ABSTRACT
Coherent light sources confining the light below the vacuum wavelength barrier will drive future concepts of nanosensing, nanospectroscopy, and photonic circuits. Here, we directly image the angular emission of such a light source based on single semiconductor nanowire lasers. It is confirmed that the lasing switches from the fundamental mode in a thin ZnO nanowire to an admixture of several transverse modes in thicker nanowires approximately at the multimode cutoff. The mode competition with higher order modes substantially slows down the laser dynamics. We show that efficient photonic mode filtering in tapered nanowires selects the desired fundamental mode for lasing with improved performance including power, efficiency, and directionality important for an optimal coupling between adjacent nanophotonic waveguides.
ABSTRACT
Single crystalline p-type CdTe:Sb nanobelts were fabricated using an Au-catalyzed chemical vapor deposition method. Low carrier concentration and low mobility even at high Sb incorporation manifest compensation in the system. From cross examination of temperature-dependent charge transport and photoluminescence measurements, two major acceptor levels induced by Sb doping are determined: a shallow level attributed to substitutional Sb dopants without lattice relaxation and an associated deeper level resulted from large lattice relaxation-AX centers. Persistent photoconductivity and hysteresis photoconductance under the thermal cycle elucidate the nature of AX centers. This comprehensive investigation of the impurity levels in the material system is essential for the design and development of nanoelectronic devices based on the CdTe nanostructures.
