Dependence Of Internal Quantum Efficiency Research Articles

Physical–Mathematical Model Of The Internal Quantum Efficiency Dependence On The Current Of Leds With Quantum Wells

A physical-mathematical model of dependence of internal quantum efficiency on current for LED structures with quantum wells has been developed. The volt-ampere characteristic is modelled with the involvement of Shockley, Noyce, Sah recombination theory, supplemented by the quantum wells distribution function. In order to obtain dependence of internal quantum efficiency of LEDs on current, model of rate of ABC recombination in quantum wells is used. The developed model was tested with variations of quantum wells parameters and external impact conditions.

Temperature dependence of internal quantum efficiency of radiation for the near-band-edge emission of GaN crystals quantified by omnidirectional photoluminescence spectroscopy

Internal quantum efficiency of radiation (IQE) for the near-band-edge (NBE) emission of freestanding-GaN crystals was observed by omnidirectional photoluminescence spectroscopy at various temperatures between 12 K and 300 K. A photoluminescence quenching ratio (Rq), defined by a spectrally integrated NBE emission obtained at 300 K to that obtained at 12 K, showed a lower value (2%) comparing with the IQE value (5.5%) for the GaN with the free electron concentration of 1 × 1017 cm−3 under cw photo-pumping density of 13 W cm−2. This difference arises from the nonlinear relationship between IQE and the external quantum efficiency owing to the photon recycling effect.

电子阻挡层Al组分对Si衬底GaN基黄光LED内量子效率的影响

电子阻挡层Al组分对Si衬底GaN基黄光LED内量子效率的影响

Investigation of heterostructure influence upon characteristics based on simulation

Basic performance characteristics of multicomponent nanoscale heterostructures are investigated. Graphs are presented of such computer-simulated performance indicators as current-voltage characteristics and the dependence of internal quantum efficiency on the doping of barriers in a quantum-size region.

Emission Wavelength Dependence of Internal Quantum Efficiency in InGaN Nanowires

The internal quantum efficiency (IQE) of InGaN nanowires with different emission wavelength of 485, 515, 555, and 580 nm has been studied by means of photoluminescence (PL) spectroscopy. It was found from the analysis of IQE as a function of excitation power density that the IQE was unchanged at about 100% under weak excitation conditions at low temperature. This indicated that the effects of nonradiative recombination processes were negligibly small at low temperature. Moreover, the IQE increased from 5 to 12% with increasing emission wavelength from 485 to 580 nm. Since the clear correlation between the IQE and the PL blue shift due to band filling effects of localized states was observed, the increase in the IQE reflected the increase in the effect of exciton localization with increasing indium composition.

Dependence of internal quantum efficiency on doping region and Si concentration in Al-rich AlGaN quantum wells

The internal quantum efficiency (IQE) of Si-doped AlGaN quantum wells has been studied by means of photoluminescence spectroscopy. Analysis of the IQE as a function of doping region revealed that the IQE increased from 19% to 40% with doping of the well layers. This increase was attributed to an improvement in the interface quality between well and barrier layers as well as a reduction in point defect density. Moreover, the IQE increased to a maximum of 50% and then decreased with increasing Si concentration of the well layers. This indicated the existence of an optimum Si concentration for IQE improvement.

Effect of localized states on internal quantum efficiency of III‐nitride LEDs

AbstractA model is suggested accounting for effects of localized electron and hole states formed by composition fluctuations in the InGaN active region of a III‐nitride LED on non‐radiative carrier recombination at threading dislocations. The model enables explanation of the abnormal temperature dependence of internal quantum efficiency (IQE) of a green LED structure recently observed at low current densities. The theoretical predictions are in quantitative agreement with experiment in the temperature range between 200 K and 453 K. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of carrier spillover and Auger recombination on the efficiency droop in InGaN-based blue LEDs

We have investigated efficiency droop in InGaN-based blue LEDs by considering radiative, nonradiative, and carrier spillover processes in the context of internal quantum efficiency (IQE) vs. injection current. If relied on fitting only, both the Auger recombination and an empirical formula for carrier spillover are consistent with experiments. However, the dependence of IQE on quantum well parameters and lack of droop in optical pumping experiments support the notion that carrier spillover is the main mechanism in play.

