A broad absorption band around 500 nm is observed in ZnS nanoparticles. The absorption becomes more intensive and shifts to the blue as the particle size is decreased. The absorption energy is lower than the band gap of the particles and is considered to be caused by the surface states. This assignment is supported by the results of the fluorescence and of the thermoluminescence of the surface states. Both the absorption and the fluorescence reveal that the surface states are size dependent. The glow peak of the semiconductor particles is not varied as much upon decreasing size, indicating the trap depth of the surface states is not sensitive to the particle size. Considering these results, a new model on the size dependence of the surface states is proposed, which may explain our observations reasonably.

The thermoluminescence (TL) of ZnS nanoparticles is reported. The TL intensity increases as the particle size is decreased. The consistency of the size dependence of the TL with that of the surface fluorescence indicates that the TL may be related to the surface states. TL may be caused by the recombination of carriers released from the surface states or defect sites by heating. Smaller particles have higher surface/volume ratio and more surface states, therefore contain more accessible carriers for TL. Besides, the carrier recombination rate increases upon decreasing size due to the increase of the overlap between the electron and hole wave functions. These two effects may make the TL increase upon decreasing size of the particles. The appearance of TL prior to any radiation reveals that trapped carriers have pre-existed. The investigation of TL may provide some useful information about the surface states that may explain the size dependence of the surface fluorescence.

Using the measured capacitance-voltage curves of Ni Schottky contacts with different areas on strained AlGaN∕GaN heterostructures and the current-voltage characteristics for the AlGaN∕GaN heterostructure field-effect transistors at low drain-source voltage, we found that the two-dimensional electron gas (2DEG) electron mobility increased as the Ni Schottky contact area increased. When the gate bias increased from negative to positive, the 2DEG electron mobility for the samples increased monotonically except for the sample with the largest Ni Schottky contact area. A new scattering mechanism is proposed, which is based on the polarization Coulomb field scattering related to the strain variation of the AlGaN barrier layer.

Sphalerite-type (Cu(2)Sn)(x/3)Zn(1-x)S (0 < or = x < or = 0.75) nanocrystals with tunable band gaps were successfully prepared via a solvothermal approach. Band gaps of the nanoparticles could be adjusted from 3.48 eV to 1.23 eV by changing the composition. Their implementation in quantum dot sensitized solar cells (QDSSCs) suggests considerable potential in solar cells.

Monodispersed metastable cubic AgInS2 nanocrystals with an average size of around 2.5 nm are obtained via a solution-phase reaction. In contrast with the usual chalcopyrite and orthorhombic phase, Ag+ and In3+ cations in metastable cubic AgInS2 are randomly coordinated by four S2− anions. A phase transition from cation-disordered cubic to orthorhombic AgInS2 occurs with the increased reaction temperature or elongated reaction time. The photoluminescence quantum yield of cation-disordered cubic AgInS2 nanocrystals could reach 10% at room temperature, which is much higher than that of orthorhombic AgInS2 nanocrystals obtained via a similar approach.

Freestanding large-size SnS thin crystals are synthesized via two-dimensional oriented attachment (OA) growth of colloidal quantum dots (CQDs) in a novel high-pressure solvothermal reaction. The SnS thin crystals present a uniform rectangular shape with a lateral size of 20-30 um and thickness of <10 nm. The evolution process demonstrates that a synergetic effect of pressure, aging time and organic ligands results in polycrystal-to-monocrystal formation and defect annihilation. Furthermore, gas sensor and photodetector devices, based on SnS thin single crystals, are also prepared. The sensing devices present high sensitivity, superior selectivity, low detection limit (≪100 ppb) and reversibility to NO2 at room temperature. The fabricated photodetector devices exhibit a high responsivity of 2.04 × 10(3) A W(1-) and high external quantum efficiency of ∼4.75 × 10(5) % at 532 nm, which are much higher than most of the photodetector devices.

Articles you may be interested inEffects of rapid thermal annealing on the electrical properties of the AlGaN/AlN/GaN heterostructure fieldeffect transistors with Ti/Al/Ni/Au gate electrodes Appl. Phys. Lett. 105, 083501 (2014); 10.1063/1.4894093 Theoretical model of the polarization Coulomb field scattering in strained AlGaN/AlN/GaN heterostructure field-effect transistors J. Appl. Phys. 116, 044507 (2014); 10.1063/1.4891258 Enhanced effect of strain-induced polarization Coulomb field scattering in AlN/GaN heterostructure field-effect transistors Appl.

Porous copper zinc tin sulfide (CZTS) thin film was prepared via a solvothermal approach. Compared with conventional dye-sensitized solar cells (DSSCs), double junction photoelectrochemical cells using dye-sensitized n-type TiO(2) (DS-TiO(2)) as the photoanode and porous p-type CZTS film as the photocathode shows an increased short circuit current, external quantum efficiency and power conversion efficiency.