III-Nitrides QD lasers are studied in detail. Two types of QD structures are considered, GaN/Al x Ga 1-x N/AlN and In x Ga 1-x N/ In 0.04 Ga 0 . 96 N /GaN. Effects of: QD size; QD and WL composition; and doping are studied through the calculations of gain, threshold current, and intensity modulation bandwidth. It is shown that GaN QDs are less sensitive to size fluctuations. Bandwidth increases with doping and reducing QD size. The study covers approximately (300-600 nm) wavelength range.

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Infrared photoconductive detectors working in the far-infrared region and room temperature were fabricated. The detectors were fabricated using three types of carbon nanotubes (CNTs); MWCNTs, COOH-MWCNTs, and short-MWCNTs. The carbon nontubes suspension is deposited by dip coating and drop–casting techniques to prepare thin films of CNTs. These films were deposited on porous silicon (PSi) substrates of n-type Si. The I-V characteristics and the figures of merit of the fabricated detectors were measured at a forward bias voltage of 3 and 5 volts as well as at dark and under illumination by IR radiation from a CO2 laser of 10.6 μm wavelengths and power of 2.2 W. The responsivity and figures of merit of the photoconductive detector are improved by coating the MWCNTs films with a thin layer of a blend (polyaniline - polymethyl methacrylate) polymer with methylene blue dye. The coated MWCNTs films showed better performances, so this type of coating can be considered as a surface treatment of the detector film, which highly increased the responsivity and specific detectivity of the fabricated IR laser detector-based MWCNTs. The photocurrent response for the coated films was increased about 25 times than that for uncoated films. The results proved the role of the polymer in the enhancement of the performance of the IR photoconductive detectors. Keywords: Carbon nanotubes, Infrared detector, Polyaniline polymer, Polymethyl methacrylate polymer, Methyl Blue dye.

Germanium antimony (Ge:Sb) thin films have been fabricated by thermal evaporation system deposition at atmospheric pressure between (5.8x10-6 to 7.5x10-6) mbar. The (Ge:Sb) thin films then exposure to Nd:YAG laser with 1064µm wavelength at different energy densities (100,200) mj/cm 2. XRD analysis show that Germanium antimony thin films are polycrystalline and the full width at half maximum (FWHM) increase as laser energy densities increases. Photocurrent and quantum efficiency of the detector increases as the laser energy densities increases.