Zhongshan, China
Zhongshan, China

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Sheng Xia C.,Crosslight Software Inc. | Simon Li Z.M.,Crosslight Software Inc. | Lu W.,CAS Shanghai Institute of Technical Physics | Hua Zhang Z.,Tongji University | And 2 more authors.
Applied Physics Letters | Year: 2011

Blue InGaN/GaN multiple quantum well light-emitting diodes with the conventional and graded last barriers (GLB) are numerically investigated. When the last GaN barrier is replaced by a linearly graded In xGa 1 - xN barrier with increasing indium composition in the growth direction, the forward voltage is reduced from 3.60 V to 3.25 V, and the efficiency droop is improved from 36 to 13. Simulation results indicate that these improvements can be attributed to the formation of a deep potential well in the GLB which enhances the electron confinement and improves the hole injection efficiency. © 2011 American Institute of Physics.


Piprek J.,NUSOD Institute LLC | Simon Li Z.M.,Crosslight Software Inc.
Applied Physics Letters | Year: 2013

We analyze efficiency droop reductions in InGaN/GaN light-emitting diodes caused by a chirped AlGaN/GaN multi-quantum barrier (MQB). Such electron barriers are expected to create an additional forbidden energy range above the natural conduction band edge, which reduces the electron leakage current. Advanced numerical device simulations reveal that energy band bending practically eliminates this MQB effect. Instead, we find that the measured efficiency improvement has its origin in enhanced hole injection, which can be more easily accomplished using a single thin AlGaN layer. © 2013 American Institute of Physics.


Piprek J.,NUSOD Institute LLC | Simon Li Z.M.,Crosslight Software Inc.
Applied Physics Letters | Year: 2013

III-nitride light-emitting diodes (LEDs) suffer from efficiency droop, which is partially attributed to electron leakage into the p-doped layers. Only very few direct measurements of such leakage are published. We here analyze leakage measurements on AlGaN LEDs with an emission wavelength near 260 nm. The electron leakage disappears after insertion of a thin undoped electron blocking layer (EBL). In good agreement with these measurements, we show that the electron blocking effect is extremely sensitive not only to the EBL material composition but also to the conduction band offset and to the net polarization, which are both not exactly known. © 2013 American Institute of Physics.


Piprek J.,NUSOD Institute LLC | Simon Li Z.M.,Crosslight Software Inc.
Applied Physics Letters | Year: 2013

High-power broad-area laser diodes often suffer from a widening of the slow-axis far-field with increasing current (lateral far-field blooming). This effect is commonly attributed to self-heating. Utilizing self-consistent electro-thermal-optical simulations, we analyze previous experimental investigations of 970 nm broad-area GaAs-based Fabry-Perot lasers and reproduce the blooming mechanism in good agreement with the measurements. The simulations reveal that a substantial part of the far field blooming is not caused by self-heating but by increasing carrier and gain non-uniformity in the quantum wells. © 2013 AIP Publishing LLC.


Li Z.Q.,Crosslight Software Inc. | Li Z.M.S.,Crosslight Software Inc.
IEEE Journal of Quantum Electronics | Year: 2010

We present a self-consistent electric and optic model for superluminescent light-emitting diodes (SLED) using 3D finite-element method. The carrier transport is calculated by the drift-diffusion method, which is coupled with the radiative recombination obtained from the solution of Shrodinger-Poison equations self-consistently. The spontaneous emission noise is described by the fundamental theory using the Green's function method. Our model allows 2D treatment of the carrier dynamics and optical confinement on the transverse plane, along with the electronic and optical variation on the longitudinal axis. The theoretical model has been benchmarked with an InP-based edge-emitting SLED. The device has nonidentical quantum wells with broad bandwidth from 1300 to 1600 nm. The results show the importance of 3D effects and demonstrate the validity of the model. © 2010 IEEE.


Sheng Xia C.,Crosslight Software Inc. | Simon Li Z.M.,Crosslight Software Inc. | Sheng Y.,Crosslight Software Inc.
Applied Physics Letters | Year: 2013

There has been confusion regarding the usefulness of AlGaN electron blocking layer (EBL) in GaN-based light-emitting diodes (LEDs) with some published experimental data indicating that the LEDs without EBL performed better than those with it. InGaN/GaN LEDs have been investigated numerically to analyze its actual effect in these devices. Simulation results show that hole blocking effect of EBL mainly determines the effectiveness of using it which is more sensitive to its Al composition, band offset ratio, and polarization charges. It is found that the choice of Al composition is critical for EBL to improve the optical performance of GaN-based LEDs. © 2013 AIP Publishing LLC.


Piprek J.,NUSOD Institute LLC | Li S.,Crosslight Software Inc.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

GaN-based vertical-cavity surface-emitting lasers (VCSELs) are expected to exhibit several advantages over their already widely used edge-emitting counterparts, including lower manufacturing costs, circular output beams, and longer lifetime. However, in contrast to the great success of GaN-based edge-emitting lasers in recent years, GaN-VCSELs still face significant challenges. Electrically pumped devices have been demonstrated only recently and they exhibit severe performance restrictions. We here analyze these recently manufactured GaN-VCSELs using advanced laser simulation software. The simulation self-consistently combines carrier transport, photon emission, and multi-mode optical wave guiding. For the quantum wells, Schrödinger and Poisson equations are solved iteratively at every bias point to account for the Quantum-Confined Stark Effect. Our analysis shows that thick quantum wells allow for the almost complete elimination of the built-in quantum well polarization field. The simulations also reveal several performance limiting effects, e.g., gain-peak offset, current crowding, and electron leakage. Design optimization options are discussed and simulated. © 2010 Copyright SPIE - The International Society for Optical Engineering.


Piprek J.,NUSOD Institute LLC | Li S.,Crosslight Software Inc.
Optical and Quantum Electronics | Year: 2010

Nitride-based light-emitting diodes suffer from a reduction (droop) of the internal quantum efficiency (IQE) with increasing injection current. Using advanced device simulation, we investigate the impact of electron leakage on the IQE droop for different properties of the electron blocker layer (EBL). The simulations show a strong influence of the EBL acceptor density on the droop. We also find that the electron leakage decreases with increasing temperature, which contradicts common assumptions. © 2011 Springer Science+Business Media, LLC.


Li Z.Q.,Crosslight Software Inc. | Lestradet M.,Crosslight Software Inc. | Xiao Y.G.,Crosslight Software Inc. | Li S.,Crosslight Software Inc.
Physica Status Solidi (A) Applications and Materials Science | Year: 2011

The effects of interface polarization charge on the photovoltaic characteristics of GaN/InGaN solar cells have been analyzed in detail using 2D drift-diffusion simulations. The polarization charge at the GaN/InGaN interface creates an electric field that forces carriers generated by light to drift in opposite direction needed for efficient collection and substantially reduces the short circuit current (I sc) and open circuit voltage (V oc). The polarization charge plays an important role in the photovoltaic properties of InGaN solar cells comparable to that of defects. For small interface charge, the potential barrier could increase the V oc. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Patent
Crosslight Software Inc. | Date: 2013-09-13

The invention relates to a method of simulation of semiconductor devices, such as wide-bandgap devices. The method employs a device substitution technique and involves simulation of a device which is structurally similar to the target device, and for which it is relatively easy to compute a model. Such a device may have a reduced material bandgap or a different doping/fixed-charge concentration. Based on the model of the simplified device, a model of the device under consideration is produced via a sequence of simulation steps, wherein simulated intermediate devices eventually transform into the target device for which a model is sought.

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