G. G. Qin

Multilayered graphene used as anode of organic light emitting devices

In this report, we find multilayered graphene, which has good transparency, conductivity and suitable work function, can be used as the anode for the organic light emitting device. Our device structure is Al/glass/multilayered graphene/V2O5/NPB/CBP:(ppy)2Ir(acac)/Bphen/Bphen:Cs2CO3/Sm/Au. The maximum luminance efficiency and maximum power efficiency reach 0.75 cd/A and 0.38 lm/W, respectively. We believe that by optimizing the hole density and uniforming the thickness of the multilayered graphene anode, the device efficiency can be remarkably increased in the future.

VISIBLE ELECTROLUMINESCENCE FROM SEMITRANSPARENT AU FILM EXTRA THIN SI-RICH SILICON-OXIDE FILM P-SI STRUCTURE

Visible electroluminescence (EL) has been reported from semitransparent Au film/extra thin Si-rich silicon oxide film/p-Si diodes at room temperature. The Si-rich silicon oxide films, with thickness of about 40 Angstrom, were grown using the magnetron sputtering technique. At forward bias of 4 V, EL spectra with peak energy of 1.9 eV and full width at half maximum of 0.5 eV can be observed from diodes with such extra thin Si-rich oxide films having not been annealed. EL peak energy shows a small red shift under low forward bias but does not shift again when increasing the bias further. Annealing at 800 degrees C, EL spectra widen and show several shoulders at about 1.5, 2.2, and 2.4 eV, and the EL peak energy shows blue shift with increasing forward bias. These results are shown to be consistent with light emission at several types of luminescence centers in the Si-rich silicon oxide films

A comparative study of ultraviolet emission with peak wavelengths around 350 nm from oxidized porous silicon and that from SiO2 powder

Ultraviolet (UV) light emission with almost the same peak wavelengths from thermally oxidized porous silicon (OPS) (340, 355, and 370 nm) and SiO2 powder (340, 350, and 370 nm) has been observed. Photoluminescence excitation spectra of OPS without Si nanoscale particles (SNP) and those of SiO2 powder are very similar, however, very different from those of the OPS with SNP. Three types of luminescence centers with luminescence wavelengths around 350 nm are responsible for UV light emission, and photoexcitation in OPS with SNP occurs in SNP as well as in Si oxide layers covering SNP.

Synthesis of high quality n-type CdS nanobelts and their applications in nanodevices

High quality n-type CdS nanobelts (NBs) were synthesized via an in situ indium doping chemical vapor deposition method and fabricated into field effect transistors (FETs). The electron concentrations and mobilities of these CdS NBs are around (1.0x10(16)-3.0x10(17))/cm(3) and 100-350 cm(2)/V s, respectively. An on-off ratio greater than 10(8) and a subthreshold swing as small as 65 mV/decade are obtained at room temperature, which give the best performance of CdS nanowire/nanobelt FETs reported so far. n-type CdS NB/p(+)-Si heterojunction light emitting diodes were fabricated. Their electroluminescence spectra are dominated by an intense sharp band-edge emission and free from deep-level defect emissions. (c) 2006 American Institute of Physics.

Luminescence studies of a Si/SiO2 superlattice

Photoluminescence and electroluminescence from a Si/SiO2 superlattice have been measured. They show similar characteristics and exhibit an inhomogeneously broadened photoluminescence band peaked at 2.06 eV. The excitation spectrum indicates that excitations occur in the Si layers. The insensitivity of the luminescence spectrum and decay to temperature and excitation wavelength suggests that luminescence originates from transitions between localized defect states. These localized states are most likely defect states residing at the Si/SiO2 interfaces, because there should be a significant concentration of defects at the interface and SiO2 due to the large lattice mismatch and the amorphous state. The close proximity of these states offers a more rapid transition path for the excited electrons. An energy band diagram of the superlattice is constructed based on our results.

