Electroluminescence explored internal behavior of carriers in InGaAsP single-junction solar cell

The internal behaviors of carriers in InGaAsP single-junction solar cell are investigated by using electroluminescence(EL) measurements. Two emission peaks can be observed in current-dependent electroluminescence spectra at low temperatures, and carrier localization exists for both peaks under low excitation. The trends of power index α extracted from excitation-dependent EL spectra at different temperatures imply that there exists a competition between Shockley–Read–Hall recombination and Auger recombination. Auger recombination becomes dominant at high temperatures, which is probably responsible for the lower current density of InGaAsP solar cell. Besides, the anomalous “S-shape” tendency with the temperature of band-edge peak position can be attributed to potential fluctuation and carrier redistribution, demonstrating delocalization, transfer, and redistribution of carriers in the continuum band-edge. Furthermore, the strong reduction of activation energy at high excitations indicates that electrons and holes escaped independently, and the faster-escaping carriers are holes.

Electron Injection Enhancement by Diamond-Like Carbon Film in Polymer Electroluminescence Devices

A diamond-like carbon （DLC） film is deposited as an electron injection layer between the polymer light-emitting layer（MEH-PPV） and aluminum （Al） cathode electrode in polymer electroluminescence devices （PLEDs） using a radio frequency plasma deposition system. The source material of the DLC is n-butylamine. The devices consist of indium tin oxide （ITO）/MEH-PPV/DLC/Al. Electron injection properties are investigated through I-V characteristics,and the mechanism of electron injection enhancement due to a thin DLC layer has been studied. It is found that： （1） a DLC layer thinner than 1.0nm leads to a higher turn-on voltage and decreased electroluminescent （EL） efficiency; （2） a 5.0nm DLC layer significantly enhances the electron injection and results in the lowest turn-on voltage and the highest EL efficiency; （3） DLC layer that exceeds 5.0nm results in poor device performance;and（4） EL emission can hardly be detected when the layer exceeds 10.0nm. The properties of ITO/MEH-PPV/DLC/Al and ITO/MEH-PPV/LiF/Al are investigated comparatively.

Measurements of Carrier Confinement at β-FeSi_2-Si Heterojunction by Electroluminescence

A Si p-π-n diode with β-FeSi 2 particles embedded in the unintentionally doped Si (p--type) was designed for determining the band offset at β-FeSi 2-Si heterojunction.When the diode is under forward bias,the electrons injected via the Si n-p- junction diffuse to and are confined in the β-FeSi 2 particles due to the band offset.The storage charge at the β-FeSi 2-Si heterojunction inversely hamper the further diffusion of electrons,giving rise to the localization of electrons in the p--Si near the Si junction,which prevents them from nonradiative recombination channels.This results in electroluminescence (EL) intensity from both Si and β-FeSi 2 quenching slowly up to room temperature.The temperature dependent ratio of EL intensity of β-FeSi 2 to Si indicates the loss of electron confinement following thermal excitation model.The conduction band offset between Si and β-FeSi 2 is determined to be about 0 2eV.

Far-infrared electroluminescence characteristics of an Si-based photodiode under a forward DC bias current

At room temperature, the bias dependence of a far-infrared electroluminescence image of a photodiode is investi-gated in the dark condition. The results show that the electroluminescence image can be used to detect defects in the photodiode. Additionally, it is found that the electroluminescence intensity has a power law dependence on the dc bias current. The photodiode ideality factor could be obtained by a fitting a relationship between the electroluminescence intensity and the bias current. The device defect levels will be easily determined according to the infrared image and the extracted ideality factor value. This work is of guiding significance for current solar cell testing and research.

Blue-Green Electroluminescence of Free-Standing Diamond Thin Films

Blue-green electroluminescence has been observed in free-standing diamond films which were deposited by microwave plasma assisted CVD on silicon substrates.The electroluminescence device is driven by a 60 Hz power supply.The threshold voltage was about 112 V peak-to-peak.The electroluminescence spectrum at room temperature,showed a blue-green band with the peak centered at 485nm suggesting band A type emission.Electroluminescence was also observed at 77K.

