Quantitative Multi-Scale, Multi-Physics Quantum Transport Modeling of GaN-Based Light Emitting Diodes (original) (raw)
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physica status solidi (a), 2014
The results of experimental investigation of forward currentvoltage characteristics of InGaN/GaN multiple quantum well light-emitting diodes are presented. A new model for explaining the complex current dependence on voltage is proposed. The model is based on the assumption of space charge limited current, and ballistic overflow of electrons through the multiple quantum well region. It is shown that electrons are captured in the shallow traps while transferring through the active region. The results of measurements indicate that the activation energy of traps decreases with a temperature decrease, which corresponds to the theory of hopping in exponential band tails.
Non-local transport in numerical simulation of GaN LED
Journal of Computational Electronics, 2015
We propose a device modeling theory based on an improved drift-diffusion solution that is suitable for simulation of the efficiency droop effect in GaN LED. Our theory modifies the drift-diffusion transport by adding a non-local carrier transport component that mimics the effect of hot carriers near the multiple quantum well region. The non-local transport model is supported by recent experimental evidence of Auger-induced hot carriers as well as explaining the experimental low turn-on voltage that conventional drift-diffusion theory fails to predict. A surprising finding from the simulation is that the hot-Auger carriers have a positive effect of reducing the junction resistance of the LED and thus help improve the overall wall-plug efficiency.
A new IV model for light-emitting devices with a quantum well
Microelectronics Journal, 2006
This letter reports a new current versus voltage model for light-emitting devices with a quantum well where electrons and holes are injected and recombine. The current is entirely caused by the recombination of electrons and holes. Historically, the equation used for light-emitting diodes (LEDs) and laser diodes (LDs) has been the renowned Sah-Noyce-Shockley (SNS) diode equation. In this equation at typical forward bias condition, most of the current is caused by the diffusion of carriers over the depletion region. It is clear that this condition is different from what actually happen in LEDs and LDs. We thus looked into the fundamental of carrier transport and developed a new model for devices with a quantum well. Based on the new model, calculated I-V curves agree well with measurement results of GaN/sapphire LEDs with GaInN quantum wells. In calculation, junction temperature T j rather than case temperature T c is used to achieve better agreement. r
Electronic and transport properties of GaN/AlGaN quantum dot-based p-i-n diodes
2008
Quantum dot (QD) systems based on III-nitride have recently shown to be very promising nanostructures for high-quality light emitters. In this work, electronic and transport properties of AlN/GaN QDs are investigated by means of the TIBERCAD software tool, which allows both a macroscopic and an atomistic approach, with the final aim to couple them in a multiscale simulation environment.
GaN-based light-emitting diodes: Efficiency at high injection levels
| Light-emitting diodes (LEDs) have become quite a high-performance device of late and are revolutionizing the display and illumination sectors of our economy. Due to demands for better performance and reduced energy consumption there is a constant race towards converting every single electron hole pair in the device to photons and extracting them as well while using only the minimum required voltage.
Physical Review Materials, 2020
The presence of alloy disorder in III-nitride materials has been demonstrated to play a significant role in device performance through effects such as carrier localization and carrier transport. Relative to blue light emitting diodes (LEDs), these effects become more severe at green wavelengths. Because of the potential fluctuations that arise due to alloy disorder, full three-dimensional (3D) simulations are necessary to accurately relate materials properties to device performance. We demonstrate experimentally and through simulation that increased quantum well (QW) number in c-plane green LEDs contributes to excess driving voltage, and therefore reduced electrical efficiency. Experimentally, we grew an LED series with the number of QWs varying from one to seven and observed a systematic increase in voltage with the addition of each QW. Trends in LED electrical properties obtained from 3D simulations, which account for the effects of random alloy fluctuations, are in agreement with experimental data. Agreement is achieved without the need for adjusting polarization parameters from their known values. From these results, we propose that the polarization induced barriers at the GaN/InGaN (lower barrier/QW) interfaces and the sequential filling of QWs both contribute significantly to the excess forward voltage in multiple QW c-plane green LEDs.
