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This article reviews the pioneering investigations of the luminescence and photoelectric phenomena in type II heterojunctions based on the GalnAsSb/GaSb system. This system is remarkable because it Is possible to create and study heterojunctions with both staggered and broken-gap alignment, the existence of adjacent dual quantum wells for electrons and holes on both sides of the interface. Simultaneous confinement of electrons and holes in these wells causes unique optical and electrical properties of such heterojunctions and greatly modifies the characteristics of optoelectronic devices. The review considers the photo-and electroluminescence spectra of GalnAsSb/GaSb heterojunctions w/!h s!iggered hind i!ignment. The impoCznce o! !unne!!ing-zssisted trzsi!ions through the interface in the radiative recombination of confined carriers is shown. The influence of these transitions on the structure and polarization characteristics of the luminescence spectra is considered. A new mechanism of photocurrent gain in isotype n-N heterojunctions due to hole confinement at the type II interface is discussed. Unusual asymmetric electrical properties of type II heterojunctions with broken-gap band alignment are demonstrated and discussed in connection with their energy band diagrams. Novel IR light sources and photodetectors for the 1.64.7 p m spectral range based on the GalnAsSb/GaSb system are briefly reviewed.

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Surface and subsurface structures of porous GaN prepared by anodizing epitaxial GaN layers grown on SiC substrates are investigated by atomic-force microscopy. Comparison of the images of the porous GaN surfaces with those taken on planes cleft perpendicular to the surface shows that the pores are formed along the boundaries of columnar structures of the original GaN films. X-ray investigations show that the porous GaN has less residual stresses than the initial GaN epitaxial layers. Use of porous GaN as a buffer layer for growth of low-stress GaN is proposed.