded in AlGaSb layers.
From AFM measurements, an average size and density of the 1.7 ML InAs QDs are found to be 45nm-diameter, 7nm-height, and 5 x 10¹⁰ /cm². This result exhibits a structural selectivity between the QD layer and a flat hetero-interface under growth conditions change in the InAs/AlGaSb system. A broad PL spectrum (FWHM:0.25eV) at a peak of approx. 1200nm is also observed from 1.7 ML InAs QDs covered with AlSb at 300 K. Therefore, it is expected that InAs QDs grown on AlGaSb are useful to realize opto-electrical QD devices, because these QDs emit the high intensity luminescent content around 1300nm as the long wavelength, and a growth of multi-stacked QDs layers is possible due to the low lattice-mismatch.

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