Red Electroluminescence and Photoluminescence from Novel Binuclear Europium Complex with Squaric Acid Ligand

A novel binuclear europium P-diketone complex with squaric acid ligand was synthesized for the first time. Its structure was elucidated by IR, UV, and Elemental Analysis. Red light emitting diode (LED) was fabricated by using the novel europium complex as an emitting layer, tris(8-quinolinolate) aluminum (III) (Alq(3)) as an electron-transporting layer, N, N'-diphenyl-N, N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as a hole-transporting layer. A cell structure of indium-tin-oxide/TPD/Eu-complex/Alq(3)/Mg: Ag was employed. Red electroluminescence was observed at room temperature with dc bias voltage of 2 V in this cell. 2 Red emission peaks at about 613 nm with maximum luminance of over 106 cd/m(2). Compared with the EL luminance from those europium complexes reported before, one from the Eu-complex is best in the same cells.

Synthesis,characterization,photoluminescence and electroluminescence properties of new 1,3,4-oxadiazole-containing rhenium(I)complex Re(CO)_3(Bphen)(PTOP)

A new 1,3,4-oxadiazole-contanining rhenium（I） complex, with the formula [Re（CO）a（Bphen）（PTOP）], （Bphen = bathophe- nardine, PTOP = 4-（5-p-tolyl-1,3, 4-oxadiazd-2-yl） pyridine）, is synthesized and characterized by elemental analysis, IR, 1H NMR, UV-vis and luminescence spectroscopy. The double-layer electroluminescence devices based on the Re（l） complex have been fabricated by spin-coating technique. The turn-on voltage, maximum efficiency, and brightness for green emission obtained from the devices are 9 V, 2.1 cd/A and 165 cd/m^2, respectively.

Evaluation of polarization field in InGaN/GaN multiple quantum well structures by using electroluminescence spectra shift

In order to investigate the inherent polarization intensity in InGaN/GaN multiple quantum well(MQW) structures,the electroluminescence(EL) spectra of three samples with different GaN barrier thicknesses of 21.3 nm, 11.4 nm, and 6.5 nm are experimentally studied. All of the EL spectra present a similar blue-shift under the low-level current injection,and then turns to a red-shift tendency when the current increases to a specific value, which is defined as the turning point.The value of this turning point differs from one another for the three InGaN/GaN MQW samples. Sample A, which has the GaN barrier thickness of 21.3 nm, shows the highest current injection level at the turning point as well as the largest value of blue-shift. It indicates that sample A has the maximum intensity of the polarization field. The red-shift of the EL spectra results from the vertical electron leakage in InGaN/GaN MQWs and the corresponding self-heating effect under the high-level current injection. As a result, it is an effective approach to evaluate the polarization field in the InGaN/GaN MQW structures by using the injection current level at the turning point and the blue-shift of the EL spectra profiles.

Mechanism of SrS∶Ce Thin Film Electroluminescence

The influence of the delocalization probability on the mixing interaction between excited levels of Ce3+ and the conduction band of SrS was analysed. The observation of emission wave forms of SrSCe thin film electroluminescence showed that only leading edge emission peak was observed for one sample and the leading and trailing edge emission peaks were observed for another in a half period of sinusoid applied voltage. This difference is related to the influences of sulphur vacancies on the excitation and emission processes. The leading edge emssion is dominated by discrete luminescence caused by direct impact excitation and the trailing edge emission and a part of leading edge emission belong to recombination luminescence caused by impact ionization and delocalization.

Doped Organic Electroluminescence from a Novel Rare Earth Complex Tb(3-metho)_3phen

A novel rare earth complex Tb(3 metho) 3phen was synthesized and characterized. The complex was doped into PVK to improve the conductivity and film forming property of Tb(3 metho) 3phen. A device with a structure of ITO/PVK∶Tb(3 metho) 3phen /Al was fabricated to study the electroluminescent properties of Tb(3 metho) 3phen. And the optoluminescent and AFM properties of this device were also studied, which proved the existence of energy transfer from PVK to Tb(3 metho) 3phen. As a result, a pure green emission with sharp spectral band at 547.5 nm was observed.