Refractive index and extinction coefficient of CH 3 NH 3 PbI 3 studied by spectroscopic ellipsometry

Research concerning CH3NH3PbI3 solar cells (SCs) has attracted great attention. However, the CH3NH3PbI3 material’s critical dispersion relationships, i.e. the refractive index and the extinction coefficient, n(λ) and k(λ), as functions of λ, have been little studied. Without this knowledge, it will be difficult to quantitively investigate the optical properties of the CH3NH3PbI3 SCs. We studied n(λ) and k(λ) of CH3NH3PbI3 with spectroscopic ellipsometry. The CH3NH3PbI3 film was fabricated by dual-source evaporation, and the surface roughness was investigated to facilitate SE modeling. With the acquired n(λ) and k(λ), we applied the finite difference time domain method to calculate the ultimate efficiency, η(d), without considering carrier recombination, of the planar CH3NH3PbI3 SC as a function of the film thickness, d, from 31.25 nm to 2 μm, and compared with those of GaAs, c-Si, and a-Si:H(10%H) SCs. It is demonstrated that, η(d) for CH3NH3PbI3 SC is a little smaller than, but very close to that for the GaAs SC, however, much larger than that for the c-Si SC, for all d calculated; and much larger than that for the a-Si:H(10%H) SC when d > 100 nm. Apart from an appropriate band gap near 1.5 eV, the larger k(λ) and smaller n(λ) of CH3NH3PbI3 explain why the CH3NH3PbI3 SC has high efficiency.

Electrical properties of Cu doped p-ZnTe nanowires

Single crystalline zincblende p-ZnTe nanowires (NWs) were synthesized via the vapour phase transport method. Based on either as-grown or Cu doped ZnTe NWs, single NW field effect transistors were fabricated and they were used to study the electrical properties of ZnTe NWs. Electrical transport measurements show that the as-grown ZnTe NWs are of p-type and very high resistivity. After 30 min immersion in Cu(NO3)2 solution, their conductivity can be increased by about three orders of magnitude. The hole concentrations of the p-type ZnTe nanowires could be controlled in a range from 7.0 × 1017 to 3.5 × 1018 cm−3 by changing the immersion duration. The doped p-type ZnTe NWs may have potential applications in nanoscale electronic and optoelectronic devices.

A top-emission organic light-emitting diode with a silicon anode and an Sm/Au cathode

A top-emission organic light-emitting diode (TEOLED) with a p-type silicon anode and a semitransparent samarium/gold cathode has been constructed and studied. With a structure of Al∕p-Si∕SiOx∕N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine(NPB)∕Tris-(8-hydroxyquinoline)aluminum(Alq)∕LiF∕Al, we have found that compared to indium-tin-oxide, the p-Si anode enhances the unbalance between electron- and hole-injection, which is a disadvantage factor for the light-emitting efficiency of the TEOLED. Selecting p-Si wafers with suitable electric resistivities and inserting an ultrathin low temperature grown SiOx layer of about 1.5nm between the anode and NPB can effectively restrict hole-injection. Moreover, a low work function Sm∕Au cathode was used to enhance electron-injection. The electroluminescence efficiency of the TEOLED depends on the thickness of the Sm layer in the cathode. A current efficiency of 0.55cd∕A and a power efficiency of 0.07lm∕W have been reached.

Schottky junction photovoltaic devices based on CdS single nanobelts

Schottky junction photovoltaic (PV) devices were fabricated on single CdS nanobelts (NBs). Au was used as the Schottky contact, and In/Au was used as the ohmic contact to CdS NB. Typically, the Schottky junction exhibits a well-defined rectifying behavior in the dark with a rectification ratio greater than 10(3) at +/- 0.3 V; and the PV device exhibits a clear PV behavior with an open circuit photovoltage of about 0.16 V, a short circuit current of about 23.8 pA, a maximum output power of about 1.6 pW, and a fill factor of 42%. Moreover, the output power can be multiplied by connecting two or more of the Schottky junction PV devices, made on a single CdS NB, in parallel or in series. This study demonstrates that the 1D Schottky junction PV devices, which have the merits of low cost, easy fabrication and material universality, can be an important candidate for power sources in nano-optoelectronic systems.

High-quality CdTe nanowires: Synthesis, characterization, and application in photoresponse devices

High-quality straight and multiply kinked CdTe nanowires (NWs) were synthesized by the facile chemical vapor deposition method at 600 °C. The as-synthesized NWs were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy, and photoluminescence (PL) spectroscopy. The straight CdTe NWs have single crystalline zinc blende structure with growth direction along the ⟨111⟩ direction. Their PL spectra consist only sharp near band edge emission around 824.3 nm. The multiply kinked CdTe NWs contain one or more fixed (∼125.2°) angle joints; each arm of the kinked NWs is single crystalline with similar selected area electron diffraction pattern as that of the straight CdTe NWs. The two growth directions in the multiply kinked CdTe NWs are ⟨200⟩ and ⟨111⟩. Single straight and kinked CdTe NW photoresponse devices were fabricated and testified to have high photocurrent decay ratio, high responsivity, fast response time, and no decay tail unde...