Arfan Bukhtiar

High performance solution-processed infrared photodetector based on PbSe quantum dots doped with low carrier mobility polymer poly(N-vinylcarbazole)

Colloidal quantum dots (CQDs) are promising materials for flexible electronics, light sensing and energy conversion. In particular, as a narrow bandgap semiconductor, lead selenide (PbSe) CQDs have attracted considerable interest due to their potential applications in infrared (IR) optoelectronics such as IR light-emitting diodes (LEDs), photodetectors and solar cells. Solution-processed photodetectors are more attractive owing to their flexible, large-scale and low-cost fabrication, and their performance depends greatly on the film quality and surface morphology. In this study, a high performance solution-processed infrared photodetector based on PbSe CQDs blended with low hole mobility polymer poly(N-vinylcarbazole) (PVK) is presented. In order to obtain a higher device performance, different volume ratios (K = VPVK/VPbSe) of PVK (20 mg ml−1 in chloroform) in PbSe CQDs (15 mg ml−1 in chlorobenzene) were investigated, and a maximum responsivity and specific detectivity of 2.93 A W−1 and 1.24 × 1012 jones, respectively, were obtained at VG = −20 V under 30 mW cm−2 980 nm laser illumination for field-effect transistor (FET)-based photodetector Au(S&D)/PbSe : PVK/PMMA/Al(G), in which PbSe : PVK nanocomposite with K = 1 : 2 acts as the active layer and poly (methyl methacrylate) (PMMA) as the dielectric layer. The reasons for the high device performance of PbSe : PVK nanocomposite as an active layer are discussed, in which PbSe nanoparticles were blended with low hole mobility polymer PVK but showed comparable detectivity as that blended with regioregular P3HT. Moreover, all these types of photodetectors are very stable for reverse fabrication using PMMA dielectric layer to shield the active layer from the environment and by inorganic ligand exchange treatment on the active layer.

Bound magnetic polaron in Zn-rich cobalt-doped ZnSe nanowires

The micro-luminescence spectra of the diluted magnetic semiconductor (DMS) can reflect the spin-exciton interaction and related relaxation process. Here the micro-photoluminescence (micro-PL) spectra and PL lifetime measurements have been done on an individual ferromagnetic (FM)-coupled cobalt (Co) doped zinc selenide (ZnSe) nanowire. There occurs a double-peak profile in its near bandedge emission spectrum: the first peak is from free exciton (FX) and the second comes from magnetic polaron (MP). In their temperature dependent PL spectra, the MP emission peak demonstrates obviously temperature-independent behavior, in contrast to the behaviors of FX and reported exciton MP in nanobelt. It is found that in this Co(II) doped ZnSe nanowires, this MPs temperature-independent emission is related to the coupling between exciton and a FM nanocluster (↑↑↓). The nanocluster is likely due to the interaction of Se vacancies of the wide bandgap semiconductors with the antiferromagnetic (AFM) arrangement transition metal (TM) ions in these Se-deficient Co doped ZnSe nanowires. These results reflect that the AFM coupling TM ions pair can give rise to FM behavior with the involvement of positive charge defect, also indicating that the micro-luminescence detection can be used to study the magnetic coupling in DMS.

EMP Formation in the Co(II) Doped ZnTe Nanowires

Co(II) doped ZnTe nanowires are prepared by a thermal evaporation method. The power and temperature dependent micro-photoluminescence spectra of single nanowire demonstrate the double bands near its band edge, and the ferromagnetism behavior for these nanowires is identified. The occurrence of excitonic magnetic polaron (EMP) can account for the second emission band for its higher binding energy and ferromagnetic coupling. This EMP formation in a nanostructure will facilitate to realize magnetic modulation on confined excitons and will find new applications for spinpolarized nanophotonic devices.

The Preparation and Optical Properties of Ni(II) and Mn(II) Doped in ZnTe Nanobelt/Nanorod by Using Chemical Vapor Deposition

The doping techniques are often used to modify the properties of semiconductors. Transition metal ion doping in semiconductor can lead to dilute magnetic semiconductors (DMSs), which may initiate some novel properties related to spins. In contrast to the wide band semiconductor ZnO, ZnSe and CdS crystal the transition metal (TM) ion aggregate can be the origin of the ferromagnetic behaviors, which influence their optical properties mainly through the exciton-spin interactions due to their high exciton binding energy. For narrow band semiconductor, the carrier-spin coupling is the main cause of magnetism as observed in ZnTe. The ZnTe nanobelt for DMS with the TM ions such as Ni(II) and Mn(II) doping mainly induce the excess carrier effect in the lattice after photo-excitation, whose optical properties are also strongly depended on the fabrication method structure and morphology. Photo-excited carriers and electron-phonon interaction (but less excitons) are responsible for their large redshifts in ZnTe nanostructures. The strong interaction between the doped magnetic ion spins and holes, electron-phonon coupling, p-d hybridization as well as local electron correlation in TM ions determined their optical properties. TM ions incorporation in ZnTe lattice has suppressed the broad defect emission band far from the bandedge and broadened the electron correlations and electron hole plasma band near bandedge when excited by the rising excitation powers. We also identified that the polarized PL of Ni(II) and Mn(II) doped samples to calculate the strain dependence of band splitting near valance band.

Structural phase transitions of tellurium nanoplates under pressure

In situ high-pressure angle dispersive x-ray diffraction experiments using synchrotron radiation on Te nanoplates were carried out with a diamond anvil cell at room temperature. The results show that Te-I with a trigonal structure transforms to triclinic Te-II at about 4.9 GPa, Te-II transforms to monoclinic Te-III at about 8.0 GPa, Te-III turns to rhombohedral Te-IV at about 23.8 GPa, and Te-IV changes to body centered cubic Te-V at 27.6 GPa. The bulk moduli B0 of Te nanoplates are higher than those of Te bulk materials.