Tin-doped cadmium sulfide nanowires reveal donor-acceptor pair transitions at low-temperature photoluminescence and furthermore exhibit ideal resonator morphology appropriate for lasing at continuous wave pumping. The continuous wave lasing mode is proven by the evolution of the emitted power and spectrum with increasing pump intensity. The high temperature stability up to 120 K at given pumping power is determined by the decreasing optical gain necessary for lasing in an electron-hole plasma.
High-quality CdS nanowires with uniform Sn doping were synthesized using a Sn-catalyzed chemical vapor deposition method. X-ray diffraction and transmission electron microscopy demonstrate the single crystalline wurtzite structure of the CdS/Sn nanowires. Both donor and acceptor levels, which originate from the amphoteric nature of Sn in II-VI semiconductors, are identified using low-temperature microphotoluminescence. This self-compensation effect was cross examined by gate modulation and temperature-dependent electrical transport measurement. They show an overall n-type behavior with relatively low carrier concentration and low carrier mobilities. Moreover, two different donor levels due to intrinsic and extrinsic doping could be distinguished. They agree well with both the electrical and optical data.
Periodic Si pillar arrays synthesized by metal assisted chemical etching method exhibit an excellent light harvesting capability, ideal for core-shell structured solar cell applications. To investigate the photovoltaic prospective, a radial heterojunction device is fabricated by conformal coating a layer of Al doped ZnO film on the p-Si pillar array. This core-shell structure has achieved low reflectance (<12%) over a broad wavelength range, and has demonstrated more than doubled enhancement of the short-circuit current as compared to the traditional planar architecture. Although reverse recovery transient measurement shows that this device with no surface passivation has shorter minority carrier life time than the planar structure, the overall efficiency is enhanced. It suggests that device efficiency could be much improved through proper surface treatment. This renders a promising path for core-shell structured solar cell with higher efficiency yet reduced material per device element.
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