Using combined microscopy and optical characterizations, the authors demonstrate effective Er doping into freestanding ZnO nanowires via ion implantation. The Er atoms are observed to take the substitutional sites in ZnO without causing obvious distortion to the host lattice. While the band gap threshold of the Er doped ZnO nanowires remains similar to that of the undoped ZnO, band tail states are created in the band structure of the ZnO upon Er doping. Room temperature 1.54μm emission is achieved in the doped nanowire sample after oxygen annealing. In particular, the generation of the band tail state(s) in the band gap of the ZnO nanowire host is found to be responsible for the 1.54μm emission under the below-band-gap indirect excitation.

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Dilute-nitride GaAsNx epilayers were grown on GaAs (001) substrates at temperatures of ∼450 °C using a radio-frequency plasma-assisted molecular/chemical beam exitaxy system. The concentration of nitrogen incorporated into the films was varied in the range between 0.01 and 0.04. High-resolution electron microscopy was used to determine the cross-sectional morphology of the epilayers, and Z-contrast imaging showed that the incorporated nitrogen was primarily interstitial. {110}-oriented microcracks, which resulted in strain relaxation, were observed in the sample with the highest N concentration ([N] ∼ 3.7%). Additionally, Z-contrast imaging indicated the formation of a thin, high-N quantum-well-like layer associated with initial ignition of the N-plasma. Significant N contamination of the GaAs barrier layers was observed in all samples, and could severely affect the carrier extraction and transport properties in future targeted devices. Dilute-nitride quantum-well-based photovoltaic solar cells were fabricated having a band-gap energy of 1.19 eV, which was attributed to the dilute-nitride layer.

The molecular beam epitaxial growth and optimization of antimony-based interband cascade photodetectors, on both GaSb and GaAs substrates, are presented. Material characterization techniques, including X-ray diffraction, atomic force microscopy, and crosssectional transmission electron microscopy, are used to evaluate the epitaxial material quality. This work has led to the demonstration of mid-infrared photodetectors operational up to a record-high 450 K, and a dark current density as low as 1.10×10 -7 A/cm 2 at 150 K. The results also suggest that further improved material quality and device performance can be expected via optimization of growth parameters.