Joachim  Piprek Author of Evaluating Organization Development
FEATURED AUTHOR

Joachim Piprek

President
NUSOD Institute LLC

Dr. Piprek is an experienced researcher, teacher, and consultant in optoelectronics, photonics, and semiconductor devices. He published four books and chaired several international conferences in these areas. He currently serves as president of the NUSOD Institute which provides technical and educational services to corporations and research labs worldwide.

Biography

Joachim Piprek received his Diploma and Doctoral degrees in physics from Humboldt University in Berlin, Germany. For more than two decades, he worked in industry and academia on design, simulation, and analysis of various semiconductor devices used in optoelectronics. Dr. Piprek has taught graduate courses at universities in Germany, Sweden, and in the United States. He is founder and co-chair of the annual conference on Numerical Simulation of Optoelectronic Devices (NUSOD) and he also chaired several SPIE conferences. Dr. Piprek was invited guest editor for several special journal issues on optoelectronic device simulation and he currently serves as executive/associate editor of two research journals. He has published 4 books, 7 book chapters, and about 250 papers with more than 8000 citations.

Websites

Books

Featured Title
 Featured Title - Handbook of Optoelectronic Device Modeling, 2 Vol Set - 1st Edition book cover

Articles

ECS Journal of Solid State Science and Technology

Energy Efficiency Analysis of GaN-Based Blue Light Emitters


Published: Jan 22, 2020 by ECS Journal of Solid State Science and Technology
Authors: J. Piprek

GaN-based light sources are in high demand for lighting, displays, medical equipment and other applications. InGaN/GaN blue light-emitting diodes (LEDs) reach an electrical-to-optical power conversion efficiency of more than 80% but less than 10% are reported for blue superluminescent light-emitting diodes (SLEDs) and less than 50% for blue laser diodes (LDs). We here analyze the physical mechanisms behind this surprising discrepancy in peak energy efficiency of GaN-based light emitters.

Optical and Quantum Electronics (2019) 51:382

What limits the efficiency of GaN‑based superluminescent light‑emitting diodes (SLEDs)?


Published: Nov 12, 2019 by Optical and Quantum Electronics (2019) 51:382
Authors: J. Piprek
Subjects: Engineering - Electrical, Materials Science, Nanoscience & Technology, Physics

Gallium-nitride-based SLEDs are attractive light sources for augmented reality displays and other applications. However, the electrical-to-optical power conversion efficiency (PCE) of SLEDs is still far below the record-high values reported for LEDs. Utilizing advanced numerical device simulation, this paper investigates the internal physical processes that cause the low PCE of SLEDs. Design improvement options are demonstrated.

Optical and Quantum Electronics (2019) 51:60

On the reliability of pulse power saturation models for broad‑area GaAs‑based lasers


Published: Feb 14, 2019 by Optical and Quantum Electronics (2019) 51:60
Authors: J. Piprek
Subjects: Engineering - Electrical, Mathematics, Physics

With short current pulses, GaAs-based lasers can achieve high output powers. However, the pulse power is still severely limited by internal saturation mechanisms. Over the past decade, various power loss mechanisms have been identified by numerical laser simulation but published conclusions differ even for the same laser diode. We here investigate the reliability of such simulations.

IEEE Photonics Technology Letters

What causes the pulse power saturation of GaAs-based broad-area lasers?


Published: May 15, 2018 by IEEE Photonics Technology Letters
Authors: J. Piprek and Z. M. Li
Subjects: Engineering - Electrical, Mathematics, Nanoscience & Technology, Physics

With short current pulses, the output power of semiconductor lasers is limited by non-thermal internal loss mechanisms. We investigate such power saturation by advanced numerical laser simulation that includes all relevant processes self-consistently. Carrier leakage and free-carrier absorption are identified as the main saturation mechanisms, followed by longitudinal spatial hole burning. Contrary to earlier studies, two-photon absorption and gain compression are found negligible.

J. Quant. Electron. 53 (2017) 2000104

What limits the efficiency of high-power InGaN/GaN lasers?


Published: Feb 01, 2017 by J. Quant. Electron. 53 (2017) 2000104
Authors: J. Piprek
Subjects: Engineering - Electrical, Materials Science, Mathematics, Nanoscience & Technology, Physics

Blue light emitting InGaN/GaN lasers currently exhibit less than 40% wall-plug efficiency, while infrared InGaAs/GaAs laser diodes exceed 70%. This paper explores the reasons behind the efficiency limitation by the numerical analysis of measured InGaN/GaN laser characteristics.

Opt. Quant. Electron. 48 (2016) 472

Electroluminescent cooling mechanism in InGaN/GaN light-emitting diodes


Published: Sep 27, 2016 by Opt. Quant. Electron. 48 (2016) 472
Authors: J. Piprek and Z. M. Li
Subjects: Engineering - Electrical, Materials Science, Mathematics, Nanoscience & Technology, Physics

GaN-based light-emitting diodes (LEDs) are able to emit photons of higher energy than the injected electrons. This phenomenon is generally attributed to heat extraction from the crystal lattice. For the first time, we here show by numerical simulation how Peltier cooling near the InGaN light-emitting layer lowers the internal LED temperature rise.

Appl. Phys. Lett. 107, 031101 (2015)

How to decide between competing efficiency droop models for GaN-based LEDs


Published: Jul 20, 2015 by Appl. Phys. Lett. 107, 031101 (2015)
Authors: J. Piprek
Subjects: Engineering - Electrical, Materials Science, Mathematics, Nanoscience & Technology, Physics

GaN-based light-emitting diodes (LEDs) exhibit a strong efficiency droop with higher current injection, which has been mainly attributed to Auger recombination and electron leakage, respectively. Advanced numerical simulations of experimental characteristics are shown to validate one or the other explanation by variation of uncertain material parameters. We here demonstrate how the comparative simulation of temperature effects enables a clear distinction between both models.