Modeling challenges for high-efficiency visible light-emitting diodes
2015 IEEE 1st International Forum on Research and Technologies for Society and Industry Leveraging a better tomorrow (RTSI), 2015
The challenges posed by the numerical modeling of GaN-based light-emitting diodes (LEDs) require the extension of current simulation approaches beyond the semiclassical limits. Any theory hoping to predict the complex carrier transport and optical properties of state-of-the-art III-nitride LEDs should combine a genuine quantum approach with an atomistic description of the electronic structure. Semiclassical discontent notwithstanding, computational considerations have elicited the inclusion of quantum corrections within drift-diffusion approaches. However, the lack of first-principles validation tools has left these quantum models largely untested, at least in the context of LED simulation. It is therefore important to compare the results obtained with currently available commercial numerical simulators, in order to assess the predictive capabilities of the advanced physics-based models complementing the driftdiffusion equations.
2014
Electroluminescence (EL) characterization of InGaN/GaN light-emitting diodes (LEDs), coupled with numerical device models of different sophistication, is routinely adopted not only to establish correlations between device efficiency and structural features, but also to make inferences about the loss mechanisms responsible for LED efficiency droop at high driving currents. The limits of this investigative approach are discussed here in a case study based on a comprehensive set of currentand temperature-dependent EL data from blue LEDs with low and high densities of threading dislocations (TDs). First, the effects limiting the applicability of simpler (closed-form and/or one-dimensional) classes of models are addressed, like lateral current crowding, vertical carrier distribution nonuniformity, and interband transition broadening. Then, the major sources of uncertainty affecting state-ofthe-art numerical device simulation are reviewed and discussed, including (i) the approximations in the transport description through the multi-quantum-well active region, (ii) the alternative valence band parametrizations proposed to calculate the spontaneous emission rate, (iii) the difficulties in defining the Auger coefficients due to inadequacies in the microscopic quantum well description and the possible presence of extra, non-Auger high-current-density recombination mechanisms and/or Auger-induced leakage. In the case of the present LED structures, the application of three-dimensional numerical-simulation-based analysis to the EL data leads to an explanation of efficiency droop in terms of TD-related and Auger-like nonradiative losses, with a C coefficient in the 10 −30 cm 6 /s range at room temperature, close to the larger theoretical calculations reported so far. However, a study of the combined effects of structural and model uncertainties suggests that the C values thus determined could be overestimated by about an order of magnitude. This preliminary attempt at uncertainty quantification confirms, beyond the present case, the need for an improved description of carrier transport and microscopic radiative and nonradiative recombination mechanisms in device-level LED
Semiconductors
The deep-center-assisted tunneling of carriers in p-n structures of light-emitting diodes (LEDs) with InGaN/GaN quantum wells (QWs) makes smaller the effective height of the injection barrier, but leads to a dependence of the radiation efficiency on the density and energy spectrum of defects in GaN. In the case of hopping conduction across the space charge region, the forward voltage mainly drops near the QW boundary, where the density of deep states at the quasi Fermi-level is the lowest. As a result, band bending at the boundary decreases, and, with increasing current, the direction of the electric field also changes, which leads to a weaker confinement of holes, to their non-radiative recombination in the n barrier, and to an efficiency droop. The low efficiency of green GaN LEDs is associated with the dominance of deep centers and insufficient density of shallow centers in the energy spectrum of defects in barrier layers near the boundaries with the QW. The proposed model is confirmed by the stepwise experimental dependences of the current, capacitance and efficiency of green and blue LEDs in the case of forward bias, which reflect the contribution of color centers responsible for the defect photoluminescence bands in GaN.
Investigation of quantum transport in nanoscaled GaN high electron mobility transistors
2014 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD), 2014
In this paper, a comprehensive investigation of quantum transport in nanoscaled gallium nitride (GaN) high electron mobility transistors (HEMTs) is presented. A simulation model for quantum transport in nanodevices on unstructured grids in arbitrary dimension and for arbitrary crystal directions has been developed. The model has been implemented as part of the Vienna-Schrödinger-Poisson simulation and modeling framework. The transport formalism is based on the quantum transmitting boundary method. A new approach to reduce its computational effort has been realized. The model has been used to achieve a consistent treatment of quantization and transport effects in deeply scaled asymmetric GaN HEMTs. The selfconsistent electron concentration, conduction band edges and ballistic current have been calculated. The effects of strain relaxation at the heterostructure interfaces on the potential and carrier concentration have been shown.