Bias dependence of internal quantum efficiency and carrier capture in a green (In,Ga)N single‐quantum‐well diode

AbstractInternal quantum efficiency (IQE) and vertical capture processes of photogenerated carriers in a c ‐plane green (In,Ga)N single‐quantum‐well light‐emitting‐diode have been investigated by comparing variation in photoluminescence (PL) intensity as a function of applied voltage over a wide temperature range (T = 20‐300 K) under direct (λex =380 nm) and indirect (λex = 325 nm) excitation. Under the direct excitation the PL intensity reflecting IQE shows a maximum value at +2.4 V irrespective of temperatures. However, it decreases to 23% from the maximum as temperature increases to 300 K. The PL intensity reduction observed at the optimized forward bias is much less as temperature increases under the indirect excitation. This difference observed between the two excitation conditions indicates an important role of efficient capture of photogenerated carriers into the active radiative recombination centers from the barriers under the presence of internal polarization fields. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Charge carrier recombination in the ITO/PEDOT:PSS/MEH-PPV/Al photodetector

In this paper we investigate charge carrier recombination processes in polymer based photodetector ITO/PEDOT:PSS/MEH-PPV/Al. The major carriers are the hole polarons created by the photoexcitation in the active MEH-PPV film. The model used in this paper is based on the continuity equation and drift-diffusion equation for hole polarons. We assume the Poole-Frenkel expression for field dependence of the hole polaron mobility. The internal quantum efficiency dependence on incident photon flux density, incident light wavelength and applied electric field is included in the model. The simulated photocurrent density spectra for two different, assumed, recombination mechanisms, linear (monomolecular) and square (bimolecular) is compared with our experimental results. The bimolecular recombination mechanism applied in our model is assumed to be of Langevin type. The agreement between the measured and the calculated data unambiguously indicate that the hole polaron recombination mechanism in the MEH-PPV film is bimolecular with bimolecular rate constant depending on the external electric field. For the established recombination mechanism the theoretical prediction of the photocurrent density spectra shows excellent agreement with the measured spectra in wide range of inverse bias voltages (from 0 to -8 V).

Deep-Etched Native-Oxide-Confined High-Index-Contrast AlGaAs Heterostructure Lasers With 1.3 $\mu$m Dilute-Nitride Quantum Wells

Using a modified, O2-enhanced nonselective wet thermal oxidation process, deep-etched ridge waveguides in AlGaAs heterostructures containing lambda = 808 nm InAlGaAs single quantum well or aluminum-free lambda = 1.3 mum GaAsP/InGaAsN dilute nitride multi-quantum-well active regions have been directly oxidized to effectively provide simultaneous electrical isolation, interface state passivation, and sidewall roughness reduction. The resulting high- index-contrast (HIC) ridge waveguide (RWG) diode lasers show improved performance relative to conventional shallow-etched devices owing to both strong optical confinement and the complete elimination of current spreading, with 5 mum stripe width dilute- nitride devices showing up to a 2.3 times threshold reduction and strong index guiding for kink-free operation. Oxidation of an AlGaAs graded-index separate confinement heterostructure is studied for varying O2 concentrations, and the interface passivation effectiveness of the native oxide is studied through comparison with deposited SiO2 and via a study of the stripe-width dependence of internal quantum efficiency and modal loss. The HIC RWG structure is shown to enable the operation of half-racetrack-ring- resonator lasers with a bend radius as small as r = 6 mum.

Surface Passivation of Thin Silicon Solar Cells Using Silicon-on-Insulator Wafer

Solar cells with various cell thicknesses were fabricated using silicon-on-insulator (SOI) wafers, and effects of applied bias voltages (V B) at the SOI layer/SiO2 back interface on cell performance were investigated. A surface passivation effect was obtained by applying negative V B to accumulate holes at the interface. Both open-circuit voltage (V oc) and short-circuit current were improved by applying negative V B. This effect becomes more dominant for thinner cells. V oc of 20- and 50-µ m-thick cells at V B=-15 V increased compared to that of a 100-µ m-thick cell. Surface recombination velocity (S) was estimated from the dependence of internal quantum efficiency on cell thickness. It was found that S decreased from about 106 to 104 cm·s-1 when V B changed from 0 to -15 V. The improvement of cell performance by V B was due to this reduction in S. Therefore, the surface passivation by applying bias voltages is noted as an important technique to realize high-efficiency thin silicon solar cells.

Schottky Barriers on a-Si:H,F/a-Si,Ge:H,F Superlattices

AbstractWe report measurements of Schottky barrier heights and minority carrier mobilitylifetime products of multilayer structures composed of a-Si:H,F and a-Si,Ge:H,F. These layers are grown by r.f. glow discharge decompostion of SiF4, GeF4, and H2 in the a-Si,Ge:H,F (well) layer and of SiF4 and H2 in the a-Si:H,F (barrier) layer.Schottky barrier height ΦB of Pt is measured using internal photoemission measurements. The minority carrier mobility-lifetime product (μτ)p is extracted from a fit of the voltage dependence of internal quantum efficiency to the Hecht expression. Both ΦB and (μτ)p are measured as a function of barrier and well thicknesses.