STRUCTURAL AND OPTICAL CHARACTERIZATION OF ALTERNATELY STRAINED GAAS GAP/GAAS/INP SUPERLATTICES GROWN BY ATOMIC LAYER MOLECULAR-BEAM EPITAXY/

A new type of highly perfect strained layer superlattices matched to G aAs substrate is presented. (GaAs)N(GaP)M(GaAs)N(InP)M superlattices w ith N = 6, 10 and 90 and M = 2 were grown by atomic layer molecular be am epitaxy. In these superlattices, strain in Gap and InP layers has o pposite signs enabling us to obtain a mean lattice parameter perfectly matched to the GaAs substrate. Thicknesses of GaP and InP layers are restricted by the critical thicknesses of these materials on the GaAs substrates. The thickness of GaAs layers in the superlattice is not li mited and plays the role of tailoring the band gap of the structure, a feature that widens the applications of similar GaP/InP strained laye r superlattices. Double crystal X-ray diffraction measurements show th at all samples studied have a high crystalline quality, thicknesses of the different layers are very close to the designed growth values, an d the superlattices as a whole are coherent with the substrate, indica ting the effectiveness of compensating strains in opposite directions in the GaP and InP layers. High resolution electron microscopy analysi s shows sharp interfaces with good lateral uniformity. Neither disloca tions nor other crystalline defects are observed.