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Zhongshan, China

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. Source


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. Source


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. Source


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. Source


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. Source

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