Research on Performance of ZnS∶TbF_3 Thin Film Electroluminescence Device

The electroluminescence of ZnS doped with terbium fluoride thin films prepared b y ra dio frequency magnetron sputtering method was reported. The characteristics of t h e ZnS∶TbF 3 thin film electroluminescence devices, such as film characteristi cs of the ZnS∶Tb active layer, substrate temperatures during magnetron sputteri ng and Tb concentration of the active layer, were systematically investigated. The results show that annealing can evidently improve the luminescence performance of the luminescence device.

Rectification and electroluminescence of nanostructured GaN/Si heterojunction based on silicon nanoporous pillar array

A GaN/Si nanoheterojunction is prepared through growing Ga N nanocrystallites（nc-GaN） on a silicon nanoporous pillar array（Si-NPA） by a chemical vapor deposition（CVD） technique at a relatively low temperature. The average size of nc-Ga N is determined to be ~10 nm. The spectral measurements disclose that the photoluminescence（PL） from GaN/SiNPA is composed of an ultraviolet（UV） band and a broad band spanned from UV to red region, with the feature that the latter band is similar to that of electroluminescence（EL）. The electron transition from the energy levels of conduction band and, or, shallow donors to that of deep acceptors of Ga N is indicated to be responsible for both the broad-band PL and the EL luminescence. A study of the I-V characteristic shows that at a low forward bias, the current across the heterojunction is contact-limited while at a high forward bias it is bulk-limited, which follows the thermionic emission model and space-charge-limited current（SCLC） model, respectively. The bandgap offset analysis indicates that the carrier transport is dominated by electron injection from n-GaN into the p-Si-NPA, and the EL starts to appear only when holes begin to be injected from Si-NPA into GaN with biases higher than a threshold voltage.

White electroluminescence of n-ZnO:Al/p-diamond heterostructure devices

An n-ZnO：A1/p-boron-doped diamond heterostructure electroluminescent device is produced, and a rectifying be- havior can be observed. The electroluminescence spectrum at room temperature exhibits two visible bands centred at 450 nm-485 nm （blue emission） and 570 nm-640 nm （yellow emission）. Light emission with a luminance of 15 cd/m2 is observed from the electroluminescent device at a forward applied voltage of 85 V, which is distinguished from white light by the naked eye.

Bias-Polarity Dependent Electroluminescence from a Single Platinum Phthalocyanine Molecule

By using scanning tunneling microscope induced luminescence(STML)technique,we investigate systematically the bias-polarity dependent electroluminescence behavior of a single platinum phthalocyanine(PtPc)molecule and the electron excitation mechanisms behind.The molecule is found to emit light at both bias polarities but with different emission energies.At negative excitation bias,only the fluorescence at 637 nm is observed,which originates from the LUMOtHOMO transition of the neutral PtPc molecule and exhibits stepwise-like increase in emission intensities over three different excitation-voltage regions.Strong fluorescence in region(I)is excited by the carrier injection mechanism with holes injected into the HOMO state first;moderate fluorescence in region(II)is excited by the inelastic electron scattering mechanism;and weak fluorescence in region(III)is associated with an up-conversion process and excited by a combined carrier injection and inelastic electron scattering mechanism involving a spintriplet relay state.At positive excitation bias,more-than-one emission peaks are observed and the excitation and emission mechanisms become complicated.The sharp moleculespecific emission peak at〜911 nm is attributed to the anionic emission of PtPc-originated from the LUMO+1 tLUMO transition,whose excitation is dominated by a carrier injection mechanism with electrons first injected into the LUMO+1 or higher-lying empty orbitals.

