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We have investigated the optical properties of metalorganic vapor phase epitaxy grown (Al0.5Ga0.5)0.52In0.48P samples with different degrees of CuPtB-type ordering. With increasing excitation intensity, the photoluminescence (PL) exhibits a blueshift (moving emission) which is typical for ordered material. At high excitation intensities, this blueshift is shown to result from filling of localized tail states. Further evidence for the existence of an exponential tail of localized states is provided by the form of the PL line shape for high, quasistationary excitation and by the carrier hopping relaxation demonstrated by time-resolved PL. Applying the variable stripe-length method, we have determined the spectra of the optical gain. Stimulated emission is shown to occur from localized states.

. Optical properties of (AlxGa1-x)(0.52)In0.48P at the crossover from a direct-gap to an indirect-gap semiconductor. Journal of Applied Physics, 83(4), 2241 -2249 . DOI: 10.1063 Optical properties of "Al x Ga 1؊x … 0.52 In 0.48 P at the crossover from a direct-gap to an indirect-gap semiconductor The optical properties and the dynamics of excitons and the electron-hole plasma have been studied in disordered (Al x Ga 1Ϫx ) 0.52 In 0.48 P near to the direct-to-indirect band gap crossover. In particular we have investigated three epitaxial layers grown by solid-source molecular beam epitaxy with varying Al content x. Two of them have compositions in the immediate vicinity of the crossover point, the other is assigned to the indirect-gap regime. Both direct and indirect recombination processes contribute to the photon emission from the material. Since the relative importance of the different recombination processes depends strongly on temperature, excitation intensity, and excitation pulse duration, the processes can be identified by changing these parameters. As a result, we can determine the relative alignment of the conduction band minima and the distribution of the electrons among them. At high excitation levels the two crossover samples show stimulated emission at a photon energy of ϳ2.29 eV, i.e., in the green spectral range. Using the variable stripe length method, we find an optical gain of up to ϳ600 cm Ϫ1 at excitation levels of ϳ350 kW/cm 2 . Stimulated emission involves direct recombination. This conclusion is reached from the experiments and from line-shape modeling, including a self-consistent treatment of populations and renormalization of the conduction band minima.

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We have investigated the nanostructure of ordered (Al0.5Ga0.5)0.52In0.48P using conventional and high-resolution transmission electron microscopy. As in the case of ternary Ga0.52In0.48P, the morphology of the ordered material depends strongly on the substrate orientation. For a substrate orientation with equal densities of [1̄10] and [11̄0] steps (and, hence, no preference for one particular ordering variant) a nanostructure is found which exhibits similarities to those observed in ternary Ga0.52In0.48P with equivalent substrate orientations. For a substrate orientation which preferentially selects one ordering variant without completely suppressing the formation of the other, we have identified a new type of nanostructure. In this structure, antiphase boundaries between domains containing the preferred variant are frequently formed by thin slices of the suppressed variant. This structural form is directly deduced from high-resolution images.