Ultra-thin superlattices (UTSL's) (InAs)n(AlAs)n for n = 1, 2, 3, and 4 have been grown by molecular beam epitaxy in order to obtain the artificial construction of a perfect layered alloy. The optimum MBE growth condition of InAs and AlAs monolayers was obtained through the calibration of RHEED intensity oscillations. It was found that a strong oscillation of the specular beam intensity during the growth of InAs can be successfully obtained only in the narrow temperature region between 450 and 480-degrees-C. The structural property of the UTSL's was investigated by X-ray diffraction, complemented by Raman scattering measurement. Coherently strained superlattices were kept up to n = 3, while in the case of (InAs)4(AlAs)4 UTSL superlattices are rather intermixed due to the large excess strain energy. Unlike the (AlAs)n(GaAs)n, the photoluminescence peak energy reaches maximum when n = 2, at the energy of about 50 meV below the fundamental gap of In0.5Al0.5As. This is the first experimental observation that gives a corresponding result with the tight-binding calculation on the subband of the strained (InAs)n(AlAs)n UTSL's.