Photoluminescence and electroluminescence properties of ZnO films on p-type silicon wafers

A simplified n-ZnO/p-Si heterojunction has been prepared by growing n-type ZnO rods on p-type silicon wafer through the chemical wpour deposition method. The reflectance spectrum of the sample shows an independent absorption peak at 384 nm, which may be originated from the bound states at the junction. In the photoluminescence spectrum a new emission band is shown at 393 nm, besides the bandedge emission at 380nm. The electroluminescence spectrum of the n-ZnO/p-Si heterojunction shows a stable yellow luminescence band centred at 560 nm, which can be attributed to the emission from trapped states. Another kind of discrete ZnO rod has also been prepared on such silicon wafer and is encapsulated with carbonated polystyrene for electroluminescence detection. This composite structure shows a weak ultraviolet electroluminescence band at 395 nm and a yellow electroluminescence band. These data prove that surface modification which blocks the transverse movement of carriers between neighbouring nanorods plays important roles in the ultraviolet emission of ZnO nanorods. These findings are vital for future display device design.

Electroluminescence of double-doped diamond thin films

A new electroluminescence device is fabricated by microwave plasma chemical vapour deposition system and electron beam vapour deposition system. It is comprised of highly doped silicon/diamond/boron/nitrogen-doped diamond/indium tin oxide thin films. Effects of process parameters on morphologies and structures of the thin films are detected and analysed by scanning electron microscopy, Raman spectrometer and x-ray photoelectron spectrometer. A direct-current （DC） power supply is used to drive the electroluminescence device. The blue light emission with a luminance of 1.2 cd·m^-2 is observed from this double-doped diamond thin film electroluminescence device at an applied voltage of 105 V.

Green-Light Electroluminescence of Conjugated Copolymer Containing p-Phenylene-ethynylene and Oxadiazole

The title copolymer(PDEBO) was synthesized. The thermal characteristics of the polymer were determined by means of DSC and TGA, revealing that the polymer has a good thermal stability. The X-ray diffraction measurements of the thin films showed that the polymer is disorder. Electroluminescence(EL) in the green region of the spectrum with a maximum at 500 nm was observed from the polymer films sandwiched between indium-tin-oxide and an Al electrode.

Direct-bandgap electroluminescence from tensile-strained Ge/SiGe multiple quantum wells at room temperature

Tensile-strained Ge/SiGe multiple quantum wells （MQWs） were grown on a Ge-on-Si virtual substrate using ultrahigh vacuum chemical vapor deposition on an n＋-Si （001） substrate. Direct-bandgap electroluminescence from the MQWs light emitting diode was observed at room temperature. The quantum confinement effect of the direct-bandgap transitions is in good agreement with the theoretical calculated results. The redshift mechanism of emission wavelength related to the thermal effect is discussed,

Room temperature direct-bandgap electroluminescence from a horizontal Ge ridge waveguide on Si

We report a lateral Ge-on-Si ridge waveguide light emitting diode （LED） grown by ultrahigh vacuum chemical vapor deposition （UHV-CVD）. Direct-bandgap electroluminescence （EL） of Ge waveguide under continuous current is observed at room temperature. The heat-enhancing luminescence and thermal radiation-induced superlinear increase of edge output optical power are found. The spontaneous emission and thermal radiation based on the generalized Planck radiation law are calculated and fit very well to the experimental results. The Ge waveguides with different lengths are studied and the shorter one shows stronger EL intensity.

Influence of Poly(methylmethacrylate) Dopant on Butadiene Derivative Electroluminescence

Organic electroluminescent (EL) devices with one layer of 1,1 bis( p diethyl aminophenyl) 4,4 diphenyl 1, 3 (DEAB) doped with different quantities of poly(methylmethacrylate) (PMMA) (DEAB/PMMA) as the EL emitting layer, sandwiched between indium/tin oxide (ITO) and aluminum electrodes, have been fabricated by spin coating onto ITO. We found that there is an optimum doping ratio of DEAB to PMMA in the emitting layer for enhancing the EL intensity and efficiency of DEAB/PMMA devices.